The zoonotic pathogenLeptospira interrogansmitigates environmental stress through cyclic-di-GMP-controlled biofilm production

The zoonotic bacteriumLeptospira interrogansis the aetiological agent of leptospirosis, a re-emerging infectious disease that is a growing public health concern. Most human cases of leptospirosis result from environmental infection. Biofilm formation and its contribution to the persistence of virulent leptospires in the environment or in the host have scarcely been addressed. Here, we examined spatial and time-domain changes in biofilm production byL. interrogans. Our observations showed that biofilm formation inL. interrogansis a highly dynamic process and leads to a polarized architecture. We notably found that the biofilm matrix is composed of extracellular DNA, which enhances the biofilm's cohesiveness. By studyingL. interrogansmutants with defective diguanylate cyclase and phosphodiesterase genes, we show that biofilm production is regulated by intracellular levels of bis-(3 '-5 ')-cyclic dimeric guanosine monophosphate (c-di-GMP) and underpins the bacterium's ability to withstand a wide variety of simulated environmental stresses. Our present results show how the c-di-GMP pathway regulates biofilm formation byL. interrogans, provide insights into the environmental persistence ofL. interrogansand, more generally, highlight leptospirosis as an environment-borne threat to human health.