Bacteria, lactic acid energy sources

Certain bacteria (lactic acid bacteria, LAB) ferment milk sugar, lactose, as a source of energy, producing lactic acid as a by-product. When sufficient... 

Lactic acid bacteria isolated from wine may use residual sugars or alcohol, or decompose organic acids as a source of carbon for growth and energy. Malic, citric, and tartaric acids may be metabolized, depending on conditions. 

These sugars are not digested well 1 by the human intestine but form good sources of energy for the bacteria of the gut. These bacteria convert the sugars to Hj, lactic acid and short-chain fatty acids. The amount of gas released after a meal containing beans is especially notorious. 

PolyCjS-hydroxyalkanoates) [poly(/3-hydroxyalkan-oic acids) PH A, PH A A]. Numerous bacteria form poly(/S-hydroxyalkanoates) (PHA) as reserve or storage substances that can serve as sources of carbon and energy when required. Monomeric components of the PHA include /5-hydroxybutyric acid, jS-hydroxyvaleric acid, and lactic acid. The linear polymer poly(jS-hy-droxybutyric acid) (PHB, PHBA) is accumulated intra-cellularly in the form of grains or granules and is one of the more important PHAA. As the polyester it is soluble in chloroform, insoluble in ether and consists on average of 60 (max. 25 000) hydroxybutyric acid units. 

Lactic acid bacteria synthesise a range of different polysaccharides, defined by their location in the cell. Some are located intracellularly and are used as energy or carbon sources others are cell wall components and some are located outside the cell wall. The latter are called extracellular polysaccharides (EPs) and are either associated with the cell wall as a slime capsule, or secreted into the environment. Many lactic acid bacteria such as Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermo-philus and Lactococcus lactis subsp. cremoris produce EPs. 

Lactose is used as an energy source as it is hydrolysed by lactase in the small intestine. A large part of the human population (as well as of other mammals) produces lactase only in childhood. In adulthood, a number of individuals have the enzyme activity reduced or completely absent, and consumption of milk is then problematic. Lactase is produced by lactic acid bacteria that break... 

Williams, A.G., Withers, S.E., and Banks, l.M. (2000) Energy sources of non-starter lactic acid bacteria isolated from Cheddar cheese. Int Dairy J10,17-23. 

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