Iron and Manganese Homeostasis in Marine Bacteria

Abstract Using a mixture of bioinformatic analyses, microarrays on cells that were grown in media that were either replete or depleted for manganese or for iron, and by making targeted mutations and reporter fusions, several important observations were made on the mechanisms of Mn and Fe homeostasis in the marine α‐proteobacterium Ruegeria pomeroyi (the main species studied here), and in other important marine bacteria. R. pomeroyi lacks most of the known Fe uptake systems, including TonB and outer‐membrane receptors, but has a predicted, but incomplete iron uptake ABC‐class transporter operon, whose expression is much enhanced in Fe‐depleted conditions, although a strain lacking these genes was unaffected in growth. The Fe‐specific regulatory network of R. pomeroyi was found to involve the Irr transcriptional regulator, which controlled the expression of several genes. Microarrays revealed many other genes whose expression was enhanced or diminished in Fe‐replete conditions, providing material for future work on the iron regulon of this bacterium, Turning to manganese, here too the expression of many genes was affected (up or down) by Mn availability. These included an operon corresponding to sitABCD, an effective ABC‐type Mn2+ transporter in many other bacteria. This was confirmed, directly, to be the case for Ruegeria. Bioinformatic analyses showed that some other Roseobacter strains lacked any previously known Mn2+ transporter, but instead, had a gene that likely encoded an inner membrane protein and was preceded by a motif (MRS box) that was known to be recognised by the Mn2+ ‐responsive transcriptional regulator Mur. It was confirmed that this gene, termed mntX, did indeed encode a manganese transporter and that MntX orthologues occurred in several other, unrelated marine bacteria, notably most strains of the pathogenic genus Vibrio (including V. cholerae) and some of the most abundant bacteria in the oceans, namely the SAR11 clade (Pelagibacter).

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2012

Author dc:creator

• Green, Robert

Language dc:language

en