• (n. pl.) Anaerobic bacteria. They are called facultative anaerobia when able to live either in the presence or absence of free oxygen; obligate, or obligatory, anaerobia when they thrive only in its absence. Found on http://thinkexist.com/dictionary/meaning/anaerobes/
1) Bacteria 
• (n. pl.) Anaerobic bacteria. They are called facultative anaerobia when able to live either in the presence or absence of free oxygen; obligate, or obligatory, anaerobia when they thrive only in its absence.