Abstract
Despite the abundance of iron in nature, iron acquisition is a challenge for life in general because the element mostly exists in the extremely insoluble ferric (Fe3+) form in oxic environments. To overcome this, microbes have evolved multiple iron uptake strategies, a common one of which is through the secretion of siderophores, which are iron-chelating metabolites generated endogenously. Siderophore-mediated iron transport, a standby when default iron transport routes are abolished under iron rich conditions, is essential under iron starvation conditions. While there has been a wealth of knowledge about the molecular basis of siderophore synthesis, uptake and regulation in model bacteria, we still know surprisingly little about siderophore biology in diverse environmental microbes. Shewanella represent a group of γ-proteobacteria capable of respiring a variety of organic and inorganic substrates, including iron ores. This respiratory process relies on a large number of iron proteins, c-type cytochromes in particular. Thus, iron plays an essential and special role in physiology of Shewanella. In addition, these bacteria use a single siderophore biosynthetic system to produce an array of macrocyclic dihydroxamate siderophores, some of which show particular biological activities. In this review, we first outline current understanding of siderophore synthesis, uptake and regulation in model bacteria, and subsequently discuss the siderophore biology in Shewanella.
Highlights
Iron is one of the most abundant metal elements on the Earth and displays a wide range of oxidation-reduction potential, a chemical property largely resulting from the transition between two stable valences, the ferrous (Fe2+) and ferric (Fe3+) forms (Andrews and Schmidt, 2007)
For most living organisms, iron on one hand is essential because iron-dependent proteins are employed to perform a myriad of functions in diverse biological processes, such as electron transport, metabolism, peroxide reduction, amino acids and nucleoside synthesis, DNA synthesis, photosynthesis, and gene expression
The biosynthesis, physiological impacts, and application of siderophores have been of interest and intensive studies have been carried out in E. coli and other model bacteria, pathogens in particular, since their discovery about 80 years ago
Summary
Shewanella represent a group of γ-proteobacteria capable of respiring a variety of organic and inorganic substrates, including iron ores. This respiratory process relies on a large number of iron proteins, c-type cytochromes in particular. Iron plays an essential and special role in physiology of Shewanella. These bacteria use a single siderophore biosynthetic system to produce an array of macrocyclic dihydroxamate siderophores, some of which show particular biological activities. We first outline current understanding of siderophore synthesis, uptake and regulation in model bacteria, and subsequently discuss the siderophore biology in Shewanella
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