Affinity of rhizobacterial chitinases towards chitin polymers from shrimp exoskeleton and fungal cell wall: Optimization for effective biocontrol potentials

Abstract

Bacteria that can hydrolyze shrimp shell chitin and fungal cell wall chitin were isolated from tomato rhizosphere soil in an effort to find chitin-degrading enzymes. Extracellular nature of chitinase was confirmed in agarose-chitin. Chitin from virulent Fusarium oxysporum f. sp. lycopersici was characterized using XRD to study crystallinity, and the presence chitin - β-glucan conjugates. Chitinase production was optimized through RSM using shrimp chitin and fungal chitin as substrates independently for temperature, pH, incubation time, and substrate concentration and statistically validated. Crude exoproteins from Achromobacter mucicolens showed increased chitinolytic index and antifungal effects against three target fungi Fusarium oxysporum f.sp. lycopersici, Fusarium equiseti and Sarocladium sp. In vivo pot culture of treated tomato seedlings observes appreciable biocontrol effects of chitinolytic rhizobacterial consortium during the late stages of vascular wilt infections. Results conclude that the rhizosphere bacteria produced chitinases preferably show effective chitinolytic index for fungal cell wall chitin than shrimp shell chitin at optimum conditions for enzyme catalysis observed in our study. Secreted chitinases possess molecular mass approximately 70 KDa classifying the enzymes into bacterial chitinases belongs to family 18 of glycosyl hydrolases. Our study observing the chitin substrate preference by rhizobacterial chitinases stresses their role in biocontrol.