The Anaerobic Reduction Of Nitrogenous Oxides By Bacteria From Thalassia Testudinum Sediments

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Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries


Dentrification by Thalassia testudinum sediments was measured with the acetylene (C(,2)H(,2)) blockage assay. Nitrogen fixation (C(,2)H(,2) reduction) and denitrification (N(,2)O production) were simultaneously measured without inhibiting fixation, when Thalassia testudinum sediment cores with 0.1 atm C(,2)H(,2) received 20 (mu)M nitrate additions. Denitrification was variable and could counteract much of the nitrogen contributed by fixation. Chemolithotrophic denitrifiers occurred in the sediments, but did not contribute significantly to endogenous denitrification. Although the denitrification assay failed during long term incubations (N(,2)O disappeared in the presence of C(,2)H(,2)), the assay for initial denitrification rates was valid. Failure of the assay was caused by denitrifiers of sufficient density and/or development confronted by a low redox potential and/or sulfide after the supplies of nitrate, nitrite, and oxygen were exhausted.Denitrifiers and organic N-oxide reducers were competitors that coexisted in the Thalassia testudinum sediments. The organic N-oxide reducing, and nitrate reducing populations were similar. The bacteria could use the same organics for growth and the oxidants suitable for anaerobic growth overlapped. However, the organic N-oxide reducing isolates were dissimilatory nitrate reducers, not denitrifiers. Thus, organic N-oxide enrichment was selective for dissimilatory nitrate reducers when denitrifiers were present.The organic N-oxide reducers reduced dimethyl S-oxide under aerobic and anaerobic conditions and they might maintain dimethylsulfide in aerobic seawater.The methodology for growth and assay of organic N-oxide reducers was greatly improved by substituting pyridine N-oxide (PNO) for trimethylamine N-oxide (TMO). PNO and TMO were interchangeable substrates for bacterial enrichment and isolation, but PNO was better for growth and enzyme assays. Using a new approach to measure organic N-oxide reduction, two simple, selective, sensitive, and rapid PNO reduction assays were developed. While traditional assays measure the oxidation of electron donors, the new assays replaced the oxidant (TMO), and measured PNO reduction. The new assays may be modified to assess fish quality during storage. The assays revealed DMSO and TMO immediately inhibited PNO reduction, while nitrate required more time to inhibit PNO reduction.


Biology, Microbiology

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