Project description:The marine bacterium Aliivibriosalmonicida (formerly Vibrio salmonicida) is the causative agent of cold water vibriosis, a disease that led to severe losses in Norwegian aquaculture during the 1980s. Genes encoding a glycoside hydrolase family 18 (GH18) chitinase and two lytic polysaccharide monooxygenases (LPMOs) containing chitin binding domains are encoded in the genome of this bacterium, indicating a chitin degrading capability. However, due to extensive gene decay, some parts of the chitinolytic pathways are believed to be dysfunctional. To investigate the chitinolytic abilities of the bacterium, we combined microbiological and biochemical experiments with proteomic analysis. The family GH18 chitinase was able to depolymerize - and -chitin, but its activity was up to 50-fold lower compared to other well-studied chitinases from Serratia marcescens and Cellvibrio japonicus. The two LPMOs showed activity on chitin, cleaving the substrate chains by oxidation. Cultivation experiments showed that Al. salmonicida was able to grow on and utilize the soluble building blocks of chitin; N-acetyl-D-glucosamine (GlcNAc) and chitobiose (GlcNAc2). Furthermore, cultivation and gene deletion studies revealed that the bacterium was able to degrade insoluble chitin, albeit at a slow rate, and that growth on this substrate was dependent on the GH18 chitinase, but to a lesser extent the LPMOs. Finally, expression of the GH18 chitinase and both LPMOs was detected by proteomic analysis of Al. salmonicida cultivated on chitin as the sole carbon source. In conclusion, our results show that Al. salmonicida LFI1238 can utilize chitin as source of nutrients and its ability depends on the GH18 chitinase.
