Bacteria associated with petroleum hydrocarbon wastes in Kupferberg landfill site, Windhoek.

Abstract

Petroleum compounds are organic contaminants of great interest due to their extensive dispersal, stubbornness, versatile structure and harmful elements that have been generally known to belong to the family of carcinogens and mutagens organic toxins. They contaminate many environments worldwide and enter the global environment through crude oil spillage, fossil fuel combustion as well as natural inputs like natural petroleum seepage. A range of indigenous microbes have the ability of decontaminating, breaking down, transforming and removing these hydrocarbon contaminants from the environment through biodegradation processes. Therefore, the aim of this study was to isolate and identify the bacterial strains present in the soil contaminated waste samples collected from the Kupferberg landfill site in Windhoek and to ascertain their ability to grow efficiently in hydrocarbon based medium. Collected bacterial strains were grown on nutrient agar and were characterised based on their colony features and biochemical reactions using the API 20NE identification database system. Sterile nutrient broth media was inoculated with a loop full of the bacterial isolates supplemented with 1 ml of sterile old diesel engine oil, and the optical density was measured spectrophotometrically on a daily basis. The highest mean bacterial count was found out to be 3.6 x 10􀬸 CFU/ml in site G, and the lowest mean bacterial count was found out to be 0.9 x 10􀬸 CFU/ml in site I. The bacterial strains isolated were Aeromonas hydrophila, Stenotrophomonas maltophilia, Sphingomonas paucimobilis, Pseudomonas luteola, Burkholderia gladioli, Photobacterium damselae, Pseudomonas aeruginosa, Pasteurella spp., Brevundimonas vesicularis, Burkholderia cepacia, Chryseobacterium indologenes and Aeromonas salmonicida, and it was observed that Sphingomonas paucimobilis was the predominant isolate in all the samples. Ten selected bacterial strains were subjected to hydrocarbon utilisation/ degradation test, and it was observed that Pseudomonas aeruginosa strain with a mean average optical density of 1.738, utilised the hydrocarbon in the medium more efficiently than the other isolates. The study demonstrated that the isolated Pseudomonas aeruginosa could be considered as good prospects for the bioremediation of hydrocarbons.