Distribution of Sphingomonas across a Southern California climate gradient after reciprocal transplantation

Microbes are essential for the functioning of all ecosystems. As global warming and anthropogenic pollution threaten ecosystems and microbial communities, it is critical to understand how microbes will respond. Here we investigated the climate response of Sphingomonas, a widespread bacterial genus that can break down pollutants. Using publicly available Sphingomonas genomes, we built a phylogenetic tree and grouped taxa into 12 clades. Next, we identified and extracted the Sphingomonas clade frequencies from an 18-month reciprocal transplant experiment across a Southern California climate gradient. The microbial communities were transplanted from desert, scrubland, grassland, pine-oak, and subalpine ecosystems onto sterilized grassland litter and placed back into each of the sites. Despite the close phylogenetic relationship of these strains, representatives of all 12 clades can be found along this gradient. We aimed to determine whether sites with different climates selected for distinct Sphingomonas clades. We hypothesized that the Sphingomonas clade distribution would correlate with climate conditions (e.g., temperature and precipitation). Additionally, we hypothesized that by the 18th month, the Sphingomonas clade distribution in the litter bags would shift toward the composition of Sphingomonas communities native to each site. Alternatively, as all transplanted microbial communities were inoculated onto grassland leaf litter, Sphingomonas clade distributions might shift to reflect those of the grassland site. Based on metagenomic data, the Sphingomonas composition in the desert and scrubland ecosystems became more similar to the grassland, but in other ecosystems, such as subalpine, the Sphingomonas composition shifted to reflect site conditions (site*inoculum interaction, PERMANOVA; p<0.001). These findings build on a growing body of microdiversity literature and may help future predictions of microbial genetic and functional response to climate change, as well as inform the potential for Sphingomonas to rehabilitate polluted habitats.