Abstract
BackgroundIron is an essential micronutrient for all living organisms, and virulence and sequestration of iron in pathogenic bacteria are believed to be correlated. As a defence mechanism, potential hosts therefore keep the level of free iron inside the body to a minimum. In general, iron metabolism is well studied for some bacteria (mostly human or animal pathogens). However, this area is still under-investigated for a number of important bacterial pathogens. Aliivibrio salmonicida is a fish pathogen, and previous studies of this bacterium have shown that production of siderophores is temperature regulated and dependent on low iron conditions. In this work we studied the immediate changes in transcription in response to a sudden decrease in iron levels in cultures of A. salmonicida. In addition, we compared our results to studies performed with Vibrio cholerae and Vibrio vulnificus using a pan-genomic approach.ResultsMicroarray technology was used to monitor global changes in transcriptional levels. Cultures of A. salmonicida were grown to mid log phase before the iron chelator 2,2’-dipyridyl was added and samples were collected after 15 minutes of growth. Using our statistical cut-off values, we retrieved thirty-two differentially expressed genes where the most up-regulated genes belong to an operon encoding proteins responsible for producing the siderophore bisucaberin. A subsequent pan-transcriptome analysis revealed that nine of the up-regulated genes from our dataset were also up-regulated in datasets from similar experiments using V. cholerae and V. vulnificus, thus indicating that these genes are involved in a shared strategy to mitigate low iron conditions.ConclusionsThe present work highlights the effect of iron limitation on the gene regulatory network of the fish pathogen A. salmonicida, and provides insights into common and unique strategies of Vibrionaceae species to mitigate low iron conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0342-7) contains supplementary material, which is available to authorized users.
Highlights
Iron is an essential micronutrient for all living organisms, and virulence and sequestration of iron in pathogenic bacteria are believed to be correlated
The cultures were grown to mid log phase (OD600nm 0.5) before 2,2’-dipyridyl was added to a final concentration of 50 μM, and samples were collected after 15 minutes to monitor immediate responses
We studied the immediate effect of low iron conditions, and compared this to similar studies where effects were examined after prolonged growth in low iron conditions
Summary
Iron is an essential micronutrient for all living organisms, and virulence and sequestration of iron in pathogenic bacteria are believed to be correlated. Iron metabolism is well studied for some bacteria (mostly human or animal pathogens). Low iron concentrations create an efficient barrier against potential invading pathogens that may have entered the organism through, for example, an open wound on the skin surface. This defence strategy puts extraordinary pressure on invading pathogens to carry extremely efficient mechanisms to sequester iron from within the host [3,6]. RyhB targets the fur mRNA in a feedback regulation loop, and targets mRNA that encode iron-using or iron-storing proteins like Bfr, SodB and FumA [16]
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