Phenotypic differences between Edwardsiella piscicida and Edwardsiella anguillarum isolates in Japan.

OBJECTIVE: Edwardsiella tarda has been regarded as the causative agent of edwardsiellosis in cultured marine and freshwater fish species in Japan. Our previous study genetically classified an E. tarda-like isolate from diseased Olive Flounder Paralichthys olivaceus as E. piscicida and that from diseased Red Seabream Pagrus major as E. anguillarum. This study aimed to understand the phenotypic differences between E. piscicida and E. anguillarum. METHODS: Fourteen E. piscicida and seven E. anguillarum isolates were used in this study. The colonies of each isolate were grown on brain-heart infusion agar plates and then subjected to DNA extraction. The extracted DNA was amplified using PCR. carbohydrate fermentation of the isolates was examined using API 50 CH test kits. Moreover, the growth of the two species was examined in defined media. Also, free amino acids in Olive Flounder and Red Seabream sera were detected and quantified via high-performance liquid chromatography-mass spectrometry. Statistical differences in the concentrations of free amino acids were analyzed using Welch's t-tests. RESULT: The API 50 CH test revealed that L-arabinose and D-mannitol were fermented by E. anguillarum isolates but not E. piscicida isolates. Furthermore, the growth of E. piscicida and E. anguillarum was reduced in the defined medium without methionine and iron sulfate. The growth of E. piscicida was reduced in the defined medium without phenylalanine, tyrosine, alanine, or nicotinic acid, whereas the growth of E. anguillarum was reduced in the defined medium without serine, cysteine, leucine, threonine, or isoleucine. Tyrosine and alanine were present in higher concentrations in the Olive Flounder serum, whereas threonine and isoleucine were present in higher concentrations in the Red Seabream serum, suggesting favorable growth conditions for E. piscicida and E. anguillarum. CONCLUSION: This study characterizes a minimal defined medium that can be used for developing vaccines against E. piscicida and E. anguillarum.

Draft Genome Sequences of Two Edwardsiella piscicida Strains, JF1307 and JF1411, Isolated from Diseased Olive Flounder (Paralichthys olivaceus) Cultured in Japan.

Edwardsiella piscicida strains JF1307 and JF1411 were isolated from cultured olive flounder that were diagnosed as being infected with edwardsiellosis. The draft genome sequences of the two isolates comprise 3,882,000 bp and 3,827,424 bp with G+C contents of 59.5% and 59.6%, respectively.

Draft Genome Sequence of Vibrio harveyi Strain GAN1709, Isolated from Diseased Greater Amberjack (Seriola dumerili) Farmed in Japan.

Vibrio harveyi strain GAN1709 was isolated from a diseased greater amberjack farmed in Nomi Bay, Japan. Here, we report the draft genome sequence of this strain, which comprises 6,265,473 bp, with a G+C content of 44.8%.

Genotypic characteristics of a Mycobacterium sp. isolated from yellowtail Seriola quinqueradiata and striped jack Pseudocaranx dentex in Japan.

In Japan, a Mycobacterium marinum-like mycobacterium was isolated from the yellowtail, Seriola quinqueradiata. The species was identified as M. marinum by a commercial mycobacterial DNA-DNA hybridization kit. Nevertheless, PCR restriction analysis of the DNA of its RNA polymerase ß-subunit gene definitively showed that this Mycobacterium sp. was M. ulcerans. PCR analysis revealed the genotypic characteristics of M. ulcerans in the Mycobacterium sp., only the mup053 gene sequence being absent, as has been found previously in other piscine mycobacteria such as M. marinum strains DL240490 and DL045 and M. pseudoshottsii. With one exception, this Mycobacterium sp. and M. pseudoshottsii had identical 16S rRNA gene sequences, which is also probably true of M. marinum strains DL240490 and DL045. Similarly, according to comparisons of the 16S rRNA gene, ITS region, and hsp65 gene sequences, this Mycobacterium sp. is more closely related to M. pseudoshottsii than to M. ulcerans or M. marinum. A PCR product of approximately 2000 bp was amplified from region of difference 9 in the Mycobacterium sp. The nucleotide sequence revealed insertion of IS2404, the sequence of which is 1366 bp long. The novel single nucleotide polymorphisms identified in this region distinguished this Mycobacterium sp. from M. marinum strain DL240490 and M. pseudoshottsii. The present findings raise the possibility that these species have a common ancestor. Further studies are required to improve our understanding of the relationship between their geographical origin and genetic diversity.

Morphological changes contribute to apoptotic cell death and are affected by caspase-3 and caspase-6 inhibitors during red sea bream iridovirus permissive replication.

Red sea bream iridovirus (RSIV) of the Iridoviridae family is a causative agent of lethal infections in many cultured marine fish species in southwestern Japan. RSIV-induced apoptosis was divided as follows: (1). cell shrinkage and rounding at the early apoptotic stage, (2). cell enlargement at the middle apoptotic stage, (3). formation of apoptotic body-like vesicles at the late apoptotic stage and phagocytosis by neighboring cells, and (4). loss of membrane integrity in apoptotic body-like vesicles without phagocytosis by neighboring cells. By affinity labeling, RSIV-induced apoptosis included caspase-dependent apoptosis. RSIV infection caused cell rounding but not cell enlargement or formation of apoptotic body-like vesicles and further restricted part of the structural protein synthesis in the presence of caspase-3 and -6 inhibitors. These findings showed the involvement of caspase-3 and -6 in the morphological changes at the middle and late apoptotic stages and viral protein synthesis in the late stage of RSIV infection.