Electron transport and oxidative stress in Zymomonas mobilis respiratory mutants.
The ethanol-producing bacterium Zymomonas mobilis is of great interest from a bioenergetic perspective because, although it has a very high respiratory capacity, the respiratory system does not appear to be primarily required for energy conservation. To investigate the regulation of respiratory genes and function of electron transport branches in Z. mobilis, several mutants of the common wild-type strain Zm6 (ATCC 29191) were constructed and analyzed. Mutant strains with a chloramphenicol-resistance determinant inserted in the genes encoding the cytochrome b subunit of the bc (1) complex (Zm6-cytB), subunit II of the cytochrome bd terminal oxidase (Zm6-cydB), and in the catalase gene (Zm6-kat) were constructed. The cytB and cydB mutants had low respiration capacity when cultivated anaerobically. Zm6-cydB lacked the cytochrome d absorbance at 630 nm, while Zm6-cytB had very low spectral signals of all cytochromes and low catalase activity. However, under aerobic growth conditions, the respiration capacity of the mutant cells was comparable to that of the parent strain. The catalase mutation did not affect aerobic growth, but rendered cells sensitive to hydrogen peroxide. Cytochrome c peroxidase activity could not be detected. An upregulation of several thiol-dependent oxidative stress-protective systems was observed in an aerobically growing ndh mutant deficient in type II NADH dehydrogenase (Zm6-ndh). It is concluded that the electron transport chain in Z. mobilis contains at least two electron pathways to oxygen and that one of its functions might be to prevent endogenous oxidative stress.
Institute of Microbiology and Biotechnology, University of Latvia, Kronvalda boulv. 4, 1586 Riga, Latvia.
Inese
I
Strazdina
Zane
Z
Kravale
Nina
N
Galinina
Reinis
R
Rutkis
Robert K
RK
Poole
Uldis
U
Kalnenieks
D002374:Catalase / Q000235:genetics / Q000378:metabolism; D003578:Cytochrome-c Peroxidase / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009245:NADH Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D017355:Zymomonas / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D006861:Hydrogen Peroxide; D003578:Cytochrome-c Peroxidase; D002374:Catalase; C088908:NADH dehydrogenase II; D009245:NADH Dehydrogenase; D014450:Electron Transport Complex III; D010100:Oxygen