Quantifying Microbial Activity In Situ: the Link between Cells and Cycles

Metagenomic sequencing of environmental samples has dramatically expanded our knowledge of microbial taxonomic and metabolic diversity and suggests metabolic interdependence is widespread. However, translating these insights into knowledge of ecosystem function and, therefore, implications for local and global chemistry, remains a challenge. In this commentary, I argue that making direct measurements of microbial activity in situ is an essential step to confirm gene-based hypotheses of microbial physiology and bridge advances in microbial ecology with a predicative understanding of global chemistry and climate. Making these measurements across a range of spatial scales and experimentally manipulated conditions contributes to a process-based understanding and, therefore, more robust predictions of how activity will respond to changing environmental conditions. I discuss recent advancements in quantifying microbial activity in situ and highlight several lines of research in marine microbiology that leverage complementary genomic and isotopic methods to connect microbes and global chemistry.