IRON REQUIREMENT AND SIDEROPHORE PRODUCTION IN BRADYRHIZOBIUM STRAINSISOLATED FROM ACACIA-MANGIUM

Fourteen Bradyrhizobium strains isolated from nitrogen-fixing Acacia m angium trees which originated from different geographical areas were a nalysed for their iron requirement and siderophore production. All str ains were affected by starvation but responded differently to it. The increase in bacterial cell yield in response to iron supplementation, as well as the strain's sensitivity towards the synthetic iron-chelato r 2,2-dipyridyl, suggested a discrimination of these strains into two groups. Four strains in one group, including a reference strain, produ ced siderophore(s) when grown under starvation. Other strains belongin g to the second group were characterized by a lower iron requirement, a higher sensitivity to 2,2-dipyridyl, and did not apparently demonstr ate any siderophore production. Two of the siderophore-producer strain s, as well as a Rhizobium reference strain, excreted citrate, which wa s under iron regulation. Citrate was shown to facilitate iron incorpor ation in strains of either group.