The efficiency of the indigenous microbial community
to transform crude oil was determined at 7 and 14
d of incubation (Figs. 1 and 2). The cultures with 10
and 20 mg mL−1 of crude oil had higher removal ratios
(90% and 88%) and cell numbers (4.2 × 108 and 6.3
× 108) at 14 d than the culture with 30 mg mL−1 of
crude oil. The increase in substrate concentration up
to 30 mg mL−1 of crude oil showed moderately toxic to
at least some microorganisms of the culture which had
the microbial cell counts of 1.0 × 108 and 2.4 × 108
and the degradation percentages of crude oil of 28%
and 50% after 7 and 14 d of incubation, respectively