Abstract:
Hydrocarbon pollution is one of the major environmental problems and this has led
to studies on use of hydrocarbon degrading bacteria for bioremediation. Isolation of
hydrocarbon degrading bacteria from a polluted environment is plausible, because
the environmental conditions can have a selection pressure on the type of bacteria
that can reside in a particular contaminated environment. Naphthalene is considered
to be a potent pollutant which is an intermediate product of hydrocarbon combustion.
Toxicity, low volatility and recalcitrance to degradation and high affinity for
sediments make naphthalene bio-degradation an important intervention. This study
reports the isolation of indigenous naphthalene degrading bacteria from hydrocarbon
contaminated soil near a filling station.
Aqueous soil extracts were prepared using three soil samples collected near a filling
station in Anuradapura. To prepare the Naphthalene supplemented Bushnell Hass
(BH) agar plates, a portion (0.3 ml) of naphthalene solution (2% w/v) in methanol
was added to the bottom agar surface and swirled to obtain an even distribution. Then
0.1 ml soil extract was mixed with 0.9 ml of molten BH agar medium and poured on
bottom agar. The plates were then swirled to spread molten agar medium over bottom
agar with a PAH layer. All plates were incubated at room temperature for 3-6 weeks
and the colony count of naphthalene degrading bacteria was recorded daily. Isolated
bacterial colonies were identified according to the Bergey’s manual of determinative
bacteriology. Appearance of bacterial colonies was observed after fifteenth day,
showing a slow degradation and number of colonies gradually increased with the
time (Figure 1). Gradual increase of number of colonies shows the ability of bacteria
to acquire the naphthalene degrading capability with time. This can be resulted due
to the decrease in naphthalene concentration below the toxicity level or ability to
acquire naphthalene degrading capability with the time of incubation. Isolated bacterial strains were identified as Staphylococcus aureus, Staphylococcus
sp. and Pseudomonas sp. and they have the potential to be used in bioremediation of
environments polluted with naphthalene.
