Comparative Transcriptome Profiling of Virulent and Attenuated Ehrlichia ruminantium Strains Highlighted Strong Regulation of map1- and Metabolism Related Genes

Abstract

The obligate intracellular pathogenic bacterium, Ehrlichia ruminantium, is the causal agent of heartwater, a fatal disease in ruminants transmitted by Amblyomma ticks. So far, three strains have been attenuated by successive passages in mammalian cells. The attenuated strains have improved capacity for growth in vitro, whereas they induced limited clinical signs in vivo and conferred strong protection against homologous challenge. However, the mechanisms of pathogenesis and attenuation remain unknown. In order to improve knowledge of E. ruminantium pathogenesis, we performed a comparative transcriptomic analysis of two distant strains of E. ruminantium, Gardel and Senegal, and their corresponding attenuated strains. Overall, our results showed an upregulation of gene expression encoding for the metabolism pathway in the attenuated strains compared to the virulent strains, which can probably be associated with higher in vitro replicative activity and a better fitness to the host cells. We also observed a significant differential expression of membrane protein-encoding genes between the virulent and attenuated strains. A major downregulation of map1-related genes was observed for the two attenuated strains, whereas upregulation of genes encoding for hypothetical membrane proteins was observed for the four strains. Moreover, CDS_05140, which encodes for a putative porin, displays the highest gene expression in both attenuated strains. For the attenuated strains, the significant downregulation of map1-related gene expression and upregulation of genes encoding other membrane proteins could be important in the implementation of efficient immune responses after vaccination with attenuated vaccines. Moreover, this study revealed an upregulation of gene expression for 8 genes encoding components of Type IV secretion system and 3 potential effectors, mainly in the virulent Gardel strain. Our transcriptomic study, supported by previous proteomic studies, provides and also confirms new information regarding the characterization of genes involved in E. ruminantium virulence and attenuation mechanisms.

Nutrition and Bipartite Metabolism of Intracellular Pathogens

“…Nutrient availability governs the biphasic lifestyle of L. pneumophila and possibly C. burnetii, since it is closely related to L. pneumophila [24,25]. When nutrient levels are high, L. pneumophila is in the replicative phase [17,26]. When nutrient levels are low, the bacterium enters a transmissive phase.…”

“…In addition, the pathogen overrides host restriction of iron [70]. A. phagocytophilum is a tick-borne an obligate intracellular pathogen that replicates within an autophagosome-like compartment [26,71]. Ats-1, a type-IV effector of A. phagocytophilum, binds to host Beclin-1 inducing autophagosome formation (Fig.…”

Proteome Analysis Revealed Changes in Protein Expression Patterns Caused by Mutations in Ehrlichia chaffeensis

“…Our previous study documented macrophage and tick cell-specific expression of p28-Omps where Omp-p28 (p28-Omp 19) transcript was detected as abundantly expressed in macrophage culture derived E. chaffeensis , whereas the transcript for Omp-1B (gene 14) was the major expressed transcript for the bacterium cultured in tick cells (Ganta et al, 2009 ). Similarly, differential expression of membrane protein-encoding genes between the virulent and attenuated strains were observed using OMICS methods in E. ruminantium (Marcelino et al, 2015 ; Pruneau et al, 2018 ). Consistent with the prior studies, p28-Omps are among the most abundantly expressed and immunogenic proteins in both wildtype and in the three mutants assessed.…”

Revisiting Ehrlichia ruminantium Replication Cycle Using Proteomics: The Host and the Bacterium Perspectives

“…RBs re-condense back into EBs towards the end of the cycle, being released after host cell lysis [3]. The relation between the stage of development and time post-infection depends on the E. ruminantium strain and its adaptation to in vitro culture conditions [4][5][6].…”

“…E. ruminantium has a small genome [7] and, to survive and replicate within host cells, it has developed complex mechanisms to hijack host cellular functions [6,8,9]. Nevertheless, many important and basic cell biology questions regarding E. ruminantium-host cell interaction remain unaddressed.…”