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The genus Cladosporium and similar dematiaceous ... - CBS - KNAW

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Arzanlou et al.<br />

To date 26 species have been named in Ramichloridium; they<br />

not only differ in morphology, but also in life style. Ramichloridium<br />

mackenziei C.K. Campb. & Al-Hedaithy is a serious human<br />

pathogen, causing cerebral phaeohyphomycosis (Al-Hedaithy et al.<br />

1988, Campbell & Al-Hedaithy 1993), whereas R. musae causes<br />

tropical speckle disease on members of the Musaceae (Stahel 1937,<br />

Jones 2000). Another plant-pathogenic species, R. pini de Hoog &<br />

Rahman, causes a needle disease on Pinus contorta (de Hoog et<br />

al. 1983). Other clinically relevant species of Ramichloridium are R.<br />

basitonum de Hoog <strong>and</strong> occasionally R. schulzeri (Sacc.) de Hoog,<br />

while the remaining species tend to be common soil saprobes.<br />

No teleomorph has thus far been linked to species of<br />

Ramichloridium. <strong>The</strong> main question that remains is whether shared<br />

morphology among the species in this <strong>genus</strong> reflects common<br />

ancestry (Seifert 1993, Untereiner & Naveau 1999). To delineate<br />

anamorphic genera adequately, morphology <strong>and</strong> conidial ontogeny<br />

alone are no longer satisfactory (Crous et al. 2006a, b), <strong>and</strong> DNA<br />

data provide additional characters to help delineate species <strong>and</strong><br />

genera (Taylor et al. 2000, Mostert et al. 2006, Zipfel et al. 2006).<br />

<strong>The</strong> aim of the present study was to integrate morphological<br />

<strong>and</strong> cultural features with DNA sequence data to resolve the<br />

species concepts <strong>and</strong> generic limits of the taxa currently placed in<br />

Periconiella, Ramichloridium, Rhinocladiella <strong>and</strong> Veronaea, <strong>and</strong> to<br />

resolve the status of several new cultures that were isolated during<br />

the course of this study.<br />

Materials <strong>and</strong> Methods<br />

Isolates<br />

Species names, substrates, geographical origins <strong>and</strong> GenBank<br />

accession numbers of the isolates included in this study are listed<br />

in Table 1. Fungal isolates are maintained in the culture collection<br />

of the Centraalbureau voor Schimmelcultures (<strong>CBS</strong>) in Utrecht, the<br />

Netherl<strong>and</strong>s.<br />

DNA extraction, amplification <strong>and</strong> sequence analysis<br />

Genomic DNA was extracted from colonies grown on 2 % malt<br />

extract agar (MEA, Difco) (Gams et al. 2007) using the FastDNA kit<br />

(BIO101, Carlsbad, CA, U.S.A.). <strong>The</strong> primers ITS1 <strong>and</strong> ITS4 (White<br />

et al. 1990) were used to amplify the internal transcribed spacer<br />

region (ITS) of the nuclear ribosomal RNA operon, including: the<br />

3’ end of the 18S rRNA gene, the first internal transcribed spacer<br />

region (ITS1), the 5.8S rRNA gene, the second internal transcribed<br />

spacer region (ITS2) <strong>and</strong> the 5’ end of 28S rRNA gene. Part of<br />

the large subunit 28S rRNA (LSU) gene was amplified with primers<br />

LR0R (Rehner & Samuels 1994) <strong>and</strong> LR5 (Vilgalys & Hester 1990).<br />

<strong>The</strong> ITS region was sequenced only for those isolates for which<br />

these data were not available. <strong>The</strong> ITS analyses confirmed the<br />

proposed classification based on LSU analysis for each major<br />

clade <strong>and</strong> are not presented here in detail; but the sequences are<br />

deposited in GenBank where applicable. <strong>The</strong> PCR reaction was<br />

performed in a mixture with 0.5 units Taq polymerase (Bioline,<br />

London, U.K.), 1× PCR buffer, 0.5 mM MgCl 2<br />

, 0.2 mM of each<br />

dNTP, 5 pmol of each primer, approximately 10–15 ng of fungal<br />

genomic DNA, with the total volume adjusted to 25 µL with<br />

sterile water. Reactions were performed on a GeneAmp PCR<br />

System 9700 (Applied Biosystems, Foster City, CA) with cycling<br />

conditions consisting of 5 min at 96 °C for primary denaturation,<br />

followed by 36 cycles at 96 °C (30 s), 52 °C (30 s), <strong>and</strong> 72 °C<br />

(60 s), with a final 7 min extension step at 72 °C to complete the<br />

reaction. <strong>The</strong> amplicons were sequenced using BigDye Terminator<br />

v. 3.1 (Applied Biosystems, Foster City, CA) or DYEnamicET<br />

Terminator (Amersham Biosciences, Freiburg, Germany) Cycle<br />

Sequencing Kits <strong>and</strong> analysed on an ABI Prism 3700 (Applied<br />

Biosystems, Foster City, CA) under conditions recommended by<br />

the manufacturer. Newly generated sequences were subjected<br />

to a Blast search of the NCBI databases, sequences with high<br />

<strong>similar</strong>ity were downloaded from GenBank <strong>and</strong> comparisons<br />

were made based on the alignment of the obtained sequences.<br />

Sequences from GenBank were also selected for <strong>similar</strong> taxa. <strong>The</strong><br />

LSU tree was rooted using sequences of Athelia epiphylla Pers.<br />

<strong>and</strong> Paullicorticium ansatum Liberta as outgroups. Phylogenetic<br />

analysis was performed with PAUP (Phylogenetic Analysis Using<br />

Parsimony) v. 4.0b10 (Swofford 2003), using the neighbour-joining<br />

algorithm with the uncorrected (“p”), the Kimura 2-parameter <strong>and</strong><br />

the HKY85 substitution models. Alignment gaps longer than 10<br />

bases were coded as single events for the phylogenetic analyses;<br />

the remaining gaps were treated as missing data. Any ties were<br />

broken r<strong>and</strong>omly when encountered. Phylogenetic relationships<br />

were also inferred with the parsimony algorithm using the heuristic<br />

search option with simple taxon additions <strong>and</strong> tree bisection <strong>and</strong><br />

reconstruction (TBR) as the branch-swapping algorithm; alignment<br />

gaps were treated as a fifth character state <strong>and</strong> all characters were<br />

unordered <strong>and</strong> of equal weight. Branches of zero length were<br />

collapsed <strong>and</strong> all multiple, equally parsimonious trees were saved.<br />

Only the first 5 000 equally most parsimonious trees were saved.<br />

Other measures calculated included tree length, consistency<br />

index, retention index <strong>and</strong> rescaled consistency index (TL, CI, RI<br />

<strong>and</strong> RC, respectively). <strong>The</strong> robustness of the obtained trees was<br />

evaluated by 1 000 bootstrap replications. Bayesian analysis was<br />

performed following the methods of Crous et al. (2006c). <strong>The</strong> best<br />

nucleotide substitution model was determined using MrModeltest<br />

v. 2.2 (Nyl<strong>and</strong>er 2004). MrBayes v. 3.1.2 (Ronquist & Huelsenbeck<br />

2003) was used to perform phylogenetic analyses, using a general<br />

time-reversible (GTR) substitution model with inverse gamma<br />

rates, dirichlet base frequencies <strong>and</strong> the temp value set to 0.5. New<br />

sequences were lodged with NCBI’s GenBank (Table 1) <strong>and</strong> the<br />

alignment <strong>and</strong> trees with TreeBASE (www.treebase.org).<br />

Morphology<br />

Cultural growth rates <strong>and</strong> morphology were recorded from colonies<br />

grown on MEA for 2 wk at 24 ºC in the dark, <strong>and</strong> colony colours<br />

were determined by reference to the colour charts of Rayner (1970).<br />

Microscopic observations were made from colonies cultivated on<br />

MEA <strong>and</strong> OA (oatmeal agar, Gams et al. 2007), using a slide culture<br />

technique. Slide cultures were set up in Petri dishes containing 2<br />

mL of sterile water, into which a U-shaped glass rod was placed,<br />

extending above the water surface. A block of freshly growing<br />

fungal colony, approx. 1 cm square was placed onto a sterile<br />

microscope slide, covered with a somewhat larger, sterile glass<br />

cover slip, <strong>and</strong> incubated in the moist chamber. Fungal sporulation<br />

was monitored over time, <strong>and</strong> when optimal, images were captured<br />

by means of a Nikon camera system (Digital Sight DS-5M, Nikon<br />

Corporation, Japan). Structures were mounted in lactic acid, <strong>and</strong><br />

30 measurements (× 1 000 magnification) determined wherever<br />

possible, with the extremes of spore measurements given in<br />

parentheses.<br />

58

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