Facultative organisms

Denitrification is a process in which facultative organisms will reduce nitrate to nitrogen gas in the absence of molecular oxygen. This consequendy results in the removal of BOD. The denitrification process also generates one hydroxyl ion so that alkalinity requirements are reduced to half when both nitrification and denitrification are practiced. 

The destructive effect of dioxygen on the iron and molybdenum-iron proteins is thought to result from the oxidation of the clusters, and the formation of superoxide and peroxide which oxidize the proteins irreversibly. In view of this, it is remarkable that aerobic and facultative organisms can fix dinitrogen. The cyanobacteria evolve dioxygen photosynthetically and simultaneously fix dinitrogen 1447... 

In the following reductions are described with cells which do not show the briefly mentioned problems of yeasts applied in the classical way. All the strictly anaerobically grown cells of anaerobic or facultative organisms are able to accept hydrogen gas, many accept formate and some carbon monoxide as electron donors and contain redox enzymes in often high activities which take up the electrons and deliver them to viologens and other artificial mediators which transfer them further (Section 1.2). The standard redox potential E° of the electron delivering reactions... 

The minimal a at which growth will occur is lower under aerobic than anaerobic conditions for facultative organisms. For example, Scott (1953) demonstrated that the minimal a at which growth of S. aureus occurred was 0.86 under aerobic conditions and 0.92 under anaerobic conditions. 

The terms obligate and facultative are also used obligate organisms can only use that form of nutrition, whilst facultative can switch from one form to another. The most common example of facultative organisms is the algae, many of which are photo autotrophs in the light, but may be chemoheterotrophs in the dark. 

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