Multiple choice Which of the following options is not free living nitrogen fixing bacteria? Anabaena Nostoc Azobacta Rhizobium Reveal answer Fill a bubble to check yourself D Correct answer Explanation Rhizobium is a symbiotic nitrogen-fixing bacteria that lives in root nodules of leguminous plants. Anabaena and Nostoc are free-living cyanobacteria, and Azobacta (likely Azotobacter) is a free-living soil bacteria.