Mutations in ehrlichia chaffeensis genes ECH-0660 and ECH-0665 cause transcriptional changes in response to zinc or iron limitation

Abstract

Ehrlichia chaffeensis causes human monocytic ehrlichiosis by replicating within phagosomes of monocytes/macrophages. A function disruption mutation within the pathogen's ECH-0660 gene, which encodes a phage head-to-tail connector protein, resulted in the rapid clearance of the pathogen in vivo, while aiding in induction of sufficient immunity in a host to protect against wild-type infection challenge. In this study, we describe the characterization of a cluster of seven genes spanning from ECH-0659 to ECH-0665, which contained four genes encoding bacterial phage proteins, including the ECH-0660 gene. Assessment of the promoter region upstream of the first gene of the seven genes (ECH-0659) in Escherichia coli demonstrated transcriptional enhancement under zinc and iron starvation conditions. Furthermore, transcription of the seven genes was significantly higher under zinc and iron starvation conditions for E. chaffeensis carrying a mutation in the ECH-0660 gene compared to the wild-type pathogen. In contrast, for the ECH-0665 gene mutant with the function disruption, transcription from the genes was mostly similar to that of the wild type or was moderately downregulated. Recently, we reported that this mutation caused a minimal impact on the pathogen's in vivo growth, as it persisted similarly to the wild type. The current study is the first to describe how zinc and iron contribute to E. chaffeensis biology. Specifically, we demonstrated that the functional disruption in the gene encoding the phage head-to-tail connector protein in E. chaffeensis results in the enhanced transcription of seven genes, including those encoding phage proteins, under zinc and iron limitation.