Lactic acid bacteria

Abstract

A typical lactic acid bacterium grown under standard conditions is aerotolerant, acid tolerant, organotrophic, and a strictly fermentative rod or coccus, producing lactic acid as a major end product. It lacks cytochromes and is unable to synthesize porphyrins. Its features can vary under certain conditions. Catalase and cytochromes may be formed in the presence of hemes and lactic acid can be further metabolized, resulting in lower lactic acid concentrations. Cell division occurs in one plane, except pediococci. The cells are usually nonmotile. They have a requirement for complex growth factors such as vitamins and amino acids. An unequivocal definition of LAB is not possible (Axelsson, Lactic acid bacteria microbiological and functional aspects. Marcel Dekker, 2004). Lactic acid bacteria are characterized by the production of lactic acid as a major catabolic end product from glucose. Some bacilli, such as Actinomyces israeli and bifidobacteria, can form lactic acid as a major end product, but these bacteria have rarely or never been isolated from must and wine. The DNA of LAB has a G+C content below 55 mol%. LAB are grouped into the Clostridium branch of gram-positive bacteria possessing a relationship to the bacilli, while Bifidobacterium belongs to the Actinomycetes. They are grouped in one order and six families. From the 33 described genera, only 26 species belonging to six genera have been isolated from must and wine.