The difference between aerobic and anaerobic bacteria

Two broad groups, five classes

By their relationship to oxygen, microorganisms divide into aerobic and anaerobic types, further split into five classes.

The five classes

Obligate aerobes (e.g. Bacillus, nitrifying bacteria, most fungi and actinomycetes); facultative anaerobes (grow mainly aerobically, also without oxygen — many yeasts); microaerophiles (e.g. Vibrio — grow only at low oxygen partial pressure); aerotolerant anaerobes (no oxygen needed, but molecular oxygen is not harmful); and obligate anaerobes, which are inhibited or killed even by brief oxygen contact and obtain energy through fermentation and anaerobic respiration (e.g. bifidobacteria, photosynthetic bacteria).