Transport of Sugars and Sugar Alcohols by Lactic Acid Bacteria

Abstract

Lactic acid bacteria (LAB) play an important role in the fermentation of beverages like wine and beer, and in the production of dairy products, sour dough, sausages and cheese. The knowledge of the genome sequence offers an insight into the metabolism of the bacteria and provides means to optimize the manufacturing of the products. By now genomes of several lactic acid bacteria are sequenced, including wine related bacteria Oenococcus oeni PSU-1, Pediococcus pentosaceus ATCC 25745, Leuconostoc mesenteroides ATCC 8293 (http://www.jgi.doe.gov/; Klaenhammer et al. 2002; Mills et al. 2005) and Lactobacillus plantarum WCFS1 (http://www.cmbi. ru.nl/plantarum/; http://www.lacplantcyc.nl/; Kleerebezem et al. 2003). Lactococcus lactis ssp. lactis, formerly Streptococcus lactis (Schleifer et al. 1985), was the first fully sequenced and annotated lactic acid bacterium (Bolotin et al. 2001). L. lactis is mainly used in the dairy industry for the production of cheese. It serves as a model organism for studies on the physiology and genetics of lactic acid bacteria and is included in the genome comparison. Lactic acid bacteria ferment carbohydrates with lactate as the main product by the homoand heterofermentative pathways. Homofermentative LAB ferment hexoses by glycolysis to lactate as the only product (>90%). P. pentosaceus is classified as homofermentative, but metabolizes pentoses by the phosphoketolase pathway to lactic acid and acetate typical for heterofermentative LAB. Lactobacillus delbrueckii ssp. bulgaricus is obligately homofermentative and is not able to grow on pentoses (Axelsson 2004; Klaenhammer et al. 2002). The homofermentative Lactococcus lactis shifts under specific conditions from homofermentative to mixed-acid fermentation with formate as an additional product (Garrigues et al. 1997). Heterofermentative lactic acid bacteria like O. oeni and L. mesenteroides ferment hexoses and pentoses by the phosphoketolase pathway (Kandler 1983; Veiga-da-Cunha et al. 1993; Mills et al. 2005). Main products are lactate, ethanol and CO 2 from hexoses, or lactate and acetate from pentoses. In the presence of alternative acceptors, heterofermentative LAB replace ethanol by varying amounts of acetate (Kandler 1983; Zaunmuller et al. 2006; Stolz et al. 1995; Unden and