Characteristics of Newly Isolated Nitrifying Bacteria from Rhizoplane of Paddy Rice

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An ammonia-oxidizing bacterium, strain NRS 527 and nitrite-oxidizing bacterium, strain NRB 5220 were newly isolated from rhizoplane of paddy rice. The cells of strain NRS527 are spiral (0.2-0.3μm wide, with 3-6 turns), gram negative, obligately aerobic, and chemolithotrophic. Intracytoplasmic membranes, a characteristic of ammmonia-oxidizing bacteria are absent. The optimum concentration of ammonium sulfate (substrate) in the medium is 38mM. The G+C content of the total DNA is 59.18mol%. The similarity of 165 rRNA (%) to Nitrosospira briensis C-128 is 94.71. The supplemental effect of organic compounds could not be recognized. The cells of strain NRB5220 are rod shaped (0.5-0.8×1.0-2.0μm), gram negative, and obligately aerobic. The G+C content is 60.37 mol%. The similarity of 16S rRNA (%) to Nitrobacter agilis ATCC14123 is 97.38. The optimum concentration of sodium nitrite (substrate) in the medium is 22 mM. Growth of strain NRB5220 is hastened when peptone and yeast extract are added to the medium as nutrients. Both strains were resistant to tetracycline at 33μg/ml. The new nitrifying bacteria isolated from rhizoplane of paddy rice were identified as Nitrosospira sp. NRS527 and Nitrobacter sp. NRB5220.
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