Select the mismatch:

Amongst the given options Rhodospirillum- mycorrhiza is mismatched. Rhodospirillum is anaerobic, free-living nitrogen fixer. Mycorrhiza is a symbiotic relationship between fungi and roots of higher plants. Anabaena is a cyanobacteria which can fix atmospheric nitrogen. Rhizobium is a symbiotic bacterium with leguminous plants which helps Nitrogen fixation. Frankia is also another cyanobacteria which is associated with Alnus and helps in nitrogen fixation.