REPORTH: Determining orthologous locations of repetitive sequences between genomes

Abstract

Repetitive sequences are a common feature of bacterial genomes. Some repetitive sequences such as REPINs are mobile within the genome but inherited only vertically from mother to daughter across bacterial genomes. Selfish elements in contrast are mobile within the genome but also travel horizontally from genome to genome. Yet, no matter the nature of the association between the repetitive elements and the host, it is difficult to study the evolutionary dynamics of repetitive sequences across genomes. If it is unclear whether two sequences in two different genomes are in orthologous positions, it is difficult to infer parameters like the replication rate, horizontal transfer rate and rate of loss. Here we present a tool to facilitate these analyses called REPORTH. REPORTH determines whether repetitive sequences in different but closely related bacterial genomes occur in orthologous genomic positions. Whether a position is orthologous or not depends on the orthology of flanking sequences. Flanking sequences are deemed orthologous if they are bidirectional best hits. All repetitive sequences that are found in orthologous positions across different genomes are grouped together. Analyses of these groups can be used to study the evolutionary dynamics of selfish repetitive elements such as insertion sequences, but also for mutualistic repetitive elements such as REPINs.