Structure, diel functional cycling and viral ecological filtering in the microbiome of a pristine coral atoll in the Indian Ocean
Given the role of microbes as both indicators and drivers of ecosystem health, establishing baselines in pristine environments is crucial to predicting the response of marine habitats to environmental change. Here we describe a survey of microbial community composition and metatranscriptomic gene expression across the Indian Ocean, encompassing the first samples from the pristine Salomon Atoll in the Chagos Archipeligo. We observed strong patterns in beta-diversty which reflected Longhurst biogeographical provinces established using primary productivity and thermohaline properties of ocean currents. Samples from within Salomon Atoll showed a highly unique community which was remarkably different even from adjacent samples despite constant water exchange. This pattern was driven by the dominance of the photosynthetic cyanobacterium Synechococcus within the lagoon, the diel activity of which was responsible for driving shifts in the transcriptional profile of samples. Inside the lagoon, increases in the expression of genes related to photosynthesis and nutrient cycling associated with the bottom-up control of bacterial populations, however the expression of viral proteins increased five-fold within the lagoon during the day, indicating a concomitant top-down control of bacterial dynamics byphage. Indeed, genome recruitment against Synechococcus reference genomes suggested viruses provide an ecological filter for determining the diversity patterns in this system. This study also represented a proof of concept for using a ‘citizen oceanography’ approach utilzing tools that may easily be adapted to deployment on any ocean going yacht, greatly expanding the scale and outreach of marine microbiology studies.