Two marine hydrocarbonoclastic bacterial
isolates, Pseudomonas fluorescens and Vibrio fluvialis,
obtained from water and sediment samples from Qua
Iboe Estuary, Niger Delta, Nigeria were exposed to
different concentrations of trivalent chromium (Cr)
(0.00, 6.25, 12.50, 25.00, 50.00, 100.00 and 200.00 mM)
and a control (0.00mM). After exposure, the isolates
were monitored for effect of Cr on growth and LC50
also determined using a linear regression line fit plot.
The generation times for P. fluorescens and V. fluvialis
increased from 1.55 to 6.24 and 1.56 to 6.93 (h/gen),
respectively as Cr concentration increased from 0.00 to
12.50mM. In contrast, the growth rates decreased from
0.447 to 0.111 and 0.443 to 0.100 (h-1
) for P. fluorescens
and V. fluvialis, respectively. At concentrations ≥
25mM, the generation times and growth rates for both
isolates dropped to zero. Control assay showed a short
lag phase and extended exponential phase, however, Cr
concentrations of 6.25 and 12.50mM showed a longer
acclimatization and short exponential phases of growth
for both isolates. Percentage survivability after one 1h
of exposure showed 0% of survived cells for both
isolates at concentrations of 100 and 200 mM.
Quadratic regression line fit plot of survivability for
both isolates gave R2
values of 0.763 and 0.905,
respectively for P. fluorescens and V. fluvialis. Linear
regression line fit plot gave LC50 values of 80.70 and
45.85 for P. fluorescens and V. fluvialis, respectively. Cr
concentrations 100mM and above were very toxic to the
test isolates in this study.
Keywords : Niger Delta, Hydrocarbon Utilizers, Chromium, Bacteria, Toxicity.