Two hydrocarbon utilizers Pseudomonas
fluorescens and Vibrio fluvialis isolated from crude oil
impacted mesotidal water and sediment samples and
identified using Microgen ID Kit (Microgen Bioproduct
Limited, UK), and 16s rRNA were exposed to different
concentrations of nickel (Ni) (0.00, 1.17, 2.34, 4.68, 9.375
and 18.75mM). Following exposure to the various Ni
concentrations, the isolates were monitored for effect on
growth every six hours for 48 hours, percentage
survability, and LC50 determined. The generation times
for P. fluorescens and V. fluvialis increased from 1.55 to
3.73 and 1.56 to 3.75 (h/gen) as Ni concentration
increased from 0.00 to 1.17Mm, respectively.
Furthermore, growth rates decreased from 0.447 to 0.186
and 0.443 to 0.185 (h-1
) for P. fluorescens and V. fluvialis,
respectively. Without the toxicant, the peak numbers of
cells were 21.77 and 21.68 log number of cells for P.
fluorescens and V. fluvialis, respectively. However, in the
presence of Ni, the peak log numbers of viable cells were
15.52 and 15.477 after 24 hours for P. fluorescens and V.
fluvialis, respectively. Comparism of the number of
surviving cells at 1.17mM showed that V. fluvialis had
76.69% of surviving cells against 9.32 % for P.
fluorescens. Linear regression line fit plots revealed R2
values of 0.5372 for P. fluorescens and 0.9341 for V.
fluvialis. The LC50 for V. fluvialis was 5.77 mM while
that of P. fluorescens could not be determined from the
model. Generally, pH values above 6.8 favoured both
isolates even in Ni concentrations above 1.17mM. The
findings in our study indicate that Ni in concentrations
above 1.17mM has the potential to reduce the growth of
Keywords : Niger Delta, Hydrocarbon Utilizers, Heavy Metals, Bacteria, Toxicity.