symbiosomes

Symbiosomes are specialized membrane-bound compartments within the cells of certain organisms that house symbiotic microorganisms. These structures are crucial for facilitating and maintaining symbiotic relationships, particularly in nitrogen fixation. In legumes, for example, symbiosomes are found in root nodules and contain nitrogen-fixing bacteria called rhizobia. The plant cell membrane encloses the rhizobia, forming the symbiosome. This enclosed environment provides a controlled setting for the bacteria to convert atmospheric nitrogen into ammonia, a form usable by the plant.

The formation of symbiosomes involves a complex interplay between the host plant and the symbiotic microbe. The plant releases signaling molecules that attract the bacteria. Upon recognition, the bacteria are enveloped by a plant membrane, forming a symbiosome. Inside the symbiosome, the bacteria undergo differentiation into bacteroids, which are the active nitrogen-fixing forms. The symbiosome membrane plays a vital role in regulating the exchange of nutrients and metabolites between the host cell and the bacteroids, ensuring the mutual benefit of the symbiosis. This compartmentalization protects the host cell from potential harm by the bacteria and allows for efficient nutrient transfer.