Fusion of cellulose binding domain to the catalytic domain improves the activity and conformational stability of chitinase in Bacilluslicheniformis DSM13

Chitinase from Bacilluslicheniformis DSM13 consists of an N-terminal catalytic domain (GH) and a C-terminal chitin binding domain (ChBD). A deletion mutant BliGH and a hybrid chitinase BliGH-CeBD were developed using polymerase chain reaction (PCR) to study the role of substrate-binding domain. Both recombinant chitinases retained their ability to bind to glycol-chitin (GC). BliGH was more effective on colloidal chitin (CC) than BliGH-CeBD as evident from the increased V_max and k_cat values. The fusion of CeBD improved the affinity to colloidal chitin, activity and conformational stability in BliGH-CeBD when compared with deletion mutant BliGH

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- andβ-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

Swapping the chitin-binding domain in Bacillus chitinases improves the substrate binding affinity and conformational stability

Chitinase from Bacillus thuringiensis and Bacillus licheniformis consisting of an N-terminal catalytic domain (GH18) and a C-terminal chitin-binding domain (ChBD), were cloned and characterised. In order to study the importance of individual domains, chimeric chitinases (BtGH-BliChBD and BliGH-BtChBD) were constructed using domain swapping as a strategy to exchange the CBD of BtGH-ChBD with that of BliGH-ChBD and vice versa. Both chimeric chitinases showed increased affinity to colloidal chitin. BtGH-BliChBD was different from the three other chitinases studied concerning optimum temperature and pH. Additionally, BtGH-BliChBD and BliGH-BtChBD showed significant improvement in functional stability, conformational stability, and binding ability towards insoluble chitinous substrates compared to those of the native chitinases

Members of Gammaproteobacteria and Bacilli represent the culturable diversity of chitinolytic bacteria in chitin-enriched soils

Culturable chitinolytic bacterial diversity was studied in chitin-rich soils collected from two industries involved in chitin production. A total of 27 chitinolytic isolates were isolated among which only 10 showed zone of clearance ≥4 mm on colloidal chitin agar plate. Using morphological, biochemical and 16S rDNA analysis, isolates were identified as Bacillus, Paenibacillus, Stenotrophomonas and Pseudomonas. Molecular phylogenetic analysis revealed that Gammaproteobacteria and Bacilli were found to be the predominant classes in these chitin-enriched soils. Chitinolytic bacterial population densities were significantly high and showed a rather simple community composition dominated by genus Bacillus and Stenotrophomonas (74%). This is the first report on assessing the chitinolytic bacterial diversity of soils from industries involved in chitin production

Biotechnological approaches to develop bacterial chitinases as a bioshield against fungal diseases of plants

Fungal diseases of plants continue to contribute to heavy crop losses in spite of the best control efforts of plant pathologists. Breeding for disease-resistant varieties and the application of synthetic chemical fungicides are the most widely accepted approaches in plant disease management. An alternative approach to avoid the undesired effects of chemical control could be biological control using antifungal bacteria that exhibit a direct action against fungal pathogens. Several biocontrol agents, with specific fungal targets, have been registered and released in the commercial market with different fungal pathogens as targets. However, these have not yet achieved their full commercial potential due to the inherent limitations in the use of living organisms, such as relatively short shelf life of the products and inconsistent performance in the field. Different mechanisms of action have been identified in microbial biocontrol of fungal plant diseases including competition for space or nutrients, production of antifungal metabolites, and secretion of hydrolytic enzymes such as chitinases and glucanases. This review focuses on the bacterial chitinases that hydrolyze the chitinous fungal cell wall, which is the most important targeted structural component of fungal pathogens. The application of the hydrolytic enzyme preparations, devoid of live bacteria, could be more efficacious in fungal control strategies. This approach, however, is still in its infancy, due to prohibitive production costs. Here, we critically examine available sources of bacterial chitinases and the approaches to improve enzymatic properties using biotechnological tools. We project that the combination of microbial and recombinant DNA technologies will yield more effective environment-friendly products of bacterial chitinases to control fungal diseases of crops

Plant growth-promoting chitinolytic paenibacillus elgii responds positively to tobacco root exudates

Bacterial strains from chitin/chitosan-rich soils, from two industries, were screened for their chitinolytic, antifungal, and mineral phosphate solubilization abilities. The isolate SMA-1-SDCH02, positive for all three properties, was selected and identified as Paenibacillus elgii based on morphological and biochemical characters and supported by 16S rRNA gene sequence analysis. P. elgii enhanced the growth of groundnut in terms of shoot height, root length, total chlorophyll, and fresh and dry weight when applied alone or in combination with chitosan. The plant growth-promoting activity of P. elgii was seen in tobacco in a specially designed gnotobiotic setup indicating its capability to promote growth of at least groundnut and tobacco. Metabolite changes in the bacteria, studied using attenuated total reflectance-infrared (ATR-IR) spectroscopy, revealed split bands of amide I at the 1659- and 1636-cm−1 regions when grown in minimal media amended with tobacco root exudates. The difference in ATR-IR bands in the presence of tobacco root exudates indicated production of compounds with differences in functional groups