Growth kinetics, i.e., the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in microbiology. However, despite more than half a century of research, many fundamental questions about the validity and application of growth kinetics as observed in the laboratory to environmental growth conditions are still unanswered. For pure cultures growing with single substrates, enormous inconsistencies exist in the growth kinetic data reported. The low quality of experimental data has so far hampered the comparison and validation of the different growth models proposed, and only recently have data collected from nutrient-controlled chemostat cultures allowed us to compare different kinetic models on a statistical basis. The problems are mainly due to (i) the analytical difficulty in measuring substrates at growth-controlling concentrations and (ii) the fact that during a kinetic experiment, particularly in batch systems, microorganisms alter their kinetic properties because of adaptation to the changing environment. For example, for Escherichia coli growing with glucose, a physiological long-term adaptation results in a change in KS for glucose from some 5 mg liter−1 to ca. 30 μg liter−1. The data suggest that a dilemma exists, namely, that either “intrinsic” KS (under substrate-controlled conditions in chemostat culture) or μmax (under substrate-excess conditions in batch culture) can be measured but both cannot be determined at the same time. The above-described conventional growth kinetics derived from single-substrate-controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in ecosystems. However, in nature, microbial cells are exposed to a wide spectrum of potential substrates, many of which they utilize simultaneously (in particular carbon sources). The kinetic data available to date for growth of pure cultures in carbon-controlled continuous culture with defined mixtures of two or more carbon sources (including pollutants) clearly demonstrate that simultaneous utilization results in lowered residual steady-state concentrations of all substrates. This should result in a competitive advantage of a cell capable of mixed-substrate growth because it can grow much faster at low substrate concentrations than one would expect from single-substrate kinetics. Additionally, the relevance of the kinetic principles obtained from defined culture systems with single, mixed, or multicomponent substrates to the kinetics of pollutant degradation as it occurs in the presence of alternative carbon sources in complex environmental systems is discussed. The presented overview indicates that many of the environmentally relevant apects in growth kinetics are still waiting to be discovered, established, and exploited.

Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

Underground hydrogen storage: A comprehensive review

Continuous culture populations of the bacterium especially coli and its virulent virus T7 have been studied as a model of a predator—prey in a simple habitat. These organisms maintain apparently stable states of coexistence in: (1) a phage—limited situation where all of the bacteria are sensitive to the coexisting virus and the sole, and potentially limiting carbon source, glucose, is present in excess; and (2) a resource—limited situation where the majority of the bacteria are resistant to these phage and in which there is little free glucose. The composition of these interacting populations is examined in detail and evidence indicating that this simple experimental culture system can support relatively complex communities is presented. In the predator—limited situation, two populations at each of two trophic levels can be maintained; the wild—type bacterial and phage strains, denoted B0 and T70, a mutant bacterial clone which is resistant to T70, denote B1 and a host range mutant phage, T71 which is capable of growth on both B0 and B1. In the resource—limited situation, three populations of bacteria and two populations of phage can coexist. The include the above described clones and a third bacterial strain, B2, which is resistant to both T70 and T71. In phage—free competition, the wild—type B0 bacterial clone has a marked advantage relative to both B1 and B2 while no difference is detected between B1 and B2. When competing for a B0 host, the wild—type T70 phage clone has a marked advantage over T71. The fit of these observations to some previously developed theory of resource—limited growth, competition and predation is discussed and a mechanism to account for the persistence of these communities is presented. The latter assumes that their stability can be attributed solely to intrinsic factors, i.e., the population growth and interaction properties of the organisms in this continuous culture habitat.

A Complex Community in a Simple Habitat: An Experimental Study with Bacteria and Phage

Microbial growth on and utilization of environmental contaminants as substrates have been studied by many researchers. Most times, substrate utilization results in removal of chemical contaminant, increase in microbial biomass and subsequent biodegradation of the contaminant. These are all aimed at detoxification of the environmental pollutants. Several microbial growth and biodegradation kinetic models have been developed, proposed and used in bioremediation schemes. Some of these models include Monod’s, Andrews, Bungay’s weighted model, general substrate inhibition models (GSIM) and sum kinetic models. Most research on microbial potentials to degrade chemical pollutants has been performed on a laboratory scale. There is a need to extend such studies to pilot scale as well as to full-scale field applications.

	 

	Key words: Microbial growth, substrate utilization, biodegradation, kinetics, detoxification, organic contaminants, models, environmental pollutants.

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Microbial growth and substrate utilization kinetics

It has been estimated that globally some 500 × 1012 kg of carbon dioxide are assimilated into biomass by autotrophic organisms annually. More than 99% of this assimilated carbon is remineralized, keeping the global biogeochemical carbon cycle roughly in balance (Hedges, 1992). In both terrestrial and aquatic ecosystems the majority of this primary biomass is not consumed directly by herbivorous animals, but decays to detritus and serves as a nutritional basis for the growth of consumers (for an extensive discussion, see Fenchel and Jorgensen, 1977). There is now substantial evidence suggesting that a large part of the energy and nutrients contained in this primary biomass is processed via the microbial detritus food chain, and this mineralizing ability makes heterotrophic microorganisms an important link in the global carbon cycle (Fenchel and Jorgensen, 1977; Paul and Voroney, 1980; Wetzel, 1984; Cole et al., 1988; Mann, 1988). In addition, their ability to mineralize man-made xenobiotic organic chemicals has become increasingly important. This is illustrated by the fact that in industrialized countries the flux of synthetically produced organic material, much of which is ending up in the environment, has increased within the past two centuries to some 40 g C m−2 year−1. This figure is equivalent to approximately 15% of the net primary biomass production in these regions (Egli, 1992).

The Ecological and Physiological Significance of the Growth of Heterotrophic Microorganisms with Mixtures of Substrates

Saccharomyces cerevisiae and a riboflavin assay strain of Lactobacillus casei have been propagated anaerobically in mixed culture. Both batch and continuous culture techniques were used. By varying...

A. G. Fredrickson

Papers

Studies in intermicrobial symbiosis. Saccharomyces cerevisiae and Lactobacillus casei.