Strong chemotaxis by marine bacteria towards polysaccharides is enhanced by the abundant organosulfur compound DMSP

Abstract

The ability of marine bacteria to direct their movement in response to chemical gradients influences inter-species interactions, nutrient turnover, and ecosystem productivity. While many bacteria are chemotactic towards small metabolites, marine organic matter is predominantly composed of large molecules and polymers. Yet, the signalling role of these large molecules is largely unknown. Using in situ and laboratory-based chemotaxis assays, we show that marine bacteria are strongly attracted to the abundant algal polysaccharides laminarin and alginate. Unexpectedly, these polysaccharides elicited stronger chemoattraction than their oligo- and monosaccharide constituents. Furthermore, chemotaxis towards laminarin was strongly enhanced by dimethylsulfoniopropionate (DMSP), another ubiquitous algal-derived metabolite. Our results indicate that DMSP acts as a methyl donor for marine bacteria, increasing their gradient detection capacity and facilitating their access to polysaccharide patches. We demonstrate that marine bacteria are capable of strong chemotaxis towards large soluble polysaccharides and uncover a new ecological role for DMSP in enhancing this attraction. These navigation behaviours may contribute to the rapid turnover of polymers in the ocean, with important consequences for marine carbon cycling.

Microfluidic approaches in microbial ecology

“…For instance, the in situ chemotaxis assay (ISCA 213,214 ) enables studies of microbial chemotaxis directly in water-based habitats, such as lakes or oceans, by sampling bacteria that swim into small wells pre-loaded with candidate chemoattractants. Such experiments have, for example, demonstrated the consistency between chemotaxis results obtained in laboratory settings and those observed in the natural ocean environment at coastal sites (for instance, chemotaxis to glutamine 213 and laminarin 215 ). A similar avenue was pursued for soil habitats, where open porous microsystems were deployed in soil environments to allow colonization and subsequent imaging of soil microorganisms.…”