A new species, Aphanomyces salsuginosus sp. nov., isolated from ice fish Salangichthys microdon

Abstract

A species of Aphanomyces was isolated from the ice fish Salangichithys microdon living in brackish water in Japan. White cotton-like growth was found on the heads and fins of the fish. Hyphae penetrated into the dermal layers, subcutaneous tissues, muscular layers, and cartilaginous tissue of the mandible and maxilla; these hyphae were associated with cellular debris and lesions in host tissue. White fluffy colonies from subcultures of these growths were isolated on glucose-yeast agar plates with 0.5% sodium chloride (NaCl). These isolates consisted of delicate, slightly wavy, and moderately branched hyphae. Zoosporangia were isodiametric with the vegetative hyphae. Oogonia were abundant and approximately 21-33 lm in diameter, with irregular short papillae. Generally they were spherical or subspherical and only rarely pyriform. Individual oogonia usually contained a single oospore, which was spherical and 19-27 lm in diameter, with a large shiny vesicle. Antheridial branches, when present, were usually androgynous; however, they were sometimes monoclinous or diclinous. The optimal growth temperature of the isolates was 20°C, and cultures grew well at low salinity (0-0.5% NaCl). Phylogenic analysis based on the internal transcribed space 1-5.8S-ITS 2 of the ribosomal RNA gene indicates that these isolates will be an as-yet unidentified species of Aphanomyces.

Re-examination of the prevalence of Aphanomyces astaci in North American crayfish populations in Central Europe by TaqMan MGB real-time PCR

“…The recently discovered A. salsuginosus (Takuma et al 2010) isolated from ice fish Salangi chthys microdon in Asia is hitherto the closest described relative of A. astaci based on the ITS-sequence data and also resembles the Aphanomyces lineage (FM955258) yielding the false positive with conventional PCR methods (Fig. 4).…”

“…For this reason, Oidtmann et al (2006) recommended the single-round PCR (not sensitive to the above-mentioned species) combined with sequencing for confirmation of A. astaci detection (OIE 2010). The product of the single-round PCR is suitable for distinguishing A. astaci from other oomycetes, as the sequence of the resulting ITS fragment is nearly invariable in all known A. astaci strains, but clearly different even from the most related known species (Diéguez-Uribeondo et al 2009, Takuma et al 2010, Makkonen et al 2011. Sequencing of PCR products after single-round PCR has so far resulted in only one discovery of a false positive result (Diéguez-Uribeondo et al 2009), demonstrating the amplification of DNA from an hitherto unknown Aphanomyces lineage closely related to A. astaci (GenBank acc.…”

The signal crayfish (Pacifastacus leniusculus) in Lake Tahoe (USA) hosts multiple Aphanomyces species

“…Recent studies contributing to knowledge of Aphanomyces diversity come from Japan (e.g., Takuma et al, 2010Takuma et al, , 2011Takuma et al, , 2013 and Europe (e.g., Ballesteros et al 2006;Diéguez-Uribeondo et al, 2009;Wolinska et al, 2009;Viljamaa-Dirks and Heinikainen, 2019), which apparently reflects the distribution of researchers rather than diversity of the genus. The closest known relative to A. astaci was detected in one individual signal crayfish in Central Europe during molecular screening for the pathogen in invasive North American crayfish populations in Czechia (Kozubíková et al, 2009;Diéguez-Uribeondo et al, 2009).…”

Aphanomyces invadans, the causal agent of Epizootic Ulcerative Syndrome, is a global threat to wild and farmed fish

“…Lilley et al, 2003;J. H. Lilley et al, 2003;Phadee et al, 2004;Robideau et al, 2011;Takuma et al, 2010;Vandersea et al, 2006). The three main lineages of A. invadans (Fig.…”