Isolation and Characterization of Cellulolytic and Lignocellulolytic Microorganisms from Tropical Rainforest Soils: Environmental Correlates and Biotechnological Potential

Abstract

Cellulolytic and lignocellulolytic microbes play an important role in the decomposition of plant biomass, but their isolation in tropical rainforest soil is often hindered by microbial competition, fungal growth dominance, and variations in pH and nutrient content that affect the viability of the isolates. This study aimed to isolate and characterize lignocellulose-degrading microorganisms from the HPPB soil of Andalas University, while also evaluating their relationship with environmental parameters. Isolation was carried out using CMC Agar and Tanat Agar on three soil composites, accompanied by soil chemical analysis. The results show a clear fertility gradient, with nitrogen decreasing from 34-15 mg/kg, phosphorus from 38-19 mg/kg, and potassium from 88-42 mg/kg. Microbial populations exhibit functional specialization: Composite B has the highest population of cellulolytic bacteria (26.9 × 104 CFU/g), while Composite C is dominated by lignocellulolytic bacteria (50.0 × 104 CFU/g). Based on colony diameter, bacteria SP2 (84.1 mm) and SP3 (69.7 mm) are the most active cellulolytic isolates, while fungi SP6 (90.0 mm) and SP8 (80.2 mm) are the dominant lignin decomposers. Enzyme dynamics over 28 days showed a sequential pattern: bacteria reached peak cellulase activity earlier, with SP1 increasing from 1.13-2.64 U/mL on day 7, while fungi worked more intensively in the later phase, marked by LiP activity of isolate SP6 reaching 0.1172 U/mL on day 28. Molecular analysis of the five selected isolates confirmed that bacteria SP1, SP2, and SP3 belong to the genus Bacillus, while fungal isolates JSP8 and JSP6 are closely related to Trichoderma and Penicillium, which are three key genera in the lignocellulosic decomposers of tropical ecosystems. Overall, these results affirm the close relationship between soil conditions, substrate composition, and the functional specialization of microbes, while also demonstrating the applicative potential of the isolates as bioactivators for biomass decomposition and organic waste processing.