Pathogenic Neisseria: Neither Aerobes nor True Anaerobes, but Dedicated Microaerophiles
J. A. Cole
from: Pathogenic Neisseria: Genomics, Molecular Biology and Disease Intervention (Edited by: John K. Davies and Charlene M. Kahler). Caister Academic Press, U.K. (2014)
Neisseria meningitidis and N. gonorrhoeae are found in contrasting sites in the human body. Meningococci are rarely oxygen-deficient, but in women, gonococci become trapped in biofilms surrounded by anaerobic, fermentative bacteria. When starved of oxygen, both species exploit low levels of nitrite for energy generation and substrate oxidation. However, too little is known about whether they are able to exploit oxidants other than nitrite and nitric oxide to survive in anaerobic environments. Although five proteins have been implicated in resistance to nitrosative stress, only for two of them has the mechanism of protection been defined. These are the nitric oxide-binding cytochrome c′, and the di-iron protein, DnrN. Both pathogens maintain very high respiration rates: multiple mechanisms contributing to defense against oxidative stress have been identified. Only subtle differences between them have so far been identified. They include the meningococcal transcription factor, FNR, which regulates adaptation to anaerobic growth, that is more tolerant to oxygen than the gonococcal FNR. The truncated denitrification pathway is totally conserved in gonococci but not in all meningococcal strains. Only in the gonococcus is there an FNR-activated cytochrome c peroxidase, and a third heme group on the cytochrome oxidase CcoP subunit that contributes significantly to electron transfer from the cytoplasmic membrane to the nitrite reductase in the outer membrane. Finally adhC, which encodes a functional S-nitrosoglutathione reductase in the meningococcus, is a pseudogene in the gonococcus. It is proposed that both species have evolved a microaerobic rather than a fully aerobic or anaerobic metabolism: both can adapt to periods of oxygen starvation, but this ability appears to be more important for the gonococcus than for the meningococcus read more ...