A THERMODYNAMIC DESCRIPTION OF PHYTOPLANKTON GROWTH
D.A. KIEFER
Department of Biological Sciences, University of Southern
California, Los Angeles, California 90089, USA
I.
INTRODUCTION
As early as 1942 Monod noted that the growth rate for a continuous
culture of bacteria was adequately described by a hyperbolic function.
Since Monod's work, there have been numerous observations of similarities in the growth kinetics of microbes and the kinetics of reactions
catalyzed by enzymes in vitro (e.g. Malek and Fencl,1966). Such similarities have suggested to researchers that the growth response of microbes may be simply explained by the kinetics of a rate limiting step
in a metabolic pathway. Thus, parameters of Michaelis-Menten kinetics,
the half saturation constant and the maximum velocity for substratesaturated systems, have been adapted for descriptions of the microbial
growth.
In addition, this kinetic description of growth has served as
the conceptual basis for the establishment of the steady state in continuous culture devices.
While the kinetic description of enzyme action has been usefully
applied to a description of phytoplankton growth (eg. Caperon,1965;
Droop,1968), its application offers little insight into the regulation
of metabolism. This limitation has been the stimulus to explore an
alternate description of steady state microbial growth, based upon principles of non-equilibrium thermodynamics (Kiefer and Enns,1976).
In
this model the biochemical reactions occurring during the conversion of
light energy into chemical bond energy are characterized by two pairs
of coupled reactions. Both pairs of reactions are described phenomenologically and are assigned a degree of coupling. In the present paper I
will describe the model and apply it to a description of light-limited
and nutrient-limited growth of phytoplankton. These predictions will
then be compared with studies of general metabolic regulation by phytoplankton grown in continuous culture.
D.A. KIEFER
Department of Biological Sciences, University of Southern
California, Los Angeles, California 90089, USA
I.
INTRODUCTION
As early as 1942 Monod noted that the growth rate for a continuous
culture of bacteria was adequately described by a hyperbolic function.
Since Monod's work, there have been numerous observations of similarities in the growth kinetics of microbes and the kinetics of reactions
catalyzed by enzymes in vitro (e.g. Malek and Fencl,1966). Such similarities have suggested to researchers that the growth response of microbes may be simply explained by the kinetics of a rate limiting step
in a metabolic pathway. Thus, parameters of Michaelis-Menten kinetics,
the half saturation constant and the maximum velocity for substratesaturated systems, have been adapted for descriptions of the microbial
growth.
In addition, this kinetic description of growth has served as
the conceptual basis for the establishment of the steady state in continuous culture devices.
While the kinetic description of enzyme action has been usefully
applied to a description of phytoplankton growth (eg. Caperon,1965;
Droop,1968), its application offers little insight into the regulation
of metabolism. This limitation has been the stimulus to explore an
alternate description of steady state microbial growth, based upon principles of non-equilibrium thermodynamics (Kiefer and Enns,1976).
In
this model the biochemical reactions occurring during the conversion of
light energy into chemical bond energy are characterized by two pairs
of coupled reactions. Both pairs of reactions are described phenomenologically and are assigned a degree of coupling. In the present paper I
will describe the model and apply it to a description of light-limited
and nutrient-limited growth of phytoplankton. These predictions will
then be compared with studies of general metabolic regulation by phytoplankton grown in continuous culture.