Affiliation:
1. Department of Microbiology and Public Health, Michigan State University, East Lansing, Michigan 48824
Abstract
Michaelis-Menten kinetic parameters for H
2
consumption by three methanogenic habitats were determined from progress curve and initial velocity experiments. The influences of mass transfer resistance, endogenous H
2
production, and growth on apparent parameter estimates were also investigated. Kinetic parameters could not be determined for undiluted rumen fluid and some digestor sludge from gas-phase measurements of H
2
, since mass transfer of H
2
across the gas-liquid interface was rate limiting. However, accurate values were obtained once the samples were diluted. H
2
consumption by digestor sludge with a long retention time and by hypereutrophic lake sediment was not phase transfer limited. The
K
m
values for H
2
uptake by these habitats were similar, with means of 5.8, 6.0, and 7.1 μM for rumen fluid, digestor sludge, and sediment, respectively.
V
max
estimates suggested a ratio of activity of approximately 100 (rumen fluid):10 (sludge):1 (sediment); their ranges were as follows: rumen fluid, 14 to 28 mM h
−1
; Holt sludge, 0.7 to 4.3 mM h
−1
; and Wintergreen sediment, 0.13 to 0.49 mM h
−1
. The principles of phase transfer limitation, studied here for H
2
, are the same for all gaseous substrates and products. The limitations and errors associated with gas phase determination of kinetic parameters were evaluated with a mathematical model that combined mass transport and Michaelis-Menten kinetics. Three criteria are described which can be used to evaluate the possibility that a phase transfer limitation exists. If it does not exist, (i) substrate consumption curves are Michaelis-Menten and not first order, (ii) the
K
m
is independent of initial substrate concentration, and (iii) the
K
m
is independent of biomass (
V
max
) and remains constant with dilution of sample. Errors in the Michaelis-Menten kinetic parameters are caused by endogenously produced H
2
, but they were <15% for rumen fluid and 10% for lake sediment and digestor sludge. Increases in
V
max
during the course of progress curve experiments were not great enough to produce systematic deviations from Michaelis-Menten kinetics.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
108 articles.
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