 |
| Titel |
A total quasi-steady-state formulation of substrate uptake kinetics in complex networks and an example application to microbial litter decomposition |
| VerfasserIn |
J. Y. Tang, W. J. Riley |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 12 ; Nr. 10, no. 12 (2013-12-16), S.8329-8351 |
| Datensatznummer |
250085483
|
| Publikation (Nr.) |
 copernicus.org/bg-10-8329-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
We demonstrate that substrate uptake kinetics in any consumer–substrate
network subject to the total quasi-steady-state assumption can be formulated
as an equilibrium chemistry (EC) problem. If the consumer-substrate
complexes equilibrate much faster than other metabolic processes, then the
relationships between consumers, substrates, and consumer-substrate
complexes are in quasi-equilibrium and the change of a given total substrate
(free plus consumer-bounded) is determined by the degradation of all its
consumer-substrate complexes. In this EC formulation, the corresponding
equilibrium reaction constants are the conventional Michaelis–Menten (MM)
substrate affinity constants. When all of the elements in a given network
are either consumer or substrate (but not both), we derived a first-order
accurate EC approximation (ECA). The ECA kinetics is compatible with almost
every existing extension of MM kinetics. In particular, for microbial
organic matter decomposition modeling, ECA kinetics explicitly predicts a
specific microbe's uptake for a specific substrate as a function of the
microbe's affinity for the substrate, other microbes' affinity for the
substrate, and the shielding effect on substrate uptake by environmental
factors, such as mineral surface adsorption.
By taking the EC solution as a reference, we evaluated MM and ECA kinetics
for their abilities to represent several differently configured
enzyme-substrate reaction networks. In applying the ECA and MM kinetics to
microbial models of different complexities, we found (i) both the ECA and MM
kinetics accurately reproduced the EC solution when multiple microbes are
competing for a single substrate; (ii) ECA outperformed MM kinetics in
reproducing the EC solution when a single microbe is feeding on multiple
substrates; (iii) the MM kinetics failed, while the ECA kinetics succeeded,
in reproducing the EC solution when multiple consumers (i.e., microbes and
mineral surfaces) were competing for multiple substrates. We then applied
the EC and ECA kinetics to a guild based C-only microbial litter
decomposition model and found that both approaches successfully simulated
the commonly observed (i) two-phase temporal evolution of the decomposition
dynamics; (ii) final asymptotic convergence of the lignocellulose index to a
constant that depends on initial litter chemistry and microbial community
structure; and (iii) microbial biomass proportion of total organic biomass
(litter plus microbes). In contrast, the MM kinetics failed to realistically
predict these metrics. We therefore conclude that the ECA kinetics are more
robust than the MM kinetics in representing complex microbial, C substrate,
and mineral surface interactions. Finally, we discuss how these concepts can
be applied to other consumer–substrate networks. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|