Trait-based approach to bacterial growth efficiency

Bacterial growth efficiency (BGE) is the proportion of assimilated carbon that is converted into biomass and reflects the balance between growth and energetic demands. Often measured as an aggregate property of the community, BGE is highly variable within and across ecosystems. To understand this variation, we first identified how species identity and resource type affect BGE using 20 bacterial isolates belonging to the phylum Proteobacteria that were enriched from north temperate lakes. Using a trait-based approach that incorporated genomic and phenotypic information, we characterized the metabolism of each isolate and tested for predicted trade-offs between growth rate and efficiency. A substantial amount of variation in BGE could be explained at broad (i.e., order, 20%) and fine (i.e., strain, 58%) taxonomic levels. While resource type was a relatively weak predictor across species, it explained >60% of the variation in BGE within a given species. A metabolic trade-off (between maximum growth rate and efficiency) and genomic features revealed that BGE may be a species-specific metabolic property. Our study suggests that genomic and phylogenetic information may help predict aggregate microbial community functions like BGE and the fate of carbon in ecosystems.