Microbial chitinases: properties, current state and biotechnological applications

Cloning, expression and characterization of a chitinase from Paenibacillus chitinolyticus strain UMBR 0002

Background

Chitinases are enzymes which degrade β-1,4-glycosidid linkages in chitin. The enzymatic degradation of shellfish waste (containing chitin) to chitooligosaccharides is used in industrial applications to generate high-value-added products from such waste. However, chitinases are currently produced with low efficiency and poor tolerance, limiting the industrial utility. Therefore, identifying chitinases with higher enzymatic activity and tolerance is of great importance.

Methods

Primers were designed using the genomic database of Paenibacillus chitinolyticus NBRC 15660. An exochitinase (CHI) was cloned into the recombinant plasmid pET-22b (+) to form pET-22b (+)-CHI, which was transformed into Escherichia coli TOP10 to construct a genomic library. Transformation was confirmed by colony-polymerase chain reaction and electrophoresis. The target sequence was verified by sequencing. Recombinant pET-22b (+)-CHI was transformed into E. coli Rosetta-gami B (DE3) for expression of chitinase. Recombinant protein was purified by Ni-NTA affinity chromatography and enzymatic analysis was carried out.

Results

The exochitinase CHI from P. chitinolyticus strain UMBR 0002 was successfully cloned and heterologously expressed in E. coli Rosetta-gami B (DE3). Purification yielded a 13.36-fold enrichment and recovery yield of 72.20%. The purified enzyme had a specific activity of 750.64 mU mg^-1. The optimum pH and temperature for degradation of colloidal chitin were 5.0 and 45 °C, respectively. The enzyme showed high stability, retaining >70% activity at pH 4.0-10.0 and 25-45 °C (maximum of 90 min). The activity of CHI strongly increased with the addition of Ca²⁺, Mn²⁺, Tween 80 and urea. Conversely, Cu²⁺, Fe³⁺, acetic acid, isoamyl alcohol, sodium dodecyl sulfate and β-mercaptoethanol significantly inhibited enzyme activity. The oligosaccharides produced by CHI from colloidal chitin exhibited a degree of polymerization, forming N-acetylglucosamine (GlcNAc) and (GlcNAc)₂ as products.

Conclusions

This is the first report of the cloning, heterologous expression and purification of a chitinase from P. chitinolyticus strain UMBR 0002. The results highlight CHI as a good candidate enzyme for green degradation of chitinous waste.

A Cold-Adapted Chitinase-Producing Bacterium from Antarctica and Its Potential in Biocontrol of Plant Pathogenic Fungi

To obtain chitinase-producing microorganisms with high chitinolytic activity at low temperature, samples collected from Fildes Peninsula in Antarctica were used as sources for bioprospecting of chitinolytic microorganisms. A cold-adapted strain, designated as GWSMS-1, was isolated from marine sediment and further characterized as Pseudomonas. To improve the chitinase production, one-factor-at-a-time and orthogonal test approaches were adopted to optimize the medium components and culture conditions. The results showed that the highest chitinolytic activity (6.36 times higher than that before optimization) was obtained with 95.41 U L^-1 with 15 g L^-1 of glucose, 1 g L^-1 of peptone, 15 g L^-1 of colloid chitin and 0.25 g L^-1 of magnesium ions contained in the medium, cultivated under pH 7.0 and a temperature of 20 °C. To better understand the application potential of this strain, the enzymatic properties and the antifungal activity of the crude chitinase secreted by the strain were further investigated. The crude enzyme showed the maximum catalytic activity at 35 °C and pH 4.5, and it also exhibited excellent low-temperature activity, which still displayed more than 50% of its maximal activity at 0 °C. Furthermore, the crude chitinase showed significant inhibition of fungi Verticillium dahlia CICC 2534 and Fusarium oxysporum f. sp. cucumerinum CICC 2532, which can cause cotton wilt and cucumber blight, respectively, suggesting that strain GWSMS-1 could be a competitive candidate for biological control in agriculture, especially at low temperature.

Capillibacterium thermochitinicola gen. nov., sp. nov., a novel anaerobic thermophilic chitinolytic bacterium from compost

A novel Gram-negative, spore forming, obligately anaerobic, thermophilic, chitin-degrading bacterium, designated UUS1-1T, was isolated from compost on Ishigaki Island, Japan by enrichment culturing using chitin powder as the carbon source. The strain has unique, long, hair-like rod morphological features and exhibits strong degradation activity toward crystalline chitin under thermophilic conditions. Growth of the novel strain was observed at 45-65 °C (optimum, 55 °C) and pH 6.5-7.5 (optimum, pH 7.0). In addition to chitin, the strain utilized several other carbon sources, including N-acetylglucosamine, glucose, galactose, mannose, maltose, cellobiose, fructose and sucrose. The end products of chitin degradation were acetate, lactate, H2 and CO2. Phylogenetic tree analysis based on 16S rRNA gene sequences revealed a clear affiliation of the proposed bacterium to the phylum Firmicutes; the most closely related species were Hydrogenispora ethanolica LX-BT and Desulfotomaculum thermobenzoicum DSM6193T with similarities of 90.4 and 87.8 %, respectively. The G+C content of the genomic DNA was 52.1 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between the genomes of UUS1-1T and H. ethanolica LX-BT were 65.5 and 21.0 %, respectively. The cellular fatty acid composition of the strain was C16 : 0, anteiso-C15 : 0, C14 : 0, C12 : 0 3-OH and dimethyl acetal-C13 : 0. Based on phenotypic, chemotaxonomic and genotypic analysis, strain UUS1-1T represents a novel genus and species, for which the name Capillibacterium thermochitinicola gen. nov., sp. nov. is proposed. The type strain is UUS1-1T (=JCM 33882T=DSM 111537T).