Dynamics of diazotroph particle colonization in the Arctic Ocean

Abstract

Global warming is causing sea ice retreat and intensifying algal blooms in the Arctic Ocean, in turn increasing nitrogen limitation insurface waters. Dinitrogen fixation by diazotrophic microorganisms, usually favored in low reactive nitrogen systems, may become anincreasingly important source of nitrogen in the Arctic. Previous studies have shown that non-cyanobacterial diazotrophs are dominantin the Arctic Ocean. Lacking a photosynthetic apparatus, non-cyanobacterial diazotrophs may utilize organic particles as carbon- andenergy-rich niches. However, cyanobacterial diazotrophs may also form particles by aggregation. To further understand diazotrophparticle associations, here we study the chemotactic behavior and colonization dynamics of diazotrophs on model organic particlesusing a modified chemotaxis assay. Artificial organic particles (agarose, alginate) were incubated with surface seawater communitiesfrom four contrasted stations in the Barents Sea, and their DNA was sequenced targeting nifH and 16S rRNA genes after 2, 36, and72 h of incubation. Our results show that diazotroph groups have selective colonization behaviors, with Gammaproteobacteria memberspreferentially colonizing alginate particles derived from brown algae, a form of organic matter becoming more common in the Arcticas it warms up. We also observe niche partitioning among microbial groups, with diazotrophs colonizing nitrogen-poor, carbon-richparticles earlier than non-diazotrophic prokaryotes. As Arctic warming proceeds, increased algal blooms may expand the niches forparticle-associated diazotrophs, whose dinitrogen fixation supports phytoplankton growth and primary productivity

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Identifiers

ORCID for Ruth Hawley: orcid.org/0009-0006-6013-0140

ORCID for Maeve Lohan: orcid.org/0000-0002-5340-3108

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