Metagenomic profile of the microbial populations associated with the spotted fever group rickettsia infected Gulf Coast ticks (Amblyomma maculatum)

Ticks harbor enormous microbial diversity but little is known about the microbial population dynamics and their potential impact on pathogen transmission. In this study, the Spotted Fever Group Rickettsia infection was identified in partially blood-fed Amblyomma maculatum by PCR amplification of the outer membrane protein A (ompA) gene followed by DNA sequencing. The nucleotide sequence similarity of the PCR amplicons revealed homology with Rickettsia parkeri, R. amblyommii and Rickettsia endosymbiont of Amblyomma maculatum. The sole detection of R. parkeri in salivary glands suggests it can pass through the hemocoel, colonize salivary gland and be transmitted to host via salivary secretions. R. parkeri was quantified by probe based amplification of ompB gene with qPCR from SFGR-infected A. maculatum tissues and was found to vary widely in ompB copy number between tick midgut and salivary gland tissues. The presence of R. parkeri was further confirmed by immunoblotting with a polyclonal R. parkeriantibody. Finally, a pyrosequencing approach was performed to survey the bacterial diversity in selected tick tissues and tick saliva.  In midgut tissues and salivary glands, Rickettsia conorii, Rickettsia rickettsii, Rickettsia sibirica were detected, which are well known tick borne disease agents. Endosymbionts of the genus Wolbachia and Francisella were other dominant bacterial species present in tick tissues. Although rickettsial DNA was present in tick saliva, most of the detected bacteria originated from the host’s skin. The differential level of rickettsial pathogens, endosymbionts and other bacterial species present in tick tissues will illuminate the complex set of vector-pathogen interactions.