Direct Ectoine Production from Chitin Waste by a Wild-Type Vibrio Strain X511: Genomic Insights and Substrate...

Chitin is the second most abundant natural renewable biomass, widely present in seafood waste. Nevertheless, its crystalline structure makes processing difficult. Ectoine, a high value compatible solute, is common in pharmaceuticals and cosmetics. However, direct ectoine production from chitinous waste using wild-type microbial strains is rarely reported. Here, we show that Vibrio diabolicus X511 possesses a complete ectoine biosynthetic gene cluster (ectABC-ask) as well as native chitinolytic genes. These genomic features are consistent with the strain's ability to directly ferment colloidal chitin, crab shell flakes, and shrimp shell powder for ectoine production, eliminating the need for exogenous chitinase supplementation. With 5 g/L yeast extract as the nitrogen source, strain X511 produced 2.172 g/L ectoine from colloidal chitin, a titer comparable to, or even higher than, those reported for several wild-type strains grown on soluble carbon sources. Using highly crystalline crab shell flakes and raw shrimp shell powder as substrates, the strain achieved titers of 0.259 g/L and 0.181 g/L respectively, accompanied by substrate weight losses of 60% and 43.47%. FESEM, XRD, and FTIR analyses confirmed the strain's capacity to effectively disrupt crystalline structure of chitin and degrade raw shrimp shell biomass. These findings suggest that X511 may be a promising biocatalyst for the effective bioconversion of chitinous waste to high value chemicals.