Anaerobe

Synonyms

Non-aerobic

Definition

Anaerobes are organisms that do not require oxygen to obtain energy or to grow. Anaerobic metabolism is restricted to microorganisms, both prokaryotic (Bacteria and Archaea) and eukaryotic (yeast, microsporidia), although an anaerobic multicellular organism (phylum Loricifera) has been recently discovered in marine sediments.

Overview

There are two main categories of anaerobic microorganisms: (1) facultative anaerobes that can use oxygen for respiration if it is present, but in its absence obtain energy from fermentation (such as enterobacteria or yeasts), anaerobic respiration (some Pseudomonas, Thiobacillus, Bacillus, and many others): and anoxygenic photosynthesis (some proteobacteria) (2) obligate anaerobes, which never use oxygen. These can, in turn, be divided into two subcategories: (a) strict or obligate anaerobes, for whom oxygen is poisonous (i.e., oxygen is extremely toxic to methanogens); and (b) aeroduric or aerotolerant anaerobes that can...