In a new paper published in mSphere, E&E professor Cathy Pfister and collaborators examined how the unique environment of seaweeds in coastal oceans might shape the genomes and metabolism of associated bacteria. Research was conducted by contrasting the genomes of seaweed-associated versus free-living bacteria in seawater by pairwise comparison of bacterial taxa. Their analyses showed that bacteria living on seaweeds had an increased occurrence of genes for B vitamin synthesis, complex carbohydrate use, and nitrogen uptake, indicating that bacterial genomes reflect both their evolutionary history and the current environment they inhabit.
This research was initiated at a workshop funded by the International Institute for Research in Paris at the University of Chicago. E&E graduate student Emma Stanfield, as well as CEB graduate students Max Bogan and Jessica Hart, were part of the workshop and contributed to the research.
Abstract
Seaweeds harbor a rich diversity of bacteria, providing them with metabolic resources and a surface for attachment and biofilm development. The host’s unique environment potentially shapes the bacterial genomes and promotes adaptations for a symbiotic lifestyle. To investigate whether the genomes of seaweed-associated bacteria are genetically and metabolically distinct from their close free-living relatives in seawater, we compared both the seaweed-associated and free-living counterparts of 72 bacterial genera across 16 seaweed hosts using whole-genome sequences or high-quality metagenome-assembled genomes. While taxonomic affiliation strongly influenced genome characteristics such as GC content, gene number, and size, host association had a lower effect overall. A reduced genome size was suggested only in Nereocystis luetkeana-associated microbes, while only Ascophyllum nodosum-associated bacteria had an increased GC content. Metabolic adaptations were indicated from the genomes of seaweed-associated bacteria, including enriched pathways for B vitamin production, complex carbohydrate utilization, and amino acid biosynthesis. In particular, Flavobacteriia showed the most pronounced differences between host-associated and free-living strains. We further hypothesized that bacteria associated with seaweed might have evolved to complement their host’s metabolism and tested this inference by analyzing the genomes of both the seaweed Ectocarpus subulatus and its 28 bacterial associates but found no evidence for such complementarity. Our analyses of 72 paired bacterial genomes highlighted significant metabolic differences in seaweed-associated strains with implications for carbon, nitrogen, and sulfur cycling in the coastal ocean.