Sequence analysis of Escherichia coli O157:H7 bacteriophage PhiV10 and identification of a phage-encoded immunity protein that modifies the O157 antigen.

Bacteriophage PhiV10 is a temperate phage, which specifically infects Escherichia coli O157:H7. The nucleotide sequence of the PhiV10 genome is 39 104 bp long and contains 55 predicted genes. PhiV10 is closely related to two previously sequenced phages, the Salmonella enterica serovar Anatum (Group E1) phage epsilon15 and a prophage from E. coli APEC O1. The attachment site of PhiV10, like those of its two closest relatives, overlaps the 3' end of guaA in the host chromosome. PhiV10 encodes an O-acetyltransferase, which modifies the O157 antigen. This modification is sufficient to block PhiV10 superinfection, indicating that the O157 antigen is most likely the PhiV10 receptor.

Molecular characterization of autoinduction of bioluminescence in the Microtox indicator strain Vibrio fischeri ATCC 49387.

Repeated attempts to clone the luxI from Vibrio fischeri ATCC 49387 failed to produce a clone carrying a functional LuxI. Sequence data from the clones revealed the presence of a polymorphism when compared with previously published luxI sequences, prompting further characterization of bioluminescence regulation in V. fischeri ATCC 49387. Further investigation of V. fischeri ATCC 49387 revealed that its LuxI protein lacks detectable LuxI activity due to the presence of a glutamine residue at position 125 in the deduced amino acid sequence. Specific bioluminescence in V. fischeri ATCC 49387 increases with increasing cell density, indicative of a typical autoinduction response. However, conditioned medium from this strain does not induce bioluminescence in an ATCC 49387 luxR-plux-based acyl homoserine lactone reporter strain, but does induce bioluminescence in ATCC 49387. It has been previously shown that a V. fischeri MJ-1 luxI mutant exhibits autoinduction of bioluminescence through N-octanoyl-L-homoserine lactone, the product of the AinS autoinducer synthase. However, a bioreporter based on luxR-plux from V. fischeri ATCC 49387 responded poorly to conditioned medium from V. fischeri ATCC 49387 and also responded poorly to authentic N-octanoyl-DL-homoserine lactone. A similar MJ-1-based bioreporter showed significant induction under the same conditions. A putative ainS gene cloned from ATCC 49387, unlike luxI from ATCC 49387, expresses V. fischeri autoinducer synthase activity in Escherichia coli. This study suggests that a regulatory mechanism independent of LuxR and LuxI but possibly involving AinS is responsible for the control of autoinduction of bioluminescence in V. fischeri ATCC 49387.