Detection of Saprolegnia parasitica in eggs of angelfish Pterophyllum scalare (Cuvier–Valenciennes) with a history of decreased hatchability

Kocuria flava, a Bacterial Endophyte of the Marine Macroalga Bryopsis plumosa, Emits 8-Nonenoic Acid Which Inhibits the Aquaculture Pathogen Saprolegnia parasitica

Secondary metabolites-organic compounds that are often bioactive-produced by endophytes, among others, provide a selective advantage by increasing the organism's survivability. Secondary metabolites mediate the symbiotic relationship between endophytes and their host, potentially providing the host with tolerance to, and protection against biotic and abiotic stressors. Secondary metabolites can be secreted as a dissolved substance or emitted as a volatile. In a previous study, we isolated bioactive endophytes from several macroalgae and tested them in vitro for their ability to inhibit major disease-causing pathogens of aquatic animals in the aquaculture industry. One endophyte (isolate Abp5, K. flava) inhibited and killed, in vitro, the pathogen Saprolegnia parasitica, an oomycete that causes saprolegniasis-a disease affecting a wide range of aquatic animals. Here, using analytical chemistry tools, we found that Abp5 produces the volatile organic compound (VOC) 8-nonenoic acid. Once we confirmed the production of this compound by the endophyte, we tested the compound's ability to treat S. parasitica in in vitro and in vivo bioassays. In the latter, we found that 5 mg/L of the compound improves the survival of larvae challenged with S. parasitica by 54.5%. Our isolation and characterization of the VOC emitted by the endophytic K. flava establish the groundwork for future studies of endophytic biocontrol agents from macroalgae. Use of this compound could enable managing oomycete agricultural pathogens in general, and S. parasitica in particular, a major causal agent in aquaculture diseases.

Screening Salamanders for Symbionts

Microbial symbionts are broadly categorized by their impacts on host fitness: commensals, pathogens, and mutualists. However, recent investigations into the physiological basis of these impacts have revealed nuanced microbial influences on a wide range of host developmental, immunological, and physiological processes, including regeneration. Exploring these impacts begins with knowing which microbes are present. This methodological pipeline contains both targeted assays using PCR and culturing, as well as culture-independent approaches, to survey host salamander tissues for common and unknown microbial symbionts.

Uncharted Diversity and Ecology of Saprolegniaceae (Oomycota) in Freshwater Environments

The fungal-like family Saprolegniaceae (Oomycota), also called "water mold," includes mostly aquatic saprophytes as well as notorious aquatic animal pathogens. Most studies on Saprolegniaceae have been biased toward pathogenic species that are important to aquaculture rather than saprotrophic species, despite the latter's crucial roles in carbon cycling of freshwater ecosystems. Few attempts have been made to study the diversity and ecology of Saprolegniaceae; thus, their ecological role is not well-known. During a survey of oomycetes between 2016 and 2021, we investigated the diversity and distribution of culturable Saprolegniaceae species in freshwater ecosystems of Korea. In the present study, members of Saprolegniaceae were isolated and identified at species level based on their cultural, morphological, and molecular phylogenetic analyses. Furthermore, substrate preference and seasonal dynamics for each were examined. Most of the species were previously reported as animal pathogens; however, in the present study, they were often isolated from other freshwater substrates, such as plant debris, algae, water, and soil sediment. The relative abundance of Saprolegniaceae was higher in the cold to cool season than that in the warm to hot season of Korea. This study enhances our understanding of the diversity and ecological attributes of Saprolegniaceae in freshwater ecosystems.

Efficacy of acriflavin chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection in Pterophyllum scalare

The article describes cases of saprolegniosis in Pterophyllum scalare in private aquaristics and assesses the therapeutic efficacy of acriflafin chloride against Saprolegnia parasitica infection. To establish the diagnosis, the clinical signs present in sick fish, the results of mycological and microscopic examinations are taken into account. Some chemical and mycological indices of aquarium water have been studied, and also mycological studies of fish feed have been carried out. It is established that the disease of fish develops against the background of adverse changes in physical, chemical composition and microbiocenosis of aquarium water. Low water temperature, high levels of phosphates and pH, a significant level of organic pollution, compared to the norm, provoke the accumulation of opportunistic microbiota, resulting in imbalance in the parasite-host system and the development of clinical manifestations of saprolegniosis in fish. It was found that 44.4% of the studied feed samples fed to fish were contaminated with epiphytic micromycetes. Micromycetes are represented by the genera Aspergillus, Penicilium, Fusarium, Mucor, Rhizopus. Among the studied feeds, the most affected by fungi were larvae of Chironomus plumosus and dry Daphnia pulex. According to the results of our studies during outbreaks of saprolegniosis, the pH of aquarium water was 8.1 ± 0.7, the content of phosphates – 5.6 ± 1.1 mg/L, micromycetes – 18.0 ± 1.2 CFU/100 cm3. Aspergillus flavus, A. niger and Penicillium canescens were detected in the studied water samples. With saprolegniosis, the angelfish have a reduced appetite, spots, ulcers, white thin threads, and a cotton-like plaque appear on certain areas of the skin, fins, eyes, and gills. It is established that effective means for the treatment of sick fish are external use in the form of a long bath of acriflavine chloride and extract of Melaleuca alternifolia. It is also effective to increase the water temperature to 25–27 °С, to ensure the normative fish-holding density in aquariums and to exclude from the diet fish feed contaminated with micromycetes. After using the drugs for two weeks every other day, water was replaced by 20% of the aquarium volume and aerated. As a result of the treatment, gradual healing of skin lesions and recovery of 65% of fish with signs of lesions of the outer coverings were registered. Thus, the article analyzes the causes of saprolegniosis in angelfish common in private aquariums, describes the clinical signs of the disease and assesses the therapeutic efficacy of acriflavine chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection. Prospects for further research lie in search of more effective and environmentally friendly means for the treatment of saprolegniosis in aquarium fish.

Development of a 3D spheroid cell culture system from fish cell lines for in vitro infection studies: Evaluation with Saprolegnia parasitica

Understanding the ways in which pathogens infect host cells is essential to improve and develop new treatment strategies. This study aimed to generate a novel in vitro infection model by establishing a reproducible 3D spheroid cell culture system that may lead to a reduced need for animals in fish disease research. 2D models (commonly cell lines) cannot replicate many key conditions of in vivo infections, but 3D spheroids have the potential to provide bridging technology between in vivo and in vitro systems. 3D spheroids were generated using cells from rainbow trout (Oncorhynchus mykiss) cell lines, RTG-2 and RTS-11. The RTG-2 spheroids were tested for their potential to be infected upon exposure to Saprolegnia parasitica spores. Positive infiltration of mycelia into the spheroids was verified by confocal microscopy. As a closer analogue of in vivo conditions encountered during infection, the straightforward model developed in this study shows promise as an additional tool that can be used to further our understanding of host-pathogen interactions for Saprolegnia and possibly a variety of other fish pathogens.

Galleria melonella as an experimental in vivo host model for the fish-pathogenic oomycete Saprolegnia parasitica

Oomycetes are eukaryotic pathogens infecting animals and plants. Amongst them Saprolegnia parasitica is a fish pathogenic oomycete causing devastating losses in the aquaculture industry. To secure fish supply, new drugs are in high demand and since fish experiments are time consuming, expensive and involve animal welfare issues the search for adequate model systems is essential. Galleria mellonella serves as a heterologous host model for bacterial and fungal infections. This study extends the use of G. mellonella for studying infections with oomycetes. Saprolegniales are highly pathogenic to the insects while in contrast, the plant pathogen Phytophthora infestans showed no pathogenicity. Melanisation of hyphae below the cuticle allowed direct macroscopic monitoring of disease progression. However, the melanin response is not systemic as for other pathogens but instead is very local. The mortality of the larvae is dose-dependent and can be induced by cysts or regenerating protoplasts as an alternative source of inoculation.

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Galleria mellonella serves as a heterologous host model system for Saprolegniales.

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The melanisation of the larvae is local around the growing hyphae.

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Regenerating protoplasts can be used as an alternative inoculum to cysts.

Effects of fluconazole based medicated feed on haemato-immunological responses and resistance of Labeo rohita against Saprolegnia parasitica

Fluconazole (FLZ) is a new azole antifungal drug having no earlier record of its utilization for the treatment of fish diseases. A 55-days experiment was carried out to delineate the role of FLZ based medicated feed on haemato-immunological responses and prevention of fungal infection in Labeo rohita fingerlings. Three hundred and sixty fingerlings were randomly distributed into four experimental groups in triplicates. Four iso-caloric and iso-nitrogenous purified medicated feeds were prepared with 0, 100, 200 and 300 mg FLZ 100 g^-1 feed. Haemato-immunological parameters like erythrocyte counts (EC), haemoglobulin (Hb), leucocyte counts (LC), packed cell volume (PCV), mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC), nitro-blue tetrazolium (NBT), albumin, globulin, total plasma protein were studied. The present study revealed that the continuous feeding of FLZ based feed for 15-30 days significantly (P < 0.05) increases the erythropoiesis, heme-synthesis, as well as the leucocytosis in rohu. However, all the doses exhibited equal protection from the infectious S. parasitica after 45 days of continuous feeding.

Feeding pyridoxine prevents Saprolegnia parasitica infection in fish Labeo rohita

A 60-day experiment was carried out to delineate the role of dietary pyridoxine (DP) in Labeo rohita fingerlings in modulating immunity and prevention of fungal infection. Two hundred and seventy fingerlings were randomly distributed into three treatments in triplicates. Three iso-caloric and iso-nitrogenous purified diets were prepared with graded levels of pyridoxine. Three experimental groups were C (0.0% DP), T1 (0.01% DP) and T2 (0.02% DP). The role of dietary pyridoxine in modulating immunity and prevention of fungal infection was assessed by haemato-immunological parameters like erythrocyte counts (EC), leucocyte counts (LC), haemoglobulin (Hb), packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), nitro-blue tetrazolium (NBT), phagocytic activity, albumin, globulin, total plasma protein, albumin/globulin and by challenge study with Saprolegnia parasitica, where relative percentage survival (RPS) were recorded. Hb, PCV, MCV, MCH, NBT, total plasma protein, albumin, globulin contents, lysozyme and phagocytic activity was significantly (P < 0.05) higher in DP fed group. Significantly (P < 0.05) higher RPS was recorded from T2 group fed with 0.02% DP for 45 days. Hence, DP has the capacity to stimulate nonspecific immunity and increase resistance to S. parasitica infection in L. rohita fingerlings.

A Comprehensive Protocol for Improving the Description of Saprolegniales (Oomycota): Two Practical Examples (Saprolegnia aenigmatica sp. nov. and Saprolegnia racemosa sp. nov.)

The description, identification and classification of organisms are the pillar in biodiversity and evolutionary studies. The fungal-like organism Saprolegnia contains important animal pathogens. However, its taxonomy is weak, making it difficult to perform further studies. This problem mainly arises from the unavailability of suitable holotypes. We propose a standardized protocol for describing Saprolegnia spp. that includes good cultural practices and proper holotype preservation. In order to illustrate this new proposal, we describe two species, Saprolegnia aenigmatica sp. nov. and Saprolegnia racemosa sp. nov., based on the recently described molecular operational taxonomic units (MOTUs), phylogenetic relationships, and the analyses of morphological features. We show that they belong to two different MOTUs that are grouped into two sister clades. Morphologically, we find that S. racemosa exhibits a species-specific character, i.e., aggrupation of oogonia in racemes, while S. aenigmatica does not have any specific characters. Analyses of a combined set of characters, i.e., length and breadth of sporangia, length/breadth ratio (l/b) of oogonia, cyst and oospore diameter, and the number of oospores per oogomium, allow distinguishing these two species. To improve Saprolegnia taxonomy, we propose to incorporate into the protologue: (i) several isolates of the new species; (ii) the rDNA sequences to compare them to data-bases of Saprolegnia sequences of reference; (iii) a phylogenetic analysis to check relationships with other species; (iv) to preserve holotypes in absolute ethanol and to include lyophilized material from holotype; and (v) the ex-type as a pure culture from single-spore isolates stored in at least two different collections.