The diatom holobiont in a changing Arctic Ocean

Abstract

Interactions between diatoms and bacteria are crucial for marine ecosystem functioning and the global climate as they largely govern primary production in marine systems and drive global biogeochemical cycles. Zooming in on the immediate surroundings of a diatom cell, a microhabitat for a diverse and overall mutualistic bacterial community can be found that enables reciprocal exchanges of metabolites benefiting both the diatom and its associated bacteria, which together form a discrete ecological unit – the holobiont. This thesis aims to improve our understanding of how diatom holobionts adapted to occupy Arctic or temperate niches and to which extent diatom-associated bacterial microbiomes help to adapt their host under environmental conditions relevant to climate change and associated climate change-mediated poleward range shifts. The main objectives are to (I) experimentally quantify the response of Arctic and temperate diatoms to abiotic factors that characterize their biogeographic separation and thereby identify potential bottlenecks for adaptation of Arctic diatoms and poleward range shifts of their temperate relatives; (II) determine the net effect of the bacterial microbiome on Arctic and temperate diatom growth under multi-driver settings of these factors to understand its role in host adaptation; (III) unravel how abiotic conditions affect diatom-associated bacterial microbiome community composition and the underlying hostmicrobiome interactions (IV) develop a methodological strategy to understand diatommicrobiome community dynamics on the single- (host-) cell level to enable necessary speciesspecific (in-situ) information of natural diatom microbiomes in the future.