Phenotypic characteristics and results of PCR tests for the presence of species-specific genes indicate that a number of strains of thermophilic lactic acid bacteria previously considered as belonging to Streptococcus thermophilus are actually closely related to enterococci. In the present study, partial (over 500 nucleotides) sequencing of 16S rRNA genes from 12 strains of thermophilic lactic acid bacteria used as starters for manufacturing sour milk products on the territory of the Commonwealth of Independent States (CIS) has been performed. According to the results of the sequencing, seven of the strains have been classified with Enterococcus durans.
View Article and Find Full Text PDFThe role of genetic recombinations is considered in the context of ecological stability of organisms. The ecological stability is taken as a special notion distinct from fitness in its original sense as the Maltusian parameter according to R. Fisher.
View Article and Find Full Text PDFAccording to DNA hybridization data, thermophilic streptococci used in Russia as starters in the dairy industry are divided into 6 different genomovars, with a degree of DNA homology not exceeding 20-50%. The analysis of genomes from these genomovars using SmaI restriction endonuclease and pulsed-field gel electrophoresis revealed a wide variability of the genome size. In some strains, the genome size considerably exceeded 2000 kbp.
View Article and Find Full Text PDFEcological stability of an organism, which determines the possibility of its existence under changing environmental conditions, can be estimated as the probability of the participation of each viable offspring in reproduction. In developing species, the periodic rises and falls in the population size (Chetverikov's "waves of life") can lead to changes in ecological stability, which is of macroevolutionary importance. Under conditions of isolation such changes generally result in specialization of intraspecific races but they could then lead to an increase in ecological stability of hybrid forms.
View Article and Find Full Text PDFPromoters in Escherichia coli that are negatively regulated by the CytR repressor are also activated by the cAMP receptor protein (CRP) complexed to cAMP; as a characteristic, these promoters encode tandem binding sites for cAMP-CRP. In one such promoter, deoP2, CytR binds to the region between the tandem CRP binding sites with a relatively low affinity; in the presence of cAMP-CRP, however, the repressor and activator bind cooperatively to the DNA. Here we have investigated this cooperativity by isolating mutants of the CRP protein that abolish CytR regulation without exhibiting a concomitant loss in their ability to activate transcription.
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