Abstract:
Bioremediation is the most harmless and efficient method for degrading petroleum
hydrocarbons. The objective of the present study was to isolate and identify potential crude
oil degrading bacteria from chronically contaminated sites located at Colombo and
Gampaha districts of Sri Lanka. Primary enrichments were prepared by inoculating sludge
and water samples separately into the Bushnell Hass Minimal Salt medium amended with
2% crude oil as the source of carbon and energy, incubated at 28 oC for 5 days at 130 rpm.
Eleven bacterial isolates were obtained from spread plates prepared after fifth enrichment.
The Gram’s staining showed that all the isolates were gram negative rod shape. Growth
kinetics were assessed by culturing each isolate in BHMS amended with 2% crude oil under
the constant culture conditions stated above with two replicates and a control. OD620 was
measured in every 24 hours interval and several isolates showed excellent growth (Isolate
1, 2, 3 and 8), high growth (isolate 5), moderate growth (isolate 11, 12 and 14) and low
growth (isolate 10 and 13) in respect to OD value. Partial gene sequences of 16S rRNA was
shown 99% and 100% identities for Pseudomonas aeruginosa. However, the morphological
variations observed in the crude oil layers and in the culture media due to the production of
pigments pertaining to different isolates revealed that among the isolates, different strains
of Pseudomonas aeruginosa might be present.
