Transcriptome profile of Corynebacterium pseudotuberculosis in response to iron limitation

Izabela Coimbra Ibraim,Emannuel Maltempi Souza,Debmalya Barh,Mariana Teixeira Dornelles Parise,Doglas Parise,Preetam Ghosh,Thiago Luiz De Paula Castro,Alice Rebecca Wattam,Vasco Azevedo,Aristóteles Góes-Neto,Anne Cybelle Pinto Gomide,Michelle Zibetti Tadra Sfeir

doi:10.1186/s12864-019-6018-1

Abstract

BackgroundIron is an essential micronutrient for the growth and development of virtually all living organisms, playing a pivotal role in the proliferative capability of many bacterial pathogens. The impact that the bioavailability of iron has on the transcriptional response of bacterial species in the CMNR group has been widely reported for some members of the group, but it hasn’t yet been as deeply explored in Corynebacterium pseudotuberculosis. Here we describe for the first time a comprehensive RNA-seq whole transcriptome analysis of the T1 wild-type and the Cp13 mutant strains of C. pseudotuberculosis under iron restriction. The Cp13 mutant strain was generated by transposition mutagenesis of the ciuA gene, which encodes a surface siderophore-binding protein involved in the acquisition of iron. Iron-regulated acquisition systems are crucial for the pathogenesis of bacteria and are relevant targets to the design of new effective therapeutic approaches.ResultsTranscriptome analyses showed differential expression in 77 genes within the wild-type parental T1 strain and 59 genes in Cp13 mutant under iron restriction. Twenty-five of these genes had similar expression patterns in both strains, including up-regulated genes homologous to the hemin uptake hmu locus and two distinct operons encoding proteins structurally like hemin and Hb-binding surface proteins of C. diphtheriae, which were remarkably expressed at higher levels in the Cp13 mutant than in the T1 wild-type strain. These hemin transport protein genes were found to be located within genomic islands associated with known virulent factors. Down-regulated genes encoding iron and heme-containing components of the respiratory chain (including ctaCEF and qcrCAB genes) and up-regulated known iron/DtxR-regulated transcription factors, namely ripA and hrrA, were also identified differentially expressed in both strains under iron restriction.ConclusionBased on our results, it can be deduced that the transcriptional response of C. pseudotuberculosis under iron restriction involves the control of intracellular utilization of iron and the up-regulation of hemin acquisition systems. These findings provide a comprehensive analysis of the transcriptional response of C. pseudotuberculosis, adding important understanding of the gene regulatory adaptation of this pathogen and revealing target genes that can aid the development of effective therapeutic strategies against this important pathogen.

Highlights

Iron is an essential micronutrient for the growth and development of virtually all living organisms, playing a pivotal role in the proliferative capability of many bacterial pathogens
Inhibition of bacterial growth was evident at 6 h 30 min of incubation, resulting in a 47.4% reduction in cellular density of the Cp13 mutant grown in the low iron (LI) condition compared to the high iron (HI) condition (Fig. 1b)
In summary, we identified a total of 77 and 59 transcripts differentially expressed between low iron and high iron cultures of the wild-type parental T1 strain and the Cp13 mutant of C. pseudotuberculosis, respectively

Summary

Introduction

Iron is an essential micronutrient for the growth and development of virtually all living organisms, playing a pivotal role in the proliferative capability of many bacterial pathogens. The impact that the bioavailability of iron has on the transcriptional response of bacterial species in the CMNR group has been widely reported for some members of the group, but it hasn’t yet been as deeply explored in Corynebacterium pseudotuberculosis. Caseous lymphadenitis (CLA) is a chronic, debilitating infection caused by the Gram-positive bacterium Corynebacterium pseudotuberculosis. The bacteria are phagocytosed by macrophages, which are drained to local lymph nodes. Bacterium proliferation results in the death of the host cell and the subsequent release of bacteria into the extracellular environment, which can spread through the lymphatic system to regional lymph nodes and internal organs [3]. Clinical signs of the disease include the formation of caseous abscesses either in superficial or internal lymph nodes. While antibiotic therapy is not usually helpful, management of the disease combines the identification and removal of infected animals along with vaccination of healthy animals [2]

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