Gene

Mathematics education

Phytoplankton

Ecology

Bacteria

Biology

Archaea

Receptor

Marine bacteriophage

Biochemistry

Microbial food web

Food web

Chemotaxis

Genetics

Biogeochemical cycle

Microbiome

Plankton

Bioinformatics

Mathematics

Microscale chemistry

Microorganism

Nutrient

Metagenomics

Ecosystem

Phylum

Nature

The capacity of planktonic marine microorganisms to actively seek out and exploit microscale chemical hotspots has been widely theorized to affect ocean-basin scale biogeochemistry1–3, but has never been examined comprehensively in situ among natural microbial communities. Here, using a field-based microfluidic platform to quantify the behavioural responses of marine bacteria and archaea, we observed significant levels of chemotaxis towards microscale hotspots of phytoplankton-derived dissolved organic matter (DOM) at a coastal field site across multiple deployments, spanning several months. Microscale metagenomics revealed that a wide diversity of marine prokaryotes, spanning 27 bacterial and 2 archaeal phyla, displayed chemotaxis towards microscale patches of DOM derived from ten globally distributed phytoplankton species. The distinct DOM composition of each phytoplankton species attracted phylogenetically and functionally discrete populations of bacteria and archaea, with 54% of chemotactic prokaryotes displaying highly specific responses to the DOM derived from only one or two phytoplankton species. Prokaryotes exhibiting chemotaxis towards phytoplankton-derived compounds were significantly enriched in the capacity to transport and metabolize specific phytoplankton-derived chemicals, and displayed enrichment in functions conducive to symbiotic relationships, including genes involved in the production of siderophores, B vitamins and growth-promoting hormones. Our findings demonstrate that the swimming behaviour of natural prokaryotic assemblages is governed by specific chemical cues, which dictate important biogeochemical transformation processes and the establishment of ecological interactions that structure the base of the marine food web. In situ experiments have demonstrated chemotaxis of marine bacteria and archaea towards specific phytoplankton-derived dissolved organic matter,&nbsp;which leads to microscale partitioning of biogeochemical transformation in the ocean.

Chemotaxis shapes the microscale organization of the ocean’s microbiome