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Abstract:
With increasing available results on molecular identification of ammonia and nitrite oxidizing
microorganism in hypersaline environment, there is a need for activity measurement of
nitrification process. The study was designed with the objective of quantifying activities of
ammonia and nitrite oxidizers in sediments of the Dead Sea and its underwater springs. To
achieve this, batch incubation of sediments and water samples was performed utilizing stable
isotope (15NH3 and 15NO3
-) tracer technique in slurry incubations with salinity of ~170. Utilizing
highly sensitive gas chromatography - isotopic ratio mass spectrometer (GC-IRMS); production
of 15NO2
- from 15NH3 varies between 0 – 1.76 nM/h across all sampled site for AO. Estimated
potential rate of AO and nitrite oxidation in the Dead Sea varies between 0 – 8.43 nM/h and 101
– 366 nM/h respectively. Nitrifying activities were higher in all sediments from the center of the
springs compared to sampled sites located at distance away from the spring. Underwater fresh
waters springs support microbial community of AO microbes and NOB in the Dead Sea through
favourable micro habitat. In this study, nitrite oxidation increased with increasing salinity. Nitrite
oxidizers in the Dead Sea are extreme halophiles, with heterotrophic nitrification as adaptation
mechanism. In general, the certainty of nitrification process occurring in the Dead Sea and its
underwater springs was based on high proportion of successful independent activity
measurement in relation to the total number of incubation performed. From this study,
nitrification activities were quantified in sediments from the Dead Sea, underwater springs and in
water column.
