Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

Abstract

The most important bioinsecticide used worldwide is Bacillus thuringiensis and its hallmark is a rich variety of insecticidal Cry protein, many of which have been genetically engineered for expression in transgenic crops. Over the past 20 years, the discovery of other insecticidal proteins and metabolites synthesized by B. thuringiensis, including chitinases, antimicrobial peptides, vegetative insecticidal proteins (VIP), and siderophores, has expanded the applied value of this bacterium for use as an antibacterial, fungicidal, and nematicidal resource. These properties allow us to view B. thuringiensis not only as an entity for the production of a particular metabolite, but also as a multifaceted microbial factory. In particular, chitinases of B. thuringiensis are secreted enzymes that hydrolyze chitin, an abundant molecule in the biosphere, second only to cellulose. The observation that chitinases increase the insecticidal activity of Cry proteins has stimulated further study of these enzymes produced by B. thuringiensis. Here, we provide a review of a subset of our knowledge of B. thuringiensis chitinases as it relates to their phylogenetic relationships, regulation of expression, biotechnological potential for controlling entomopathogens, fungi, and nematodes, and their use in generating chitin-derived oligosaccharides (ChOGs) that possess antibacterial activities against a number of clinically significant bacterial pathogens. Recent advances in the structural organization of these enzymes are also discussed, as are our perspective for future studies.

Bioactivity of Bacillus thuringiensis (Bacillales: Bacillaceae) on Diatraea saccharalis (Lepidoptera: Crambidae) eggs

“…43 Eggs have specialized structures, such as the chorion 32,44 and extraembryonic membranes, 45 which reduce their vulnerability to the action of chemical and biological insecticides. 32,[44][45][46] We suggest that Bta toxins may permeate these structures 47 via different pathways 48 using Bta chitinases, 49 which are similar to pore-forming toxins, protoxins or active toxins, 48 indicating the high adaptability of Bt toxins to various biological environments 50 and that these toxic effects depend on receptor-binding sites. 51 Our results suggest that Bta protein toxins may affect the cells that form the serosal membrane, an extraembryonic membrane which acts as a multifunctional barrier limiting the passage of macromolecules and microorganisms in insect eggs.…”

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

“…Antifungal action of Bt on Fusarium solani, F. oxysporum, F. proliferatum, Colletotrichum sp., Rhizoctonia cerealis, Rh. solani, Verticillium dahliae, and Bipolaris papendorfii [ 16 , 93 , 94 ] was reported. It is likely that these activities may impair the arbuscular mycorrhizal fungi.…”

“…Two other major groups of virulence-enhancing enzymes include phosphoinositide-specific phospholipases C (PLC), chitinases, and metalloproteases. While the activity of chitinases and PLCs is mainly confined to the eradication of peritrophic structures (reviewed in [ 16 ]), metalloproteases demonstrate a more versatile range of functions. Most of them degrade either peritrophic membranes [ 17 ] or basal lamina [ 18 , 19 , 20 ]; however, members of the InhA family also mitigate the host’s cellular [ 21 ] and humoral [ 22 ] immunity, and CalY process biofilm matrix proteins [ 23 ] and regulate the activity of other proteases and Cry toxins [ 24 , 25 , 26 ].…”

Bacillus-based nano-bioformulations for phytopathogens and insect–pest management

“…Chitinase enzymes can enhance the insecticidal properties of Cry proteins. Bt chitinases have the potential to control nematodes, fungi, and entomopathogens and are also used to produce chitin-derived oligosaccharides that possess antibacterial properties (Martínez-Zavala et al 2020).…”