Microbial chitinase

Microbial chitinase has been proposed as a syngergist for Bt (71). Its role would be to digest holes in the insect gut wall and facilitate penetration of Bt toxin. However, unless the caterpillar s gut pH can be manipulated (71), this is unlikely to be effective with Bt, but might be feasible with NPV (Figure 4). 

Figure 4. Binding of a protein (hemoglobin) to several tannin extracts (tannic acid, sugar maple tannins, yellow birch tannins, quebracho tannins see 29) at various pH values. Ranges of microbial chitinase activity, NPV activity, and Bt toxicity are given. See text for discussion and references.

Microbial polysaccharides have been shown to stress plant cells, resulting in elicitation (induction) and increased metabolite synthesis. Induction of various enzymes has been reported. Chitosan successfully elicited chitinase production in carrot (Daucus carota) cell cultures and elicitation of desired food ingredients and processing aids via chitosan has been attempted. 

Presently, the most promising raw material for commercial production of chitinase (in terms of cost per unit activity and ready availability to satisfy present and future demand) is soybean seeds. Table I shows a comparison of cost (based on the retail prices) for the production of chitinase from microbial sources by three commercial suppliers and from soybean seeds. The cost is very high for the commercially prepared enzyme. The method used to purify the soybean enzyme (33) has an average yield of 3.6 I.U./kg or 3600 I.U./metric ton soyEean seeds. The cost for producing 3600 I.U. chitinase from the three suppliers has been calculated and shown in Table I. The Sigma ana Calbiochem-Behring preparations contained the lowest specific activities. 

Cell walls are biochemically rather inert with reduced digestibility to many organisms because of their complex cellulose, pectin, and lignin molecules. Callose and lignin are often accumulated at the site of infection or wounding (6,7) and form a penetration barrier. Synthesis of inhibitory proteins (e.g., lectins, protease inhibitors) or enzymes (e.g., chitinase, lysozyme, hydrolases, nucleases) that could degrade microbial cell walls or other microbial constituents would be protective, as well as synthesis of peroxidase and phe-nolase, which could help inactivate phytotoxins produced by many bacteria and fungi. These proteins are either stored in the vacuole... 

The only way for microbes to enter a healthy plant is via the stomata or at sites of injury, inflicted by herbivory, wind, or other accidents. At the site of wounding, plants often accumulate suberin, lignin, callose, gums, or other resinous substances which close off the respective areas (4.17). In addition, antimicrobial agents are produced such as lysozyme and chitinase, lytic enzymes stored in the vacuole which can degrade bacterial and fungal cell walls, protease inhibitors which can inhibit microbial proteases, or secondary metabolites with antimicrobial activity. 

Other Non-Catalytic Domains. Many polysaccharide depolymerizing enzymes are secreted by bacteria and fungi from their intracellular site of synthesis across the periplasmic space and cell wall into the surroundings. These exported enzymes reach their destination via the general secretory pathway [246] which involves membrane protein complexes such as the bacterial ABC transporters [247] that recognize domains on the secreted proteins. There are several examples of non-catalytic domains on microbial carbohydrases that may play a role in transport from the cells. These include a repeat domain on a chitinase involved... 

Wang, S.-L. and Hwang, J.-R. 2001. Microbial reclamation of shellfish wastes for the production of chitinases. Enzyme Microb Technol. 28 376-382. 

Mitsutomi, M., M. Ueda, M. Arai, A. Ando, and T. Watanabe. 1996. Action patterns of microbial chitinases and chitosanases on partially V-acetylated chitosan. In Chitin Enzymology, Vol. 2, ed. R. A. A. Muzzarelli, pp. 272-284. Grottamare, Italy Atec. 

Felse, P.A. and Panda, T. 1999. Regulation and cloning of microbial chitinase genes. Appl. Microbiol. BiotechnoL, 51 141-151. 

Sandhya, C., Binod, P., Nampoothiri, K.M., Szakacs, G., and Pandey, A. 2005. Microbial synthesis of chitinase in solid cultures and its potential as a biocontrol agent against phytopathogenic fungus Colletotrichum gloeosporioides. Appl. Biochem. Biotechnol., 127 1-15. 

Chitin that occurs in the exoskeleton of invertebrates (such as mollusks and arthropods) is composed of N-acetyl-D-glucosamine residues linked by 1,4 /3-Iinkages. A partially deacetylated chitin also occurs naturally as chit-osan. Microbial species responsible for the breakdown of chitin and chitosan have not been comprehensively studied. Micro-organisms found in a variety of environments (for instance, in fresh water [29], marine sediment [30], garden soil [31], and even anaerobic environments [32]) are known to produce chitinases and/or chitosanases. Table 56.1 shows a listing of some reported species of bacteria and fungi that yield these enzymes and are therefore, able to biodegrade these polysaccharides. 

Sakuda S, Isogai A, Matsumoio S, Suzuki A. Search for microbial insect growth regularors. 11. Altosamidin, a novel insect chitinase inhibitor. J Antibiot 1987 40 296-300. 

Felse PA, Panda T. 2000. Production of microbial chitinases - A revisit. Bioprocess Eng 23 127-134. 

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