Propionic acid bacteria (PAB) possess a set of physiological and biochemical properties that allows their inclusion in probiotic compositions. Their potential resources are underestimated as yet. The list of the described probiotic characteristics of PAB must be enlarged by the addition of antimutagenic, reactivative and protective activities, first discovered by our group. Live and dead cells of PAB and Luteococcus casei as well as their cultural liquid (CL) revealed antimutagenic (AM) effect on spontaneous and induced mutagenesis. Protective and reactivative activities of Propionibacterium freudenreichii cells are bound up with the intracellular protein, identified as cystein synthase, whose synthesis is induced by some stress factors. Under unfavourable conditions leading to lysis of the majority of cells, the released protein may play a vitally important role in the cell population as a whole, supporting the existence of the species. The active protein reveals cross-reactive properties, both the protective and reactivative effects on cells of Escherichia coli and yeasts Saccharomyces cerevisiae and Candida guilliermondii. Phylogenetically close to PAB, L. casei produces and excretes in the medium a proteinaceous metabolite, possessing protective and reactivative effects on cells of the producer, E. coli, S. cerevisiae and C. scottii, treated by heating and UV irradiation. The exometabolite is synthezed by cells in the log phase of growth. The effectiveness of its impact inversely depends on the survival of microbes. CL of L. casei is considered as the source of a new prebiotic with reactivative and protective properties.

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