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PhD Vermeiren Lieve Compleet - Hogeschool Gent

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1.4.4.3. Classification<br />

Although earlier subdivisions exist, the classical division of the lactobacilli is based on their<br />

fermentation characteristics: (1) obligately homofermentative; (2) facultatively<br />

heterofermentative and (3) obligately heterofermentative (Kandler & Weiss, 1986; Stiles &<br />

Holzapfel, 1997).<br />

The obligately homofermentative lactobacilli (group 1) possess aldolase but no<br />

phophoketolase (Kandler & Weiss, 1986) and degrade hexoses almost exclusively to lactic<br />

acid by the Embden-Meyerhof pathway and do not ferment pentoses or gluconate<br />

(Vandamme et al., 1996). Some important food associated species of this group are<br />

Lactobacillus acidophilus, Lactobacillus delbrueckii and Lactobacillus helveticus (Stiles &<br />

Holzapfel, 1997).<br />

The facultatively heterofermentative lactobacilli (group 2) ferment hexoses almost exclusively<br />

to DL-lactic acid by the Embden-Meyerhof pathway or to lactic acid, acetic acid, ethanol and<br />

formic acid under glucose limitation. Pentoses are fermented to lactic acid and acetic acid via<br />

an inducible pentose phosphoketolase (Kandler & Weiss, 1986; Vandamme et al., 1996).<br />

They may produce gas from gluconate but not from glucose. Important food-associated<br />

species in this group are Lactobacillus casei, Lactobacillus plantarum, Lactobacillus sakei<br />

and Lactobacillus curvatus (Stiles & Holzapfel, 1997).<br />

The obligately heterofermentative lactobacilli (group 3) lack aldolase and ferment hexoses to<br />

DL-lactic acid, acetic acid, ethanol and CO2 via the 6-phosphogluconate pathway. Pentoses<br />

are fermented to lactic acid and acetic acid. In general, a pentose phosphoketolase is involved<br />

in both pathways (Kandler & Weiss, 1986; Vandamme et al., 1996). The production of gas<br />

from glucose is a characteristic feature of these bacteria. The most important food-associated<br />

species of this group are Lactobacillus sanfranciscensis involved in the production of<br />

sourdough bread, Lactobacillus reuteri of interest because of its antimicrobial metabolite<br />

reuterin and Lactobacillus brevis causing spoilage in citrus fruits, beer, wine and some meat<br />

products (Stiles & Holzapfel, 1997).<br />

The past two decades, a whole range of taxonomic reassignments occurred within the genus<br />

Lactobacillus, based almost exclusively on the results of rRNA-sequencing or DNA-DNA<br />

hybridisations. The large number of nomenclature revisions is a striking indication of the<br />

discrepancies between the results obtained by former traditional phenotypic tests (classical<br />

Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 6

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