Masayo Okuzumi

Photobacterium histaminum sp. nov., a Histamine-Producing Marine Bacterium

A total of 23 strains of halophilic histamine-producing bacteria previously isolated from marine fish and seawater were studied phenotypically, genotypically, and phylogenetically. These organisms are facultatively anaerobic, gram-negative, short rods that are motile by means of one to three unsheathed polar flagella. They are mesophilic and nonluminescent, produce oxidase, utilize d-glucose but not d-mannitol as a carbon and energy source, and accumulate poly-β-hydroxybutyrate. The guanine-plus-cytosine contents of the DNAs are ca. 41 mol%. Genomic DNA hybridization experiments revealed that some of the isolates exhibited low levels of reassociation (less than 40%) with previously described Photobacterium species. 16S rRNA gene sequence information confirmed the phylogenetic position of one of the isolates, strain C-8T (T = type strain), as a member of the genus Photobacterium. Therefore, we concluded that these organisms are members of a new species of the genus Photobacterium and propose the name Photobacterium histaminum sp. nov. for them. The type strain is strain C-8 (= JCM 8968).

Marinospirillum gen. nov., with descriptions of Marinospirillum megaterium sp. nov., isolated from kusaya gravy, and transfer of Oceanospirillum minutulum to Marinospirillum minutulum comb. nov.

Two strains of helical, halophilic, Gram-negative, heterotrophic bacteria were isolated from kusaya gravy which is a traditional Japanese fermented brine. These strains were motile by means of a single polar or bipolar tuft flagellum. They had a large cell size, were helical, formed coccoid bodies, were microaerophilic and had quinone type Q-8. The DNA G + C content of the strains was 44-45 mol %. A detailed investigation of the phenotypic, chemotaxonomic and phylogenetic characteristics of the strains revealed that they represent a new species of halophilic helical bacteria. The sequence of the 16S rRNA gene of strain H7T, designated the type strain of the new isolates, and all of the Oceanospirillum species except for Oceanospirillum linum were determined. Phylogenetic analysis indicated that these strains were closely related to Oceanospirillum minutulum, with enough distance to separate the O. minutulum/new isolate H7T cluster from Oceanospirillum sensu stricto on the genus level. It is proposed that a new genus, Marinospirillum, be created; this genus should include Marinospirillum minutulum ATCC 19193T (formerly Oceanospirillum minutulum) as the type species, as well as Marinospirillum megaterium JCM 10129T (= H7T).

Viability and Histidine Decarboxylase Activity of Halophilic Histamine-Forming Bacteria During Frozen Storage

The specific activity of histidine-decarboxylase of halophilic histamine-forming bacteria, Photobacterium phosphoreum and Photobacterium histaminum sp. nov., remained 27~53% of the initial value after seven days storage at -20°C, while the viable cells decreased by more than 6 log cycles of the initial counts. This finding suggests the possibility that outbreaks of scombroid fish poisoning are caused by the ingestion of frozen-thawed fish and its products, even when the viable count of histamine-forming bacteria is low.

Studies on Biochemistry of the Thiobacilli:Part VI. Oxidation of Thiosulfate to Tetrathionate by T. thiooxidans

In the oxidation of thiosulfate at pH 4.5 tetrathionate was formed as an intermediate, and the thiosulfate-oxidizing enzyme was active in acidic pH range in contrast to the enzyme of T. thioparus and Thiobacillus X.Phosphate did not seem to affect the oxidation of thiosulfate but rather affect the conversion of tetrathionate. In the absence of phosphate, tetrathionate, which was produced from thiosulfate oxidation, seemed to accumulate without undergoing further conversion.Quantitative oxidation of tetrathionate to sulfate was achieved with freshly harvested cells of T. thiooxidans; pH optimum for the oxidation of tetrathionate by the washed cells was 2~3, and the activity fell markedly at pH above 3.5.Tetrathionate might be enzymatically dismuted to pentathionate and trithionate under anaerobic conditions with crude extracts of T. thiooxidans; pH optimum for the reaction was about 2.7 and the activity fell strikingly at pH 4.7. The formed trithionate might be further hydrolyzed to thiosulfate and sulfate.

Effect of Culture Conditions on Bacterial Production of Tetrodotoxins.

The effect of various culture conditions on tetrodotoxins formation was studied using a strain F-9 isolated from the puffer fish Takifugu rubripes. The strain was identified as that similar to Vibrio nereis. The TTXs formation by the strain was proved by GC/MS analysis and the major toxin was identified as 4-epi TTX by HPLC. ORI medium gave a high toxin formation. Cells in the stationary phase showed a high toxicity. As compared with static culture, shaking culture was suitable for high toxin formation. Optimum temperatures for both growth and toxin formation were 27.5°C, but optimum NaCl concentrations for growth and toxin formation were 3 and 5%, respectively. These results suggested that various culture conditions influenced the productive ability of tetrodotoxins in the strain.