Evolution of PE35 and PPE68 Gene Families in Mycobacterium: Roles of Horizontal Gene Transfer and Evolutionary Constraints

Ashay Bavishi, Lin Lin, Madhusudan Choudhary, Todd P. Primm^*

Department of Biological Sciences, Sam Houston State University, Huntsville, USA.

DOI: 10.4236/jtr.2014.24023                

Abstract

Mycobacterium is a genus of bacteria with over a hundred non-pathogenic and pathogenic species, best recognized for certain members known to cause diseases such as tuberculosis and leprosy. Two novel protein families important in the pathogenesis of Mycobacterium species are the PE and PPE families. These two protein families affect the antigenic profiles, disturbing host immunity. To better understand the origin and evolution of these gene families and the differences in their composition between pathogenic and non-pathogenic strains, several bioinformatic analyses were conducted both among Mycobacterium and closely related species that contain PE35 and PPE68 gene homologs. The methods included protein homology searches (BLASTP), horizontal gene transfer analysis (IslandViewer), phylogenetic analysis, gene cluster analysis and structural and functional constraints. Results revealed that PE and PPE gene homologs were not only limited to Mycobacterium, but also existed in three other non-mycobacterial genera, Rhodococcus, Tsukamurella and Segniliparus, and were possibly initially acquired from non-mycobacterial microorganisms by multiple horizontal gene transfers. Results also demonstrated that PE and PPE genes were more diverse and more rapidly evolving in pathogenic Mycobacterium as compared with non-pathogenic Mycobacterium and other non-mycobacterial species. These findings possibly shed light on the diverse functions and origins of the PE/PPE proteins among these organisms.

Keywords

PE35, PPE68, Horizontal Gene Transfer, Mycobacterium

Conflicts of Interest

The authors declare no conflicts of interest.

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