Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: February 27, 2004
Publication Date: May 23, 2004
Citation: Bearson, B.L., Casey, T., Bearson, S.M. 2004. Expression of ldrd in E. coli O157:H7 and Salmonella enterica serovar Typhimurium inhibits growth [abstract]. American Society for Microbiology. p. 297. Technical Abstract: Four copies of a toxin-antisense RNA module designated ldr are present in the genome of E. coli K-12. Expression of ldrD from a multicopy plasmid inhibits cell growth of E. coli (Kawano et al, Mol. Micro. 2002. 45:333). Homology searches indicate that the ldr modules are present in the genomes of E. coli O157:H7 and Salmonella enterica serovar Typhimurium. To determine if expression of ldrD inhibits E. coli O157:H7 and S. typhimurium cell growth, the ldrD gene from E. coli O157:H7 was cloned into a plasmid containing an arabinose inducible promoter. E. coli O157:H7 transformed with the ldrD plasmid followed by plating onto media containing arabinose have a small flat, translucent colony morphology. S. typhimurium transduced with phage containing the ldrD plasmid do not form visible colonies on inducible media. Expression of ldrD in E. coli O157:H7 or S. typhimurium also inhibits log-phase cell growth for up to seven hours. Although the cultures overcome the inhibition following overnight growth, data indicates it is due to loss of the plasmid expressing ldrD. Furthermore, E. coli O157:H7 containing the ldrD plasmid can be rescued from an inhibited log-phase culture and once again be induced to inhibit cell growth. Single colony isolation of E. coli O157:H7 containing the ldrD plasmid onto MacConkey arabinose media only formed single colonies in the primary quadrant where growth would usually be confluent. As LdrD is predicted to be a membrane protein based on topology algorithms, a component of MacConkey media such as bile salts or crystal violet may disrupt the membrane of bacterial cells expressing ldrD. Recently, chromosome-encoded toxin modules (relBE and mazEF) have been shown to be involved in the regulation of cellular physiology. As the ldr modules may also regulate aspects of cellular physiology, their cellular role is being investigated.