Stimulatory effect of phosphate on colicin V synthesis/secretion by strains of Escherichia coli

Abstract

Larger inhibitory zones were produced by ColV+ strains on sensitive indicators if the strains were grown on nutrient agar and phosphate rather than nutrient agar. This was due to an effect of phosphate on colicin V synthesis/secretion and not to an effect on the response of the indicator. Phosphate produced an effect at 25 degrees C as well as at 37 degrees C (although zones were larger at 37 degrees C). It seems likely that phosphate stimulation of colicin V synthesis/secretion results from its effect in reducing divalent cation levels in NA because adding EDTA to NA also increased colicin V synthesis/secretion whereas the addition of magnesium or calcium salts had the opposite effect. It is possible that the extent of colicin V synthesis/secretion may depend on the strength of the LPS-LPS bonds in the outer membrane. Phosphate also stimulated synthesis/secretion of colicins E4, G and N but not of the other colicins or microcins tested. Studies with a wild Col+ E. coli isolate suggest that production of some colicins may not be detected on nutrient agar and that addition of phosphate may reveal the synthesis of new colicins.