AT Homopolymer Strings in Salmonella enterica Subspecies I Contribute to Speciation and Serovar Diversity.

Adenine and thymine homopolymer strings of at least 8 nucleotides (AT 8+mers) were characterized in Salmonella enterica subspecies I. The motif differed between other taxonomic classes but not between Salmonella enterica serovars. The motif in plasmids was possibly associated with serovar. Approximately 12.3% of the S. enterica motif loci had mutations. Mutability of AT 8+mers suggests that genomes undergo frequent repair to maintain optimal gene content, and that the motif facilitates self-recognition; in addition, serovar diversity is associated with plasmid content. A theory that genome regeneration accounts for both persistence of predominant Salmonella serovars and serovar diversity provides a new framework for investigating root causes of foodborne illness.