Siderophore production and iron transport inRhizobium legummosarumbv. viciae MNF710

Abstract

Abstract Rhizobium leguminosarum bv. viciae MNF 710, an isolate from wild vetch in Japan, excretes an hydroxamate siderophore (maximum levels approximately 300 nmol ml‐1 Desferal equivalents) when grown in medium containing low (0.5 μM) but not high (20 μM) added iron. Resuspension experiments, in which washed cells where transferred from low or high iron media to differing iron regimes (0, 0.5,1.0,5.0,10.0 and 20 μM added iron) suggest that the extent of hydroxamate production is dependent on the prior growth history of the cells; cells grown under high iron were more sensitive to iron repression than those grown under low iron. Washed cells of R. leguminosarum bv. viciae MNF710 grown under low iron conditions transport 55Fe when complexed with either the partially purified hydroxamate siderophore (0.27 nmol min‐1(mg protein)‐1), or when citrate is present (0.13 nmol min‐1(mg protein)‐1), but not as 55FeCl3 or in the presence of nitrilotriacetate. Washed cells grown with 20 μM added iron do not transport 55Fe labelled hydroxamate but do transport 55Fe‐citrate at a very low rate (0.01 nmol min‐1 (mg protein)‐1).