Abstract: Microorganisms play a fundamental role in maintaining ecosystem functioning by controlling the fluxes of carbon in and out of the soil. The genetic and taxonomic diversity of microbial communities affects the rates and levels of microbial activities and processes. However, it remains unclear what aspects of diversity are relevant for a community’s response to environmental change and any corresponding changes in functioning. In this regard, trait-based approaches offer a plausible solution to improve our predictive abilities to link biodiversity and ecosystem functioning. In particular, if variation in microbial traits correlates with environmental variables, then such variation can be used as a first prediction of how microorganisms might respond to environmental change. Previous studies suggest that bacterial trait variation along an environmental gradient may depend on the complexity and degree of phylogenetic conservation of each trait. Traits that involve different genes and regulatory networks might be more deeply conserved (less variable across the phylogenetic tree of a microbial community) than traits that are less genetically complex (i.e., coded by a single gene). Based on this idea, we hypothesize that optimal temperature and pH preference traits will be more deeply conserved than carbon substrate utilization traits. To test this hypothesis, we are surveying the traits of an abundant and culturable leaf litter bacteria (Curtobacterium) involved in litter decomposition that has been shown to encompass ample genetic, phenotypic, and biogeographic variation. We isolated strains from the leaf litter from 24 sites within the University of California Natural Reserves System. These reserves encompass a wide range of climatic conditions (temperature and moisture) and plant communities, resulting in variation in the carbon compounds and pH of the leaf litter. We then sequenced the genomes of these isolates and identified 164 Curtobacterium strains. The strains include representatives of the known phylogenetic variation across the genus as well as new subclades. Comparative genomic analysis demonstrates significant differences in potential carbon substrate utilization. Culturing experiments in the lab demonstrate that the strains vary in their optimal growth temperature and pH preference. Finally, we will evaluate the depth at which traits are conserved by mapping the trait data to a reference phylogeny of the Curtobacterium clades and testing for a correlation between phylogenetic distance and phenotypic distance. Overall, these findings will indicate whether a phylogenetic perspective can link biogeographic variation of microbial traits to their responses to environmental variation.
