Nitrogen-fixing bacteria (Rhizobium leguminosarum) Science Image

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Coloured scanning electron micrograph (SEM) of Rhizobium leguminosarum nitrogen fixing bacteria (brown) in ruptured root nodule cells of a plant. These bacteria take nitrogen gas from the air and bind it up in compounds which the plant can use for its nutrition. They do this using an iron- containing protein called leghaemoglobin, similar to the haemoglobin found in red blood cells. The plant benefits from this symbiosis as it means they can grow in soils with a low nitrogen content, soils which are inaccessible to other plants. Magnification: x475 at 6x7cm size.