Superoxide free radicals , which are unstable and therefore toxic, are formed during normal respiration. Since H202 is also toxic, some organisms produce catalase to convert this peroxide into H20 and 02. Obligate anaerobes are not able to produce either. Aerotolerant anaerobes can t use oxygen, but produce SOD to neutralize the free radicals. Many ferment carbohydrates to lactic acid.
Microaerophilic organisms require less oxygen than is found in our atmosphere.
Certain of these, called Capnophiles, require decreased oxygen and higher C02. Autotrophs Utilize inorganic molecules for energy. Heterotrophs Utilize an organic carbon source for energy. Phototrophs Use light as their primary energy source. Usually autotrophic, but can also be heterotrophic.