Abstract

A cryptic plasmid pSFKW33 from psychrotrophic bacterium Shewanella sp. 33B, an isolate from the Gulf of Gdansk (the Baltic Sea), was sequenced and characterized. It is an 8021 bpcircular molecule with 38% GC content, which shows a distinctive nucleotide sequence without homology to other known plasmids. The nucleotide sequence analysis predicts eight open reading frames. The deduced amino acid sequence of ORF-1 shared significant similarity with the phage integrase protein from Pseudomonas putida GB-1. The ORF2 product showed some similarity with the hypothetical protein Shal_1786 from Shewanella halifaxensis HAW-EB4. The ORF-3 product revealed high amino acid sequence homology with the Escherichia coli replication initiation protein similar to pi protein of R6K plasmid. Five repeat regions (three perfect 22-bp repeats and two imperfect motifs), a putative ribosome binding site, and -10 and -35 promotor sequences were identified upstream of the ORF-3(rep). The rep module is very similar to several theta replicating iteron family plasmids,suggesting that pSFKW33 replication follows the same course. The ORF-5 product revealedsignificant identity with the entry exclusion protein 1 of plasmid pIS2 from enteropathogenicstrain E. coli 0111:H. The ORF-6 product showed significant identity with the putativetranscriptional regulator protein from Shewanella benthica KT99 belonging to HTH-XREfamilyprotein. The ORF-8 encoded protein that showed some similarity with the hypotheticalprotein KT99_00146 from Shewanella benthica KT99. The ORF-4 and ORF-7 encodedputative proteins of 189 and 118 amino acid residues, respectively, with no homologiesto any known proteins. The absolute copy number of pSFKW33 was estimated to be fivecopies per chromosome by real-time PCR.

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