Inheritance of broadcast enzymes enables high dispersal of chitin-associated marine bacteria

Insoluble in water, chitin, one of the most abundant biopolymers, sinks through the ocean and sediments as small particles termed ‘marine snow’. The biodegradation of these particles is central to the global carbon and nitrogen cycles. We studied the degradation of chitin by a marine bacterium of the Vibrio species. We found that two co-existing, exponentially growing sub-populations emerged: a minority attached to the particles and a dispersed planktonic majority. We demonstrated that while planktonic cells could not replicate, their increase was due to the detachment of the replicating cells resident on the particles. Proteomic analysis showed that chitin degrading enzymes were “broadcast” extra-cellularly by the entire population and accumulated on the particles. The resident minority thus “inherited” these enzymes, which enabled its fast replication, sustaining the overall growth of the population. This “inheritance” effect allows the level of chitinase synthesis to dictate the population growth rate, irrespective of the number of attached cells and thus of the dispersal rate. It provides a novel mechanism through which small growing colonies can be maintained on particles while the majority of the population is shed. Evolutionary rationales favoring the eager dispersal of cells from their sole nutrient source will be discussed.