A Gram-negative, non-motile, psychrotolerant bacterium exhibiting high catalase activity, designated strain T-3-2 T , was isolated from a drain of a fish-processing plant. Its catalase activity was 12 000 U (mg protein) "1 , much higher than the activity of the other Psychrobacter strains tested. The strain grew at 0-30 6C and in the presence of 0-12 % NaCl. The predominant isoprenoid quinone was ubiquinone-8 (Q-8), and C 16 : 1 v9c and C 18 : 1 v9c were the predominant cellular fatty acids. The DNA G+C content of strain T-3-2 T was 43.9 mol%. 16S rRNA gene sequence phylogeny suggested that strain T-3-2 T is a member of the genus Psychrobacter, with the closest relatives being the type strains of Psychrobacter nivimaris (99.2 % similarity), P. aquimaris (98.7 %) and P. proteolyticus (98.5 %). DNA-DNA hybridization showed less than 65 % relatedness with these strains. A phylogenetic tree based on gyrB gene sequences was more reliable, with higher bootstrap values than the 16S rRNA gene sequence-based tree. The result also differentiated the isolate from previously reported Psychrobacter species. Owing to the significant differences in phenotypic and chemotaxonomic characteristics and the phylogenetic and DNA-DNA relatedness data, the isolate merits classification within a novel species, for which the name Psychrobacter piscatorii sp. nov. is proposed. The type strain is T-3-2 T (5JCM 15603 T 5NCIMB 14510 T ).
A psychrotolerant bacterium, strain T-3 (identified as Psychrobacter piscatorii), that exhibited an extraordinarily high catalase activity was isolated from the drain pool of a plant that uses H2O2 as a bleaching agent. Its cell extract exhibited a catalase activity (19,700 U·mg protein−1) that was higher than that of Micrococcus luteus used for industrial catalase production. Catalase was approximately 10% of the total proteins in the cell extract of the strain. The catalase (PktA) was purified homogeneously by only two purification steps, anion exchange and hydrophobic chromatographies. The purified catalase exhibited higher catalytic efficiency and higher sensitivity of activity at high temperatures than M. luteus catalase. The deduced amino acid sequence showed the highest homology with catalase of Psycrobacter cryohalolentis, a psychrotolelant bacterium obtained from Siberian permafrost. These findings suggest that the characteristics of the PktA molecule reflected the taxonomic relationship of the isolate as well as the environmental conditions (low temperatures and high concentrations of H2O2) under which the bacterium survives. Strain T-3 efficiently produces a catalase (PktA) at a higher rate than Exiguobacterium oxidotolerans, which produces a very strong activity of catalase (EktA) at a moderate rate, in order to adapt to high concentration of H2O2.
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