The ColE1-plasmids shared extensive regions of high sequence homology in coding and in non-coding regions, indicating frequent horizontal gene transfer and AZD8931 recombination events among plasmids within the genus Rahnella. Interestingly, none of the ColE1-like plasmids found in this study possessed a mobilisation system. In contrast, the other plasmids analysed (one ColE2-like plasmid and three rolling circle plasmids) contained mobilisation genes. pHW121 is a member of the pC194/pUB110

family. pHW104 and pHW126 belong to different groups of poorly-characterised plasmids and might form a super-family with pSN2-like plasmids and pJW1. To our surprise the plasmids lacked genes which confer an obvious benefit upon their hosts. Of course some of the genes with unknown function might encode proteins with advantageous functions but at least for some of the plasmids the term “”selfish DNA”" seems appropriate. The best example is pHW126, the smallest plasmid found

in Rahnella. This plasmid possessed only two ORFs, a putative replication gene and one for mobilisation. Since these coding sequences cover more than 70% of the plasmid, and additional regions are expected to function as oriV and oriT, the plasmid is simply too small Nutlin-3a in vitro to bear any gene beneficial to the host. The low G+C content of this plasmid might indicate that JQ1 ic50 Rahnella is not its normal host. In contrast, the close similarities among the ColE1-like plasmids provided

compelling evidence that Rahnella is their normal host. The presence of genes probably derived from P. luminescens on pHW4594 and stretches of the chromosome of E. tasmaniensis highly homologous to parts of pHW66 highlight the importance of plasmids for genetic exchange of even chromosomal sequences among different genera. Methods Media and growth conditions E. coli and Rahnella strains were grown in MLB medium (10 g/l peptone, 5 g/l yeast extract, tuclazepam 5 g/l NaCl, pH 7) at 37°C and 30°C, respectively, if not otherwise indicated. When necessary, ampicillin was added to a concentration of 100 mg/l. Isolation and identification of Rahnella strains Different types of plant materials (Table 1) were homogenised in sterile PBS and dilutions plated on Levine-EMB agar (Merck, Darmstadt, Germany). After incubation at 36°C for 48 ± 8 h dark colonies were sampled and restreaked twice on MLB plates to obtain pure cultures. Strains were classified by routine biochemical tests and partial 16S rRNA gene sequencing [6]. For amplification of the 16S rRNA gene the primer pair fD2 and rP1 was employed. The PCR product was purified with a Nucleospin Kit (Macherey-Nagel, Düren, Germany) and directly sequenced using the primers 16S-3 and 16S-5. Primer sequences are shown in Additional file 4.