Characterisation of petrochemical degrading bacteria from oil contaminated soils in automechanic workshops in Arua city, Uganda

Abstract

Unregulated, indiscriminate disposal and poor handling of used oil products from automotive mechanic workshops in Uganda contaminate vast areas of soil and groundwater. The use of bacteria to clean up contaminated sites is considered to be a desirable bioremediation strategy. Soils from automobile workshops that have had continuous exposure to oil spills provide a suitable environment for isolating adapted bacteria for bioremediation. This study aimed to isolate, characterize, and identify petroleum hydrocarbon-degrading bacteria in oil-contaminated soils collected from auto mechanic workshops in Arua City, Uganda. The isolation and identification of cultured bacteria were performed using standard microbiological methods, including morphology and biochemical tests. The effectiveness of the bacteria in degrading petroleum hydrocarbons was evaluated following the dichlorophenol-indophenol redox indicator method during the 5-day treatment, using diesel as the sole carbon source. Molecular identification of the isolated petroleum hydrocarbon-degrading bacteria was conducted by PCR amplification and sequencing of the 16S rRNA gene. MEGA 11 software was used to draw a phylogenetic tree showing the relationships between the bacterial isolates. Results showed that the fifteen morphologically and biochemically distinct bacterial colonies mostly had gram-negative-rod-shaped catalase-positive bacteria, capable of utilising diesel as their sole carbon source at varying degrees. Isolates, particularly from genera such as Acinetobacter and Bacillus, known for hydrocarbon degradation, exhibited higher petrochemical degradation potential up to 90%. Molecular characterization identified all the isolates as Shewanella xiamenensis, Jeotgalibacillus marinus, Bacillus thuringiensis, Pseudomonas putida, Peribacillus simplex, Stutzerimonas chloritidismutans, Pseudomonas fluorescens, Acinetobacter johnsonii, Psychrobacillus insolitus, Acinetobacter pittii, Raoultella ornithinolytica, Acinetobacter calcoaceticus, Rhodococcus erythropolis, Enterococcus gallinarum, and Comamonas jiangduensis. These findings therefore provide valuable insights into the potential application of these microbial isolates in the bioremediation of diesel-contaminated environments.