Carbapenem antibiotic biosynthesis in Erwinia carotovora is regulated by physiological and genetic factors modulating the quorum sensing‐dependent control pathway

Abstract

SummaryErwinia carotovora produces the b b b b -lactam antibiotic, carbapenem, in response to a quorum sensing signalling molecule, N-(3-oxohexanoyl)-L -homoserine lactone (OHHL). We have mapped the OHHL-dependent promoter upstream of the first of the biosynthetic genes, carA . We have also analysed the effect on this promoter of the known genetic regulators of carbapenem expression, carR , carI (encoding homologues of LuxR and LuxI respectively) and hor (encoding a SlyA/MarR-like transcriptional regulator). We describe a previously unknown promoter located within the carA-H operon. This promoter does not respond to CarR and is required for quorum sensing-independent expression of the carbapenem resistance determinants encoded by the carFG genes. We have mapped the carR , carI and hor transcription start points, shown that CarR is positively autoregulated in the presence of OHHL, and have demonstrated negative feedback affecting transcription of carI . In addition, various environmental and physiological factors were shown to impinge on the transcription of the car biosynthetic genes. The nature of the carbon source and the temperature of growth influence carbapenem production by modulating the level of the OHHL signalling molecule, and thereby physiologically fine-tune the quorum sensing regulatory system.

Mutations in rpsL that confer streptomycin resistance show pleiotropic effects on virulence and the production of a carbapenem antibiotic in Erwinia carotovora

“…It is interesting that the Car phenotypes of K43N and K43T rpsL mutants can be partially bypassed by the addition of 3-oxo-C6-HSL. The Car and exoenzyme phenotypes of hor mutants have also been shown to be bypassed by a physiological excess of 3-oxo-C6-HSL (McGowan et al, 2005). Therefore, it is an attractive hypothesis that Hor protein levels may be altered in these rpsL mutants, as this could account for the observed Car, exoenzyme and virulence phenotypes.…”

“…The expR gene is located adjacent to carI in the genome; however, the function of ExpR is unclear since an expR mutant appears to have no obvious phenotype in this strain (Rivet, 1998). Exoenzymes are controlled via the LuxR homologue VirR (Burr et al, 2006), while Car production is activated by the third LuxR homologue, CarR (McGowan et al, 1995(McGowan et al, , 2005. In addition to these QS inputs, Car and exoenzyme production are coordinately regulated by the Hor global activator, which is a member of the SlyA family of transcriptional regulators (Thomson et al, 1997;McGowan et al, 2005).…”

Exploitation of a β-lactamase reporter gene fusion in the carbapenem antibiotic production operon to study adaptive evolution in Erwinia carotovora

“…It is thought that the CarR : OHHL complex activates transcription of the carABCDEFGH operon, and that this leads to production of Car (McGowan et al, 1997). The second promoter (P2) is located within carD and is not regulated by quorum sensing (McGowan et al, 2005). P2 is a weak promoter that allows low levels of expression of a carG : : lacZ transcriptional fusion (McGowan et al, 2005).…”

“…It has been shown recently that the ATTn10 carABCDEFGH gene cluster contains two promoters (McGowan et al, 2005). The first promoter (P1) is located immediately upstream of carA.…”

Quorum Sensing and Microbial Interactions in Coral Black Band Disease and Coral-Associated Bacteria

“…In addition, QS systems have been linked to antibiotic biosynthesis in Erwinia carotovora (McGowan et al 2005) and…”