Iron Starvation Conditions Upregulate Ehrlichia ruminantium Type IV Secretion System, tr1 Transcription Factor and map1 Genes Family through the Master Regulatory Protein ErxR

Abstract

Ehrlichia ruminantium is an obligatory intracellular bacterium that causes heartwater, a fatal disease in ruminants. Due to its intracellular nature, E. ruminantium requires a set of specific virulence factors, such as the type IV secretion system (T4SS), and outer membrane proteins (Map proteins) in order to avoid and subvert the host's immune response. Several studies have been conducted to understand the regulation of the T4SS or outer membrane proteins, in Ehrlichia, but no integrated approach has been used to understand the regulation of Ehrlichia pathogenicity determinants in response to environmental cues. Iron is known to be a key nutrient for bacterial growth both in the environment and within hosts. In this study, we experimentally demonstrated the regulation of virB, map1, and tr1 genes by the newly identified master regulator ErxR (for Ehrlichia ruminantium expression regulator). We also analyzed the effect of iron depletion on the expression of erxR gene, tr1 transcription factor, T4SS and map1 genes clusters in E. ruminantium. We show that exposure of E. ruminantium to iron starvation induces erxR and subsequently tr1, virB, and map1 genes. Our results reveal tight co-regulation of T4SS and map1 genes via the ErxR regulatory protein at the transcriptional level, and, for the first time link map genes to the virulence function sensu stricto, thereby advancing our understanding of Ehrlichia's infection process. These results suggest that Ehrlichia is able to sense changes in iron concentrations in the environment and to regulate the expression of virulence factors accordingly.

Nutrition and Bipartite Metabolism of Intracellular Pathogens

“…The autophagosomes are delivered to and fuse with the A. phagocytophilum-containing compartment, providing the amino acids needed for replication ( Fig. 3) [3], and host restriction of iron triggers virulence [72]. The pathogen subverts the tick host carbohydrate metabolism but it is not known whether similar process are exhibited in the mammalian host [73,74].…”

Insights into the mechanism regulating the differential expression of the P28-OMP outer membrane proteins in obligatory intracellular pathogen Ehrlichia chaffeensis

“…EcxR, ApxR and ErxR are orthologs in E. chaffeensis , Anaplasma phagocytophilum , and Ehrlichia ruminantium , respectively [ 16–18 ]. The P44 major surface proteins of A. phagocytophilum are also differentially expressed, and contribute to bacterial survival and infection [ 19 , 20 ].…”

“…ApxR has a regulatory role in the expression of tr1 and p44E [ 21 ]. In E. ruminantium ErxR is responsible for the coordinated regulation of the expression of tr1 and map genes that are orthologs of the p28-omp genes [ 16 ]. However, the role of EcxR in regulating the expression of tr1 and the p28-omp genes in E. chaffeensis is still unknown.…”

Tick–Pathogen Interactions: The Metabolic Perspective

“…The tick-borne pathogen Ehrlichia ruminantium senses iron levels in mammalian cells and responds to iron starvation by upregulating virulence genes such as those involved in the type IV secretion system (T4SS), which, in turn, may participate in iron acquisition by the pathogen [14]. A similar mechanism may be at play during pathogen infection in ticks.…”