Abstract
BackgroundIron homeostasis is an essential process over the entire lives of both hosts and bacterial pathogens, and also plays roles in many other metabolic functions. Currently, knowledge is limited on the iron scavenging mechanism of the cell envelope in the aquatic pathogen, Aeromonas hydrophila. To understand the iron homeostasis mechanism in A. hydrophila, a dimethyl labelling based quantitative proteomics method was used to compare the differential expression of cell envelope proteins under iron starvation.ResultsA total of 542 cell envelope proteins were identified by LC-MS/MS, with 66 down-regulated and 104 up-regulated proteins. Bioinformatics analysis showed that outer membrane siderophores, heme and iron receptors, periplasmic iron binding proteins, inner membrane ABC transporters and H+-ATP synthase subunits increased in abundance while iron-cluster proteins, electron transport chain and redox proteins were down-regulated. Further q-PCR validation, in vivo addition of exogenous metabolites, and an enzyme inhibition assay revealed that redox, the energy generation process, and ATP synthase elevated the susceptibility of A. hydrophila to iron starvation.ConclusionsOur study demonstrates that the redox and energy generation process, and ATP synthase in A. hydrophila may play critical roles in iron acquisition under conditions of iron-stress. An understanding of the iron scavenging mechanism may be helpful for the development of strategies for preventing and treating A. hydrophila infection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0769-5) contains supplementary material, which is available to authorized users.
Highlights
Iron homeostasis is an essential process over the entire lives of both hosts and bacterial pathogens, and plays roles in many other metabolic functions
Characterization and identification of the envelope protein fraction in A. hydrophila According to the growth curve of A. hydrophila, the strain treated with 150 μM 2, 2′-dipyridyl (DIP) grew slower than the control strain, especially after the middle exponential phase (Fig. 1a)
Further LC Liquid chromatography tandem mass spectrometry (MS/MS) analysis identified 837 proteins with at least two peptides required for identification and a false discovery rate (FDR) less than 1 % filtered in the total number of 1024 proteins (Table 1 and a complete list in Additional file 1: Table S1)
Summary
Iron homeostasis is an essential process over the entire lives of both hosts and bacterial pathogens, and plays roles in many other metabolic functions. Iron is the second most abundant metal in the earth’s crust; ferrous iron, the useable form, is scarce, due to an oxidative environment [1,2,3] It is an essential element for most bacteria with irreplaceable functions in many basic biological processes, including the Fe3+ cofactor of metabolic respiratory chain reactions. Bacteria have evolved effective ways to survive in this harsh environment Under this process, cell envelope proteins in Gram-negative bacteria, including periplasmic, outer and inner membrane proteins, are essential in the transport of iron related compounds into the intracellular environment. Some other OMPs, such as OmpW, TsX and OmpX function as either iron exporters or receivers [7] During this process, the periplasmic protein TonB and inner membrane proteins (IMPs) ExbB and ExbD form a protein complex to mediate the transport of iron compounds from the
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