Influence of Clay Minerals on Microorganisms: I. Montmorillonite and Kaolinite on Bacteria

Respiration of bacteria was stimulated most by montmorillonite, primarily as the result of this clay maintaining the pH at levels adequate for sustained growth; additional mechanisms also appeared to be involved. Kaolinite and montmorillonite served equally as a source of minerals for bacterial nutrition, and the stimulation by montmorillonite above that elicited by kaolinite and attributable to its buffering capacity was, therefore, not related to its ability to supply inorganic nutrients. Montmorillonite stimulated respiration of a wide spectrum of bacterial species differing in morphology, motility, Gram reaction, etc. at all stages of their development, but especially by shortening the lag phase. These results suggest a possible relationship between clay minerals and activity, ecology, and population dynamics of microorganisms in natural habitats.