Extracellular siderophores from Aspergillus ochraceous

Abstract

A large number of iron-chelating compounds (siderophores) were isolated from supernatants of irondeficient cultures of a mold isolate, subsequently identified as Aspergillus ochraceous. Siderophores in their iron chelate form were purified to homogeneity by using Bio-Gel P2, silica gel, and C-18 bonded silica gel (reverse-phase) columns. Most of these compounds, as identified by 'H and 13C nuclear magnetic resonance spectroscopy and X-ray crystallography, belong to the ferrichrome family. The organism produces ferrirubin and ferrichrysin as the predominant and the second major compound (62 and 15% of the total siderophores), respectively. Ferrichrysin appears as the first siderophore in the medium on day 2 of growth. Several of the other siderophores are novel and ranged in quantities from 0.2 to 5% of the total. The trivial names asperchrome A, Bi, B2, C, DI, D2, and D3 are proposed for these novel compounds, which are all members of the ferrichrome family, and all but the first one contain a common Orn,-Orn2-Orn3-Ser1-Ser2-Gly cyclic hexapeptide ring with three dissimilar ornithyl 8-N-acyl groups. Another compound which appeared late in the growth period was similar to fusarinine C (fusigen). All of these compounds showed growth factor activity to various extents in bioassays with Arthrobacter flavescens Jg-9. None of these compounds showed antibacterial activity against Escherichia coli or Bacillus megaterium.

Identification and substrate specificity of a ferrichrome-type siderophore transporter (Arn1p) in Saccharomyces cerevisiae

“…Using the two asperchromes which had been previously isolated from A. ochraceus by van der Helm et al [3] we were able to demonstrate that the number of branched‐chain trans ‐anhydromevalonyl residues is also an important factor for recognition and transport by the Arn1p. Compared to ferrirubin, possessing three trans ‐anhydromevalonyl (AMV) residues, asperchrome B1 contains two AMV and one acetyl residue, while asperchrome D1 contains one AMV and two acetyl residues as shown in Fig.…”

“…While ferrichrysin shares the same ser‐ser‐gly cyclic peptide sequence with ferrirubin, ferrirhodin and ferrichrome A, it is still excluded by the Arn1 transporter. Additional proof of this observation comes from studies with DDF, a ferrirhodin analog lacking a cyclic backbone which has been found as a natural byproduct in siderophores from A. ochraceus [3]. Although ferric DDF was not well transported by the wild type, it was excluded by the disruptant, confirming that branched‐chain N ‐acyl residues need to interact with the Arn1 transporter even in the absence of any peptide backbone.…”

“…Asperchrome B1, D1 and DDF [14] were kindly provided by D. van der Helm, Norman, OK, USA. Ferrirubin, asperchromes and DDF were isolated from A. ochraceus according to Jalal et al [3] and ferrirhodin was isolated from Botrytis cinerea [15]. Hexahydroferrirhodin was obtained by hydrogenation of ferrirhodin using hydrogen and palladium as a catalyst.…”

“…Three groups of ferrichrome‐type siderophores have been described so far (reviewed in [2]: (1) ferrichromes (i.e. ferrichrome, ferricrocin, ferrichrysin, tetraglycylferrichrome) which contain exclusively ornithine‐ N 5 ‐acetyl‐hydroxamic acid residues; (2) ferrichromes that contain branched‐chain N 5 ‐acyl residues, such as cis ‐anhydromevalonic acid (ferrirubin), trans ‐anhydromevalonic acid (ferrirhodin, des(diserylgylcyl)‐ferrirhodin (DDF)), trans ‐β‐methylglutaconic acid (ferrichrome A) or malonic acid (malonichrome) and (3) ferrichromes that contain a mixture of different ornithine‐ N 5 ‐acyl residues, as found in asperchromes produced by Aspergillus ochraceus [3]. In most fungi a mixture of different siderophores is produced which may vary depending on the cultivation conditions.…”

Evidence for a common siderophore transport system but different siderophore receptors in Neurospora crassa

“…Aspergillaceae family members are known to be a good source of various siderophores (4,17,23). Recently, a large number of asperchromes all belonging to the ferrichrorne family were isolated from low-iron cultures of Aspergillus ochraceus (11).…”