Nutrient Uptake by Microorganisms according to Kinetic Parameters from Theory as Related to Cytoarchitecture

Abstract

SUMMARY The abilities of organisms to sequester substrate are described by the two kinetic constants specific affinity, a°, and maximal velocity Vmax. Specific affinity is derived from the frequency of substrate-molecule collisions with permease sites on the cell surface at subsaturating concentrations of substrates. Vmax is derived from the number of permeases and the effective residence time, τ, of the transported molecule on the permease. The results may be analyzed with affinity plots (v/S versus v, where v is the rate of substrate uptake), which extrapolate to the specific affinity and are usually concave up. A third derived parameter, the affinity constant KA, is similar to KM but is compared to the specific affinity rather than Vmax and is defined as the concentration of substrate necessary to reduce the specific affinity by half. It can be determined in the absence of a maximal velocity measurement and is equal to the Michaelis constant for a system with hyperbolic kinetics. Both are taken as a measure of τ, with departure of KM from KA being affected by permease/enzyme ratios. Compilation of kinetic data indicates a 108-fold range in specific affinities and a smaller (103-fold) range in Vmax values. Data suggest that both specific affinities and maximal velocities can be underestimated by protocols which interrupt nutrient flow prior to kinetic analysis. A previously reported inverse relationship between specific affinity and saturation constants was confirmed. Comparisons of affinities with ambient concentrations of substrates indicated that only the largest a°S values are compatible with growth in natural systems.

Effects of long-term nitrogen fertilization on the uptake kinetics of atmospheric methane in temperate forest soils

“…Whether atmospheric CH 4 consumption in soil provides energy for growth remains a fundamental question regarding the physiology of the active organisms. In nature, most bacteria must survive and grow in an oligotrophic environment, and enzymatic affinity for growth substrate is the fundamental factor limiting population growth [47]. If some soil methanotrophs use atmospheric CH 4 for growth, then a correlation between enzymatic affinity and in situ steady-state substrate supply might be expected in soils that are supplied only (or mostly) with CH 4 from the atmosphere.…”

“…Based on these assumptions, a decreased methanotroph population with a lower K m is more consistent with the observed kinetics. A caveat of this interpretation is that we must assume that K m reflects the specific affinity (V max /K m normalized for population size or enzyme concentration) of the dominant population [47]. However, some nitrifiers exhibit K m values for CH 4 that are similar to cultured methanotrophs, but with much lower specific affinities [31] (i.e.…”

Pelagic microbial activity in an arctic polynya: Testing for temperature and substrate interactions using a kinetic approach

“…Selection of uptake kinetics with labeled substrates for assessing temperature effects on microbial activity was based on the direct link that the approach provides between substrate uptake and availability. Recent advances in microbial uptake kinetic theory (Button 1998;Koch 1998) have also allowed for fine-tuned interpretations of such experimental results, particularly as they relate to microbial activity at low substrate concentration.…”

“…The ability to take up substrate (S) depends on membrane transport systems and thus on transporter density and capacity and can be described by the following cell-specific kinetic parameters (Button 1998): maximum specific utilization rate, V (g-S g-cells Ϫ1 h Ϫ1 ); half-saturation or Michaelis S max constant, K m (g-S L Ϫ1 ), and specific affinity, a (L g-cells Ϫ1 o s h Ϫ1 ). V reflects the density of membrane transporters as S max well as the most rate-limiting step in cytoplasmic enzymatic processing.…”

Bridging the gap between omics and earth system science to better understand how environmental change impacts marine microbes

“…The model includes ecophysiological constraints [e.g. diffusive nutrient uptake, (Button, 1998)] and costs, for example both resource allocation to macromolecular components and running costs, including nutrient, energy and reductant budgets (Shuter, 1979;Raven, Fig. 2 Bridging the gap: a model-centred approach to integrating omics approaches with marine microbial ecology.…”