Inorganic phosphate (Pi) concentration modulates polyphosphate (polyP) levels in diverse bacteria, affecting their physiology and survival. Lactiplantibacillus paraplantarum CRL 1905 is a lactic acid bacterium isolated from quinoa sourdough with biotechnological potential as starter, for initiating fermentation processes in food, and as antimicrobial-producing organism. The aim of this work was to evaluate the influence of the environmental Pi concentration on different physiological and molecular aspects of the CRL 1905 strain. Cells grown in a chemically defined medium containing high Pi (CDM + P) maintained elevated polyP levels up to late stationary phase and showed an enhanced bacterial survival and tolerance to oxidative stress. In Pi sufficiency condition (CDM-P), cells were ~ 25% longer than those grown in CDM + P, presented membrane vesicles and a ~ 3-fold higher capacity to form biofilm. Proteomic analysis indicated that proteins involved in the “carbohydrate transport and metabolism” and “energy production and conversion” categories were up-regulated in high Pi stationary phase cells, implying an active metabolism in this condition. On the other hand, stress-related chaperones and enzymes involved in cell surface modification were up-regulated in the CDM-P medium. Our results provide new insights to understand the CRL 1905 adaptations in response to differential Pi conditions. The adjustment of environmental Pi concentration constitutes a simple strategy to improve the cellular fitness of L. paraplantarum CRL 1905, which would benefit its potential as a microbial cell factory.

Urinary tract infections (UTIs) are one of the most common bacterial infections in hospital settings and are increasingly difficult to treat due to the rise of antibiotic-resistant uropathogens (UP). Therefore, exploring alternatives to antibiotic therapy is crucial to control the spread of these pathogens. Lactic acid bacteria (LAB) have demonstrated broad antimicrobial activity against various microorganisms, and postbiotics, bioactive compounds derived from these probiotic bacteria, are emerging as a promising tool for controlling such infections. In this study, several LAB strains exhibited antagonistic activity against different clinical UP isolates. To assess whether this activity was due to secreted metabolites, cell-free supernatants (CFSs) were obtained from 24 h LAB cultures. CFSs exhibited variable antimicrobial activity against most UP isolates. Notably, these inhibitory effects were completely lost after pH neutralization and partially reduced by heat or protease treatment, suggesting the involvement of organic acids and/or proteinaceous molecules. CFSs were able to inhibit biofilm formation and partially disrupt mature biofilms of Staphylococcus aureus and Pseudomonas aeruginosa, demonstrating their potential to manage persistent infections. Finally, safety assessment in Caenorhabditis elegans demonstrated that concentrations up to 25% were non-toxic, with no adverse effects on survival, locomotion, or reproduction. Using this infection model, CFS from Lactiplantibacillus paraplantarum CRL 1905 enhanced survival against both pathogens when administered before, during, or after infection, with dose-dependent protective effects. Our findings highlight the potential of LAB-derived postbiotics as safe and effective strategies for preventing and controlling UTIs, particularly in the context of rising antibiotic resistance.