Elsevier

Waste Management

Volume 18, Issue 5, August 1998, Pages 293-299
Waste Management

Studies on relative capabilities of bacterial and yeast isolates from tropical soil in degrading crude oil

https://doi.org/10.1016/S0956-053X(98)00037-3Get rights and content

Abstract

The relative capabilities of two bacterial isolates Serratia marcescens OCS-21 and Acinetobacter calcoaceticus COU-27 from Ebubu oil polluted soil of Rivers State, Nigeria and a yeast isolate, Candida tropicalis PFS-95 from unpolluted soil of the University of Calabar campus, in degrading transniger pipeline crude oil were investigated. Crude oil degradation was measured by gravimetric analysis and capillary gas chromatographic techniques. Candida tropicalis PFS-95 exhibited a more efficient ability in degrading the crude oil than either S. marcescens OCS-21 or A. calcoaceticus COU-27. The yeast isolate PFS-95 degraded 68.9% of crude oil after 16 days of incubation whereas OCS-21 and COU-27 degraded 51.5% and 45.5% of crude oil respectively over the same incubation period. Capillary gas chromatographic analysis of the degraded crude oil revealed that crude oil components of chain length C12 to C32 were extensively degraded by PFS-95 after 16 days of incubation while OCS-21 caused a moderate degradation of the crude oil components (C20 to C28) over the same period. Acinetobacter calcoaceticus COU-27 was able to degrade only C22 to C30 components of the crude oil after 16 days of incubation. Results of crude oil adherence/emulsification tests revealed that OCS-21 was unable to emulsify the crude oil but exhibited maximal adherence to the crude oil whereas PFS-95 and COU-27 exhibited minimal adherence to, but maximal emulsification of the crude oil. Results obtained suggest that C. tropicalis PFS-95 may be a better microorganism for clearing oil spills in tropical soils than either S. marcescens OCS-21 or A. calcoaceticus COU-27. ©

Introduction

Frequent oil spills are inevitable in oil producing areas like the Niger Delta Area of Nigeria. Oil spills devastate soil and aquatic ecosystems, and cause alteration in important microbial processes. This therefore necessitates studies in microbial degradation of crude oil as a means of clearing up oil polluted environments. Specifically, such studies are directed towards the isolation and identification of superior crude oil degrading microorganisms from soil and aquatic ecosystem. Besides, studies on the rate and total extent of crude oil degradation by microbial isolates are important as these will enable the oil industries to explore the possibility of using the efficient crude oil degraders for seeding oil polluted environments, particularly in areas with difficult terrain, where mechanical clean-up operations are not possible. The Niger Delta Area of Nigeria from where two of the isolates used in this study were isolated have difficult terrain and present problems in oil spill abatement using non-biological approaches.

The relative contribution of bacteria and fungi to hydrocarbon mineralization in soil has been reported by Song et al.[1]. The investigators observed that in a sandy loam soil with no history of hydrocarbon pollution, 82% of n-hexadecane was mineralized by bacteria whereas fungi were able to mineralize only 13% of the hydrocarbon. Similarly, many other investigators have reported2, 3, 4, 5, 6the involvement of bacteria and yeasts in crude oil biodegradation. In these reports, bacteria have been identified as more efficient crude oil degraders than yeasts. On the contrary, there is scanty information that yeasts are better crude oil degraders than bacteria[7]. The present study contributes information in this area.

The growth of microorganisms on hydrocarbons is often accompanied by the emulsification of the insoluble carbon source in the culture medium8, 9, 10. In most cases, this has been due to the production of extracellular emulsifying agents during the breakdown of hydrocarbons. The propensity of hydrocarbon grown microorganism to adhere to hydrocarbon has also been reported11, 12, 13. These processes aid microorganisms in growing on and metabolizing crude oil.

The aims of the present study were to investigate the relative capabilities of two bacterial isolates from oil polluted soil and a yeast isolate from unpolluted soil, in degrading a Nigerian light crude oil, transniger pipeline crude and to examine their ability to adhere to and emulsify crude oil so that the results could point to a better candidate for cleaning up oil spills in tropical soils.

Section snippets

Materials and methods

Mineral salts medium (MSM) of Zajic and Supplisson[14]and oil agar (OA) were used for biodegradation studies. The MSM had the following composition: 1.8 g K2PO4, 1.2 g KH2PO4, 4.0 g NH4Cl, 0.2 g MgSO4 · 7H2O, 0.1 g NaCl, 0.01 g FeSO4 · 7H2O in 1 l of distilled water (pH 7.4). Oil agar is MSM plus 1.0% crude oil and 20 g of agar (Oxoid).

Results

Based on rapid growth on crude oil and their considerably high ability in degrading crude oil, two isolates designated COU-27 and OCS-21, out of the 20 crude oil degrading bacterial isolates and one (PFS-95) out of the 10 crude oil degrading yeast isolates screened, were selected for this study. COU-27 was isolated from crude oil polluted soil while OCS-21 and PFS-92 were isolated from crude oil free soil. It was observed that bacterial isolate OCS-21 was a gram negative, motile rod while

Discussion

Soil microorganisms participate in soil processes including transformation of nutrients. They are also active degraders of crude oil3, 4, 5, 6, 18, 21, 22. The present study revealed that crude oil degrading microorganisms are not restricted to oil polluted soil as A. calcoaceticus COU-27 and C. tropicalis PFS-95 isolated from soil with no history of oil pollution and S. marcescens OCS-21 isolated from oil polluted soil degraded crude oil. This finding supports the report of Odu23, 24that crude

Acknowledgements

The author is grateful to Prof. Dr. B. Witholt for providing financial assistance and facilities for this study. Dr. Hans Preusting is also acknowledged for his assistance with the GLC analysis. The author wishes to thank Prof. S.P. Antai, Prof. E.D. Okon and Dr. A.A. Opara for their suggestions and the Nigerian National petroleum Corporation (NNPC) for the provision of the crude oil sample used in this study.

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