Mechanisms of survival of lactic acid bacteria in silanol-humate gels with organic acids

Bacterial survival under unfavorable growth conditions is one of the fundamental problems of microbiology. The applied aspect of this problem – long-term preservation of bacterial cell viability – is of particular importance for storage of lactic acid bacteria due to the biotechnological significance of this group of microorganisms and their high rates of death during long-term storage. The aim of this study was to investigate the long-term survival of lactic acid bacteria of different physiological groups (heterofermentative Enterococcus faecium M3185 and homofermentative Lactobacillus paracasei AK 508) in silanol-humate gels (SHG) containing various organic acids used as titrants in obtaining SHG (malic, lactic, acetic, ascorbic, citric). Placing cells in CHG with organic acids resulted in a significant increase in the titer of viable cells relative to the control during long-term storage (up to 200 times) and depended on the bacterial culture, the acid used and the storage period (up to 5 months). The experimentally proven reasons for the long-term survival of bacteria in CHG are: 1) most of the cells are in a state of hypometabolism and consume organic acids, which is evidenced by a decrease in their concentration during storage, as well as by the release of CO2 in the case of E. faecium (in this case, the metabolic rate is 1000 times lower than that of growing cells); 2) the absence of mass autolysis of cells, which is presumably due to the “disunity” of the cells in the gel and the impossibility of creating sufficient concentrations of autoregulators and autolysis enzymes; 3) some of the cells are in a state of rest, in the form of stress-resistant cyst-like cells. There is also reason to believe that when transferred to a gel, an alternative (biofilm) phenotype is formed, which has increased stress resistance. The results obtained indicate the feasibility of immobilizing lactic acid bacteria cells in SGG with organic acids for long-term storage.