Indigenous hydrocarbon-tolerant bacteria from refinery activated sludge (ETP II, Skikda, Algeria): isolation,...

This study aimed to isolate, identify, and characterize individual bacterial isolates obtained from the activated sludge of the biological treatment basin at the new industrial wastewater treatment plant of the Skikda refinery (ETP II, Algeria). Seven distinct bacterial strains were isolated and identified as Bacillus licheniformis, Bacillus cereus, Bacillus aerius, Pseudomonas mucidolens, Pseudomonas stutzeri, Microbacterium oryzae, and Micrococcus aloeverae. Identification was based on morphological and biochemical characterization (API galleries) and confirmed by sequencing of the 16S rRNA gene.The biodegradation potential of these isolates was evaluated in Bushnell-Haas medium enriched with 2% (v/v) crude oil as the sole carbon source. The effects of temperature, pH, and salinity on bacterial growth and oil tolerance were investigated to assess optimal environmental conditions for hydrocarbon degradation. The results revealed maximum bacterial growth and crude oil degradation efficiency between 30-35°C, pH 6-9, and 4-6% NaCl. Among the isolates, Bacillus licheniformis, Bacillus cereus, and Pseudomonas stutzeri exhibited superior performance under extreme physicochemical conditions and demonstrated high tolerance to crude oil concentrations up to 25% (v/v).These findings highlight the remarkable adaptability of indigenous hydrocarbon-degrading bacteria and their potential application in optimizing biological treatment processes and bioremediating oil-contaminated industrial effluents.