CONICET | Buscador de Institutos y Recursos Humanos

The twin-arginine translocation (Tat) pathway exports fully folded proteins out of the cytoplasm of Gram-negative andGram-positive bacteria. Although much progress has been made in unraveling the molecular mechanism and biochemicalcharacterization of the Tat system, little is known concerning its functionality and biological role to confer adaptive skills,symbiosis or pathogenesis in the a-proteobacteria class. A comparative genomic analysis in the a-proteobacteria classconfirmed the presence of tatA, tatB, and tatC genes in almost all genomes, but significant variations in gene synteny andrearrangements were found in the order Rickettsiales with respect to the typically described operon organization.Transcription of tat genes was confirmed for Anaplasma marginale str. St. Maries and Brucella abortus 2308, two aproteobacteriawith full and partial intracellular lifestyles, respectively. The tat genes of A. marginale are scatteredthroughout the genome, in contrast to the more generalized operon organization. Particularly, tatA showed anapproximately 20-fold increase in mRNA levels relative to tatB and tatC. We showed Tat functionality in B. abortus 2308 forthe first time, and confirmed conservation of functionality in A. marginale. We present the first experimental description ofthe Tat system in the Anaplasmataceae and Brucellaceae families. In particular, in A. marginale Tat functionality is conserveddespite operon splitting as a consequence of genome rearrangements. Further studies will be required to understand howthe proper stoichiometry of the Tat protein complex and its biological role are achieved. In addition, the predictedsubstrates might be the evidence of role of the Tat translocation system in the transition process from a free-living to aparasitic lifestyle in these a-proteobacteria