4. Discussion
Survival of microorganisms in petroleum hydrocarbons
medium after their inoculation is a key deciding factor in
the rate of biodegradation of hydrocarbons either in soil or
in liquid phase (Ramos et al., 1991). Since all the bacteria in
the present study were isolated from a petroleum contaminated
soil sample, they survived and adopted the oilcontaminated
soil/liquid environment very easily as also
reported by other authors (Rahman et al., 2003; Sugiura
et al., 1997). This was evident from the signiWcant increase
(p<0.01) in the population of B. subtilis and P. aeruginosa
in soil as compared to control. However, higher growth rate
(p<0.05) of Pseudomonas strains compared to Bacillus
strain might be related to higher breakdown and utilization
of petroleum hydrocarbons by former strains. Besides, the
necessity for seeding with hydrocarbon degrading bacteria
might have arisen from the fact that indigenous microbes of
soil were not eYcient degraders of a wide range of complex
compounds of crude petroleum-oil and therefore, introduction
of eYcient hydrocarbon degraders would be essential
in order to eVectively degrade all of the hydrocarbons in a
complex petroleum mixture (Atlas, 1977). Since the supplementation
of glucose as co-carbon source enhanced the rate of biodegradation of PAH by bacterial strains used in this
study (Das and Mukherjee, in press), glucose was added in
the oil-contaminated soil after a regular interval to increase
the rate of biodegradation of TPH by the seeded bacteria.
However, present results were in contradiction to report of
Chhatre et al. (1996) describing addition of nutrients in the
soil was unlikely to have dramatic eVect on the microbial
degradation of crude oil.
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