Trichodesmium holobiont metaranscriptome. Trichodesmium holobiont

Trichodesmium is a marine, diazotrophic cyanobacterium that plays a central role in the biogeochemical cycling of carbon and nitrogen. Colonies ubiquitously co-occur with a diverse microbiome of heterotrophic bacteria. Here we show that manipulation of the microbiome with quorum sensing acyl homoserine lactone (AHL) molecules significantly modulated rates of N2 fixation by Trichodesmium collected from the western North Atlantic, with both positive and negative effects of varied magnitude. Changes in Trichodesmium N2 fixation did not clearly correlate with changes in microbiome composition or geochemical patterns. Metatranscriptome sequencing revealed significant changes in the relative abundance of microbiome transcripts encoding metabolic functions consistent with quorum sensing responses in model bacteria. There was little overlap in specific microbiome transcriptional responses to AHL addition between stations, and this variability in microbiome gene expression may underpin the heterogeneous changes in Trichodesmium N2 fixation. These data suggest that host-microbiome interactions are a complex interplay of biotic and environmental factors that together form a previously overlooked mechanism modulating Trichodesmium N2 fixation.