bacterial species have evolved over millions of years to fill almost every available environmental niche on this planet. despite this impressive radiation, bacteria are still limited by the availability of carbon and nitrogen sources for their metabolisms. bacteria may express many different proteins required for uptake and utilization of these compounds for use in their metabolisms. organic compounds containing carbon and nitrogen are required for both anabolic and catabolic reactions that comprise a cell’s metabolism. not all bacterial species have the same abilities, so you can use this characteristic to differentiate bacterial species by determining which carbon- and nitrogen-containing media support the growth of the bacteria.