Oil degrading and heterotrophic bacteria composition in the oil-spilled affected mangrove forest sediment in Mactan Island, Central Philippines

Abstract

Oil spill increases the amount of hydrocarbons in marine ecosystems that disrupts the ecological balance with severe economic consequences. This study was conducted to assess the microbial composition in the sediments of oil affected areas in Mactan Island, Cebu eight months after the incident. Four sites designated as S1 (low) , S2 (mid) and S3 (high) representing oil spill contamination gradient were established. A reference site (Ref) was selected. Sediment samples from each site were collected for microbial count enumeration (heterotrophic and oil degrading bacteria) using the spread plate technique and the MPN method respectively. An increasing pattern of heterotrophic bacteria and decreasing trend of oil degrading bacteria counts were observed along S1, S2 and S3. Results revealed the heterotrophic bacteria count in all sites did not vary significantly. In addition, Ref exhibited highest and lowest count for heterotrophic and oil degrading bacteria respectively whereas S3 and S2 displayed highest in density for the oil degrading bacteria. The proliferation of oil degrading microbe implies the possible presence of oil residues including those PAH components that gets more toxic through time.