ESCHERICHIA COLI DIE-OUT FROM NORMAL SOIL AS RELATED TO NUTRIENT AVAILABILITY AND THE INDIGENOUS MICROFLORA

Abstract

Addition of a small portion of autoclaved soil to normal soil provided some degree of protection against die-out for Escherichia coli cells also introduced into this soil. This protection was associated with organic carbon (glucose) availability, but not with nitrogen (ammonium nitrate) availability. An E. coli population was stabilized, at least temporarily, in soil by glucose feeding, and the protective effect of glucose was temperature dependent. Indigenous micro-organisms also multiplied in the glucose-amended soil, and, therefore, colonizing space and microbial production of compounds toxic to E. coli were not considered to be major controlling factors in E. coli die-out in soil. E. coli cells recovered after residence in this soil demonstrated an initial decreased growth rate which was less pronounced in cells recovered from glucose-amended soil and which disappeared for both cell types on subculture. It was concluded that a major factor in E. coli die-out from natural soil is its inability to step down its metabolic rate to meet the low availability of usable organic carbon in soil.