Hypothetical strain of E. coli

An open reading frame is a DNA sequence that contains a start codon and a stop codon in the same reading frame.  In a gene, ORFs are located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon). ORFs are usually encountered when shifting through pieces of DNA while trying to locate a gene. The existence of an ORF, especially a long one, is usually a good indication of the presence of a gene in the surrounding sequence. My guess is, a coliphage (bacteriophage) must have infected the E. coli that was isolated from the gut with a specific gene within a pre-existing ORF - however, I'm not totally sure .