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Food Microbiology 22 (2005) 561–568<br />

FOOD<br />

MICROBIOLOGY<br />

<strong>Comparison</strong> <strong>of</strong> <strong>RAPDs</strong>,<strong>AFLPs</strong> <strong>and</strong> <strong>SSR</strong> <strong>markers</strong> <strong>for</strong> <strong>the</strong> <strong>genetic</strong><br />

analysis <strong>of</strong> yeast strains <strong>of</strong> Saccharomyces cerevisiae<br />

F. Javier Gallego a ,M. Angeles Pe´ rez b ,Yol<strong>and</strong>a Nu´ n˜ ez c ,Pilar Hidalgo b,<br />

a<br />

Departamento de Genética, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain<br />

b<br />

Instituto Madrileño de Investigación Agraria y Alimentaria (IMIA), Comunidad de Madrid, Finca El Encín, Apdo. 127, 28800 Alcalá de Henares,<br />

Madrid, Spain<br />

c<br />

Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Autovía A-6, Km 7.5, 28040 Madrid, Spain<br />

Abstract<br />

Received 3 March 2004; received in revised <strong>for</strong>m 8 November 2004; accepted 16 November 2004<br />

We evaluated <strong>the</strong> usefulness <strong>of</strong> different molecular techniques <strong>for</strong> <strong>the</strong> <strong>genetic</strong> analysis <strong>of</strong> Saccharomyces cerevisiae strains. Three<br />

commonly used PCR-derived <strong>genetic</strong> methods,r<strong>and</strong>om amplified polymorphic DNA (<strong>RAPDs</strong>),amplified fragment length<br />

polymorphism (<strong>AFLPs</strong>) <strong>and</strong> simple sequence repeats (<strong>SSR</strong>s; microsatellites),were used to characterize 27 wine yeast strains <strong>of</strong> S.<br />

cerevisiae from <strong>the</strong> ‘‘Denominacio´ n de Origen Vinos de Madrid’’ (Spain). Using <strong>the</strong>se methods,we were able to overcome certain<br />

limitations associated with classical taxonomic methods. Based on <strong>the</strong> presence or absence <strong>of</strong> amplified fragments <strong>for</strong> each genotype,<br />

<strong>AFLPs</strong> <strong>and</strong> <strong>SSR</strong>s showed a similar discriminatory power superior to that <strong>of</strong> <strong>the</strong> <strong>RAPDs</strong>. Genetic relationships between strains were<br />

also estimated using <strong>the</strong> three methods. In general,very poor correlations were found,reflecting <strong>the</strong> different genomic regions <strong>for</strong><br />

which <strong>the</strong> methods are screened. Results are discussed in terms <strong>of</strong> which molecular technique is most appropriate <strong>for</strong> use with a<br />

particular aspect <strong>of</strong> <strong>genetic</strong> evaluation.<br />

r 2005 Elsevier Ltd. All rights reserved.<br />

Keywords: <strong>RAPDs</strong>; <strong>AFLPs</strong>; <strong>SSR</strong>s; Molecular <strong>markers</strong>; Genetic analysis; Saccharomyces cerevisiae<br />

1. Introduction<br />

The use <strong>of</strong> molecular <strong>markers</strong> has provided important<br />

advances in <strong>the</strong> characterization <strong>and</strong> <strong>genetic</strong> identification<br />

<strong>of</strong> Saccharomyces cerevisiae strains,<strong>the</strong> species that<br />

plays <strong>the</strong> major role in <strong>the</strong> fermentation <strong>of</strong> alcoholic<br />

beverages. The usefulness <strong>of</strong> <strong>the</strong>se molecular methods<br />

<strong>for</strong> <strong>the</strong> identification <strong>of</strong> S. cerevisiae at <strong>the</strong> strain level is<br />

<strong>of</strong> particular interest in enology,where <strong>the</strong>y can be used<br />

to investigate <strong>the</strong> ecology <strong>and</strong> <strong>genetic</strong> diversity <strong>of</strong> a<br />

species that predominates during spontaneous fermentation<br />

<strong>of</strong> <strong>the</strong> must. Moreover,<strong>the</strong>y can be used <strong>for</strong><br />

typing,monitoring <strong>and</strong> controlling commercially selected<br />

strains <strong>of</strong> S. cerevisiae.<br />

Corresponding author. Tel.: +34 918879489; fax: +34 918879492.<br />

E-mail address: pilar.hidalgo@madrid.org (P. Hidalgo).<br />

0740-0020/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.<br />

doi:10.1016/j.fm.2004.11.019<br />

ARTICLE IN PRESS<br />

www.elsevier.com/locate/fm<br />

PCR-based techniques,including interdelta analysis<br />

(Ness et al.,1993; Legras <strong>and</strong> Karst,2003) <strong>and</strong> <strong>the</strong> use<br />

<strong>of</strong> intro splice site primers (deBarros Lopes et al.,1996),<br />

r<strong>and</strong>omly amplified polymorphic DNA (<strong>RAPDs</strong>)<br />

(Quesada <strong>and</strong> Cenı´ s,1995; Van der Westhuizen et al.,<br />

1999),simple sequence repeats (<strong>SSR</strong>s) (Gallego et al.,<br />

1998; Gonza´ lez Techera et al.,2001; Hennequin<br />

et al.,2001; Pe´ rez et al.,2001),<strong>and</strong> amplified fragment<br />

length polymorphism (<strong>AFLPs</strong>) (deBarros Lopes<br />

et al.,1999),have previously allowed <strong>the</strong> discrimination<br />

as well as estimation <strong>of</strong> <strong>genetic</strong> variation in S. cerevisiae<br />

strains. Differences exist,however,among <strong>the</strong> methods<br />

used with respect to complexity,cost,speed <strong>of</strong> use,<br />

<strong>and</strong> resolution power. This paper compares <strong>the</strong> usefulness<br />

<strong>of</strong> three PCR-based methods—<strong>RAPDs</strong>,<strong>AFLPs</strong><br />

<strong>and</strong> <strong>SSR</strong>s—<strong>for</strong> <strong>the</strong> <strong>genetic</strong> analysis <strong>of</strong> S. cerevisiae<br />

strains.


562<br />

2. Materials <strong>and</strong> methods<br />

2.1. Yeast strains<br />

Must samples undergoing spontaneous fermentation<br />

were collected from wineries (A,B <strong>and</strong> C) representing<br />

three viticultural areas (Arg<strong>and</strong>a,Navalcarnero <strong>and</strong> San<br />

Martı´ n de Valdeiglesias) <strong>of</strong> <strong>the</strong> ‘‘Denominacio´ n de<br />

Origen Vinos de Madrid’’ (Spain). The number <strong>of</strong> tanks<br />

sampled in cellars A,B <strong>and</strong> C were two,four <strong>and</strong> two,<br />

respectively. Fermentation processes were conducted at<br />

temperatures between 18 <strong>and</strong> 20 1C. Populations <strong>of</strong><br />

viable yeast cells in each step <strong>of</strong> <strong>the</strong> fermentation process<br />

were <strong>of</strong> <strong>the</strong> order <strong>of</strong> 10 7 cfu/mL. From <strong>the</strong>se populations,a<br />

total <strong>of</strong> 27 S. cerevisiae (Kreger Van Rij,1984;<br />

Kurtzman <strong>and</strong> Fell,1998) strains were isolated <strong>and</strong><br />

chosen at r<strong>and</strong>om <strong>for</strong> use in this study. These strains<br />

have been included in <strong>the</strong> culture collection <strong>of</strong> <strong>the</strong> IMIA<br />

(El Encı´ n,Madrid). The reference code,origin <strong>and</strong><br />

source <strong>of</strong> each yeast strain are listed in Table 1.<br />

2.2. DNA extraction<br />

This process was carried out following <strong>the</strong> technique<br />

described by Pe´ rez et al. (2001).<br />

Table 1<br />

S. cerevisiae strains used in this study<br />

Strain<br />

(reference code)<br />

Viticultural<br />

area<br />

Winery Isolation<br />

sample<br />

ARTICLE IN PRESS<br />

Step <strong>of</strong><br />

fermentation<br />

1a Arg<strong>and</strong>a A 20 Middle<br />

2a Arg<strong>and</strong>a A 20 Middle<br />

3a Arg<strong>and</strong>a A 20 Middle<br />

4a Arg<strong>and</strong>a A 20 Middle<br />

5a Arg<strong>and</strong>a A 20 End<br />

6a Arg<strong>and</strong>a A 21 Middle<br />

7a Arg<strong>and</strong>a A 21 Middle<br />

8a Arg<strong>and</strong>a A 21 Middle<br />

9a Arg<strong>and</strong>a A 21 End<br />

1n Navalcarnero B 32 End<br />

2n Navalcarnero B 32 Middle<br />

3n Navalcarnero B 32 End<br />

4n Navalcarnero B 33 Middle<br />

5n Navalcarnero B 33 End<br />

6n Navalcarnero B 33 End<br />

7n Navalcarnero B 33 End<br />

8n Navalcarnero B 34 End<br />

9n Navalcarnero B 35 Middle<br />

1s San Martín C 46 Middle<br />

2s San Martín C 46 Middle<br />

3s San Martín C 46 End<br />

4s San Martín C 46 End<br />

5s San Martín C 47 Middle<br />

6s San Martín C 47 End<br />

7s San Martín C 47 End<br />

8s San Martín C 47 End<br />

9s San Martín C 47 End<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568<br />

2.3. RAPD analysis<br />

RAPD amplifications were carried out according to<br />

<strong>the</strong> methodology described by Gallego <strong>and</strong> Martı´ nez<br />

(1997) using a DNA Thermal Cycler 9600 (Applied<br />

Biosystems) under <strong>the</strong> following conditions: a preliminary<br />

step <strong>of</strong> 2 min at 94 1C; 10 cycles each <strong>of</strong> 30 s at 94 1C,<br />

a ramp <strong>of</strong> 1.5 1Cs 1 to reach annealing temperature,<br />

1 min at 55 1C (decreasing 1 1C per cycle to a final<br />

temperature <strong>of</strong> 46 1C),<strong>and</strong> a ramp <strong>of</strong> 1.5 min to reach<br />

72 1C followed by 4.5 min at this temperature; 25 cycles<br />

each <strong>of</strong> 30 s at 94 1C,a ramp <strong>of</strong> 1.5 1Cs 1 to reach<br />

annealing temperature,1 min at 45 1C,<strong>and</strong> a ramp <strong>of</strong><br />

1.5 min to reach 72 1C followed by 4.5 min at this<br />

temperature; <strong>and</strong> a final step <strong>of</strong> 1 min at 72 1C.<br />

Forty primers from sets B <strong>and</strong> C <strong>of</strong> Operon<br />

Technologies (Alameda,CA) were used in preliminary<br />

experiments in order to evaluate <strong>the</strong>ir per<strong>for</strong>mance.<br />

Thirty-two resulted in satisfactory amplifications <strong>and</strong><br />

were selected <strong>for</strong> use in <strong>the</strong> remainder <strong>of</strong> <strong>the</strong> assay.<br />

Amplification products were separated by electrophoresis<br />

in 1.5% (w/v) agarose gels,<strong>and</strong> visualized under UV<br />

light after staining with ethidium bromide.<br />

2.4. AFLP analysis<br />

AFLP <strong>markers</strong> were developed following <strong>the</strong> protocol<br />

supplied by Applied Biosystems (Foster City,Cali<strong>for</strong>nia,USA),based<br />

on Vos et al. (1995). DNA digestion<br />

was carried out using <strong>the</strong> restriction enzymes EcoRI <strong>and</strong><br />

MseI. Six selective amplifications were per<strong>for</strong>med using<br />

five primers. Two <strong>of</strong> <strong>the</strong> primers included <strong>the</strong> MseI<br />

adaptor sequence plus <strong>the</strong> selective CTT <strong>and</strong> CAA. The<br />

remaining three primers contained <strong>the</strong> EcoRI adaptor<br />

sequence plus AC,AT <strong>and</strong> AAG. The EcoRI selective<br />

primers were 5 0 -labeled with one <strong>of</strong> <strong>the</strong> following<br />

fluorescent dyes: 6-FAM,TET or HEX (Applied<br />

Biosystems). PCR products were separated by capillary<br />

electrophoresis in an ABI Prism 310 DNA Sequencer<br />

(Applied Biosystems). The number <strong>of</strong> fragments generated<br />

by each primer pair was obtained directly from<br />

Genescan Analysis s<strong>of</strong>tware,using <strong>the</strong> local Sou<strong>the</strong>rn<br />

method to size <strong>the</strong> fragments.<br />

2.5. <strong>SSR</strong> analysis<br />

<strong>SSR</strong> analysis was per<strong>for</strong>med according to <strong>the</strong><br />

methodology developed by Pe´ rez et al. (2001),using a<br />

panel <strong>of</strong> six effective microsatellite loci as sequencetagged<br />

site <strong>markers</strong>.<br />

Loci were amplified using two multiple PCR reactions,including<br />

ScAAT2,ScAAT3,ScAAT5 in <strong>the</strong> first<br />

reaction (PCR1) <strong>and</strong> ScAAT1,ScAAT4,<strong>and</strong> ScAAT6<br />

in <strong>the</strong> second (PCR2). Each PCR reaction was<br />

per<strong>for</strong>med in 25 mL final volume containing 10–400 ng<br />

<strong>of</strong> template DNA <strong>and</strong> 0.2 mM <strong>of</strong> each dNTP (Applied


Biosystems,Foster City,Cali<strong>for</strong>nia,USA). PCR1<br />

reaction mix contained 5 pmol <strong>of</strong> ScAAT2 primer pair<br />

fluorescent-dye labeled with HEX (yellow),5 pmol <strong>of</strong><br />

ScAAT3 primer pair fluorescent-dye labeled with 6-<br />

FAM (blue),7.5 pmol <strong>of</strong> ScAAT5 primer pair fluorescent-dye<br />

labeled with TET (green),<strong>and</strong> 1 U <strong>of</strong> Taq<br />

DNA polymerase (Biotools,Biotechnological <strong>and</strong> Medical<br />

Laboratories,S.A.,Madrid,Spain) in 1 reaction<br />

buffer (75 mM Tris HCl pH 9.0,50 mM KCl,20 mM<br />

(NH4)2SO4). PCR2 reaction mix contained 2.5 pmol <strong>of</strong><br />

ScAAT4 primer pair fluorescent-dye labeled with TET,<br />

2.5 pmol <strong>of</strong> ScAAT6 primer pair fluorescent-dye labeled<br />

with HEX,10 pmol <strong>of</strong> ScAAT1 primer pair fluorescentdye<br />

labeled with 6-FAM,<strong>and</strong> 1.5 U <strong>of</strong> Taq DNA<br />

polymerase.<br />

The amplification reactions were carried out using a<br />

DNA Thermal Cycler 9600 (Applied Biosystems) under<br />

<strong>the</strong> following conditions: a preliminary step <strong>of</strong> 5 min at<br />

94 1C; 10 cycles each <strong>of</strong> 15 s at 94 1C,30 s at 58 1C<br />

(decreasing 1 1C per cycle to reach a final temperature <strong>of</strong><br />

47 1C),<strong>and</strong> 30 s at 72 1C; 25 cycles each <strong>of</strong> 15 s at 94 1C,<br />

30 s at 48 1C,<strong>and</strong> 30 s at 72 1C; <strong>and</strong> a final step <strong>of</strong> 5 min<br />

at 72 1C. Amplifications were confirmed by running<br />

10 mL <strong>of</strong> <strong>the</strong> PCR product on 2.5% agarose gel.<br />

Aliquots (1–2 mL) <strong>of</strong> <strong>the</strong> PCR product were mixed<br />

with 12 mL <strong>of</strong> <strong>for</strong>mamide <strong>and</strong> 0.5 mL <strong>of</strong> a red DNA size<br />

st<strong>and</strong>ard (Genescan-500 ROX,Applied Biosystems).<br />

Samples were denatured at 94 1C <strong>for</strong> 3 min prior to<br />

separation by capillary electrophoresis at 15 KV <strong>for</strong><br />

24 min in an ABI Prism 310 DNA Sequencer (Applied<br />

Biosystems),<strong>and</strong> subsequently analysed using Genescan<br />

s<strong>of</strong>tware (Applied Biosystems).<br />

The reproducibility <strong>of</strong> <strong>the</strong> three analysis techniques<br />

was assessed by comparing results from two additional<br />

independent DNA extractions from half <strong>of</strong> <strong>the</strong> study<br />

strains that were chosen r<strong>and</strong>omly.<br />

2.6. Data analysis<br />

Data matrices were built based on <strong>the</strong> presence or<br />

absence <strong>of</strong> amplification products. Genetic distances<br />

were estimated from <strong>the</strong>se matrices using Dice’s algorithm<br />

(Dice,1945). This coefficient was used <strong>for</strong><br />

clustering data according to <strong>the</strong> UPGMA method.<br />

Bootstrap resampling <strong>of</strong> 1000 replicates was per<strong>for</strong>med<br />

to test <strong>the</strong> robustness <strong>of</strong> <strong>the</strong> topology <strong>of</strong> <strong>the</strong> dendrograms.<br />

Differences between dendrograms were tested by<br />

generating cophenetic values <strong>for</strong> each dendrogram <strong>and</strong><br />

assembling a cophenetic matrix <strong>for</strong> each marker type.<br />

The Mantel matrix correspondence test was <strong>the</strong>n used to<br />

compare cophenetic matrices (Mantel,1967). Computing<br />

was per<strong>for</strong>med using NTSYSpc s<strong>of</strong>tware version 2.0<br />

(Rohlf,1993) <strong>and</strong> TFPGA s<strong>of</strong>tware version 1.3 (Miller,<br />

1997).<br />

In order to evaluate <strong>the</strong> usefulness <strong>of</strong> each marker<br />

system,all <strong>of</strong> <strong>the</strong> following were calculated: <strong>the</strong><br />

ARTICLE IN PRESS<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568 563<br />

arithmetic mean <strong>of</strong> Diversity Index per polymorphic<br />

locus (DIavp ¼ [1–Spi 2 ]/np,where p i is <strong>the</strong> allele<br />

frequency <strong>for</strong> <strong>the</strong> i allele <strong>and</strong> np is <strong>the</strong> number <strong>of</strong><br />

polymorphic loci),<strong>the</strong> arithmetic mean <strong>of</strong> Effective<br />

Number <strong>of</strong> Alleles per polymorphic locus (ENA avp ¼ [1/<br />

Sp i 2 ]/np),<strong>the</strong> total number <strong>of</strong> effective alleles per<br />

polymorphic locus (Ne ¼ sumat ENAavp),<strong>and</strong> <strong>the</strong><br />

Assay Efficiency Index (Ai ¼ Ne/P). Ai combines <strong>the</strong><br />

ENA identified per locus <strong>and</strong> <strong>the</strong> number <strong>of</strong> polymorphic<br />

b<strong>and</strong>s detected in each assay (P). For dominant<br />

<strong>markers</strong> (<strong>RAPDs</strong> <strong>and</strong> <strong>AFLPs</strong>) where one <strong>of</strong> only two<br />

states (+,present or ,absent) can be distinguished at<br />

each position,we assumed that each b<strong>and</strong> position<br />

corresponded to a locus with two alleles: presence <strong>and</strong><br />

absence <strong>of</strong> <strong>the</strong> b<strong>and</strong>.<br />

3. Results<br />

3.1. Efficiency <strong>of</strong> polymorphism detection<br />

The level <strong>of</strong> polymorphism detected with each marker<br />

system is summarized in Table 2,as well as a<br />

comparison between systems.<br />

A total <strong>of</strong> 155 b<strong>and</strong>s were amplified by <strong>the</strong> 32<br />

primers used in <strong>the</strong> RAPD analysis (Fig. 1). Eight<br />

primers—OPB (01,06,07,12,13,15) <strong>and</strong> OPC (01,<br />

03)—allowed <strong>the</strong> intraspecific differentiation <strong>of</strong> <strong>the</strong><br />

yeasts,with a total <strong>of</strong> 13 polymorphic b<strong>and</strong>s. By<br />

combining <strong>the</strong> electrophoretic pr<strong>of</strong>iles <strong>of</strong> seven primers<br />

(OPB01,OPB06,OPB07,OPB13,OPB15,OPC01 <strong>and</strong><br />

OPC03),we were able to use <strong>the</strong>se polymorphisms to<br />

differentiate 13 <strong>of</strong> <strong>the</strong> 27 S. cerevisiae strains in this<br />

study. The number <strong>of</strong> amplified b<strong>and</strong>s varied between<br />

primers,ranging between two <strong>and</strong> 10,with sizes from<br />

400 up to 2000 bp. Duplicate analysis <strong>of</strong> r<strong>and</strong>om strains<br />

revealed no significant differences in b<strong>and</strong>ing patterns,<br />

although some b<strong>and</strong>s varied in intensity.<br />

Analysis <strong>of</strong> AFLP b<strong>and</strong>ing patterns (Fig. 2) yielded<br />

137 DNA fragments,with sizes ranging from 130 to<br />

410 bp. A total <strong>of</strong> 15 <strong>of</strong> <strong>the</strong>se b<strong>and</strong>s were polymorphic,<br />

allowing <strong>the</strong> differentiation <strong>of</strong> 19 <strong>of</strong> <strong>the</strong> 27 strains in this<br />

study. In<strong>for</strong>mation from four additional primer combinations<br />

(MseI-CTT/EcoRI-AC, MseI-CTT/EcoRI-AT,<br />

MseI-CAA/EcoRI-AC <strong>and</strong> MseI-CAA/EcoRI-AT) was<br />

also used in <strong>the</strong> differentiation process. The repetition <strong>of</strong><br />

this AFLP analysis obtained similar results.<br />

<strong>SSR</strong> analysis (Fig. 3) detected a number <strong>of</strong> alleles <strong>for</strong><br />

each locus,ranging from four (loci ScAAT5 <strong>and</strong><br />

ScAAT6) to 10 (loci ScAAT1 <strong>and</strong> ScAAT3),with 39<br />

total alleles identified. Twenty <strong>of</strong> <strong>the</strong> 27 S. cerevisiae<br />

strains in this study were differentiated. To complete <strong>the</strong><br />

<strong>SSR</strong> analysis,in<strong>for</strong>mation from three microsatellites<br />

was combined: ScAAT1,ScAAT3 <strong>and</strong> ScAAT4. Amplification<br />

products varied in size from 165 to 445 bp.<br />

Despite this allelic diversity,percent heterozygosity


564<br />

Fig. 1. Patterns <strong>of</strong> amplified DNA obtained with nine S. cerevisiae<br />

strains,in reactions with primer OPC-01. Lane M: Size marker f 174<br />

DNA, Hae III. Polymorphic b<strong>and</strong>s are indicated by arrows.<br />

between loci ranged from 7% at locus ScAAT6 to 67%<br />

at locus ScAAT1. Duplicate analysis <strong>of</strong> r<strong>and</strong>om strains<br />

resulted in identical pr<strong>of</strong>iles.<br />

In<strong>for</strong>mation content,measured as IDavp,was higher<br />

<strong>for</strong> <strong>the</strong> <strong>SSR</strong> analysis (0.62),although Ai was highest<br />

using AFLP analysis (4.0),followed by <strong>the</strong> <strong>SSR</strong> method<br />

(3.4) <strong>and</strong> finally <strong>RAPDs</strong> (2.1). Values obtained <strong>for</strong> <strong>the</strong><br />

average ENA avp were greatest using <strong>SSR</strong> analysis at 3.4,<br />

with <strong>the</strong> extremes measuring 1.16 <strong>and</strong> 6.08. Values<br />

obtained using AFLP <strong>and</strong> RAPD analysis were lower,<br />

averaging 1.6 <strong>and</strong> 1.3,respectively.<br />

3.2. Genetic similarity<br />

A summary <strong>of</strong> <strong>genetic</strong> similarity estimates,calculated<br />

<strong>for</strong> each marker system,is recorded in Table 3. Average<br />

estimates obtained using RAPD <strong>and</strong> AFLP analysis<br />

were both high (higher than 0.981),with a small range in<br />

variation. Estimates obtained from <strong>the</strong> <strong>SSR</strong> analysis<br />

were significantly lower,with a mean value <strong>of</strong> 0.437 <strong>and</strong><br />

ARTICLE IN PRESS<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568<br />

Table 2<br />

Level <strong>of</strong> polymorphism detected <strong>and</strong> comparison <strong>of</strong> in<strong>for</strong>mativeness obtained with RAPD,AFLP,<strong>and</strong> <strong>SSR</strong> methods in <strong>the</strong> 27 Sacharomyces<br />

cerevisiae strains studied<br />

variation ranging from 0.000 to 1.000. The correlation<br />

among similarity matrices derived <strong>for</strong> each method<br />

(Table 4) was very low in all cases,with AFLP/<strong>SSR</strong><br />

correlation (0.43) being <strong>the</strong> greatest.<br />

Genetic similarity trees <strong>for</strong> each marker type individually,<strong>and</strong><br />

as a whole,are presented in Figs. 4a–d.<br />

Cophenetic correlations (Table 4) indicate <strong>the</strong> extent to<br />

which <strong>the</strong> dendrograms derived from <strong>the</strong> different<br />

techniques accurately represent estimates <strong>of</strong> <strong>the</strong> original<br />

similarity matrices. High cophenetic correlations were<br />

obtained <strong>for</strong> RAPD (0.81) <strong>and</strong> AFLP marker types<br />

(0.81),with <strong>SSR</strong> <strong>markers</strong> achieving an even higher<br />

correlation <strong>of</strong> 0.91. Never<strong>the</strong>less,low correlations were<br />

observed among <strong>the</strong> different dendrograms (Table 4),<br />

topping out at 0.56 <strong>for</strong> <strong>the</strong> AFLP/<strong>SSR</strong> correlation.<br />

4. Discussion<br />

<strong>RAPDs</strong> <strong>AFLPs</strong> <strong>SSR</strong>s<br />

Number <strong>of</strong> assay units 32 6 6<br />

Average number <strong>of</strong> b<strong>and</strong>s per assay unit 4.8 22.8 6.5<br />

Polymorphic b<strong>and</strong>s (%) 8.38 10.94 100<br />

Number <strong>of</strong> loci 155 137 6<br />

Average number <strong>of</strong> alleles per locus 1.08 1.10 6.5<br />

Number <strong>of</strong> strains discriminated 13 19 20<br />

Number <strong>of</strong> assay units necessary to achieve <strong>the</strong> highest discrimination <strong>of</strong> <strong>the</strong> strains 7 4 3<br />

DI avp 0.20 0.35 0.62<br />

ENA avp 1.3 1.6 3.4<br />

Ne 16.9 24.0 20.4<br />

Ai 2.1 4.0 3.4/10.2<br />

DIavp: diversity index per polymorphic locus.ENAavp: effective number <strong>of</strong> alleles per polymorphic locus.Ne: number <strong>of</strong> effective alleles per<br />

polymorphic locus.Ai: assay efficiency index.<br />

All three techniques employed in this study (RAPD,<br />

AFLP <strong>and</strong> <strong>SSR</strong> analysis) resulted in sufficient resolution<br />

to detect differences between <strong>the</strong> <strong>genetic</strong> pr<strong>of</strong>iles <strong>of</strong><br />

various strains <strong>of</strong> <strong>the</strong> same species (S. cerevisiae). While<br />

<strong>the</strong> use <strong>of</strong> <strong>the</strong>se methods may overcome certain<br />

limitations associated with classical taxonomic methods,<br />

differences between <strong>the</strong>m exist with regards to <strong>the</strong> level<br />

<strong>of</strong> polymorphism detected,discriminatory power,effectiveness,<strong>and</strong><br />

speed <strong>of</strong> use.<br />

AFLP analysis generated <strong>the</strong> greatest number <strong>of</strong><br />

b<strong>and</strong>s per assay unit,due to <strong>the</strong> high number <strong>of</strong> loci<br />

identified per assay. The most polymorphic b<strong>and</strong>s,<br />

however,were obtained by microsatellite analysis<br />

(100%). Based on <strong>the</strong> small size <strong>of</strong> <strong>the</strong> S. cerevisiae<br />

genome <strong>and</strong> <strong>the</strong> number <strong>of</strong> amplification products<br />

obtained in this work,primers containing fewer selective<br />

bases will be used in order to increase <strong>the</strong> number <strong>of</strong><br />

b<strong>and</strong>s per assay unit.


ARTICLE IN PRESS<br />

Fig. 2. Patterns <strong>of</strong> amplified DNA <strong>of</strong> three S. cerevisiae strains,obtained by <strong>AFLPs</strong>.<br />

Fig. 3. Electrophoregram pr<strong>of</strong>iles <strong>of</strong> three S. cerevisiae strains generated by multiple PCR reaction amplifying <strong>the</strong> loci ScAAT2,ScAAT3 <strong>and</strong><br />

ScAAT5.<br />

Table 3<br />

<strong>Comparison</strong> <strong>of</strong> <strong>genetic</strong> similarity estimates obtained from three PCRderived<br />

techniques,using Dice coefficient<br />

Minimum Maximum Mean<br />

<strong>RAPDs</strong> 0.983 1.000 0.992<br />

<strong>AFLPs</strong> 0.961 1.000 0.981<br />

<strong>SSR</strong>s 0.000 1.000 0.437<br />

Table 4<br />

Correlation between cophenetic matrices (above diagonal) <strong>and</strong><br />

similarity matrices (below diagonal) obtained with different marker<br />

types<br />

<strong>RAPDs</strong> <strong>AFLPs</strong> <strong>SSR</strong>s<br />

<strong>RAPDs</strong> 0.81 0.35 0.50<br />

<strong>AFLPs</strong> 0.14 0.81 0.56<br />

<strong>SSR</strong>s 0.24 0.43 0.91<br />

Cophenetic correlation coefficients between <strong>the</strong> similarity <strong>and</strong> <strong>the</strong><br />

corresponding cophenetic matrices are given in bold on <strong>the</strong> leading<br />

diagonal.<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568 565<br />

While <strong>the</strong> <strong>SSR</strong> <strong>and</strong> AFLP techniques showed a higher<br />

discriminatory power than that <strong>of</strong> <strong>the</strong> RAPD analysis,<br />

all three techniques were able to detect <strong>genetic</strong><br />

variability between S. cerevisiae populations in this<br />

study. AFLP <strong>and</strong> <strong>SSR</strong> analysis distinguished a combined<br />

total <strong>of</strong> 23 <strong>of</strong> <strong>the</strong> 27 strains tested. All three<br />

techniques resulted in identical DNA pr<strong>of</strong>iles <strong>for</strong> three<br />

groups <strong>of</strong> isolates (1a,6a <strong>and</strong> 7a; 4n <strong>and</strong> 5n; <strong>and</strong> 6 s <strong>and</strong><br />

8 s). It is interesting to note that <strong>the</strong>se three groups were<br />

isolated ei<strong>the</strong>r from <strong>the</strong> same must or from different<br />

musts collected at <strong>the</strong> same winery (A,B,<strong>and</strong> C,<br />

respectively, Table 1). These observations may support<br />

<strong>the</strong> hypo<strong>the</strong>sis that those isolates not characterized in<br />

this study were actually <strong>of</strong> <strong>the</strong> same strain. Fur<strong>the</strong>r<br />

physiological <strong>and</strong> <strong>genetic</strong> analyses are needed to confirm<br />

this assumption.<br />

Microsatellite analysis resulted in <strong>the</strong> highest level <strong>of</strong><br />

in<strong>for</strong>mation content,measured as ID avp. This increased<br />

level <strong>of</strong> polymorphism may be due to some <strong>of</strong> <strong>the</strong><br />

mechanisms responsible <strong>for</strong> generating <strong>SSR</strong> allelic<br />

diversity: replication slippage <strong>and</strong> errors during


566<br />

crossing-over in meiosis. In our study,<strong>the</strong> microsatellite<br />

analysis yielded nearly twice as much in<strong>for</strong>mation as <strong>the</strong><br />

AFLP <strong>markers</strong>,<strong>and</strong> three times more in<strong>for</strong>mation than<br />

<strong>the</strong> <strong>RAPDs</strong>. This high level <strong>of</strong> polymorphism provided<br />

by <strong>the</strong> <strong>SSR</strong> technique is similar to that reported in o<strong>the</strong>r<br />

comparative studies (in soybean, Powell et al.,1996; in<br />

maize, Pejic et al.,1998; inMusa, Crouch et al.,1999; in<br />

table grapes, Cenı´ s<strong>and</strong>Sa´ nchez Escribano,1999).<br />

The Assay Efficiency Index (Ai),or <strong>the</strong> ENA<br />

identified per assay,is <strong>of</strong> particular interest,as it<br />

combines <strong>the</strong> ENA identified per locus <strong>and</strong> <strong>the</strong> number<br />

<strong>of</strong> polymorphic b<strong>and</strong>s detected per assay. For our study,<br />

this index allowed us to compare techniques that detect<br />

multiple alleles <strong>and</strong> one or two b<strong>and</strong>s per assay,such as<br />

<strong>SSR</strong> analysis,with techniques that detect two alleles <strong>and</strong><br />

multiple b<strong>and</strong>s per assay,such as RAPD <strong>and</strong> AFLP<br />

analysis. The highest value <strong>of</strong> Ai was obtained by <strong>the</strong><br />

AFLP method,with 4.0,compared with 3.4 <strong>for</strong> <strong>SSR</strong>s<br />

ARTICLE IN PRESS<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568<br />

1a<br />

2a<br />

6a<br />

69<br />

1a<br />

2a<br />

6a<br />

7a<br />

8a<br />

9a<br />

6s<br />

8s<br />

3a<br />

2n<br />

5a<br />

4n<br />

7s<br />

5n<br />

8n<br />

7n<br />

6n<br />

9n<br />

1n<br />

3n<br />

3s<br />

5s<br />

4a<br />

2s<br />

9s<br />

4s<br />

1s<br />

53<br />

61<br />

75<br />

7a<br />

8a<br />

9a<br />

3a<br />

5a<br />

4a<br />

1s<br />

4s<br />

9s<br />

7n<br />

9n<br />

2n<br />

8n<br />

1n<br />

3n<br />

6n<br />

4n<br />

5n<br />

2s<br />

7s<br />

3s<br />

6s<br />

8s<br />

5s<br />

0.988 0.991 0.994 0.997 1.000 0.975 0.981 0.987 0.994 1.000<br />

(a) (b)<br />

1a<br />

6a<br />

7a<br />

50<br />

87<br />

66<br />

90<br />

1a<br />

6a<br />

7a<br />

9a<br />

8a<br />

2a<br />

4a<br />

1s<br />

9s<br />

2s<br />

4s<br />

6s<br />

8s<br />

5a<br />

1n<br />

2n<br />

3n<br />

6n<br />

9n<br />

3a<br />

3s<br />

4n<br />

5n<br />

8n<br />

7s<br />

7n<br />

5s<br />

98<br />

54<br />

88<br />

99<br />

76<br />

8a<br />

9a<br />

2a<br />

5a<br />

3a<br />

4a<br />

4s<br />

9s<br />

2s<br />

1s<br />

6s<br />

8s<br />

1n<br />

3n<br />

6n<br />

9n<br />

2n<br />

4n<br />

5n<br />

8n<br />

7s<br />

7n<br />

5s<br />

3s<br />

0.234 0.425 0.617 0.808 1.000 0.964 0.973 0.982 0.991 1.000<br />

(c) (d)<br />

Fig. 4. Dendrograms showing <strong>the</strong> clustering <strong>of</strong> <strong>the</strong> 27 Sacharomyces cerevisiae strains in this study. Dendrograms were created using (a) RAPD<br />

analysis (b) AFLP analysis,(c) <strong>SSR</strong> analysis,<strong>and</strong> (d) <strong>the</strong> combination <strong>of</strong> <strong>the</strong> three marker types. The numbers at <strong>the</strong> <strong>for</strong>ks indicate <strong>the</strong> percentage <strong>of</strong><br />

a group’s occurrence in a bootstrap resampling <strong>of</strong> 1000 trees.<br />

<strong>and</strong> 2.1 <strong>for</strong> <strong>RAPDs</strong>,in agreement with <strong>the</strong> results<br />

obtained by o<strong>the</strong>r authors (in maize, Pejic et al.,1998).<br />

This is due to <strong>the</strong> simultaneous detection <strong>of</strong> a large<br />

number <strong>of</strong> polymorphic b<strong>and</strong>s per assay unit by AFLP<br />

<strong>markers</strong>.<br />

Based on <strong>the</strong> above results,it appears that microsatellite<br />

analysis is capable <strong>of</strong> revealing <strong>the</strong> highest level<br />

<strong>of</strong> in<strong>for</strong>mation per single marker,whereas AFLP<br />

<strong>markers</strong> can detect <strong>the</strong> highest number <strong>of</strong> polymorphisms<br />

in a single assay. However,<strong>the</strong> Assay Efficiency<br />

Index can be experimentally modified,<strong>and</strong> will increase<br />

in <strong>the</strong> case <strong>of</strong> <strong>SSR</strong> analysis if multiplex PCR is adopted.<br />

In this particular study,two types <strong>of</strong> multiple PCR<br />

reactions were used,each permitting <strong>the</strong> amplification <strong>of</strong><br />

three loci. As a result,<strong>the</strong> number <strong>of</strong> assay units<br />

decreased from six to two,in turn causing Ai to increase<br />

from 3.4 to 10.2 <strong>for</strong> microsatellite analysis. Thus,<strong>SSR</strong><br />

<strong>markers</strong> obtained <strong>the</strong> highest value <strong>for</strong> Ai,making <strong>the</strong>m


<strong>the</strong> most efficient <strong>markers</strong> in <strong>the</strong> study. This value may<br />

rise even higher if attempts to optimize this technique<br />

into a single multiple reaction involving all six microsatellites<br />

prove successful.<br />

Ano<strong>the</strong>r important factor to consider when evaluating<br />

marker efficiency is <strong>the</strong> ability to determine relationships<br />

between yeast strains based on an estimation <strong>of</strong><br />

<strong>genetic</strong> similarity (Figs. 4a–c). Genetic similarity coefficients<br />

were obtained (Table 3) <strong>for</strong> all three PCR-derived<br />

techniques,reflecting <strong>the</strong> extreme variability <strong>and</strong> high<br />

resolving power <strong>of</strong> <strong>the</strong>se methods. These same results,<br />

including lower similarity estimates <strong>for</strong> <strong>SSR</strong> analysis<br />

than <strong>for</strong> both <strong>RAPDs</strong> <strong>and</strong> <strong>AFLPs</strong>,have been reported<br />

in equivalent studies per<strong>for</strong>med using o<strong>the</strong>r organisms<br />

(in soybean, Powell et al.,1996; in maize, Pejic et al.,<br />

1998; in Musa, Crouch et al.,1999). These findings<br />

suggest that differences exist between a technique that<br />

amplifies unique sequences,such as microsatellite<br />

analysis,<strong>and</strong> o<strong>the</strong>r methods that amplify multiple<br />

sequences,such as RAPD <strong>and</strong> AFLP techniques.<br />

Poor correlation between estimates <strong>of</strong> <strong>genetic</strong> similarity<br />

based on <strong>the</strong> three different techniques evaluated<br />

in this study indicates that <strong>the</strong>se methods may selectively<br />

screen <strong>for</strong> different regions <strong>of</strong> <strong>the</strong> genome. To fur<strong>the</strong>r<br />

explore this issue,as well as <strong>the</strong> close similarity between<br />

<strong>the</strong> strains assayed,a greater number <strong>of</strong> loci should be<br />

analysed. In an ef<strong>for</strong>t to increase <strong>the</strong> integrity <strong>of</strong> our<br />

analysis,a single dendrogram was constructed that<br />

combines <strong>the</strong> in<strong>for</strong>mation obtained from all three<br />

marker types (Fig. 4d). This <strong>genetic</strong> tree revealed that<br />

only <strong>the</strong> topology <strong>of</strong> some groupings is conserved,with<br />

non-significant groups appearing r<strong>and</strong>om regardless <strong>of</strong><br />

<strong>the</strong> number <strong>of</strong> <strong>markers</strong> studied. Fur<strong>the</strong>r physiological<br />

experimentation is needed in order to determine if <strong>the</strong><br />

conserved groups are correlated with traits <strong>of</strong> interest.<br />

Based on <strong>the</strong> results <strong>of</strong> this study,RAPD <strong>markers</strong><br />

were <strong>the</strong> least polymorphic <strong>markers</strong> <strong>of</strong> those evaluated,<br />

<strong>and</strong> consequently had <strong>the</strong> least resolving power.<br />

Although <strong>the</strong> amount <strong>of</strong> variability detected with<br />

RAPD analysis is dependent upon <strong>the</strong> selection <strong>of</strong><br />

appropriate primers,this method has <strong>the</strong> advantage <strong>of</strong><br />

being inexpensive <strong>and</strong> simple to per<strong>for</strong>m,<strong>and</strong> does not<br />

require a previous knowledge <strong>of</strong> <strong>the</strong> genome. Problems<br />

with reproducibility have plagued <strong>the</strong> use <strong>of</strong> this<br />

technique in <strong>the</strong> past,due to <strong>the</strong> low temperature <strong>of</strong><br />

<strong>the</strong> hybridization <strong>of</strong> <strong>the</strong> primers. However,we were able<br />

to limit <strong>the</strong>se problems in this study,as evidenced by <strong>the</strong><br />

results <strong>of</strong> our duplicate analysis,by careful DNA<br />

preparation,strict adherence to amplification protocols<br />

<strong>and</strong> a rigorous interpretation <strong>of</strong> <strong>the</strong> results.<br />

The AFLP technique resulted in high resolution <strong>and</strong><br />

good reproducibility in this study,a finding substantiated<br />

by <strong>the</strong> recent use <strong>of</strong> AFLP <strong>markers</strong> in <strong>the</strong><br />

identification <strong>and</strong> intraspecific differentiation <strong>of</strong> S.<br />

cerevisiae strains (deBarros Lopes et al.,1999). This<br />

technique,however,is much more technically complex<br />

ARTICLE IN PRESS<br />

F. Javier Gallego et al. / Food Microbiology 22 (2005) 561–568 567<br />

than <strong>the</strong> use <strong>of</strong> <strong>SSR</strong> <strong>markers</strong>,requiring numerous<br />

experimental steps at a higher cost per in<strong>for</strong>mative<br />

marker. Despite <strong>the</strong>se limitations,<strong>the</strong> AFLP technique<br />

has great value as a tool <strong>for</strong> use in <strong>genetic</strong> mapping <strong>and</strong><br />

evolutionary studies,as it can test a large number <strong>of</strong> loci<br />

distributed r<strong>and</strong>omly throughout a genome. Unlike<br />

microsatellites,AFLP <strong>markers</strong> are not highly variable,<br />

providing a less biased estimate <strong>of</strong> population variability.<br />

<strong>SSR</strong> analysis revealed <strong>the</strong> highest <strong>genetic</strong> variability in<br />

<strong>the</strong> microbial population studied,also achieving <strong>the</strong><br />

greatest discriminatory power. It also proved to be <strong>the</strong><br />

most efficient method,with <strong>the</strong> highest number <strong>of</strong><br />

effective alleles per assay. We also found <strong>the</strong> results <strong>of</strong><br />

<strong>SSR</strong> to be faster <strong>and</strong> easier to interpret than <strong>the</strong> o<strong>the</strong>r<br />

techniques studied,making it an ideal technique <strong>for</strong> use<br />

in <strong>the</strong> characterization <strong>and</strong> identification <strong>of</strong> S. cerevisiae<br />

strains. Successful <strong>SSR</strong> analysis,however,depends on<br />

<strong>the</strong> proper design <strong>and</strong> syn<strong>the</strong>sis <strong>of</strong> primers,requiring a<br />

considerable amount <strong>of</strong> ef<strong>for</strong>t in <strong>the</strong> selection <strong>of</strong><br />

polymorphic microsatellites that af<strong>for</strong>d specific amplifications.<br />

Our study benefited from an available panel <strong>of</strong><br />

six microsatellite loci <strong>and</strong> <strong>the</strong> appropriate primers<br />

needed <strong>for</strong> its specific amplification (Pe´ rez et al.,2001).<br />

In summary,<strong>SSR</strong> amplifications is a simple <strong>and</strong><br />

effective method,with a high degree <strong>of</strong> discrimination<br />

<strong>and</strong> reproducibility,that can be used in <strong>the</strong> identification<br />

<strong>and</strong> intraspecific differentiation <strong>of</strong> S. cerevisiae strains,a<br />

species <strong>of</strong> great importance in industrial fermentations.<br />

Acknowledgments<br />

This research was supported by grants SC94-126 from<br />

<strong>the</strong> Programa Sectorial I+D Agrario y Alimentario <strong>and</strong><br />

RM00-001 from <strong>the</strong> Accio´ n Estratégica ‘‘Conservacio´ n<br />

de los recursos gene´ ticos de interés agroalimentario’’ del<br />

Plan Nacional de Investigacio´ n Cientı´ fica,Desarrollo e<br />

Innovacio´ n Tecnolo´ gica (I+D+I) from <strong>the</strong> Instituto<br />

Nacional de Investigacio´ n y Tecnologı´ a Agraria y<br />

Alimentaria (INIA) (Spain).<br />

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