Role of Orphan ParA Proteins in Replication and Cell Division in <i>Rhodococcus erythropolis</i> PR4

Bacteria have a very well-regulated mechanism for chromosome segregation and cell division. This process requires a large number of complex proteins to participate and mediate their functionality. Among these complex proteins, ParA and ParB play a vital role for the faithful segregation of chromosome. In Rhodococcus erythropolis PR4, besides the essential parAB operon, there are three orphan copies of parA genes. Here, we report that the orphan ParA2 and ParA3 have distinct roles in the cell cycle. The disruption of the orphan parA2 or parA3 gene resulted in elongated cells. Multiple septal rings and mislocalised septa were observed in ΔparA3 and ΔparA2 mutants, respectively. The subcellular localization of ParA2 revealed a distinct ring- and ribbon-like structure. On the other hand, orphan ParA3 was localized slightly away from the poles. The orphan ParA proteins were found to interact with ParB, the strongest interaction was observed with ParA2. Further, asynchronous replication initiation was observed in ΔparA3 mutants suggesting its role in replication. This is the first report demonstrating the distinct roles of orphan parA genes from Rhodococcus.