A temperature-induced chitosanase bacterial cell-surface display system for the efficient production of chitooligosaccharides

OBJECTIVE

To establish a temperature-induced chitosanase bacterial cell-surface display system to produce chitooligosaccharides (COSs) efficiently for industrial applications.

RESULTS

Temperature-inducible chitosanase CSN46A bacterial surface display systems containing one or two copies of ice nucleation protein (InaQ-N) as anchoring motifs were successfully constructed on the basis of Escherichia coli and named as InaQ-N-CSN46A (1 copy) and 2InaQ-N-CSN46A (2 copies). The specific enzyme activity of 2InaQ-N-CSN46A reached 761.34 ± 0.78 U/g cell dry weight, which was 45.6% higher than that of InaQ-N-CSN46A. However, few proteins were detected in the 2InaQ-N-CSN46A hydrolysis system. Therefore, 2InaQ-N-CSN46A had higher hydrolysis efficiency and stability than InaQ-N-CSN46A. Gel permeation chromatography revealed that under the optimum enzymatic hydrolysis temperature, the final products were mainly chitobiose and chitotriose. Chitopentaose accumulated (77.62%) when the hydrolysis temperature reached 60 °C. FTIR and NMR analysis demonstrated that the structures of the two hydrolysis products were consistent with those of COSs.

CONCLUSIONS

In this study, chitosanase was expressed on the surfaces of E. coli by increasing the induction temperature, and chitosan was hydrolysed directly without enzyme purification steps. This study provides a novel strategy for industrial COS production.

Ethanol production from chitosan by the nematophagous fungus Pochonia chlamydosporia and the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana

Chitin is the second most abundant biopolymer after cellulose and virtually unexplored as raw material for bioethanol production. In this paper, we investigate chitosan, the deacetylated form of chitin which is the main component of shellfish waste, as substrate for bioethanol production by fungi. Fungal parasites of invertebrates such as the nematophagous Pochonia chlamydosporia (Pc) or the entomopathogens Beauveria bassiana (Bb) and Metarhizium anisopliae (Ma) are biocontrol agents of plant parasitic nematodes (eg. Meloidogyne spp.) or insect pests such as the red palm weevil (Rhynchophorus ferrugineus). These fungi degrade chitin-rich barriers for host penetration. We have therefore tested the chitin/chitosanolytic capabilities of Pc, Bb and Ma for generating reducing sugars using chitosan as only nutrient. Among the microorganisms used in this study, Pc is the best chitosan degrader, even under anaerobic conditions. These fungi have alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) encoding genes in their genomes. We have therefore analyzed their ethanol production under anaerobic conditions using chitosan as raw material. P. chlamydosporia is the largest ethanol producer from chitosan. Our studies are a starting point to develop chitin-chitosan based biofuels.