Microbial Mergers: Collaborations on a Minute Scale

Over millions of years of evolution, we humans have worked out a mutually beneficial partnership with the microbes that came to inhabit our guts. In return for their aid in digestion, we give them a stable, protected home and plenty of nutrients via the food we eat. We need them as much as they need us.

Microbes break down food molecules our body’s enzymes and acids can’t dissolve, helping us squeeze all the nutrients out of our food. Some make valuable vitamins that our body needs.

Many microbial species have proved to be consummate evolutionary wheelers and dealers, arranging collaborations, mergers, and acquisitions that usually serve both partners well.

The pea root sends a chemical message that attracts Rhizobia, then surrounds the bacteria, which set up housekeeping inside the root’s cells. © Bert Dodson

MERGERS OF NOTE

Rhizobia are bacteria that form nodules on the roots of legumes to supply them with nitrogen; in return, the plants provide the bacteria with carbohydrates.

Mycorrhizae are soil-dwelling fungi that act as extensions of plants’ roots, enabling them to vastly increase their nutrient-absorbing network. The plants provide the fungi energy in the form of carbohydrates.

Zooxanthelle are photosynthetic algae that live inside the body tissues of coral polyps. They provide nutrients to their polyp hosts in exchange for a protected, stable environment and nutrients they need for growth.

Lichens are an alliance of fungi and algae that allows each to grow in environments where neither could survive alone, like deserts, rocks, or tree bark.