New review in press at Annual Review in Marine Science

New microbial biodiversity in marine sediments

Microbes in marine sediments represent a large portion of the biosphere, and resolving their ecology is crucial for understanding global ocean processes. Single-gene diversity surveys have revealed several uncultured lineages that are widespread in ocean sediments and whose ecological roles are unknown, and advancements in the computational analysis of increasingly large genomic data sets have made it possible to reconstruct individual genomes from complex microbial communities. Using these metagenomic approaches to characterize sediments is transforming our view of microbial communities on the ocean floor and the biodiversity of the planet. In recent years, marine sediments have been a prominent source of new lineages in the tree of life. The incorporation of these lineages into existing phylogenies has revealed that many belong to distinct phyla, including archaeal phyla that are advancing our understanding of the origins of cellular complexity and eukaryotes. Detailed comparisons of the metabolic potentials of these new lineages have made it clear that uncultured bacteria and archaea are capable of mediating key previously undescribed steps in carbon and nutrient cycling.

Congrats Ian Rambo on his publication about HAB microbiomes!

Metabolic relationships of uncultured bacteria associated with the microalgae Gambierdiscus

Summary

Microbial communities inhabit algae cell surfaces and produce a variety of compounds that can impact the fitness of the host. These interactions have been studied via culturing, single‐gene diversity, and metagenomic read survey methods that are limited by culturing biases and fragmented genetic characterizations. Higher‐resolution frameworks are needed to resolve the physiological interactions within these algal‐bacterial communities. Here, we infer the encoded metabolic capabilities of four uncultured bacterial genomes (reconstructed using metagenomic assembly and binning) associated with the marine dinoflagellates Gambierdiscus carolinianus and G. caribaeus. Phylogenetic analyses revealed that two of the genomes belong to the commonly algae‐associated families Rhodobacteraceae and Flavobacteriaceae. The other two genomes belong to the Phycisphaeraceae and include the first algae‐associated representative within the uncultured SM1A02 group. Analyses of all four genomes suggest these bacteria are facultative aerobes, with some capable of metabolizing phytoplanktonic organosulfur compounds including dimethylsulfoniopropionate and sulfated polysaccharides. These communities may biosynthesize compounds beneficial to both the algal host and other bacteria, including iron chelators, B vitamins, methionine, lycopene, squalene, and polyketides. These findings have implications for marine carbon and nutrient cycling and provide a greater depth of understanding regarding the genetic potential for complex physiological interactions between microalgae and their associated bacteria.