Isolation Of Biosurfactant Producing Bacteria From Tannery Effluents In Sokoto Metropolis, Nigeria

Abstract

Tannery effluents provide an environment for growth of different types of microorganisms. Possibility of occurrence of biosurfactant producers in such effluents collected from local tanneries was investigated in this study. Samples of tannery effluents were collected from three different tanneries. Physicochemical analyses revealed that the effluents contained large amounts of total dissolved solids, total suspended solids, organic and inorganic matter and Chromium beyond the limits stipulated by Federal Environmental Protection Agency (FEPA). Forty seven bacteria species were isolated by enrichment culture technique using Mineral salt media (supplemented with 0.1% v/v Bonny light crude oil) and identified using biochemical characterization. Bacillus (61.70%) and Proteus (12.76%) species were the predominant bacteria, followed by Pseudomonas and Serratia (8.51% each) species. The remaining isolates were Citrobacter diversus, Aeromonas hydrophila, Micrococcus luteus and Enterobacter faecalis which had 2.12% of occurrence each. Hemolysis, oil emulsification, drop collapse and oil spreading methods were used to screening the isolates for biosurfactant production. Of the twenty two isolates tested, only seven (31.8%) and five (22.72%) were hemolytic and able to emulsify the oil respectively. Similarly, only two isolates – Bacillus sphaericus EN3 and Bacillus azotoformans EN16 were positive for drop collapse and oil spreading. Results showed that Bacillus sphaericus EN3 could cause the collapse and spread of oil drop at the rate of 10 and 7 min respectively with an average diameter of 3.4cm, while Bacillus azotoformans EN16 could do same at the rate of 15 and 12 min respectively with 2.9cm diameter. Although Bacillus azotoformans EN16 had higher emulsification index (ER24 R= 58.0 ± 5.5) than Bacillus sphaericus EN3 (ER24 R= 47.8±1.15), the former might have more active surfactants than the latter, considering the period and diameter of oil spreading. Therefore, the two organisms proved to be biosurfactant producers and tannery effluents is a good source for biosurfactant producing bacteria.