Mode of action and antifungal properties of two cold-adapted chitinases

Metagenome-Sourced Microbial Chitinases as Potential Insecticide Proteins

Microbial chitinases are gaining interest as promising candidates for controlling plant pests. These enzymes can be used directly as biocontrol agents as well as in combination with chemical pesticides or other biopesticides, reducing their environmental impact and/or enhancing their efficacy. Chitinolytic enzymes can target two different structures in insects: the cuticle and the peritrophic matrix (PM). PM, formed by chitin fibrils connected to glycoproteins and proteoglycans, represents a physical barrier that plays an essential role in midgut physiology and insect digestion, and protects the absorptive midgut epithelium from food abrasion or pathogen infections. In this paper, we investigate how two recently discovered metagenome-sourced chitinases (Chi18H8 and 53D1) affect, in vitro and in vivo, the PM integrity of Bombyx mori, a model system among Lepidoptera. The two chitinases were produced in Escherichia coli or, alternatively, in the unconventional – but more environmentally acceptable – Streptomyces coelicolor. Although both the proteins dramatically altered the structure of B. mori PM in vitro, when administered orally only 53D1 caused adverse and marked effects on larval growth and development, inducing mortality and reducing pupal weight. These in vivo results demonstrate that 53D1 is a promising candidate as insecticide protein.

Characterization of β-N-acetylglucosaminidase from a marine Pseudoalteromonas sp. for application in N-acetyl-glucosamine production

The psychrotolerant Pseudoalteromonas issachenkonii PAMC 22718 was isolated for its high exo-acting chitinase activity in the Kara Sea, Arctic. An exo-acting chitinase (W-Chi22718) was homogeneously purified from the culture supernatant of PAMC 22718, the molecular weight of which was estimated to be approximately 112 kDa. Due to its β-N-acetylglucosaminidase activity, W-Chi22718 was able to produce N-acetyl-D-glucosamine (GlcNAc) monomers from chitin oligosaccharide substrates. W-Chi22718 displayed chitinase activity from 0 to 37°C (optimal temperature of 30°C) and maintained activity from pH 6.0 to 9.0 (optimal pH of 7.6). W-Chi22718 exhibited a relative activity of 13 and 35% of maximal activity at 0 and 10°C, respectively, which is comparable to the activities of previously characterized, cold-adapted bacterial chitinases. W-Chi22718 activity was enhanced by K⁺, Ca²⁺, and Fe²⁺, but completely inhibited by Cu²⁺ and SDS. We found that W-Chi22718 can produce much more (GlcNAcs) from colloidal chitin, working together with previously characterized cold-active endochitinase W-Chi21702. Genome sequencing revealed that the corresponding gene (chi22718_IV) was 2,856 bp encoding a 951 amino acid protein with a calculated molecular weight of approximately 102 kDa.

A new approach for discovering cold-active enzymes in a cell mixture of pure-cultured bacteria

To overcome the intrinsic problems of conventional approaches, such as the unavailability of source microorganisms in metagenomic libraries and the production of inactive aggregates, a new method was tested for discovering new enzymes (e.g. cold-active chitinase). A metagenome-like library was constructed using genomes extracted from a cell mixture of pure-cultured chitinolytic bacteria, followed by activity-based screening for Escherichia coli clones that exhibit chitinase activity on selective medium. Within one positive chitinolytic clone, one chitinase gene (chi22718_III) was detected and assigned to the arctic marine bacterium, Pseudoalteromonas issachenkonii PAMC 22718, by colony-PCR with chi22718_III-specific primers. When expressed in E. coli, recombinant R-Chi22718_III lost 85 % of its enzyme activity when pre-incubated at 40 °C for 1 h, whereas its mesophilic counterpart R-ChiK only lost 10 % of its activity under the same conditions indicating that R-Chi22718_III is thermolabile, a characteristic of cold-active enzymes.

Biotechnology of cold-active proteases

The bulk of Earth's biosphere is cold (<5 °C) and inhabited by psychrophiles. Biocatalysts from psychrophilic organisms (psychrozymes) have attracted attention because of their application in the ongoing efforts to decrease energy consumption. Proteinases as a class represent the largest category of industrial enzymes. There has been an emphasis on employing cold-active proteases in detergents because this allows laundry operations at ambient temperatures. Proteases have been used in environmental bioremediation, food industry and molecular biology. In view of the present limited understanding and availability of cold-active proteases with diverse characteristics, it is essential to explore Earth's surface more in search of an ideal cold-active protease. The understanding of molecular and mechanistic details of these proteases will open up new avenues to tailor proteases with the desired properties. A detailed account of the developments in the production and applications of cold-active proteases is presented in this review.

Antifungal Activity of Chitinases from Trichoderma aureoviride DY-59 and Rhizopus microsporus VS-9

Two chitinolytic fungal strains, Trichoderma aureoviride DY-59 and Rhizopus microsporus VS-9, were isolated from soil samples of Korea and Vietnam, respectively. DY-59 and VS-9 crude chitinases secreted by these fungi in the 0.5% swollen chitin culture medium had an optimal pH of 4 and the optimal temperatures of 40 degrees C and 60 degrees C, respectively. Enzymatic hydrolysis products from crab swollen chitin were N-acetyl-beta-D-glucosamine (GlcNAc) by DY-59 chitinase, and GlcNAc and N, N'-diacetylchitobiose (GlcNAc)2 by VS-9 chitinases. The chitinases degraded the cell wall of Fusarium solani hyphae to produce oligosaccharides, among which GlcNAc, (GlcNAc)2, and pentamer (GlcNAc)5 were identified by high-pressure liquid chromatography. DY-59 and VS-9 chitinases inhibited F. solani microconidial germination by more than 70% and 60% at final protein concentrations of 5 and 27 microg mL(-1), respectively, at 30 degrees C for 20 h treatment.