Survival of myxobacter strain 8 in natural soil in the presence and absence of host cells

Abstract

Myxobacter strain 8 is one component of a sequence of three predatory bacteria that develop in soil when Micrococcus luteus host cells are added to the soil. The survival of strain 8 in the presence and absence of added host cells in natural soil not allowed to dry out was examined. Strain 8 vegetative cells died relatively rapidly in unamended soil. Death was faster and occurred to a greater extent in acidic than in neutral pH soil. However, in both cases death was accompanied by formation of sonication-resistant myxospores so that they comprised the ultimate population. These myxospores survived for prolonged periods in both acidic and neutral pH soils. Vegetative cells added in high numbers to soil did not multiply under any of the conditions tested. They did multiply, however, when they were added in low numbers to soil (including acidic soil) receiving sequential (additive) amendments of heart infusion broth or living M. luteus cells. This multiplication produced strain 8 cell numbers approximating those in the above experiments receiving high strain 8 cell number inoculations. Possibly, this represents a maximum vegetative cell number for soil. Germination of the myxospores in soil, followed by growth, seemed to require an approximately neutral pH and the presence of a proper host organism. Germination occurred with M. luteus as host, but not with Escherichia coli. A delayed germination occurred when sequential amendments of heart infusion broth, instead of M. luteus host cells, were made, but this could reflect a growth response by some indigenous components of the soil microflora that then served as host cells for germination.