摘要：

We isolated four new ammonia-oxidizing bacterial strains from leucaena (Leucaena leucocephala) grown in fields of an acid sulfate soil (ASS) in Thailand; 17SS from the surface soil and 17RS from the rhizoplane of a non-limed plot; 9SS from the surface soil and 9RS from the rhizoplane in a limed plot. The cells of all strains had the typical lobate shape of the genus Nitrosospira ("Nitrosolobus"). The percentage similarity of the 16S rRNA genes of these strains to that of Nitrosospira ("Nitrosolobus") multiformis ATCC25196^T (ATCC25196^T) was 99.52% (strains 17SS, 17RS and 9SS) and 99.66% (strain 9RS). These newly isolated bacteria were all identified as Nitrosospira sp. Each strain, especially 17SS isolated from ASS, had higher urease activity than that of ATCC25196^T. The o-acetylserine(thiol)lyase activity of 17SS was the highest of all the isolates. At pH 6.0, every isolate and ATCC25196^T were able to utilize urea as the sole nitrogen source, in particular, strain 17SS grew best. The isolates from ASS showed higher urea utility than the isolates from the rhizoplane. Strain 17SS tolerated copper at levels up to 6.3mmol L^, but ATCC25196^T was inhibited at that concentration.

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