Microbial characterization and plant growth–promoting traits of bacteria isolated from rubber industry effluent

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Industrial discharge of rubber-processing whey/effluents poses persistent environmental challenges, particularly in regions where treatment efficiency and reuse pathways remain poorly characterized. Our study evaluated the microbiological and physicochemical characteristics of raw and treated rubber effluent obtained from the Rubber Research Institute of Nigeria, Iyanomo, with emphasis on cultivable bacterial populations and in vitro plant growth–associated traits. The effluent samples (raw and treated) were collected monthly over a three-month period and analyzed using standard microbiological methods to assess bacterial and fungal population dynamics. Representative bacterial isolates were identified using molecular techniques and screened in vitro for nitrogen fixation, phosphate solubilization, ammonia production, and indole-3-acetic acid (IAA) production using recognized protocols. Physicochemical parameters, including biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), pH, salinity, electrical conductivity, and selected heavy metals, were determined following standard analytical procedures. The microbial enumeration revealed significantly higher bacterial (5.04 ± 1.37 log₁₀ CFU/mL) and fungal counts (4.51 ± 1.53 log₁₀ CFU/mL) in raw effluent compared with treated samples (3.18 ± 0.55 and 3.05 ± 0.36 log₁₀ CFU/mL, respectively), indicating a measurable reduction in microbial load following treatment. Molecular identification showed that the recovered isolates were predominantly affiliated with the class Gammaproteobacteria, alongside Bacillus species. Several isolates exhibited measurable in vitro plant growth–associated traits, including phosphate solubilization and IAA production, with significant variation observed among isolates. The physicochemical analysis indicated partial improvement in treated effluent quality, including reductions in TDS and electrical conductivity, although some parameters remained above recommended regulatory limits. Our study provide a baseline characterization of microbial populations, in vitro functional traits, and physicochemical properties of rubber-processing effluent. While the observed traits suggest potential relevance for agricultural or environmental applications, further validation through controlled plant growth experiments and biosafety assessments is required before practical use can be considered.