Project Summary

Diseases caused by mycobacteria, such as Mycobacterium tuberculosis, are some of the most significant causes of death worldwide. Pathogenic species of the bacterial genus Mycobacterium, including M. tuberculosis, carry these integrated viral genomes (prophage) that are hypothesized to contribute to virulence. Bacteriophage (phage) are viruses that infect bacteria.  Lysogenic phage are capable of inserting their genome into that of the bacterial hosts, often carrying genes that add function to the host cell leading to increased bacterial fitness and pathogenicity. Given that nearly all pathogenic bacteria contain prophage, understanding how phage alter pathogenicity and fitness in bacterial hosts is highly relevant to preventing and treating disease. Though we know many of the ways in which phage genes directly contribute to pathogenesis, e.g. CTX phage encodes the toxin in Vibrio cholera, we know little about the impact of phage that encode no obvious toxin or virulence gene.  Through RNAseq analysis of both pathogenic (M. chelonae) and non-pathogenic (M. smegmatis) mycobacterial species, we have determined that prophage significantly affect host gene expression.  The types of bacterial genes and pathways that are significantly up- or downregulated in the presence of prophage vary with the type of prophage; however, we have found that many of the most significantly upregulated genes in pathogenic mycobacteria potentially play roles in host fitness or virulence.  This presents us with an alternative mechanism for the role of prophage in host virulence and pathogenicity.  This project aims to characterize the impact of prophage on mycobacterial fitness and virulence by exploring the role of prophage activity in altering host gene expression. This proposed research will 1.) confirm the upregulation of mycobacterial genes of interest, particularly those that are homologues of M. tuberculosis virulence factors; 2) compare patterns of host differentially expressed genes induced by a single type of virus in multiple mycobacterial hosts; 3) characterize functional differences in mycobacteria that carry prophage such as their ability to survive in macrophage or their resistance to antibiotics; and 4) identify phage genes that potentially drive changes in host gene expression.

Relevance of Research

Tuberculosis, caused by bacteria of the genus Mycobacterium, is one the top ten causes of death worldwide.  The majority of pathogenic bacteria, including M. tuberculosis, carry viral genomes (prophage) within the bacterial genome that are thought to contribute to virulence. Determining how prophage within non-tuberculosis pathogenic mycobacteria contribute to virulence will provide opportunities to develop and improve treatment of bacterial diseases.

Sally Malloy at University of Maine