This tutorial presented the diversity of prokaryotic nutritional modes and carbon sources. Bacteria can use simple sugars, as well as complex sources of carbon. Some bacteria can live off oil, and some can decompose cellulose. The ability to breakdown complex carbon sources has been utilized for a variety of purposes. The field of bioremediation is based, to a large extent, on the use of bacteria that can breakdown harmful compounds that have been introduced into the environment from various industrial and agricultural sources. For example, bacteria are capable of breaking down TNT and PCBs.
A great deal of life on the planet depends on prokaryotes, either directly or indirectly. Many prokaryotes form intimate associations with other species. These symbiotic relationships can take on a variety of forms. At one extreme are the mutualistic relationships. In a mutualistic symbiosis, both species derive benefit from the association; the bacteria that live in our lower digestive tract provide us with a number of vitamins and, in turn, we provide them with a source of carbon from the food we do not digest ourselves. At the other extreme is a parasitic symbiosis, in which the symbiont benefits at the expense of the host. Such parasitic bacteria are usually termed pathogenic because they can cause serious diseases. Microbiologists have provided us with an appreciation for prokaryotes, and their discoveries have led to new opportunities for using prokaryotes to better humanity and to combat diseases caused by pathogenic bacteria.
Prokaryotes are an important component of ecosystems. Many bacteria degrade material from dead organic matter, and in doing so make nitrogen and carbon available to other life forms. Without them, nutrients would quickly be tied up in the carcasses of dead organisms and unavailable for other organisms in the ecosystem.
We also examined the relationships between oxygen and metabolism, and later in the course we will explore, in more detail, the relationship between oxygen, energy and metabolic processes.