Rhizobia Nodule (IMAGE) Penn State Caption Colonizing bacteria that supply nitrogen to legumes -- rhizobia, reside in protective nodules formed by the plant. The bright red color of the opened nodule is an indication of healthy rhizobia inside. Credit Jennifer Dean Usage Restrictions Non advertising use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.