ABSTRACT:  Seagrasses are marine flowering plants growing in sediments of intertidal and shallow subtidal zones. They play an important role in coastal ecosystems by stabilising sediments, providing food and shelter for animals, and recycling nutrients. Like other plants, seagrasses live intimately with both beneficial and unfavourable microorganisms. Although much is known about the microbiomes of terrestrial plants, little is known about the microbiomes of seagrasses. Here I present the results of a detailed study on the rhizosphere microbiome (‘rhizobiome’) of seagrass species and their role in sulfur cycling. For this, we used 16S Amplicon and metagenomic sequencing, microsensor measurements and fluorescent in situ hybridisation combined with confocal microscopy. 16S Amplicon sequencing showed that the rhizobiomes were shaped by the plant but did not coevolve with their host. It furthermore showed that the core rhizobiome was dominated by bacteria involved in the sulfur cycle. Metagenomic analysis of the rhizobiome of the seagrass Zostera marina showed the presence of sulfur-oxidising bacteria related to endosymbionts. One of the metagenome-assembled-genomes (MAGs) harbored genes involved in different carbon, sulfur and nitrogen cycling pathways indicating a great metabolic flexibility. Our results support the hypothesis that seagrass meadows might function as a source of symbionts for invertebrates that inhabit within or around seagrass meadows. While providing ideal conditions for the proliferation of these free-living forms of symbionts, seagrasses would benefit from their genetic versatility, which contributes to sulfide detoxification and ammonium production, the seagrasses’ preferred nitrogen source.

BIOGRAPHY: Gerard Muyzer is a Professor in Microbial Systems Ecology at the University of Amsterdam and coordinator of the research priority area Systems Biology. He studies the structure, function and dynamics of microbial communities, their role in biogeochemical cycles and their application in biotechnological processes. In 2012 he obtained an ERC-grant to study the microbial sulfur cycle in hypersaline soda lakes. Currently, he is working on host-microbe interactions in seagrasses, sponges, and algae, i.e., the brown alga Sargassum and the green alga Caulerpa. In his research, he uses a systems biology approach in which he combines experimental work, state-of-the-art omics techniques, and mathematical modelling. For more information: https://orcid.org/0000-0002-2422-0732