One of the most important of these services is to provide the energy needed to carry out the metabolic activities necessary to all living organisms. Microbes are essential for the recycling of elements so they can be used over and over again. The cycles of elements are called biogeochemical cycles. In the carbon cycle, carbon atoms are transferred from organism to organism.
Bacteria have essential roles in the nitrogen cycle.
All organisms require organic molecules containing nitrogen atoms, but only certain bacteria can convert nitrogen in the atmosphere to forms that are accessible to other organisms. Without the nitrogen-fixing activities of these bacteria, nitrogen would eventually become locked up in the atmosphere and life as we know it would cease. Ecology is the study of the interrelationships of organisms with each other and with their environment. Therefore, natural populations of microorganisms are used in the experiments in this manual. For years, microbiology focused on isolating pure cultures of microbes.