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The remaining bacteria listed do not form endospores. [5] Several species of the Mycobacterium, Streptomyces, and Rhodococcus genera are examples of obligate anaerobe found in soil. [10] Obligate anaerobes are also found in the digestive tracts of humans and other animals as well as in the first stomach of ruminants. [11]
[5] [6] 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. [7] Facultative anaerobes, which can grow without oxygen but use oxygen if it is present. [7]
Bacteroides is a genus of Gram-negative, obligate anaerobic bacteria. Bacteroides species are non endospore–forming bacilli, and may be either motile or nonmotile, depending on the species. [3] The DNA base composition is 40–48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids.
A unique obligate aerobe is Streptomyces coelicolor which is gram-positive, soil-dwelling, and belongs to the phylum Actinomycetota. [7] It is unique because the genome of this obligate aerobe encodes numerous enzymes with functions that are usually attributed to anaerobic metabolism in facultatively and strictly anaerobic bacteria. [7]
Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube. A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O 2 ; typically 2–10% O 2 ) for optimal growth. [ 1 ]
Anaerobic bacteria can be identified by growing them in test tubes of thioglycollate broth: 1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest.
Anaerobic bacteria can be divided into strict anaerobes that can not grow in the presence of more than 0.5% oxygen and moderate anaerobic bacteria that are able of growing between 2 and 8% oxygen. [1] Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen.
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. [1] [2] Some examples of facultatively anaerobic bacteria are Staphylococcus spp., [3] Escherichia coli, Salmonella, Listeria spp., [4] Shewanella oneidensis and Yersinia ...