, 2011). This biosynthetic pathway may therefore be evolutionarily distinct from other reported DFO pathways. blastp analysis revealed a putative DmdR repressor in S. arenicola CNS-205 (Sare_1414) and S. tropica CNB-440 (Strop_1456), with 62/63% identity and 72/73% similarity to DmdR1 in S. coelicolor A3(2) (Flores & Martín, 2004). blastn and EMBOSS Palindrome analyses identified four putative DmdR-binding sites

(iron boxes) in each of the Salinispora genomes. Two of the iron boxes are upstream of desE and desF in both species (Fig. 1). The des gene cluster organization is conserved in Streptomyces (Barona-Gómez et al., 2006) with all six genes in one locus whereas, in Salinispora, desF is 13- to 21-kb upstream Seliciclib manufacturer of desEABCD. Despite these differences, iron repression of des is consistent in both genera, as confirmed in Salinispora by transcript analysis (Fig. 2). The remaining two iron boxes are upstream of a periplasmic binding protein similar to ferric-enterobactin transporters, and a putative siderophore utilization protein in StBac1/SaBac2, which may encode a Class

I bacteriocin (Penn et al., 2009). No iron boxes were identified near sid2–sid4. Alignment of the eight putative iron box sequences enabled the prediction of a DmdR-binding consensus sequence for Salinispora: TAGGTTArCCT (Fig. 4). Although sid2 from S. tropica Protein Tyrosine Kinase inhibitor CNB-440 was transcribed in iron-limited cultures, the lack of detectable Rho siderophores in the des mutants, and their poor growth without iron, suggests that the sid2 compound was either not produced in detectable quantities or that it is unable to chelate iron. As iron supplementation increased the growth of the des mutant, another iron chelator may be produced at very low levels or with a lower affinity for iron than CAS, which would

not be detected by our methods. Because of the differential transcriptional response of sid2 to iron in the des mutants, however, it is unlikely that this additional iron chelator is associated with sid2. Sid2 possesses similarity to ybt (Bearden et al., 1997; Pelludat et al., 1998); however, there are several differences between the two gene clusters (Fig. 1b). The three methyltransferases in sid2 are not integrated into the NRPS/PKS genes, and several essential ybt genes are absent in sid2, namely the reductase ybtU, salicylate synthase ybtS and regulator ybtT (Fig. 1b) (Geoffroy et al., 2000; Miller et al., 2002), which may explain the lack of yersiniabactin-like siderophore production. Sid2 in S. arenicola CNS-205 is transcribed under iron-replete rather than iron-limited conditions, although no chemotypic difference was detected between the wild-type and sid2 mutant in iron-sufficient conditions. The altered transcriptional regulation may be due to mobilization of the sid2 cluster 846-kb downstream on a separate genomic island. The putative CoA ligase remains in the original locus with respect to the S. tropica CNB-440 sid2 gene cluster (Fig.