engleski

Evolution of multi-niche bacteria Lactobacillus brevis and Lactobacillus plantarum during prolonged stationary phase

The fluctuating stress conditions such as chemical and physical agents, low pH, low temperature and starvation increase the genomic mutation rate and influence on the lactic acid bacteria (LAB) evolution. On the base of common specific gene sets, species Lactobacillus brevis and Lactobacillus plantarum are classified as multi-niche LAB. We studied the survival response of L. brevis L62 and L. plantarum L73 during prolonged period of starvation, first cultured to the stationary phase in rich (MRS) and minimal (MML) medium and further kept in resultant spent medium, in terms of plasmid and chromosomal DNA status. The medium in which the cells were kept had a significant effect on the survival, plasmid status and chromosomal integrity of L. brevis L62 during 10 days starvation, as was shown in comparison between the MRS and MML medium. After 10 days starvation of L. brevis plasmid status has been investigated. The parent cells of L. brevis L62 and L. plantarum L73 contained three and two plasmids, respectively. The bacterium L. brevis L62 bears plasmids in size 5, 7 and 25 kb, while L. plantarum L73 harbors two plasmids approximately of 20 and 2.5 kb in size. These three plasmids were kept up in L. brevis during 10 days starvation in MML medium ; however after cultivation in rich MRS medium the smallest plasmid has been lost. It was noticed that curing of L. brevis L62 is connected with cell growth and low acidity media. Therefore, changes in gene expression of tested species were examined directly with observing protein status and indirectly controlling of appearance of antibiotic resistance, bacteriocins synthesis and sensitivity to hidrocloric acid and hydrogen peroxide. The antibiotic - resistance status of the both examined species was changed after prolonged pheriod of starvation. Better knowledge of L. brevis and L.plantarum genome evolution during prolonged starvation may facilitate new strategies for their development with advantageous characteristics.

Evolution; multi-niche bacteria

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