rhizobies

Rhizobies are a group of Gram-negative bacteria that are well-known for their symbiotic relationship with legumes. This association, called symbiosis, is a mutually beneficial partnership where both the bacteria and the plant gain something essential. The rhizobies are capable of converting atmospheric nitrogen, which is unusable by plants, into ammonia, a form that legumes can absorb and utilize for growth. This process, known as biological nitrogen fixation, significantly enhances the fertility of the soil where legumes are grown, reducing the need for synthetic nitrogen fertilizers.

The symbiotic relationship begins when legume roots release chemical signals that attract rhizobies from the soil. The bacteria then enter the root hairs, triggering the formation of specialized structures called nodules. Within these nodules, the rhizobies proliferate and differentiate into bacteroids, the form in which they perform nitrogen fixation. The plant provides the bacteria with carbohydrates for energy and a protected environment, while the bacteria supply the plant with essential nitrogen. This partnership is vital for many agricultural systems, particularly in sustainable farming practices. Different species of rhizobies are specific to particular legume hosts, forming a complex and ancient ecological alliance.