Investigating potential protease activity of psychrotrophic bacteria from a municipal landfill for solid waste management

A municipal landfill contains different waste materials that support the growth of a diverse community of enzyme-secreting microorganisms that degrade and detoxify the wastes. The present study aimed to explore psychrotrophic protein-degrading bacteria for converting proteinaceous waste into the nutrient-rich end product of agricultural applications. During the study, twenty five morphologically different psychrotrophic proteolytic bacteria were isolated from the landfill soil samples using standard serial dilution and spread plate techniques. The isolates showed variable protease activities at different incubation temperatures (5 °C, 10 °C, 15 °C, and 20 °C). However, isolate PB₂ showed significantly (p < 0.05) highest protease activity (1.53 ± 0.8 1U/mL) at 20 °C with corresponding hydrolysis zone of average diameter of 17 ± 2 mm through primary screening. The isolate (PB2) also exhibited the hydrolysis of several protein substrates, including elastin and gelatin. According to protease inhibition studies, the extracellular proteases released by isolating PB2 were primarily serine and metalloproteases. The morphological, biochemical, and molecular characterization (16S rRNA) demonstrated that the isolate had 99% similarity with Pseudomonas fluorescens strain SU003 (NCBI, Accession No. MH266220). The results indicated that psychrotrophic bacteria isolated from the temperate landfill site displayed promising protease activities at lower temperatures and can be utilized for converting voluminous organic wastes generated in Himalayan regions via cold composting to produce nutrient-rich compost of agricultural importance.