Unraveling the mechanism of interspecies quorum sensing in a synthetic consortium.

This project aimed at deciphering the molecular mechanism of interspecies cell-cell communication in complex microbial communities using a synthetic bacterial consortium composed of two workhouses organism E. coli and N. vulgaris. These are ubiquitous and can be found in various environments (soil, gut microbiota, etc.). Previous studies pointed towards the involvement of Quorum Sensing (QS) through the secretion of AI2 signal in triggering collective behaviors (including cell-cell interactions, metabolic cross-feeding, etc.) between these two microorganisms. While AI2 type QS mechanism has been well characterized in E. coli, little is known on QS mechanisms in N. vulgaris. Using bioinformatic survey, we showed that N. vulgaris lacks the gene involved in the AI2 synthesis (luxS). Nevertheless, we have identified in the genome of N. vulgaris homologs of lsr genes potentially involved in signal transduction via the phosphorylation of AI2 inside the cell (DVU_3134 coding for LsrK-like) and a transcriptional repressor (DVU_3131 coding for LsrR-like). This suggested that even though N. vulgaris cannot produce AI2, it might sense the signal in the environment. Hence, to challenge the role of interspecies QS mechanism in the synthetic ecosystem, this proposal was articulated into 2 work packages. WP1: First, the role of the putative QS actors was validated in vitro, using a combination of enzymatic, gel shift, and trans-complementation assays. The results obtained here, clearly pointed towards a functional AI2 QS pathway in D. vulgaris involved in the regulation of its metabolism. WP2: Whether AI2 could trigger metabolic coupling between different members in complex communities remained to be challenged. For this purpose, the E. coli and N. vulgaris synthetic consortium was used as model of simplified community. First, bacterial cooperation between these two bacteria was validated. Then, we showed that the presence of N. vulgaris impact the AI2 signal accumulation in the co-culture supporting a role of AI2 in interspecies bacterial communication. The exact mechanism of AI2 QS is currently under investigation using mutant strains and RT-qPCR analysis.