A Rickettsiella Bacterium from the Hard Tick, Ixodes woodi: Molecular Taxonomy Combining Multilocus Sequence Typing (MLST) with Significance Testing

Andreas Leclerque,Regina G Kleespies,Ulrike Gertrud Munderloh

doi:10.1371/journal.pone.0038062

Andreas Leclerque, Regina G Kleespies + Show 1 more

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https://doi.org/10.1371/journal.pone.0038062

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Journal: PloS one	Publication Date: May 31, 2012
Citations: 47	License type: CC BY 4.0

Affiliation: Julius Kühn-Institut

Abstract

Hard ticks (Acari: Ixodidae) are known to harbour intracellular bacteria from several phylogenetic groups that can develop both mutualistic and pathogenic relationships to the host. This is of particular importance for public health as tick derived bacteria can potentially be transmitted to mammals, including humans, where e.g. Rickettsia or Coxiella act as severe pathogens. Exact molecular taxonomic identification of tick associated prokaryotes is a necessary prerequisite of the investigation of their relationship to both the tick and possible vertebrate hosts. Previously, an intracellular bacterium had been isolated from a monosexual, parthenogenetically reproducing laboratory colony of females of the hard tick, Ixodes woodi Bishopp, and had preliminarily been characterized as a “Rickettsiella-related bacterium”. In the present molecular taxonomic study that is based on phylogenetic reconstruction from both 16 S ribosomal RNA and protein-encoding marker sequences complemented with likelihood-based significance testing, the bacterium from I. woodi has been identified as a strain of the taxonomic species Rickettsiella grylli. It is the first time that a multilocus sequence typing (MLST) approach based on a four genes comprising MLST scheme has been implemented in order to classify a Rickettsiella-like bacterium to this species. The study demonstrated that MLST holds potential for a better resolution of phylogenetic relationships within the genus Rickettsiella, but requires sequence determination from further Rickettsiella-like bacteria in order to complete the current still fragmentary picture of Rickettsiella systematics.

Highlights

Ticks are prominently known to harbour intracellular bacteria from different taxonomic groups as, for instance, the alpha and gamma subdivisions of the proteobacteria
As part of the original description of the hard tick associated bacterium under study, its 16 S rRNA gene sequence had been determined and compared to a set of orthologous sequences from selected representatives of the main groups of bacteria commonly known to be associated with ticks
It had become clear that the new specimen clustered among the Gammaproteobacteria and was, different from the Alphaproteobacteria, e.g. the Rickettsiales, as well as the Chlamydiales

Summary

Introduction

Ticks are prominently known to harbour intracellular bacteria from different taxonomic groups as, for instance, the alpha and gamma subdivisions of the proteobacteria. Whereas some of these bacteria as e.g. those of the genera Rickettsia or Coxiella are important tick-transmitted human or animal pathogens, others as e.g. those assigned to the genus Wolbachia are commonly referred to as endosymbionts. As a rule, the latter are transmitted transovarially and have established a putatively mutualistic interaction with the host. In the light of these results, the I. woodi associated new specimen was consistently classified as a ‘‘Rickettsiella-related bacterium’’ [3]

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