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UNESCO-IHE Institute for Water Education, Delft (2016)

Exploring the metabolic versatility of Nitrococcus mobilis

Torun, F.

Titre : Exploring the metabolic versatility of Nitrococcus mobilis

Auteur : Torun, F.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2016

Résumé
Nowadays there is an increasing worldwide concern about anthropogenic alterations in the global nitrogen cycle. The high load of nitrogen input from sewage and wastewater treatment plants can cause tremendous environmental damages such as algal blooms and eutrophication by causing a threat to the aquatic life and increasing concerns about global warming. Nitrification including nitrite oxidation, is a key process to remove nitrogen from sewage in biological wastewater treatment plants. However nitrite oxidizing bacteria (NOB) have scarcely been studied since NOB have been considered as physiologically limited organisms whose metabolisms have been restricted to chemolithoautotrophic nitrite oxidation. In contrast, new discoveries have enlightened unexpected metabolic versatilities of NOB, indicating a new basis for future studies. In present study, metabolic versatility of a rarely studied marine NOB, Nitrococcus mobilis has been investigated. N. mobilis is highly abundant in suboxic marine environment, however it appears to thrive using alternative metabolisms than nitrite oxidation to gain energy under oxygen limited conditions (Füssel et al., 2012). Therefore utilization of possible organic carbon sources by N. mobilis was investigated conducting anaerobic batch experiments under denitrifying conditions and testing respective substrates using oxygen microrespirometry. Based on our results, it was seen that N. mobilis could perform nitrate reduction by using carbon sources such as peptone and possibly yeast extract, however it could not further reduce nitrite to NO or N2O. Moreover oxygen microrespirometry tests also indicated that cysteine could be utilized by N. mobilis under aerobic conditions. However the growth of N. mobilis in the presence of these organic substrates, still needs to be investigated. The potential of N. mobilis to oxidize sulfide aerobically and anaerobically has been investigated as an alternative metabolism. N. mobilis could oxidize sulfide under aerobic conditions and appears to oxidize it anaerobically by coupling it with nitrate reduction. However no growth could be observed from anaerobic sulfide oxidation incubations in the current study. In a comparative study, a globally distributed NOB, Nitrospira moscoviensis was also tested for its ability to oxidize sulfide under aerobic conditions. It was observed that Ns. moscoviensis might oxidize sulfide aerobically and appears to grow using sulfide as a sole electron donor. The ability of Ns. moscoviensis to perform anaerobic sulfide oxidation remains a puzzle to be investigated in the future research.

Sujets  : microorganisms wastewater treatment plants nitrate oxidizing bacteria (NOB) Microbiology

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