AUTHOR=Patzelt Diana , Michael Victoria , Päuker Orsola , Ebert Matthias , Tielen Petra , Jahn Dieter , Tomasch Jürgen , Petersen Jörn , Wagner-Döbler Irene 

TITLE=Gene Flow Across Genus Barriers – Conjugation of Dinoroseobacter shibae’s 191-kb Killer Plasmid into Phaeobacter inhibens and AHL-mediated Expression of Type IV Secretion Systems

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.00742

DOI=10.3389/fmicb.2016.00742

ISSN=1664-302X

ABSTRACT=<p><italic>Rhodobacteraceae</italic> harbor a conspicuous wealth of extrachromosomal replicons (ECRs) and therefore the exchange of genetic material via horizontal transfer has been supposed to be a major evolutionary driving force. Many plasmids in this group encode type IV secretion systems (T4SS) that are expected to mediate transfer of proteins and/or DNA into host cells, but no experimental evidence of either has yet been provided. <italic>Dinoroseobacter shibae</italic>, a species of the <italic>Roseobacter</italic> group within the <italic>Rhodobacteraceae</italic> family, contains five ECRs that are crucial for anaerobic growth, survival under starvation and the pathogenicity of this model organism. Here we tagged two syntenous but compatible RepABC-type plasmids of 191 and 126-kb size, each encoding a T4SS, with antibiotic resistance genes and demonstrated their conjugational transfer into a distantly related <italic>Roseobacter</italic> species, namely <italic>Phaeobacter inhibens</italic>. Pulsed field gel electrophoresis showed transfer of those replicons into the recipient both individually but also together documenting the efficiency of conjugation. We then studied the influence of externally added quorum sensing (QS) signals on the expression of the T4SS located on the sister plasmids. A QS deficient <italic>D. shibae</italic> null mutant (Δ<italic>luxI<sub>1</sub></italic>) lacking synthesis of <italic>N</italic>-acyl-homoserine lactones (AHLs) was cultivated with a wide spectrum of chemically diverse long-chain AHLs. All AHLs with lengths of the acid side-chain ≥14 reverted the Δ<italic>luxI<sub>1</sub></italic> phenotype to wild-type. Expression of the T4SS was induced up to log2 ∼3fold above wild-type level. We hypothesize that conjugation in roseobacters is QS-controlled and that the QS system may detect a wide array of long-chain AHLs at the cell surface.</p>