Evolutionary dynamics of rhomboid proteases in Streptomycetes

Proteolytic enzymes are ubiquitous and active in a myriad of biochemical pathways. One type, the rhomboids are intramembrane serine proteases that release their products extracellularly. These proteases are present in all forms of life and their function is not fully understood, although some evidence suggests they participate in cell signaling. Streptomycetes are prolific soil bacteria with diverse physiological and metabolic properties that respond to signals from other cells and from the environment. In the present study, we investigate the evolutionary dynamics of rhomboids in Streptomycetes, as this can shed light into the possible involvement of rhomboids in the complex lifestyles of these bacteria.

Analysis of Streptomyces genomes revealed that they harbor up to five divergent putative rhomboid genes (arbitrarily labeled families A-E), two of which are orthologous to rhomboids previously described in Mycobacteria. Characterization of each of these rhomboid families reveals that each group is distinctive, and has its own evolutionary history. Two of the Streptomyces rhomboid families are highly conserved across all analyzed genomes suggesting they are essential. At least one family has been horizontally transferred, while others have been lost in several genomes. Additionally, the transcription of the four rhomboid genes identified in Streptomyces coelicolor, the model organism of this genus, was verified by reverse transcription.

Using phylogenetic and genomic analysis, this study demonstrates the existence of five distinct families of rhomboid genes in Streptomycetes. Families A and D are present in all nine species analyzed indicating a potentially important role for these genes. The four rhomboids present in S. coelicolor are transcribed suggesting they could participate in cellular metabolism. Future studies are needed to provide insight into the involvement of rhomboids in Streptomyces physiology. We are currently constructing knock out (KO) mutants for each of the rhomboid genes from S. coelicolor and will compare the phenotypes of the KOs to the wild type strain.