Uptake of the herbicidal glyphosate by Escherichia coli K-12.

The uptake of the aminoacid biosynthesis inhibitor, used as the broad-spectrum herbicide ingredient, glyphosate (N-[phosphonomethyl]-glycine) was investigated in E. coli as a model to study mechanisms of cell resistance to antimetabolites as drugs and pesticides. Unlike the glyphosate-degrading Arthrobacter sp. strain for which the first successful measurement of glyphosate uptake and its inhibition by orthophosphate was reported, E. coli K-12 cannot take up this inhibitor either in the presence of orthophosphate, or after a prolonged starvation for it. However, cells made "competent" after an overnight cold CaCl2 exposure followed by dimethyl sulfoxide (DMSO) treatment could take up this compound (Km for glyphosate uptake, 274 microM). Neither amino acids, belonging to a single transport system, nor orthophosphate gave essential inhibition of glyphosate uptake by these cells.