Effects of a clay mineral on microbial predation and parasitism ofEscherichia coli

Montmorillonitic clay influences the biological control ofEscherichia coli in aquatic systems, the magnitude of the effects being dependent on the state of the clay and the type of host-antagonist interaction. The interaction ofBdellovibrio andE. coli was partially inhibited by the presence of montmorillonite. Because it is highly motile,Bdellovibrio apparently could penetrate any colloidal clay barrier aroundE. coli if the clay envelope was thin enough. Colloidal clay had little effect on predation ofE. coli by the myxobacteriumPolyangium, and had no effect on the activity of the amoebaVexillifera. Crude clay, on the other hand, resulted in a physical separation of predator and prey, and this completely inhibited theE. coli-Polyangium interaction and slowed the rate of engulfment ofE. coli byVexillifera.The interference of natural biological control by clays may alter the microbial balance favoring survival of fecal microorganisms and resulting in their accumulation in saline sediments. This could constitute a health hazard if these organisms were released by upwelling of bottom waters or were desorbed in estuarine systems by dilution during heavy rains.