Abstract

Sinorhizobium meliloti 2011 is a free living soil bacterium notable for being the intracellular nitrogen fixing symbiont of Medicago sativa. Like most bacteria iron is vital to its survival in both symbiotic and free living conditions. It produces an asymmetrically lipidated siderophore, rhizobactin 1021 (rhz1021), in response to iron limitation. Previous studies have attributed rhz1021 production to the gene products of the operon rhbABCDEF. The roles of two acetyltransferases in rhz1021 biosynthesis, rhbD and an unstudied gene sma2339 have been assessed. Analysis shows that S. meliloti 2011sma2339 is capable of producing an intact rhz1021 structure but at a reduced rate to wild type and that the sma2339 gene can poorly complement rhbD. The rhbD mutant strain is highly defective in siderophore production confirming its central role in biosynthesis.