Evaluation of the potential agricultural biocontrol of chitin-degrading Paenibacillus alvei FS1 through dual screening approaches and poison food agar assay.

Agricultural pests, such as insects and fungi, contain chitin in their exoskeleton and cell walls, respectively. Chitin has become the target for biocontrol of these pests as an alternative to chemical pesticides. Thus, this study aims to isolate and characterise chitin-degrading bacteria from soil using dual screening approaches and poisoned food agar assay. Seven bacteria were isolated from soil samples. The selection of chitin-degrading bacteria was carried out using dual screening methods. Screening via agar well diffusion assay showed that isolate FS2 exhibited the largest halo zone diameter at 30.83 mm, followed by FS1. However, only isolate FS1 exhibited chitin degradation in the secondary screening via shrimp shell degradation. Thus, the antifungal activity of isolate FS1 was further investigated via the poisoned food agar assay involving cell-free supernatant (CFS) and bacterial culture against Curvularia lunata and Colletotrichum truncatum, which yielded the highest growth inhibition by CFS against C. lunata at 18.33 mm. Media culture screening exhibited that isolate FS1 in Trypticase Soy Broth showed the highest chitinase activity at 25.33 mm via agar well diffusion assay. Next, isolate FS1 at 3% of chitin yielded the highest chitinase activity at 350.30 U/mL. This isolate was further identified as Paenibacillus alvei with 99.79% accuracy via 16S rRNA gene sequencing and phylogenetic tree construction. These findings revealed that P. alvei FS1, isolated from soil, can degrade chitin and may be considered a potential biocontrol agent for insect and fungal pathogens in agriculture.