Abstract
Quorum sensing systems regulate gene expression in response to bacterial population density. Acyl-homoserine lactones are a class of quorum sensing molecules found in cattle rumen that are thought to regulate the gene expression of enterohemorrhagic Escherichia coli and thus help this pathogen survive in animal gastrointestinal tracts. However, the specific bacteria that produce these signaling molecules in bovine and porcine gastrointestinal tracts are unknown. Here we developed methods to concentrate gastrointestinal fluids and screen the bacteria that produce acyl-homoserine lactones. We isolated a Pseudomonas aeruginosa strain YZ1 from cattle rumen, and an Aeromonas hydrophila strain YZ2 from pig intestine. Mass spectrometry analysis of culture supernatants indicated at least three specific classes of acyl-homoserine lactones produced by YZ1, and a C4-acyl-homoserine lactone produced by YZ2. Transformation of E. coli with P. aeruginosa or A. hydrophila luxI homologs,which can produce short- or long-chain acyl-homoserine lactones conferred upon E. coli the ability to synthesize acyl-homoserine lactones and affected gene expression, motility, and acid tolerance of E. coli. This is the first study reporting the isolation and characterization of acyl-homoserine lactone synthase-positive bacteria from cattle rumen and swine intestines.
Highlights
Quorum sensing (QS) systems regulate gene expression in response to bacterial population density
We screened ∼500 isolated bacterial colonies for acyl-homoserine lactone (AHL) production by seeding the individual colonies into Luria broth (LB) for overnight growth and extracted culture supernatants with ethyl acetate. These extracts were added to the AHL reporter strain JZA1 in the presence of X-gal to monitor AHLs in the extracted supernatants by quantifying AHL-dependent JZA1 β-galactosidase activity
We found that the culture supernatant derived from two single isolated colonies induced β-galactosidase activity (Figures 1A,B). β-galactosidase activity was highest when YZ1 was grown for at least 6 h (Figure 1A) and was more variable for YZ2 (Figure 1B)
Summary
Quorum sensing (QS) systems regulate gene expression in response to bacterial population density. Cattle are the primary animal reservoir of enterohemorrhagic E. coli (EHEC) (Andrade et al, 2012; Borriello et al, 2012; Duan et al, 2012, 2013; Yang et al, 2013), an important foodborne
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