Transcriptional organization of the temperature-sensitive transfer system from the IncHI1 plasmid R27

Abstract

One of the characteristic features of IncHI1 plasmids is a thermosensitive process of conjugation, which is optimal between 22 6C and 30 6C but inhibited at 37 6C. R27, the prototypical IncHI1 plasmid, contains transfer genes clustered in two regions of the plasmid, Tra1 and Tra2. In the present study, transcriptional analyses of the tra genes were undertaken at both 30 6C and 37 6C. Screening of 38 tra genes showed that tra genes are transcriptionally linked in six operons, three in each Tra region. RT-PCR analysis showed that gene expression was reduced at 37 6C relative to that observed at 30 6C. The transcription start sites of the six transcripts were identified, promoters and upstream regions were cloned, and transcription was tested at both temperatures. In cells grown at 37 6C, in the presence of R27, the promoters were inhibited, except for promoters of the H operon and AN operon. Conditions that influenced DNA topology, such as osmolarity, anaerobiosis, quorum sensing and acidity, showed no significant influence on transfer frequency. These results should facilitate future understanding of the basis of temperature-sensitive transfer in this large conjugative plasmid.

Horizontal Transfer of the Salmonella enterica Serovar Infantis Resistance and Virulence Plasmid pESI to the Gut Microbiota of Warm-Blooded Hosts

“…It was also found that under moderately acidic pH and physiological temperatures, transcription of the conjugation system ( pilV ) was increased. Temperature-dependent conjugation has been previously reported for the transfer-thermosensitive IncHI1 plasmids, such as R27, as its conjugation frequency is optimal at low temperature (25 to 30°C) and declines when temperature increases (33). In contrast to the IncHI1 plasmids, pESI conjugation and pil gene expression are minimal at 27°C while increasing at 37 to 41°C.…”

The diversity of conjugative relaxases and its application in plasmid classification

“…The IncHI1 plasmid R27 has been analysed in most detail (Sherburne et al , 2000). This 180‐kb‐long plasmid is temperature sensitive for conjugation, with optimal mating temperature at 22–28 °C due to transcriptional regulation of its tra genes (Alonso et al , 2005). Most genes coding for its T4SS are encoded in one plasmid region called Tra2 (Sherburne et al , 2000), whereas the oriT , all relaxosomal components and some additional T4SS genes are encoded in Tra1 (Lawley et al , 2002, 2003).…”

Conjugative plasmids: vessels of the communal gene pool

“…Expression of conjugative pili can normally be triggered by external cues such as a change in temperature (Alonso et al 2005), but also by encountering plasmid-free cells, which subsequently results in the epidemic spread of the plasmid through whole plasmid-free populations. This phenomenon is known as transitory de-repression (Lundquist & Levin 1986).…”