Elucidation of the aerobic respiratory chains in mycobacteria
Date
2006-10-27T07:51:11Z
Authors
Matsoso, Limenako
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Abstract
The aerobic respiratory chain of mycobacteria consists of at least two branches, a
cytochrome c branch terminating in an aa3-type cytochrome c oxidase, and a quinol
branch terminating in cytochrome bd oxidase. The structure and function of the former
branch, leading from the menaquinone-menaquinol pool to the cytochrome bc1 complex
and terminating in the aa3-type cytochrome c oxidase, was characterized in
Mycobacterium smegmatis. Allelic exchange mutants of M. smegmatis in the bc1
complex (ΔqcrCAB::hyg) and in subunit II of the aa3-type cytochome c oxidase
(ΔctaC::hyg) were constructed and analyzed for growth, and gene expression using lacZ
reporter assays and genome expression profiling by DNA microarray. Both mutants were
found to be profoundly growth impaired. Disruption of this pathway resulted in an
adaptation of the respiratory network that is characterized by a marked up-regulation of
cydAB, which encodes the bioenergetically less-efficient and microaerobically induced
cytochrome bd-type menaquinol oxidase that is required for the growth of M. smegmatis
under O2-limiting conditions. Other adaptations to re-routing of the electron flux through
the branch terminating in the bd-type oxidase were revealed by comparative expression
profiling of the bc1-deficient mutant and its parental wild type strain using a partialgenome
microarray of M. smegmatis that is enriched in essential genes. The majority of
the genes up-regulated in the mutant are involved in intermediary metabolism and
respiration. Also induced were several genes including, uspL and a homologue of
Rv1592c, which were previously shown to be up-regulated by hypoxia in M. smegmatis
(uspL) and M. tuberculosis (uspL and Rv1592). The cytochrome bc1-aa3 branch is
required for growth of M. smegmatis under aerobic conditions and its disruption results in
growth attenuation and up-regulation of cytochrome bd oxidase.
Description
Faculty of science
School of Pathology
9602685e
limenako.matsoso@nhls.co.za
Keywords
aerobic, structure, function, growth, DNA