Diesel degradation and biosurfactant production by Gram-positive isolates

Abstract

Accidental leakages during hydrocarbon fuels transportation and other activities are inevitable, making these hydrocarbons the most common global environmental pollutants. Current understanding in diesel degradation involves the study of Gram-negative microorganisms. Seven Gram-positive and one Gram-negative diesel degrading bacteria isolated from contaminated soil were used in this study. The overnight bacterial cultures were standardized and transferred into Bushnell-Haas medium
supplemented with glucose and incubated at 30°C at 160 rpm for 48 h. The level of diesel degradation was determined using gravimetric analysis. Cell numbers were calculated using total heterotrophic plate count. All isolates were capable of degrading 70 - 80% of n-paraffin whilst isolates D2, D9, D10 and DJLB possessed better abilities of diesel degradation at 65.4 - 83.12% under the standard conditions. Diesel degradation rates and microbial cell number, increased with an increase in glucose composition. The addition of glucose to the liquid medium had a positive effect, with an increase in growth of the isolates thus leading to significantly (p < 0.05) higher percentages of diesel degradation and greater emulsification activity. The ability of Gram-positive bacteria to degrade diesel increased in a comparable trend as its biosurfactant production increased. The E24 index was highest at 87.6% for
isolate D9. Isolates D2, D9 and D10, were identified as Paenibacillus sp. whilst isolate DJLB was found to belong to Stenotrophomonas sp. This study clearly demonstrates that Gram-positive biosurfactant producing bacteria are effective in diesel degradation.