Polyphosphate in Lactobacillus and Its Link to Stress Tolerance and Probiotic Properties.

Cristina Alcántara,Carlos Jadán-Piedra,Vicenta Devesa,Manuel Zúñiga,Dinoraz Vélez,José M Coll-Marqués,Vicente Monedero

doi:10.3389/fmicb.2018.01944

Abstract

The synthesis of the inorganic polymer polyphosphate (poly-P) in bacteria has been linked to stress survival and to the capacity of some strains to sequester heavy metals. In addition, synthesis of poly-P by certain strains of probiotic lactobacilli has been evidenced as a probiotic mechanism due to the homeostatic properties of this compound at the intestinal epithelium. We analyzed the link between poly-P synthesis, stress response, and mercury toxicity/accumulation by comparing wild-type strains of Lactobacillus and their corresponding mutants devoid of poly-P synthesis capacity (defective in the poly-P kinase, ppk, gene). Results showed that resistance to salt (NaCl) and acidic (pH 4) stresses upon ppk mutation was affected in Lactobacillus casei, while no effect was observed in two different Lactobacillus plantarum strains. Inorganic [Hg(II)] and organic (CH3Hg) mercury toxicity was generally increased upon ppk mutation, but no influence was seen on the capacity to retain both mercurial forms by the bacteria. Notwithstanding, the culture supernatants of ppk-defective L. plantarum strains possessed a diminished capacity to induce HSP27 expression, a marker for cell protection, in cultured Caco-2 cells compared to wild-type strains. In summary, our results illustrate that the role of poly-P in stress tolerance can vary between strains and they reinforce the idea of probiotic-derived poly-P as a molecule that modulates host-signaling pathways. They also question the relevance of this polymer to the capacity to retain mercury of probiotics.

Highlights

Polyphosphate is an inorganic phosphate polymer of hundreds of phosphates that can be synthesized in bacteria by the action of the enzyme poly-P kinase (PPK) (Rao et al, 2009)
We had previously obtained a defective mutant in the polyP kinase gene in Lactobacillus casei BL23 that showed detected after specific poly-P staining, compared to the wild type (Figure 1A)
This phenomenon does not seem to apply to all species because, contrarily to L. casei, no effect on the resistance to NaCl or acidic stresses was evidenced for two L. plantarum strains

Summary

Introduction

Polyphosphate (poly-P) is an inorganic phosphate polymer of hundreds of phosphates that can be synthesized in bacteria by the action of the enzyme poly-P kinase (PPK) (Rao et al, 2009). Many bacterial strains possess the capacity to intracellularly accumulate this compound in high amounts in the form of poly-P granules and this characteristic is relevant, for example, in the process of biological phosphate removal in wastewater treatment plants (Yuan et al, 2012). Poly-P has diverse physiological roles, some of them not totally understood yet. Besides its function as a storage compound, poly-P can be involved in stress response [e.g., starvation, acid or oxidative stresses (Gray and Jakob, 2015), virulence, motility or biofilm formation, among others physiological processes (Albi and Serrano, 2016)]

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