obligate aerobes require oxygen by using cellular respiration or fermentation in order to survive. obligate anaerobes do not require it and will die if they are exposed to oxygen.
An Archean extremophile that is not only tolerant of water with a high salt concentration but must live in such an environment to carry out metabolic processes and survive.
According to the Wikipedia article at: http://en.wikipedia.org/wiki/Obligate_anaerobe there are several reasons that obligate anaerobes are killed by oxygen. One common answer, that they do not have...
Clostridium tetani is an example of an obligate anaerobe. It can survive as a spore in the presence of oxygen, however, vegetative cell growth can only happen in the absence of oxygen. This is why...