Cloning and sequencing of a chitinase gene from Vibrio alginolyticus H-8

Microbial chitinases: properties, enhancement and potential applications

Chitinases are a category of hydrolytic enzymes that catalyze chitin and are formed by a wide variety of microorganisms. In nature, microbial chitinases are primarily responsible for chitin decomposition and play a vital role in the balance of carbon and nitrogen ratio in the ecosystem. The physicochemical attributes and the source of chitinase are the main bases that determine their functional characteristics and hydrolyzed products. Several chitinases have been reported and characterized, and they obtain a wider consideration for their utilization in a large number of uses such as in agriculture, food, environment, medicine and pharmaceutical companies. The antifungal and insecticidal impacts of several chitinases have been extensively studied, aiming to protect crops from phytopathogenic fungi and insects. Chitooligosaccharides synthesized by chitin degradation have been shown to improve human health through their antimicrobial, antioxidant, anti-inflammatory and antitumor properties. This review aims at investigating chitinase production, properties and their potential applications in various biotechnological fields.

Identification of Vibrio alginolyticus virulent strain-specific DNA regions by suppression subtractive hybridization and PCR

AIMS

Vibrio alginolyticus was frequently isolated from diseased farmed fish in the coaster waters of Hainan Island over the past two decades. In this study, we attempted to identify candidates of virulent strain-specific DNA regions for this pathogen.

METHODS AND RESULTS

Suppression subtractive hybridization (SSH) and PCR were successively performed between the typical virulent strain and avirulent strain of V. alginolyticus, in which they shared 99·54% homology of 16S rDNAs. Out of 2873 subtracted clones, nine clones were finally indicated to harbour virulent strain-specific DNA fragments. The receivable functions of the major fragments in the nine clones were believed to encode methyl-accepting chemotaxis protein (n = 1), type VI secretion system-associated FHA domain protein TagH (n = 1), diguanylate cyclase (n = 1), AraC family transcriptional regulator (n = 1), ABC-type uncharacterized transport system permease component (n = 1) and hypothetical proteins (n = 4). Two hypothetical proteins contain several disordered regions.

CONCLUSIONS

Some specific DNA regions existed in the virulent strain of V. alginolyticus, and the SSH assay could be a highly sensitive method for identifying virulent regions in pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This report is the first to describe the identification of virulent strain-specific DNA regions in the V. alginolyticus genome, which is helpful in developing virulent strain-specific rapid detection methods and is a pivotal precondition for clarifying the molecular virulence mechanism of V. alginolyticus.

Microbial chitinases: properties, current state and biotechnological applications

Chitinases are a group of hydrolytic enzymes that catalyze chitin, nd are synthesized by a wide variety of organisms. In nature, microbial chitinases are primarily responsible for chitin decomposition. Several chitinases have been reported and characterized, and they are garnering increasing attention for their uses in a wide range of applications. In the food industry, the direct fermentation of seafood, such as crab and shrimp shells, using chitinolytic microorganisms has contributed to increased nutritional benefits through the enhancement of chitin degradation into chitooligosaccharides. These compounds have been demonstrated to improve human health through their antitumor, antimicrobial, immunomodulatory, antioxidant, and anti-inflammatory properties. Moreover, chitinase and chitinous materials are used in the food industry for other purposes, such as the production of single-cell proteins, chitooligosaccharides, N-acetyl D-glucosamines, biocontrol, functional foods, and various medicines. The functional properties and hydrolyzed products of chitinase, however, depend upon its source and physicochemical characteristics. The present review strives to clarify these perspectives and critically discusses the advances and limitations of microbial chitinase in the further production of functional foods.

Bacterial chitin binding proteins show differential substrate binding and synergy with chitinases

Glycosyl hydrolase (GH) family 18 chitinases (Chi) and family 33 chitin binding proteins (CBPs) from Bacillus thuringiensis serovar kurstaki (BtChi and BtCBP), B. licheniformis DSM13 (BliChi and BliCBP) and Serratia proteamaculans 568 (SpChiB and SpCBP21) were used to study the efficiency and synergistic action of BtChi, BliChi and SpChiB individually with BtCBP, BliCBP or SpCBP21. Chitinase assay revealed that only BtChi and SpChiB showed synergism in hydrolysis of chitin, while there was no increase in products generated by BliChi, in the presence of the three above mentioned CBPs. This suggests that some (specific) CBPs are able to exert a synergistic effect on (specific) chitinases. A mutant of BliChi, designated as BliGH, was constructed by deleting the C-terminal fibronectin III (FnIII) and carbohydrate binding module 5 (CBM5) to assess the contribution of FnIII and CBM5 domains in the synergistic interactions of GH18 chitinases with CBPs. Chitinase assay with BliGH revealed that the accessory domains play a major role in making BliChi an efficient enzyme. We studied binding of BtCBP and BliCBP to α- and β-chitin. The BtCBP, BliCBP or SpCBP21 did not act synergistically with chitinases in hydrolysis of the chitin, interspersed with other polymers, present in fungal cell walls.

Cloning and sequencing of the deacetylase gene from Vibrio alginolyticus H-8

A gene encoding deacetylase DA1 that is specific for N, N'-diacetylchitobiose was cloned using the shot-gun method with pUC118 and sequenced. The open reading frame encoded a protein of 427 amino acids including the signal peptide. The molecular mass of the mature enzyme estimated from the amino acid sequence data was 44.7 kDa, which is approximately similar to that, estimated by SDS-PAGE (48.0 kDa), of the purified enzyme reported previously. The N-terminal amino acid sequence deduced from the cloned deacetylase gene showed partial sequence homology with the Nod B protein from Rhizobium sp. (37% identity) and chitin deacetylase from Mucor rouxii (28%). It contained a domain, which showed homology with a chitin-binding domain of chitinase A from Bacillus circulans (39%).

Identification and characterization of the gene cluster involved in chitin degradation in a marine bacterium, Alteromonas sp. strain O-7

Alteromonas sp. strain O-7 secretes chitinase A (ChiA), chitinase B (ChiB), and chitinase C (ChiC) in the presence of chitin. A gene cluster involved in the chitinolytic system of the strain was cloned and sequenced upstream of and including the chiA gene. The gene cluster consisted of three different open reading frames organized in the order chiD, cbp1, and chiA. The chiD, cbp1, and chiA genes were closely linked and transcribed in the same direction. Sequence analysis indicated that Cbp1 (475 amino acids) was a chitin-binding protein composed of two discrete functional regions. ChiD (1,037 amino acids) showed sequence similarity to bacterial chitinases classified into family 18 of glycosyl hydrolases. The cbp1 and chiD genes were expressed in Escherichia coli, and the recombinant proteins were purified to homogeneity. The highest binding activities of Cbp1 and ChiD were observed when alpha-chitin was used as a substrate. Cbp1 and ChiD possessed a chitin-binding domain (ChtBD) belonging to ChtBD type 3. ChiD rapidly hydrolyzed chitin oligosaccharides in sizes from trimers to hexamers, but not chitin. However, after prolonged incubation with large amounts of ChiD, the enzyme produced a small amount of (GlcNAc)(2) from chitin. The optimum temperature and pH of ChiD were 50 degrees C and 7.0, respectively.