Accumulation of Polyphosphate in Lactobacillus spp. and Its Involvement in Stress Resistance

Abstract

ABSTRACTPolyphosphate (poly-P) is a polymer of phosphate residues synthesized and in some cases accumulated by microorganisms, where it plays crucial physiological roles such as the participation in the response to nutritional stringencies and environmental stresses. Poly-P metabolism has received little attention inLactobacillus, a genus of lactic acid bacteria of relevance for food production and health of humans and animals. We show that among 34 strains ofLactobacillus, 18 of them accumulated intracellular poly-P granules, as revealed by specific staining and electron microscopy. Poly-P accumulation was generally dependent on the presence of elevated phosphate concentrations in the culture medium, and it correlated with the presence of polyphosphate kinase (ppk) genes in the genomes. Theppkgene fromLactobacillusdisplayed a genetic arrangement in which it was flanked by two genes encoding exopolyphosphatases of the Ppx-GppA family. Theppkfunctionality was corroborated by its disruption (LCABL_27820 gene) inLactobacillus caseiBL23 strain. The constructedppkmutant showed a lack of intracellular poly-P granules and a drastic reduction in poly-P synthesis. Resistance to several stresses was tested in theppk-disrupted strain, showing that it presented a diminished growth under high-salt or low-pH conditions and an increased sensitivity to oxidative stress. These results show that poly-P accumulation is a characteristic of some strains of lactobacilli and may thus play important roles in the physiology of these microorganisms.