The difference between aerobic and anaerobic bacteria

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