Ecology of siderophores with special reference to the fungi

Abstract

Ecology of siderophores, as described in the present review, analyzes the factors that allow the production and function of siderophores under various environmental conditions. Microorganisms that excrete siderophores are able to grow in natural low-iron environments by extracting residual iron from insoluble iron hydroxides, protein-bound iron or from other iron chelates. Compared to the predominantly mobile bacteria, the fungi represent mostly immobile microorganisms that rely on local nutrient concentrations. Feeding the immobile is a general strategy of fungi and plants, which depend on the local nutrient resources. This also applies to iron nutrition, which can be improved by excretion of siderophores. Most fungi produce a variety of different siderophores, which cover a wide range of physico-chemical properties in order to overcome adverse local conditions of iron solubility. Resource zones will be temporally and spatially dynamic which eventually results in conidiospore production, transport to new places and outgrow of mycelia from conidiospores. Typically, extracellular and intracellular siderophores exist in fungi which function either in transport or storage of ferric iron. Consequently, extracellular and intracellular reduction of siderophores may occur depending on the fungal strain, although in most fungi transport of the intact siderophore iron complex has been observed. Regulation of siderophore biosynthesis is essential in fungi and allows an economic use of siderophores and metabolic resources. Finally, the chemical stability of fungal siderophores is an important aspect of microbial life in soil and in the rhizosphere. Thus, insolubility of iron in the environment is counteracted by dissolution and chelation through organic acids and siderophores by various fungi.

Microbial Siderophores Exert a Subtle Role in Arabidopsis during Infection by Manipulating the Immune Response and the Iron Status

“…Microorganisms have developed powerful iron acquisition systems based on the production of siderophores, which are selective ferric ion chelators secreted in response to iron deficiency (Andrews et al, 2003;Winkelmann, 2007). Siderophores have low molecular weights and very diverse chemical structures that can contain one or a combination of several types of ironbinding moieties: hydroxamate, catecholate, and hydroxycarboxylate.…”

Siderophore Production by Microorganisms Isolated From a Podzol Soil Profile

“…The second major group of bacterial siderophores is hydroxamates, which have both linear and cyclic compounds containing 1-amino-5-hydroxyaminopentane (Dhungana et al, 2001). Hydroxamates are resistant to hydrolysis and enzymatic degradation in the natural environment due to their hexadentate structure (Winkelmann, 2007). Bacterial hydroxamates such as schizokinen, aerobactin, and ferrioxamines are produced for example by Streptomyces spp., Enterobacteriaceae, and Arthrobacter spp.…”

“…Soil fungi mainly produce four different groups of siderophores included in the hydroxamate family, i.e. ferrichromes, coprogens, fusarinines, and rhodotorulic acids (Winkelmann, 2007).…”

“…Ferrichromes are further divided into five groups depending on the side chain of the hydroxamate functional and cis-anhydromevalonyl (ferrirhodin) (Renshaw et al, 2002;Winkelmann, 2007). Common soil fungi that produce ferrichrome type siderophores are U. sphaerogena for ferrichrome (Emery, 1971), Aspergillus fumigatus for ferricrocin (Wallner et al, 2009), Neurospora crassa for tetraglycylferrichrome (Winkelmann, 2007) and Cenococcum geophilum and Hebeloma crustuliniforme for ferrichrysin (Martino and Perotto, 2010). Coprogens consist of a diketopiperazine ring formed by two N5-acyl-N5-hydroxy-L-Orn units (Budzikiewicz, 2010).…”

“…Among the different siderophore types, the hydroxamates have received much attention since they are highly resistant to environmental degradation due to their cyclic hexapeptide structure (Winkelmann, 2007). It is known that a wide range of soil fungal isolates have the ability to produce one or several types of hydroxamates (Haselwandter and Winkelmann, 2007;Haselwandter et al, 2013).…”