Question

Describe some beneficial symbiotic relationships that bacteria form?

Answer 1

Nitrogen is essential for all plants and animals, but despite being surrounded by it--the element constitutes 79% of air on earth--only a few bacteria can absorb it directly from the environment. All other species are ultimately dependent on these microbes as a source. A new paper published this week in the open-access journal PLoS Biology investigates the genetics behind the symbiotic relationship between these nitrogen-fixing bacteria and plants, and presents evidence of specific genetic changes that might have led to the evolution of symbioses with nitrogen-fixing bacteria from a more ancient form of symbiosis.

About 80% of all land plants have a symbiotic relationship with fungi of the phylum Glomeromycota. The fungus penetrates cells in the plant's roots, and provides the plant with phosphates and other nutrients from the soil. This kind of symbiosis is called an arbuscular mycorrhiza, and evolved more than 400 million years ago. Professor Martin Parniske and colleagues started their study by looking at genes known to be involved in arbuscular mycorrhiza, to see whether they could find evidence of any specific genetic differences in plants that form symbioses also with nitrogen-fixing bacteria.

"In this so-called root nodule symbiosis bacteria live in the root cells of the host plants, where they bind elementary nitrogen from the air in special organs, the nodules," says Parniske. In return, the microbes get high-energy carbohydrates produced by photosynthesis in the host plant...
http://www.sciencedaily.com/releases/2008/03/080304075746.htm


Research suggests that the relationship between gut flora and humans is not merely commensal (a non-harmful coexistence), but rather a symbiotic relationship.[3] Though people can survive without gut flora,[4] the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful, pathogenic bacteria,[2] regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats...
http://en.wikipedia.org/wiki/Gut_flora

Answer 2

http://remineralize.org/blog/magazine/earthworms-and-bacteria-enjoy-a-symbiotic-relationship-with-rockdust