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Temporal expression of Mycobacterium smegmatis respiratory terminal oxidases

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Terminal oxidases provide the final step in aerobic respiration by reducing oxygen. The mycobacteria possess two terminal oxidases: a cytochrome c aa 3 type and a quinol bd type. We previously isolated a bd-type oxidase knockout mutant of Mycobacterium smegmatis that allowed for functional analysis of the aa 3 type without the contribution of bd-type activity. Growth of M. smegmatis LR222 and JAM1 (LR222bd::kan) was monitored and the cytochrome content at different time points examined. No difference in aerobic growth was observed between M. smegmatis LR222 and JAM1. Membranes were obtained from these cultures and the oxidase concentrations were calculated from their spectrum. Although the mutant was producing only one oxidase type, this oxidase did not reach wild-type levels of expression, suggesting an additional mechanism for energizing the membrane. Moreover, the concentration of both oxidases in the wild-type strain dropped when cultures entered stationary phase, which was not the case for the aa 3-type oxidase of the mutant strain. This oxidase remained at a constant concentration post mid-log phase. RNase protection assays also demonstrated late growth phase dependent message expression of the bd oxidase and that the subunits I and II genes were cotranscribed as an operon.

Keywords: cytochrome c; cytochromes respiratoires; mycobacteria; mycobactéries; oxydase terminale; respiratory cytochromes; terminal oxidase; tuberculose; tuberculosis

Document Type: Research Article


Publication date: March 1, 2007

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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