Oomycetes are a curious group of multicellular aquatic Eucaryotes. They resemble Fungi in their morphology, and were previously thought to belong to this group, but genetic phylogeny has demonstrated that they in fact Stramenopile, members of the group which also contains Brown Algae, Diatoms, and a variety of single-celled organisms. All known Oomycetes are either saprotrophic (obtaining energy from the chemical breakdown of organic matter) or pathogenic (infecting living organisms). Members of the genus Saprolegnia, sometimes known as Cotton Molds, are primarily saprotrophs, but many species are also opportunistic pathogens, causing patches of cottony growth on Fish or other infected organisms. The taxonomy of these organisms has traditionally relied upon morphology, which is problematic as they are both variable in habit within species and similar to one-another in overall form; the advent of genetic tools has simplified this considerably.
In a paper published in the journal PLoS One on 20 March 2024, Viktória Verebély, Noémi Erdei, Tímea Hardy, and Edit Eszterbauer of the Hungarian Veterinary Medical Research Institute, describe a new species of Saprolegnia from Lake Velence in Hungary.
Lake Velence is the third largest lake in Hungary, with a surface area of 24.5 km² and a maximum depth of 1.4 km. The large surface area and shallow depth of this lake means that it is easily warmed by the Sun, with summer temperatures typically reaching 26–28˚C, which makes it one of the warmest lakes in Europe. It is also chemically distinctive, with a high pH (typically between 7.8 and 9.2) and a high dissolved salt level.
The new species is described upon the basis of two strains cultivated from samples collected from a sailing port near the town of Velence at the northeastern end of the lake. These were provisionally identified as belonging to a new species on the basis of their morphology, but this was confirmed by genetic analysis.
The new species is named Saprolegnia velencensis, where 'velencensis' means 'from Velence'. It produces colourless, transparent, and smooth hyphae, slightly over 13 μm in width, with moderate branching and few septae. Few oogonia (female spore-producing bodies) are produced, these being spherical with slightly pitted walls, and supported on short necks. More abundant are gemmae, masses of cells which can detach and go on to form a new colony. These are typically elongate, and form chains, with the terminal gemmae having a thicker, club-like structure. Sporangia (asexual bodies which produce motile spores called 'zoospores' are also quite common, and also tend to be elongate in form.
Because Saprolegnia velencensis was cultivated from collected water samples, it is unclear if this species has the capacity to be pathogenic. Most Saprolegnia infections found in Fish are actually caused by a single species, Saprolegnia parasitica, although Fish populations can also be badly impacted by two other species, Saprolegnia australis and Saprolegnia ferax, both of which infect Fish eggs, with Saprolegnia ferax also known to infect the eggs of Amphibians, and to have played a role in the population collapse of several Amphibian species around the globe.
The discovery of a novel species of Saprolegnia in Lake Velence may relate to the lake's distinctive physical and chemical properties, although the relationship between water chemistry and the ability of Oomycetes to survive and thrive is unclear. Some studies have suggested that zoosporangia production may be suppressed in hard water, although studies in Egypt have indicated that Saprolegnia spp. are more affected by temperature than salinity. In South Korea, these Water Molds have been found to be more abundant in the winter than the summer, and studies have shown that different species are variable in their ability to cope with different water temperatures. Other studies have suggested that variations in water temperature and chemistry may in fact be affecting Bacteria which can suppress the growth of Water Molds, rather than the Molds directly.
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