IRON REQUIREMENT AND SIDEROPHORE PRODUCTION IN BRADYRHIZOBIUM STRAINS ISOLATED FROM ACACIA-MANGIUM

Fourteen Bradyrhizobium strains isolated from nitrogen-fixing Acacia mangium trees which originated from different geographical areas were analysed for their iron requirement and siderophore production. All strains 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-chelator 2,2-dipyridyl, suggested a discrimination of these strains into two groups. Four strains in one group, including a reference strain, produced siderophore(s) when grown under starvation. Other strains belonging to the second group were characterized by a lower iron requirement, a higher sensitivity to 2,2-dipyridyl, and did not apparently demonstrate any siderophore production. Two of the siderophore-producer strains, as well as a Rhizobium reference strain, excreted citrate, which was under iron regulation. Citrate was shown to facilitate iron incorporation in strains of either group.