Isolation of <i>Bacillus spp</i>. with multi-enzyme activity for enhanced degradation of kitchen organic waste and PLA/PBAT bioplastics

The increasing accumulation of municipal organic waste along with bioplastics presents a pressing environmental challenge. The present study aimed to isolate and characterize multi-enzyme-producing bacteria from wood-feeding termites and mangrove soil, with a focus on their potential applications in the degradation of organic waste and bioplastics. Bacterial isolates were collected from termites and mangrove soil samples, and subjected to preliminary screening. Cellulolytic activity was assessed using carboxymethyl cellulose (CMC) agar plates and quantitative CMCase assays. Multi-enzyme production was evaluated through specific enzymatic assays for amylase, protease, lipase, gelatinase, and ligninase activities. Bacterial identification was performed using biochemical tests and 16S rRNA gene sequencing. Kitchen waste degradation studies were conducted over 90 days under controlled conditions, while bioplastic Polylactic Acid (PLA)/Polybutylene Adipate Terephthalate (PBAT] degradation was monitored for 45 days. Structural changes in bioplastics were analyzed using Scanning Electron Microscopy (SEM) and Fourier-transform Infrared Spectroscopy (FT-IR). Among nineteen bacterial isolates (Eleven from mangrove soil (M) and eight from termites (T)), isolates M9 and T3 exhibited the highest cellulase activity. Further screening revealed their ability to produce a suite of enzymes, including amylase, protease, lipase, gelatinase, and ligninase. Biochemical and molecular analyses identified both isolates as Bacillus spp.. These strains demonstrated effective degradation of kitchen waste over 90 days, producing a paste-like residue compared to control samples. However, only partial degradation of bioplastics (PLA/PBAT) was observed after 45 days, as confirmed by Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR), indicating limited structural changes. The findings underscore the potential of Bacillus spp. from natural ecosystems as bioresource candidates for multi-enzyme production and organic waste bioconversion. However, the limited bioplastic degradation observed also raises concerns about the environmental persistence of commercially marketed bioplastics. This study emphasizes the significance of examining microbial diversity for sustainable waste management solutions and challenges the degradability claims associated with certain bioplastic products.