Siderophore biosynthesis genes of Rhizobium sp. isolated from Cicer arietinum L.

Abstract

Rhizobium BICC 651, a fast-growing strain isolated from root nodule of chickpea (Cicer arietinum L.), produced a catechol siderophore to acquire iron under iron poor condition. A Tn5-induced mutant (B153) of the strain, BICC 651 impaired in siderophore biosynthesis was isolated and characterized. The mutant failed to grow on medium supplemented with iron chelator and grew less efficiently in deferrated broth indicating its higher iron requirement. The mutant produced less number of nodules than its parent strain. The Tn5 insertion in the mutant strain, B153, was located on a 2.8 kb SalI fragment of the chromosomal DNA. DNA sequence analysis revealed that the Tn5-adjoining genomic DNA region contained a coding sequence homologous to agbB gene of Agrobacterium tumefaciens MAFF301001. About 5 kb genomic DNA region of the strain BICC 651 was amplified using the primers designed from DNA sequence of agrobactin biosynthesis genes of A. tumefaciens MAFF 301001 found in the database. From the PCR product of the strain BICC 651, a 4,921 bp DNA fragment was identified which contained four open reading frames. These genes were designated as sid, after siderophore. The genes were identified to be located in the order of sidC, sidE, sidB, and sidA. Narrow intergenic spaces between the genes indicated that they constitute an operon. Phylogenetic analyses of deduced sid gene products suggested their sequence similarity with the sequences of the enzymes involved in biosynthesis of catechol siderophore in other bacteria.