Heterotrophic community

Mineralization of organic residues in soil is mainly carried out by an extremely diverse heterotrophic community referred to as the soil microbial biomass. The soil environment is a rather peculiar natural environment for the growth of microorganisms, in that they have had to adapt to quite extreme growth-limiting factors (a) discontinuous availability of substrates and water and (b) high variability of soil chemical properties (pH, temperature, oxygen supply) that can vary in the soil environment on both the micro and macro scales (Jenkinson and Ladd, 1981). 

J. L. Garland and A. L. Mills, Classification and characterisation of heterotrophic microbial communities on the basis of patterns of community-level sole carbon-source utilisation, Appl. Environ. Microbiol. 57 2351 (1991). 

Garland JL, Mills AL (1991) Classification and characterization of heterotrophic microbial communities on the basis of patterns of community-level sole-carbon-source utilization. Appl Environ Microbiol 57 2351-2359 Giuffre L, Piccolo G, Rosell R, Pascale C, Heredia OS, Ciarlo E (2001) Anthropogenic effect on soil organic phosphorus fractions in tropical ecosystems. Commun Soil Sci Plant Anal 32 1621-1628 Gottlieb S (1976) The production and role of antibiotics in soil. J Antibiot 29 987-1000... 

Measurement of exoenzymatic activities is potentially useful in detecting the effects of toxicants on heterotrophic biofilm communities. Sensitivity and direct relationship with organic matter use and, therefore, microbial growth make extracellular enzyme activities a relevant tool to assess the toxicity of specific compounds. Use of novel approaches that combine enzymatic and microscopic tools (e.g. ELF-phosphatase) may be extremely useful to detect anomalies at the sub-cellular scale. 

In a system defined by wastewater in a sewer network, the heterotrophic bacteria dominate the microbial community, i.e., organic compounds are required as a carbon source. Furthermore, the energy source (electron donor) for the heterotrophs is primarily also organic compounds, i.e., the heterotrophs that dominate wastewater in sewers are chemoheterotrophic (chemoorganotrophic) microorganisms. 

Seasonal shifts at mid-latitudes in the standing stocks of nutrients, phytoplankton, and the heterotrophic consumer community of bacteria, protozoa, and zooplankton. Also shown are seasonal changes in density stratification of the mixed layer. Source From Black, J. A. (1986). Oceans and Coasts, Wm. C. Brown Publishers, p. 143. 

Barkay, T. Olson, B. H. (1986). Phenotypic and genotypic adaptation of aerobic heterotrophic sediment bacterial communities to mercury stress. Applied and Environmental Microbiology, 52, 403-6. 

Hobbie, J. E. 1969. Heterotrophic bacteria in aquatic ecosystems Some results of studies with organic radioisotopes. In The Structure and Function of Fresh-Water Microbial Communities (John Cairns, Jr., Ed.), American Microscopical Society Symposium, pp. 181-194. Blacksburg, VA.l... 

A major experimental issue to be addressed is the rate and means by which particles are hydrolyzed and solubilized to provide substrates for heterotrophic bacteria, and the role of free enzymes in this process. Burns (1982) reviewed the possible locations and origin of enzyme activities in soils, and particularly underscored the potential importance of enzyme-humic complexes in microbial catalysis of substrates. As Burns (1982) discussed, enzymes associated with soil particles or humic substances are not subject to the same biochemical and physical restraints as are enzymes newly produced by microbial cells. Soil-held (or sediment-held) enzymes may therefore play a catalytic trigger role in substrate degradation, providing critical signals about substrate availability to the local microbial community. The conceptual model presented by Vetter et al. (1998) suggested that release of free enzymes into the environment may in fact represent... 

Aside from adding defined compounds, experimental additions of natural DOM mixtures suspected to vary in lability have helped test ideas about the contribution of various DOM sources to aquatic ecosystems. In a nice example using manipulation of natural DOM sources, Battin et al. (1999) used flowthrough microcosms to measure the relative uptake rates of allochthonous and autochthonous DOM by stream sediments. They documented greater than fivefold differences or more in uptake and respiration, depending on whether the DOM was extracted from soil or periphyton. Moreover, they were able to show, via transplant experiments, several cases where prior exposure to a particular source of DOM increased the ability of that community to metabolize the DOM supplied. There appears to be some preadaptation of microbial catabolic capacity when these stream biofilms were re-exposed to a familiar type of DOM. Similarly, the response of heterotrophic bacteria to carbon or nutrient addition was greatest when the source community was particularly active (Foreman et al., 1998). Kaplan et al. (1996) showed that fixed film bioreactors, colonized on one water source, were unable to rapidly metabolize DOC in water from another source. 

In freshwater ecosystems, particularly streams and wetlands, biofilms account for a large portion of heterotrophic metabolism, as well as primary production (Edwards etal., 1990 see Chapter 12), acting as both sources and sinks for DOM. As the depth of the overlying water in the system increases, attached communities account for a declining share of system metabolism. 

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