Effect of Flavonoids on the Ecology of Enterobacteria

The effect of flavonoids, natural plant metabolites, on the growth and viability of enterobacteria was studied using S. typhimurium and E. coli strains defective in some components of the DNA repair system. The minimal inhibitory concentrations of several flavonoids were measured. These agents were shown to have a weak bactericidal and a marked bacteriostatic effect, the latter increasing under anaerobic conditions. It is proposed that the mechanism of the bacteriostatic action of flavonoids is based on topoisomerase II inhibition. On the basis of these results, the ability of flavonoids to differentially suppress bacterial growth and their probable influence on the ecology of microorganisms (the formation, species composition, and ecological balance of natural microbial communities) are discussed.     

Biological diversity of nitrile-metabolizing bacteria in soils of the Perm region affected by human activities

The diversity of bacteria metabolizing nitriles of carbonic acids was studied in soils of the Perm region affected by human activities. Effective methods for selective isolation of cultures possessing the nitrile hydratase and nitrilase activities were developed. Most microorganisms capable of utilizing nitriles were Grampositive Nocardia-like bacteria of the genus Rhodococcus. Isolates with a detectable nitrilase activity were also represented by Gram-negative forms (Gram-negative aerobic/microaerophilic bacilli and cocci of the genera Pseudomonas, Azomonas, Azotobacter, and Acidovorax). Two enzyme systems for nitrile hydrolysis were found in 27% of cultures. The nitrile hydratase and nitrilase activities of the studied strains exceeded these enzymatic activities in bacteria isolated from native soils, which indicates that natural selection of saprophytic microflora occurs in chemically altered soils.