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Response of Nitrosomonas,
Nitrobacter and Escherichia coli to drilling
fluids
L. O. Odokuma* and E. Akponah
Department of
Microbiology, University of Port Harcourt, Port Harcourt
*Corresponding
author. E-mail:
luckyodokuma@yahoo.co.in.
Accepted 28
January 2008
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Inhibition of ammonia oxidation by Nitrosomonas, nitrite oxidation
by Nitrobacter and carbon IV oxide evolution by
Escherichia coli were employed as indices to
determine the effect of four drilling fluids (Paradril,
IMC0-W, IMC0-O and Gel/KCL/polymer to these bacteria. The
percentage survival (determined by aerobic spread plate
count) of these bacteria when exposed to these fluids was
also used as toxicity index. Ammonia oxidation (nitrite
accumulation) and nitrite oxidation (consumption) were
determined by coupling of diazotised sulfanilic acid with a-napthyl-ethylene
diamine dihydrochloride. Carbon IV oxide evolution was
monitored by passing air from inoculated lactose broth into
calcium hydroxide solution and titration with sulphuric
acid. Toxicity indices were determined throughout the
following exposure period (0, 1, 2, 3, 4, 8, 12, 24, 36 and
48 h) in static
shake flask systems.
Percentage survival decreased with increasing
concentration of the drilling fluids and increasing exposure
period of the three bacteria especially at high
concentrations (10.0, 100 and 1000 mg/l). At lower
concentrations (0.01, 0.1 and 1.0 mg/l) some fluids
stimulated bacterial growth. Controls revealed bacterial
growth through out the exposure period. Nitrite accumulation
by Nitrosomonas, nitrite consumption by
Nitrobacter and carbon IV oxide evolution by E.
coli decreased with increase in concentration and
exposure time of the four fluids. Controls revealed an
increase in these indices with increase in exposure period.
Results showed that the drilling fluids inhibited the two
stages of the nitrification in the nitrogen cycle and
respiration (by E. coli). This may affect the
agricultural productivity of ecosystems in the Niger Delta
where they are employed by causing dislocations in the
nitrogen cycle where nitrifying and aerobic bacteria
participate.
Key words:
Nitrite
accumulation, nitrite consumption, respiration, drilling
fluids.
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