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. They may be facultative anaerobes , obligate anaerobes or aerobes. Photoheterotrophic bacteria- include purple nonsulfur bacteria. These use light as a source of energy but obtain carbon from organic molecules.