Preliminary Screening of Bio-surfactant Producing Bacteria Isolated from an Oil Contaminated Soil

Abstract

Spent motor oil represents one of the most prominent and tenacious contaminants of soil within mechanic workshops across Nigeria. Adaptation and natural evolution proffer a rich array of a microorganism capable of producing bio-surfactants which are of high value to industry, particularly in hydrocarbon degradation. This study was undertaken to isolate and screen for bio-surfactant producing bacterial strains isolated from engine oil contaminated mechanic sites. Data obtained revealed that using 0.3% Fluconazole supplemented nutrient agar media, bacterial isolates were obtained from soil samples within Apo mechanic village, Abuja, Nigeria. Hemolytic assay method and foam capacity test were used for screening. The positive strains were grown in liquid medium and the emulsification index (EI24) was determined. A total of 3 bacterial isolates referred to as A2, B1 and C8 were positive for the hemolytic and foam capacity tests, with an emulsification index (EI24) of 40.0, 11.7 and 36.7 respectively. Growth measurements were determined by measuring optical density of the cells in broth using spectrophotometer at 605nm over a 96 hour incubatory period in nutrient broth at 4ºC, 37ºC, 42ºC. All isolates displayed mesophilic characteristics withprogressive growth. At 37ºC, isolate A2 had the highest growth rate via optical density readout 1.95, 2.11, 2.32, 2.55, measured at 605nm. Isolate A2 also the best performing isolate at 42ºC with optical density readings of 1.32, 1.00, 0.91 and 1.68, thereby suggestive of thermotolerant ability. All isolates demonstrated good growth in broth medium with pH ranging from 8.97-9.16 at 37ºC. All isolates were positive for catalase and citrate, negative for methyl red, Voges-Proskauer and indole tests. Isolate A2 was the only gram-positive, oxidase negative and non-motile bacteria. The bio-surfactants produced by the three different bacterial isolates would possess chemically distinct signatures that can be harnessed for multiple applications ranging from bioremediation to degradable detergent uses.