Abstract
Comparative genome analyses have revealed a number of regions of difference (RD) among mycobacterial species. The functional consequences of most of these genome variations have not been studied. RD4, which encompasses Rv1506c-Rv1516c of Mycobacterium tuberculosis (M. tb) H37Rv, is absent in the closely related Mycobacterium bovis and M. bovis Bacille Calmette-Guérin (BCG). On the other hand, we previously found that Mycobacterium marinum has an extended RD4 which includes a number of genes involved in the biosynthesis of lipooligosaccharides (LOSs). As such, there appears to be a gradual decay of RD4 in mycobacterial genomes in the order of M. marinum, M. tb, and M. bovis (including BCG). To understand the potential effect of RD4 on mycobacterial virulence, in this study, we cloned the entire (Rv1501–1516c) and partial (Rv1501–1508c) RD4 into an integrating vector. These constructs were introduced to M. bovis BCG and M. marinum and the virulence of the RD4 knock-in strains were evaluated in the SCID mice and zebrafish infection models, respectively. BCG containing the entire RD4 exhibited similar levels of virulence to the parental strain but BCG containing partial RD4 (Rv1501–Rv1508c) was more attenuated. Similarly, zebrafish infection experiments showed that addition of partial RD4 also appeared to attenuate the virulence of M. marinum. However, M. marinum containing entire RD4 was more virulent than the wild type strain. Interestingly, BCG strains containing the entire or partial RD4 exhibited better protection of zebrafish against M. marinum challenge than the parental BCG. Taken together, our data suggest that RD4 plays a role in mycobacterial virulence and that RD4 knock-in BCG strains confer improved protection. Our study has provided new insights into the biological function of RD4 and evolution of mycobacterial genomes.
Highlights
The Mycobacterium tuberculosis (M. tb) complex (MTBC) comprises a group of closely related subspecies that shares 99.9% identical genome sequences but differs widely in terms of host tropisms and pathogenicity
Results showed that Rv1501 and Rv1507c transcripts were detected in all knock-in strains, while Rv1516c was expressed only in the strains containing the entire RD4
The RD4 of M. tb H37Rv is present in most members of the MTBC including all the examined strains of M. tb, M. africanum, M. canettii, and M. microti (Brosch et al, 2002)
Summary
The Mycobacterium tuberculosis (M. tb) complex (MTBC) comprises a group of closely related subspecies that shares 99.9% identical genome sequences but differs widely in terms of host tropisms and pathogenicity. These include the human-adapted M. tb, Mycobacterium africanum, and Mycobacterium canettii and the animal-adapted M. bovis, Mycobacterium caprae, Impact of RD4 on BCG. Compared to M. tb H37Rv, 14 regions of difference (RD1-14), ranging in size from 2 to 12.7 kb, are absent in the genome of M. bovis BCG-Pasteur (Mahairas et al, 1996; Brosch et al, 1998, 2002; Behr et al, 1999; Gordon et al, 1999; Mostowy et al, 2003). Analyses of the distribution of these variable genome regions in multiple MTBC strains isolated from different human populations and diverse animal species have established the genetic lineage of the MTBC (Brosch et al, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
