RESUMO
Lactic acid bacteria (LAB) synthesize exopolysaccharides (EPS), which are structurally diverse biopolymers with a broad range of technological properties and bioactivities. There is scientific evidence that these polymers have health-promoting properties. Most commercialized probiotic microorganisms for consumption by humans and farmed animals are LAB and some of them are EPS-producers indicating that some of their beneficial properties could be due to these polymers. Probiotic LAB are currently used to improve human health and for the prevention and treatment of specific pathologic conditions. They are also used in food-producing animal husbandry, mainly due to their abilities to promote growth and inhibit pathogens via different mechanisms, among which the production of EPS could be involved. Thus, the aim of this review is to discuss the current knowledge of the characteristics, usage and biological role of EPS from LAB, as well as their postbiotic action in humans and animals, and to predict the future contribution that they could have on the diet of food animals to improve productivity, animal health status and impact on public health.
RESUMO
Unsaturated fatty acid (UFA) biosynthesis is essential for the maintenance of membrane structure and function in many groups of anaerobic bacteria. Like Escherichia coli, the human pathogen Streptococcus pneumoniae produces straight-chain saturated fatty acids (SFA) and monounsaturated fatty acids. In E. coli UFA synthesis requires the action of two gene products, the essential isomerase/dehydratase encoded by fabA and an elongation condensing enzyme encoded by fabB. S. pneumoniae lacks both genes and instead employs a single enzyme with only an isomerase function encoded by the fabM gene. In this paper we report the construction and characterization of an S. pneumoniae 708 fabM mutant. This mutant failed to grow in complex medium, and the defect was overcome by addition of UFAs to the growth medium. S. pneumoniae fabM mutants did not produce detectable levels of monounsaturated fatty acids as determined by gas chromatography-mass spectrometry and thin-layer chromatography analysis of the radiolabeled phospholipids. We also demonstrate that a fabM null mutant of the cariogenic organism Streptococcus mutants is a UFA auxotroph, indicating that FabM is the only enzyme involved in the control of membrane fluidity in streptococci. Finally we report that the fabN gene of Enterococcus faecalis, coding for a dehydratase/isomerase, complements the growth of S. pneumoniae fabM mutants. Taken together, these results suggest that FabM is a potential target for chemotherapeutic agents against streptococci and that S. pneumoniae UFA auxotrophs could help identify novel genes encoding enzymes involved in UFA biosynthesis.