Phylogenetic analysis of the bacterial intracellular R-body killer proteins indicates extensive horizontal gene transfer and signature Reb sequence motifs

The fascinating spiral proteinaceous structures named 'R-bodies' can be produced by a number of bacterial species and are known to cause the so-called 'killer-effect' in paramecia. The genetic determinants of the R-bodies are the 'reb genes', which are widespread among diverse proteobacteria, presumably due to horizontal gene transfer. However, the extent of their taxonomic spread, genetic sequence diversity, and gene cluster synteny has not been analyzed exhaustively using the present genetic databases. In this study we have performed an extensive genetic survey for Reb homologous proteins, including those in previously unknown taxa. Our study reveals key amino acids of Reb protein sequences that are highly conserved and may hint at the biological role of the individual Reb proteins. We also show that the genetic synteny of reb gene clusters is diverse but can be clustered into distinct groups. Further, we analyze possible horizontal gene transfer events and pathways for reb genes and indicate context with the bacterial habitat. By identifying key aspects of R-body spread and functionality with our genetic analysis we pave the way for more targeted lab experiments that will allow R-bodies to be used for biotechnological or biomedical applications.