Genetic evidence for an activator required for induction of colicin-like bacteriocin 28b production in Serratia marcescens by DNA-damaging agents

Abstract

Bacteriocin 28b production is induced by mitomycin in wild-type Serratia marcescens 2170 but not in Escherichia coli harboring the bacteriocin 28b structural gene (bss). Studies with a bss-lacZ transcriptional fusion showed that mitomycin increased the level of bss gene transcription in S. marcescens but not in the E. coli background. A S. marcescens Tn5 insertion mutant was obtained (S. marcescens 2170 reg::Tn5) whose bacteriocin 28b production and bss gene transcription were not increased by mitomycin treatment. Cloning and DNA sequencing of the mutated region showed that the Tn5 insertion was flanked by an SOS box sequence and three genes that are probably cotranscribed (regA, regB, and regC). These three genes had homology to phage holins, phage lysozymes, and the Ogr transcriptional activator of P2 and related bacteriophages, respectively. Recombinant plasmid containing this wild-type DNA region complemented the reg::Tn5 regulatory mutant. A transcriptional fusion between a 157-bp DNA fragment, containing the apparent SOS box upstream of the regA gene, and the cat gene showed increased chloramphenicol acetyltransferase activity upon mitomycin treatment. Upstream of the bss gene, a sequence similar to the consensus sequence proposed to bind Ogr protein was found, but no sequence similar to an SOS box was detected. Our results suggest that transcriptional induction of bacteriocin 28b upon mitomycin treatment is mediated by the regC gene whose own transcription would be LexA dependent.Serratia marcescens has been shown to produce bacteriocins upon induction with DNA-damaging agents (50). These bacteriocins have been classified into two groups (23): fraction 1 bacteriocins are active against Escherichia coli but not against S. marcescens, and fraction 2 bacteriocins are active against S. marcescens but not against E. coli (50). Bacteriocins belonging to fraction 1 are simple polypeptides that resemble colicins (50). Only colicin-like bacteriocins L and 28b have been studied in some detail. Bacteriocin L from S. marcescens JF246 has been isolated and characterized, and the effects of this bacteriocin on the incorporation of labelled leucine and thymidine and on the cellular levels of ATP in E. coli were similar to those produced by pore-forming colicins (17,18,40). On the other hand, the bacteriocin 28b structural gene (bss) has been cloned and sequenced, and the predicted amino acid sequence of the C-terminal part of this bacteriocin has been shown to have a high degree of similarity to the C-terminal domains of pore-forming colicins (56). The two bacteriocins are very closely related, if not the same, and similar bacteriocins are produced by most S. marcescens biotypes (21).Colicin production is induced by mitomycin and other DNAdamaging agents (38). Determinants for colicin production studied so far are encoded by either small high-copy-number colicinogenic plasmids (type I) or large low-copy-number colicinogenic plasmids (type II) (38). An important feature of these plasmids is that they confer on their host...

Colicin Biology

“…A role of the E8 lysis protein in the regulation of colicin E8 synthesis has been reported (386). An activator has been found to be required for the transcription of colicin-like bacteriocin 28b (201). Regulation of the colicin operons is complex and may vary from one operon to the other.…”

Heterogeneity in expression of the Escherichia coli colicin K activity gene cka is controlled by the SOS system and stochastic factors

“…The ssDNA is bound by RecA and the formed nucleoprotein Wlament activates the autoproteolytic cleavage of LexA. A number of other bacterial species, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, K. oxytoca, Serratia marcescens, Hafnia alvei and others, synthesize bacteriocins that are also regulated by the LexA protein (Riley et al 2001;Michel-Briand and Baysee 2002;Ferrer et al 1996;Wertz and Riley 2004).…”

Microbial defense systems in foods and feeds

“…Colicins the largest representative of gram-negative pore forming bacteriocins, range in size from 449 to 629 amino acids. Colicins expressed by E.coli are encoded on plasmids (Pugsley and Oudega, 1987) and genes for bacteriocins of Serratia marcesens which are also similar to colicins are located on both plasmids and genomic DNA (Ferrer et al, 1996). In colicins, the central domain is composed of half the protein and is involved in the recognition of specific cell surface receptors.…”