High-cell-density cultivation of Vibrio natriegens N5.3 on chitin monomers: a step toward chitin valorization

Chitin valorization through microbial bioprocessing relies on efficient utilization of its monomeric units as fermentation substrates. In this study, the effects of salt concentration and the mixing ratio of N-acetylglucosamine (GlcNAc) to glucosamine hydrochloride (GlcN·HCl) on the specific growth rate of our previously isolated V. natriegens N5.3 was investigated in the shake-flask. Batch and fed-batch fermentations using chitin-derived amino sugars were further performed to assess high-cell-density cultivation potential.Although the maximum specific growth rate ( ${\mu }_{\max }$ ) at 60 g/L NaCl was nearly two-fold lower than that at the optimal concentration of 15 g/L, strain N5.3 retained robust growth with ${\mu }_{\max }$ values of 0.37 h^-1 on GlcN·HCl and 0.66 h^-1 on GlcNAc. Fed-batch cultivation yielded a maximum cell dry weight (CDW) of 42.3 g/L within 9 h on GlcNAc, with ${\mu }_{\max }$ of 0.53 h^-1, but with a low biomass yield ( $Y_{X/S}$ = 0.16 g/g). In contrast, a substrate mixture containing 5% (w/w) GlcNAc and 95% (w/w) GlcN·HCl maintained a high ${\mu }_{\max }$ (0.49 h^-1) while substantially improving $Y_{X/S}$ (0.29 g/g), resulting in a CDW of 35.5 g/L after 9 h. Due to low solubility of both amino sugars, exponential feeding with non-sterilized powders was successfully applied. The absence of contamination demonstrate the feasibility of this approach. These results demonstrate that the mixture of GlcNAc:GlcN·HCl (1:19 ratio) is effective substrate for cultivation of V. natriegens N5.3. This provides a promising foundation for the microbial conversion of chitin-derived feedstocks into high-value products.