Effects of Environmental Conditions and Nutritional Factors on Biosurfactant Production by Bacteria from Diesel Contaminated Soil.

Abstract

The aim of this work is to determine the effects of ecological and nutritional factors on biosurfactant production by bacteria isolated from diesel polluted soil. Serial dilution of the polluted soil sample was done. 1ml of 10^-6 dilution was inoculated into nutrient agar plates using pour plate method and incubated at 37^oC for 24hours. The mean bacteria count ranged from 35x10⁵cfu/ml to 74x10⁵cfu/ml. After subsequent sub culturing, 15 different bacteria isolates were obtained. The isolates were identified using colonial morphology, biochemical characteristics and molecular tools using 16S rRNA gene sequence. The isolates identified include; Stenotrophomonas maltophilia T7D7 Pseudomonas aeruginosa TCSS2, Pseudomonas aeruginosa BP4, Pseudomonas aeruginosa GB24, Alicaligenes sp. CIFRID-TSB1, Bacillus subtilis B-28, Bacillus sp. AH6, Alicaligenes faecalis 138C-1, Bacillus safensis HKG 214, Alicaligenes faecalis RAJ4, Bacillus pumilus TW3, Bacillus sp. KYLS-CU05, Bacillus subtilis Y2, Pseudomonas sp. YA6 16S, Klebsiella Pneumoniae NGB- FR75. These isolates were screened for biosurfactant production qualitatively using different methods including Blood agar haemolysis test, drop collapse test, Oil spreading test. Furthermore, Strains of Stenotrophomonas maltophilia, Pseudomonas aeruginosa and Bacillus subtilis were positive for all the qualitative tests above and were further screened quantitatively using emulsification index test and they all showed good emulsification activity indicating the production of biosurfactants. Stenotrophomonas maltophilia T7D7 had the highest emulsification activity of 73% and was used for the study on the effect of environmental conditions and nutritional factors on biosurfactant production. Biosurfactant production by bacteria is affected by different environmental and nutritional factors. These factors should therefore be optimized for large scale production and purification of biosurfactants for application in industries and bioremediation processes.

Keywords: Biosurfactant; Bacteria; Emulsification; Haemolysis; Contaminated soil.