Negative and neutral interactions are prevalent in interactions between marine chitin degraders

Bacterial chitin degradation contributes to global carbon cycling, particularly in marine environments where it is a highly abundant polysaccharide. Despite the taxonomic diversity of co-occurring chitin-degrading bacteria, the influence of individual traits on interactions between them remains poorly understood. Here, we measured key physiological traits of seven chitin degraders and investigated how these traits shape interaction outcomes and chitin degradation in pairwise cocultures. We found mainly negative and neutral interactions among degraders, contrasting with the synergistic dynamics observed with other complex polysaccharides. However, chitin degradation was not consistently diminished. These interaction types could be attributed to the limited partitioning of degradation products, alongside variations in enzyme repertoires and attachment behaviours that help some degraders to prevail over others. Further, we showed that one degrader can strongly inhibit the growth of others, even those possessing favourable physiological traits, likely due to the secretion of inhibitory compounds. These findings extend our understanding of the breadth of interactions among primary polysaccharide degraders and their implications for the degradation process. One-sentence SummaryThe physiological traits of bacteria that degrade chitin, a highly abundant biopolymer in marine environments, promote a range of neutral and negative interactions among them.