COS 229-5 - Distribution of Sphingomonas across a Southern California climate gradient after reciprocal transplantation

Abstract: As global warming and anthropogenic pollution threaten ecosystems, it is critical to understand microbial responses to shifting environments. Here we investigated the climate response of Sphingomonas, a widespread bacterial genus, after an 18-month microbial community reciprocal transplant experiment across a Southern California climate gradient. Communities were taken from five ecosystems (desert, scrubland, grassland, pine-oak, and subalpine), inoculated onto sterilized grassland litter, and transplanted back into each of the sites. We aimed to determine whether Sphingomonas ecotype diversity and functional potential varied across the climate gradient and in response to transplantation. We hypothesized that after 18 months, the transplanted Sphingomonas clade and functional composition would correspond with site climate and reflect the Sphingomonas composition of native communities. Alternatively, since all the transplanted microbial communities were inoculated onto grassland litter, we hypothesized that the Sphingomonas clade and functional composition might converge on the litter type. Using publicly available Sphingomonas genomes, we built a phylogenetic tree and grouped taxa into 12 clades. Next, we identified Sphingomonas clade composition from metagenomic data across the gradient and inferred their functional composition. Representatives of all 12 clades were found at varying relative abundances along the climate gradient, and transplanted Sphingomonas clade composition shifted after 18 months. Furthermore, our findings best supported our hypothesis that climate drives shifts in composition, since site had the largest effect (PERMANOVA; p < 0.001) on the distribution of both Sphingomonas functional (R² = 0.522) and clade composition (R² = 0.467). Transplanted samples in the desert and scrubland sites reflected partial support for our alternative hypothesis that the grassland substrate was responsible for clade and trait convergence. These findings are in line with previous microbial research from the same climate gradient and together support consistent bacterial response to climate at various phylogenetic levels. This understanding of how microbes respond to perturbation from various phylogenetic levels may aid future predictions of microbial responses to climate change.