Saprolegnia species in Norwegian salmon hatcheries: field survey identifies S. diclina sub-clade IIIB as the dominating taxon.

Saprolegnia isolates within the recognized clades encompassing the taxa S. parasitica and S. diclina act as opportunist and aggressive pathogens to both fish and their eggs. They are responsible for significant economic losses in aquaculture, particularly in salmonid hatcheries. However, the identity, distribution and pathogenic significance of involved species often remain unexplored. In this study, 89 Saprolegnia isolates were recovered from water, eggs and salmon tissue samples that originated from salmon (Salmo salar) hatcheries along the coast of Norway. The cultures were characterized morphologically and molecularly in order to provide an overview of the species composition of Saprolegnia spp. present in Norwegian salmon hatcheries. We demonstrate that S. diclina clearly dominated and contributed to 79% of the recovered isolates. Parsimony analyses of the nuclear ribosomal internal transcribed spacer (ITS) region split these isolates into 2 strongly supported sub-clades, S. diclina sub-clade IIIA and IIIB, where sub-clade IIIB accounted for 66% of all isolates. A minor portion of the isolates constituted other taxa that were either conspecific or showed strong affinity to S. parasitica, S. ferax, S. hypogyna and Scoliolegnia asterophora. The unique sub-clade IIIB of S. diclina was most prevalent in water and salmon eggs, while S. parasitica isolates were more frequently isolated from post hatching stages. The study demonstrated that morphological criteria in many cases were insufficient for species delimitation due to lack of sexual structures or incoherent morphological expression of such features within the tested replicates.

Expanding ecological assessment by integrating microorganisms into routine freshwater biomonitoring.

Bioindication has become an indispensable part of water quality monitoring in most countries of the world, with the presence and abundance of bioindicator taxa, mostly multicellular eukaryotes, used for biotic indices. In contrast, microbes (bacteria, archaea and protists) are seldom used as bioindicators in routine assessments, although they have been recognized for their importance in environmental processes. Recently, the use of molecular methods has revealed unexpected diversity within known functional groups and novel metabolic pathways that are particularly important in energy and nutrient cycling. In various habitats, microbial communities respond to eutrophication, metals, and natural or anthropogenic organic pollutants through changes in diversity and function. In this review, we evaluated the common trends in these changes, documenting that they have value as bioindicators and can be used not only for monitoring but also for improving our understanding of the major processes in lotic and lentic environments. Current knowledge provides a solid foundation for exploiting microbial taxa, community structures and diversity, as well as functional genes, in novel monitoring programs. These microbial community measures can also be combined into biotic indices, improving the resolution of individual bioindicators. Here, we assess particular molecular approaches complemented by advanced bioinformatic analysis, as these are the most promising with respect to detailed bioindication value. We conclude that microbial community dynamics are a missing link important for our understanding of rapid changes in the structure and function of aquatic ecosystems, and should be addressed in the future environmental monitoring of freshwater ecosystems.

Timing and quantifying Aphanomyces astaci sporulation from the noble crayfish suffering from the crayfish plague.

Aphanomyces astaci sporulation is crucial for the spreading potential of this disease agent. For the first time, we are reporting timing and quantity of A. astaci spores released from noble crayfish (Astacus astacus) suffering from crayfish plague under practical aquatic conditions. We infected nine noble crayfish with A. astaci PsI-genotype and maintained them in individual 8L tanks. Spores (zoospores and cysts) were quantified from water samples (3 × 1 mL) taken every 12h over 10 d using A. astaci specific qPCR. A clear sporulation trend was found, together with a high individual spore estimate variation. The median spore counts from two days before death to 12h post mortem were from ~500 to ~2000 spores L(-1). A significant sporulation increase occurred after 24h post mortem (~12,000 spores L(-1)) and reached a peak after two days (~65,000 spores L(-1)) before declining to or below pre mortem levels from the fourth day. The single most sporulating crayfish released from ~75,000 to ~400,000 spores L(-1) during the mass sporulating period, yielding a maximum estimate of ~3,200,000 spores released from a single crayfish if we assume homogeneous spore distribution. The results confirm a mass A. astaci spore release from moribund and recently dead infected noble crayfish, with a sporulation peak one to three days post mortem. The acute crayfish mortality only three days after zoospore exposure confirm the lethal potential of the PsI-genotype. The powerful sporulation potential observed here may be one of the key virulence factors of this genotype.

Copper-adapted Suillus luteus, a symbiotic solution for pines colonizing Cu mine spoils.

Natural populations thriving in heavy-metal-contaminated ecosystems are often subjected to selective pressures for increased resistance to toxic metals. In the present study we describe a population of the ectomycorrhizal fungus Suillus luteus that colonized a toxic Cu mine spoil in Norway. We hypothesized that this population had developed adaptive Cu tolerance and was able to protect pine trees against Cu toxicity. We also tested for the existence of cotolerance to Cu and Zn in S. luteus. Isolates from Cu-polluted, Zn-polluted, and nonpolluted sites were grown in vitro on Cu- or Zn-supplemented medium. The Cu mine isolates exhibited high Cu tolerance, whereas the Zn-tolerant isolates were shown to be Cu sensitive, and vice versa. This indicates the evolution of metal-specific tolerance mechanisms is strongly triggered by the pollution in the local environment. Cotolerance does not occur in the S. luteus isolates studied. In a dose-response experiment, the Cu sensitivity of nonmycorrhizal Pinus sylvestris seedlings was compared to the sensitivity of mycorrhizal seedlings colonized either by a Cu-sensitive or Cu-tolerant S. luteus isolate. In nonmycorrhizal plants and plants colonized by the Cu-sensitive isolate, root growth and nutrient uptake were strongly inhibited under Cu stress conditions. In contrast, plants colonized by the Cu-tolerant isolate were hardly affected. The Cu-adapted S. luteus isolate provided excellent insurance against Cu toxicity in pine seedlings exposed to elevated Cu levels. Such a metal-adapted Suillus-Pinus combination might be suitable for large-scale land reclamation at phytotoxic metalliferous and industrial sites.

The postfire discomycete Geopyxis carbonaria (Ascomycota) is a biotrophic root associate with Norway spruce (Picea abies) in nature.

The hypothesis that the postfire discomycete Geopyxis carbonaria (Ascomycota, Pezizales, Pyronemataceae) has a biotrophic association with roots of Norway spruce (Picea abies) in nature was tested by isolation of fungal strains from fresh, brown, smooth mycorrhiza-like root tips of Norway spruce collected from below the depth of detrimental heat penetration in a postfire site. The morphology of seven culture isolates originating from the smooth mycorrhiza-like root tips of two different spruce trees was congruent with the morphology of axenic culture isolates obtained from ascospores of G. carbonaria. DNA sequences of the nuclear ribosomal internal transcribed spacers ITS1 and ITS2 from these root-derived cultures and the ascosporic G. carbonaria culture isolates were found to be identical, further supporting the conclusion that the isolates were conspecific. The extensive ascocarp and ascospore formation of G. carbonaria which succeeds a forest fire may be explained in terms of a fungal escape from a moribund tree associate. Possible ecological adaptations of G. carbonaria to the pre- and postfire community are discussed.