Many are ecologically important chemoheterotrophs capable of metabolizing usual organic materials plus some which can't be used by other heterotrophs. Medically important ones are Mycobacterium leprae and M. tuberculosis . Streptomycin and other important antibiotics are obtained from this group. Some species are nitrogen fixers. Metabolic Diversity Among Bacteria Bacteria play a significant role in ecosystems .
Saprobes derive their nourishment from dead organic material.
Autotrophic bacteria derive energy from light or oxidation of inorganic molecules. Photoautotrophic bacteria use light as a source of energy and CO 2 as a source of carbon. Cyanobacteria use chlorophyll a and produce oxygen as a byproduct of noncyclic photophosphorylation. Heterotrophic bacteria - include most bacteria. These derive energy from the breakdown of organic molecules derived from other organisms.