From culture to community: the physiology, regulation and community functions of alginate degradation by marine Gammaproteobacteria and Bacteroidetes

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The bacterial degradation of abundant marine polysaccharides, such as alginate, is fundamental for the remineralization of organic matter in the oceans. However, still little is known about the regulation of alginate degradation, the identity and abundance of alginate-degrading bacteria, and how alginolytic capacities affect the functional diversity of natural bacterial assemblages. The present follow-up proposal on my 'Eigene Stelle' project addresses a thorough investigation of marine bacterial alginate utilization on the regulatory, genomic and community level. This relies on established alginolytic model isolates, co-culture and microcosm systems, as well as molecular investigations of natural bacterioplankton communities. Quantitative real-time PCR of alginate-processing genes in established Alteromonas and Maribacter model isolates will elucidate the expression of alginolytic genes in relation to growth phase and polymer size. In combination with transcriptomics and high-resolution exometabolomics, this will provide a holistic view of gene regulation and metabolic processes associated with bacterial alginate degradation. In addition, fluorescent labelling and real-time microscopy of Alteromonas and Maribacter model isolates will enable to track their growth and motility in natural communities, illuminating whether alginolytic traits provide a competitive advantage when alginate particles are added. The culture-based work will be complemented by molecular GeneFISH analyses to identify alginate-degrading taxa in various oceanic biomes. Using environmental samples from the Southern, Atlantic and Pacific Oceans, this will reveal biogeographic patterns in alginolytic abilities over wide geographical and environmental gradients. Furthermore, GeneFISH will be applied to microcosms with alginate-amended Pacific and North Sea water to elucidate the community succession during different stages of alginate breakdown from polymer to monomer. The project will benefit from a range of national and international collaborations and substantially contribute to the understanding of alginolytic activities on the species and community level, which has implications for global marine carbon cycling.