Abstract
The genome-wide Campylobacter jejuni transcriptional response under iron replete and iron limited conditions was characterized using RNA-seq. We have identified 111 novel C. jejuni 5’UTRs and mapped 377 co-transcribed genes into 230 transcriptional operons. In contrast to previous microarray results, the C. jejuni iron stimulon is less extensive than previously believed and consists of 77 iron activated genes and 50 iron repressed genes. As anticipated, the iron repressed genes are primarily those involved in iron acquisition or oxidative stress defense. Interestingly, these experiments have revealed that iron is an important modulator of flagellar biogenesis with almost all the components of the flagella found to be iron activated. Given that motility is a well-known C. jejuni colonization factor, this suggests that there is an important regulatory coupling of flagellar biogenesis and iron level in C. jejuni. In addition we have identified several consensus mutations in the C. jejuni NCTC11168 strain that are widespread in the Campylobacter research community and which may explain conflicting phenotypic reports for this strain. Comparative analysis of iron responsive genes with the known Fur regulon indicates that many iron responsive genes are not Fur responsive; suggesting that additional iron regulatory factors remain to be characterized in C. jejuni. Further analysis of the RNA-seq data identified multiple novel transcripts including 19 potential ncRNAs. The expression of selected ncRNAs was confirmed and quantified with qRT-PCR. The qRT-PCR results indicate that several of these novel transcripts are either Fur and/or iron responsive. The fact that several of these ncRNAs are iron responsive or Fur regulated suggests that they may perform regulatory roles in iron homeostasis.
Highlights
Iron is crucial for microbial growth as it forms the active center of a variety of diverse enzymes involved in essential cellular processes such as energy metabolism and redox reactions [1]
Iron homeostasis is well established in Campylobacter jejuni, much remains to be understood about the regulatory mechanisms of the iron regulated genes
As compared to the previous transcriptomic studies in C. jejuni, our work has revealed 12 new ncRNAs and characterized the structure of 111 additional mRNA transcripts
Summary
Iron is crucial for microbial growth as it forms the active center of a variety of diverse enzymes involved in essential cellular processes such as energy metabolism and redox reactions [1]. Microorganisms have evolved elaborate strategies to acquire iron from their environment. Pathogens such as Campylobacter jejuni face additional challenges in acquiring sufficient iron as their hosts typically restrict free iron to prevent unwanted microbial growth [2]. Pathogens subvert this defense system by expressing multiple iron acquisition pathways under conditions of iron limitation. Microorganisms must carefully regulate iron metabolism to ensure that they acquire sufficient iron to grow yet avoid iron toxicity [1,2]
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