AUTHOR=Garushyants Sofya K. , Beliavskaia Alexandra Y. , Malko Dmitry B. , Logacheva Maria D. , Rautian Maria S. , Gelfand Mikhail S. 

TITLE=Comparative Genomic Analysis of Holospora spp., Intranuclear Symbionts of Paramecia

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00738

DOI=10.3389/fmicb.2018.00738

ISSN=1664-302X

ABSTRACT=<p>While most endosymbiotic bacteria are transmitted only vertically, <italic>Holospora</italic> spp., an alphaproteobacterium from the <italic>Rickettsiales</italic> order, can desert its host and invade a new one. All bacteria from the genus <italic>Holospora</italic> are intranuclear symbionts of ciliates <italic>Paramecium</italic> spp. with strict species and nuclear specificity. Comparative metabolic reconstruction based on the newly sequenced genome of <italic>Holospora curviuscula</italic>, a macronuclear symbiont of <italic>Paramecium bursaria</italic>, and known genomes of other <italic>Holospora</italic> species shows that even though all <italic>Holospora</italic> spp. can persist outside the host, they cannot synthesize most of the essential small molecules, such as amino acids, and lack some central energy metabolic pathways, including glycolysis and the citric acid cycle. As the main energy source, <italic>Holospora</italic> spp. likely rely on nucleotides pirated from the host. <italic>Holospora</italic>-specific genes absent from other <italic>Rickettsiales</italic> are possibly involved in the lifestyle switch from the infectious to the reproductive form and in cell invasion.</p>