Functional Characterization of Multiple <i>Ehrlichia chaffeensis</i> Sodium (Cation)/Proton Antiporter Genes Involved in the Bacterial pH Homeostasis

• Main Authors: Lanjing Wei, Huitao Liu, Kimia Alizadeh, Maria D. Juarez-Rodriguez, Roman R. Ganta
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: International Journal of Molecular Sciences
• Subjects: functional genomics; rickettsial diseases; tick-borne diseases; antiporters; pH homeostasis
• Online Access: https://www.mdpi.com/1422-0067/22/16/8420
• ISSN: 1661-6596; 1422-0067

<i>Ehrlichia chaffeensis</i> causes human monocytic ehrlichiosis. Little is known about how this and other related tick-borne rickettsia pathogens maintain pH homeostasis in acidified phagosomes and the extracellular milieu. The membrane-bound sodium (cation)/proton antiporters are found in a wide range of organisms aiding pH homeostasis. We recently reported a mutation in an antiporter gene of <i>E. chaffeensis</i> (ECH_0379) which causes bacterial in vivo attenuation. The <i>E. chaffeensis</i> genome contains 10 protein coding sequences encoding for predicted antiporters. We report here that nine of these genes are transcribed during the bacterial growth in macrophages and tick cells. All <i>E. chaffeensis</i> antiporter genes functionally complemented antiporter deficient <i>Escherichia coli</i>. Antiporter activity for all predicted <i>E. chaffeensis</i> genes was observed at pH 5.5, while gene products of ECH_0179 and ECH_0379 were also active at pH 8.0, and ECH_0179 protein was complemented at pH 7.0. The antiporter activity was independently verified for the ECH_0379 protein by proteoliposome diffusion analysis. This is the first description of antiporters in <i>E. chaffeensis</i> and demonstrates that the pathogen contains multiple antiporters with varying biological functions, which are likely important for the pH homeostasis of the pathogen’s replicating and infectious forms.