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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]
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]
However, this classification has been questioned after recent research showed that human "obligate anaerobes" (such as Finegoldia magna or the methanogenic archaea Methanobrevibacter smithii) can be grown in aerobic atmosphere if the culture medium is supplemented with antioxidants such as ascorbic acid, glutathione and uric acid. [8] [9] [10] [11]
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.
Obligate aerobes need oxygen to grow. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) and generate energy. [6] Facultative anaerobes use oxygen if it is available, but also have anaerobic methods of energy production. [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 ]
Clostridium is a genus of anaerobic, Gram-positive bacteria.Species of Clostridium inhabit soils and the intestinal tracts of animals, including humans. [1] This genus includes several significant human pathogens, including the causative agents of botulism and tetanus.