Phototrophy improves the aerial fitness in a photoheterotrophic Methylobacterium isolated from clouds

Résumé fourni par la source

A diverse microbiome from surface ecosystems is transported in the atmosphere, where fluctuating environmental conditions and limited nutrients challenge its survival and functioning. Among the viable bacteria frequently recovered from air are potential photoheterotrophs usually associated with vegetation. Such a specific biological trait is known to be beneficial to survival in oligotrophic environments, and we postulate here that this may contribute to the maintenance and survival during aerial transport. In this study, aerobic photoheterotrophic bacteria isolated from clouds ( Methylobacterium sp. R17b-9) and expressing or lacking bacteriochlorophyll pigment, i.e., phototrophic capabilities ([Bchl +] or [Bchl-] phenotype, respectively), were injected into an atmospheric simulation chamber and monitored for their abundance, viability, cultivability and ATP content while exposed to different light intensities as aerosols. We demonstrate that phototrophy strongly enhances bacterial viability during aerial transport: whereas the fraction of cultivable cells devoid of phototrophic pigment sharply decreased under exposure to light, halving every 2 h or less, no significant loss could be observed in phototrophic cells, which also exhibited higher ATP content. The phototrophic phenotype also directly influenced the aerial dispersal range of bacteria by shortening Bchl + cells’ atmospheric residence time by a factor of 1.7, with half-times of ~ 152 min versus ~ 89 min, due to ~ 8% larger size. Our results imply that atmospheric transport selects bacteria for specific phenotypes. This may have implications for biogeochemical processes in the atmosphere (C and N cycles), and participate in the ecology, maintenance and evolution of this ancient and widespread biological function.

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