Mapping of mutations that alleviate a retron-mediated phenotype in Salmonella

Salmonella enterica subsp. enterica ser. Typhimurium (STm) contains a retron (retron-Sen2), a prokaryotic genetic retroelement which produces small single-stranded DNA (msDNA). Gene deletions that abrogate msDNA biosynthesis of retron-Sen2 (?rrtT, ?xseA, ?msrmsd) lead to inhibition of bacterial growth in cold-temperatures (cold-sensitivity). To understand why msDNA is required for growth in cold, we isolated suppressor strains that exhibited restored growth in cold (starting from cold-sensitive mutants ?rrtT, ?xseA, and ?msrmsd), and sequenced their genomes in order to map mutations that potentially alleviate the retron-dependent cold-sensitivity phenotype.