Cross-protection and cross-feeding mediated by signaling molecules enhanced the viability of P. fluorescens S01 and R. erythropolis S02 under the dual stresses of polycyclic aromatic hydrocarbons (PAHs) and low temperature.

In harsh environments, microbes employ varieties of strategies, including cross-feeding and biofilm formation, to enhance their survival. Signaling molecules played a regulatory role in these processes. However, it remains unclear whether cross-feeding and biofilm formation can offer protection to others and precise regulatory mechanisms of signaling molecules in facilitating cross-protection. Herein, we constructed a synthetic microbial community (SynCom) using two bacteria isolated from PAHs-contaminated soil and analyzed the cross-protection patterns. Cross-protection within SynCom composed of P. fluorescens S01 and R. erythropolis S02 was facilitated through cross-feeding and biofilm formation. Cross-feeding of intermediate metabolites not only promoted PAHs degradation but also indirectly protected R. erythropolis S02. Biofilm formation of SynCom was regulated by signaling molecules, with P. fluorescens S01 and R. erythropolis S02 operating in a relay mode. Specifically, under regulation of c-di-GMP, R. erythropolis S02 produced sugar nucleotides, which were precursors for biofilm. P. fluorescens S01 absorbed sugar nucleotides under the influence of PQS and RhlI, accelerated biofilm synthesis, thereby protected both P. fluorescens S01 and R. erythropolis S02 from environmental stress. Our study deciphered a novel mechanism by which SynCom employed relayed signaling molecules to coordinately regulate biofilm formation in response to combined cold-pollutant stress. The findings provided both theoretical foundations for targeted SynCom construction and technical pathways for their application in contaminated environment remediation.