Effects of Clay Minerals, Oxyhydroxides, and Humic Matter on Microbial Communities of Soil, Sediment, and Water

Microbial communities in soils, sediments, and natural waters comprise a variety of coexisting species occupying diverse ecological niches. Clay minerals, oxyhydroxides, humic matter, and combinations of these colloids affect the vital functions and mutual relations of microbial populations in soils, sediments, and water in a wide variety of ways ranging from highly beneficial to strongly inhibitory. As with clay minerals, humic substances have long been known, from both field and laboratory studies, to have important, diverse, and seemingly contradictory effects on microorganisms. Humic substances are thought to benefit microbes by performing a wide range of special biochemical and physiological functions other than the binding and release of nutrients and toxic substances. In addition to organic nutrient substrates, natural environments contain active extracellular enzymes that assist microbes in breaking down the substrates, and so it is necessary to consider the biochemical consequences of the binding of enzymes by mineral colloids and humic matter.