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Journal of Bacteriology, June 1999, p. 3375-3381, Vol. 181, No. 11
Department of Fermentation Technology,
Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8527, Japan
Received 26 October 1998/Accepted 31 March 1999
Two plasmids were discovered in the ammonia-oxidizing bacterium
Nitrosomonas sp. strain ENI-11, which was isolated from
activated sludge. The plasmids, designated pAYS and pAYL, were
relatively small, being approximately 1.9 kb long. They were cryptic
plasmids, having no detectable plasmid-linked antibiotic resistance or
heavy metal resistance markers. The complete nucleotide sequences of pAYS and pAYL were determined, and their physical maps were
constructed. There existed two major open reading frames, ORF1 in pAYS
and ORF2 in pAYL, each of which was more than 500 bp long. The
predicted product of ORF2 was 28% identical to part of the replication
protein of a Bacillus plasmid, pBAA1. However, no
significant similarity to any known protein sequences was detected with
the predicted product of ORF1. pAYS and pAYL had a highly homologous
region, designated HHR, of 262 bp. The overall identity was 98%
between the two nucleotide sequences. Interestingly, HHR-homologous
sequences were also detected in the genomes of ENI-11 and the
plasmidless strain Nitrosomonas europaea IFO14298. Deletion
analysis of pAYS and pAYL indicated that HHR, together with either ORF1
or ORF2, was essential for plasmid maintenance in ENI-11. To our
knowledge, pAYS and pAYL are the first plasmids found in the
ammonia-oxidizing autotrophic bacteria.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Isolation and Characterization of Two Cryptic Plasmids in
the Ammonia-Oxidizing Bacterium Nitrosomonas sp.
Strain ENI-11
*
Corresponding author. Mailing address: Department of
Fermentation Technology, Hiroshima University, Higashi-Hiroshima,
Hiroshima 739-8527, Japan. Phone: 81-824-24-7756. Fax: 81-824-22-3758. E-mail: hohtake{at}ipc.hiroshima-u.ac.jp.
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