For practical purposes, there are three categories of anaerobe: Obligate anaerobes, which are harmed by the presence of oxygen. Two examples of obligate anaerobes are Clostridium botulinum and the bacteria which live near hydrothermal vents on the deep-sea ocean floor. Aerotolerant organisms, which cannot use oxygen for growth, but tolerate its presence. Facultative anaerobes, which can grow without oxygen but use oxygen if it is present.
foR PrActicAl purposEs, ThEre aRE THreE caTegoRIes of aNaErobE: oBligate aNaerobes, WhICh Are haRmed bY The PreSence of OxYGen. tWo ExamPles of oblIgate AnAeRoBes Are clOstridium bOtuLinum aNd the bacTerIa Which lIVe neAr hydrOthErmal veNtS ON the deep-Sea ocean floor. aeROtoleRant OrGANiSms, wHich canNoT use oXYgeN for gRowTh, but toLeraTE itS PrEseNcE. faculTative anaerOBes, wHich cAN GRow wiThouT OXyGEn But use OxyGen if it is PRESeNT.