Marine Bacteroidetes enzymatically digest xylans from terrestrial plants

Abstract

Marine Bacteroidetes that degrade polysaccharides contribute to carbon cycling in the ocean. Organic matter, including glycans from terrestrial plants, might enter the oceans through rivers. Whether marine bacteria degrade structurally related glycans from diverse sources including terrestrial plants and marine algae was previously unknown. We show that the marine bacterium Flavimarina sp. Hel_I_48 encodes two polysaccharide utilization loci (PULs) which degrade xylans from terrestrial plants and marine algae. Biochemical experiments revealed activity and specificity of the encoded xylanases and associated enzymes of these PULs. Proteomics indicated that these genomic regions respond to glucuronoxylans and arabinoxylans. Substrate specificities of key enzymes suggest dedicated metabolic pathways for xylan utilization. Some of the xylanases were active on different xylans with the conserved β‐1,4‐linked xylose main chain. Enzyme activity was consistent with growth curves showing Flavimarina sp. Hel_I_48 uses structurally different xylans. The observed abundance of related xylan‐degrading enzyme repertoires in genomes of other marine Bacteroidetes indicates similar activities are common in the ocean. The here presented data show that certain marine bacteria are genetically and biochemically variable enough to access parts of structurally diverse xylans from terrestrial plants as well as from marine algal sources.

Metagenome-assembled genomes of deep-sea sediments: changes in microbial functional potential lag behind redox transitions

“…In addition, distinguishing between anabolic and catabolic enzymes is not straightforward. Carbohydrate-active enzymes (CAZymes) are often specific to particular glycosidic bonds within particular substrates [ 33 ], and microbes that degrade complex polysaccharides often possess large arsenals of CAZyme genes [ 34 ]. As a significant fraction of organic matter in marine sediments are carbohydrates [ 5 ], it is feasible that changes in microbial community composition could be driven by the ability of microorganisms to mineralize carbohydrates.…”