Isolation and characterization of a novel facultatively alkaliphilic Nitrobacter species, N. alkalicus sp. nov. |
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Authors: | Dimitry Y Sorokin Gerard Muyzer Thorsten Brinkhoff J Gijs Kuenen M S M Jetten |
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Institution: | (1) Institute of Microbiology, Russian Academy of Sciences, Prospect 60-let Octyabrya, 7/2, 117811 Moscow, Russia, RU;(2) Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-23539 Bremen, Germany, DE;(3) Kluyver Institute for Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands e-mail: m.jetten@stm.tudelft.nl Tel. +31-15-2781193; Fax +31-15-2782355, NL |
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Abstract: | Five strains of lithotrophic, nitrite-oxidizing bacteria (AN1-AN5) were isolated from sediments of three soda lakes (Kunkur
Steppe, Siberia; Crater Lake and Lake Nakuru, Kenya) and from a soda soil (Kunkur Steppe, Siberia) after enrichment at pH
10 with nitrite as sole electron source. Morphologically, the isolates resembled representatives of the genus Nitrobacter. However, they differed from recognized species of this genus by the presence of an additional S-layer in their cell wall
and by their unique capacity to grow and oxidize nitrite under highly alkaline conditions. The influence of pH on growth of
one of the strains (AN1) was investigated in detail by using nitrite-limited continuous cultivation. Under such conditions,
strain AN1 was able to grow at a broad pH range from 6.5 to 10.2, with an optimum at 9.5. Cells grown at pH higher than 9
exhibited a clear shift in the optimal operation of the nitrite-oxidizing system towards the alkaline pH region with respect
to both reaction rates and the affinity. Cells grown at neutral pH values behaved more like neutrophilic Nitrobacter species. These data demonstrated the remarkable potential of the new nitrite-oxidizing bacteria for adaptation to varying
alkaline conditions. The 16S rRNA gene sequences of isolates AN1, AN2, and AN4 showed high similarity (≥ 99.8%) to each other,
and to sequences of Nitrobacter strain R6 and of Nitrobacter winogradskyi. However, the DNA-DNA homology in hybridization studies was too low to consider these isolates as new strains. Therefore,
the new isolates from the alkaline habitats are described as a new species of the genus Nitrobacter, N. alkalicus, on the basis of their substantial morphological, physiological, and genetic differences from the recognized neutrophilic
representatives of this genus.
Received: 3 April 1998 / Accepted: 2 July 1998 |
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Keywords: | Nitrobacter Nitrite-oxidizing bacteria pH Alkaline environments Continuous culture |
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