Potential Growth\nof Anammox Bacteria under Aerobic\nConditions

Anammox bacteria are obligate anaerobic bacteria that\nexist widely\nin nature with sufficient amounts of dissolved oxygen. However, whether\nanammox bacteria can grow under aerobic conditions remains unclear.\nIn this study, we found that the production of nitrate in the anammox\nsystem under aerobic conditions was significantly higher than that\nunder anaerobic conditions without total nitrogen loss. Anammox bacteria\ncan grow by oxidizing nitrite and dehydrogenating hydrazine to produce\nelectrons for carbon fixation. The hydrazine dehydrogenase in anammox\nbacteria was inhibited under aerobic conditions, and the nitrite oxidoreductase\ntranscription expression of anammox bacteria increased by 2.7 times\ncompared to that under anaerobic conditions, which was the main way\nfor anammox bacteria perform carbon fixation. DNA-stable isotope probing\nwith <sup>13</sup>C bicarbonate found the existence of anammox bacteria\nwith <sup>13</sup>C isotopes in aerobic cultivation, further proving\nthat anammox bacteria can grow under aerobic condition. More than\nhalf of the pathways in glycolysis, the Wood-Ljungdahl pathway, and\nthe tricarboxylic acid cycle were upregulated in anammox bacteria\nin aerobic condition. Large amounts of bacterioferritins are the important\nantioxidative enzymes in anammox bacteria in the aerobic environment,\nwhich contributes to their stronger oxygen adaptation than other anaerobes.\nThis study expands our understanding of the growth mechanism of anammox\nbacteria as well as the oxygen adaptation strategies of obligate anaerobic\nbacteria.