Le point des connaissances sur Brevibacterium linens

Abstract - Current state of research on Brevibacterium linens
Coryneform bacteria have been encountered in a wide variety of habitats, ranging from soil and sea water to poultry litter and cheese. B. linens is often involved in cheese ripening. It is reported to tolerate a high NaCl concentration (200 g / l). The fact that B. linens is strictly aerobic enables it to exert its proteolvtic activities mainly on the surface of the cheese in association with yeasts, molds and other bacteria. In addition to their contribution to the product's flavour, the catabolites of B. linens inhibit growth of_: many Gram-positive and Gram-negative food poisoning bacteria as well as several yeasts and molds. The cell watt composition of B. linens is uncommon: unusual teichoïc acids, meso-diamino-pimelic acid directly cross-linked, lack of galactose and arabinose. No mycolic acid, lypical of numerous coryneform bacteria, is present in its lipids. Its pigments of aromatic carotenoïd type are unusual in bacteria. B. linens is able to produce methanethiol from L-methionine. These results and the low rates obtained for DNA-DNA and DNA-RNA hybridizations between B. linens and other coryneform bacteria, prompted bacteriologists to redefine the species B. linens.
It is difficult to find a selective culture medium for B. linens because of its complex nutritional requirements. Most of strains of B. linens require organic nitrogen. Pantothenic acid or para-amino-benzoïc acid appears essential for its growth which is optimum with lactate or acetate as carbon source. This alkalophilic bacteria grows well at 25° C if the strain cornes from a natural source other than animal. Extracellular proteolvtic activities are very variable among the strains. An extracellular aminopeptidase has been extracted and purified from B. linens ATCC 9174. B. linens produces volatile fatty acids from carbohydrates and butter fat between pH 5.0 and 8.8. Its deamination activity is the source of a considerable production of ammoniac. The large population of bacteria related to B. linens produces specific flavour components which play an important role in the formation of cheese aromas.

Résumé - Brevibacterium linens est un des agents de l'affinage de nombreux fromages. Ses activités protéolytiques s'exercent à la surface des pâtes où ses catabolites (produits soufrés, ammoniac, aminés, composés aromatiques) contribuent à la flaveur finale des produits.
La composition de la paroi de B. linens est exceptionnelle : présence d'acides teichoïques particuliers, d'acide méso-diaminopimélique lié sans pont peptidique à la D-alanine voisine, absence de galactose et d'arabinose.
Ses lipides ne contiennent pas d'acide mycolique, caractéristique de nombreuses bactéries corynéformes. Ses pigments, de type caroténoïde aromatique, sont très peu fréquents chez les bactéries. Les faibles taux d'hybridation ADN-ADN et ADN-ARN ribosomique entre B. linens et les autres bactéries de type corynéforme incitent également à redéfinir l'espèce B. linens.
La plupart des souches de B. linens n'utilisent l'azote que sous forme organique. La présence d'acide pantothénique ou d'acide para-aminobenzoïque paraît indispensable à la croissance qui est optimale en présence de lactate ou d'acétate.