Amino Acid Residues Controlling Domain Interaction and Interdomain Electron Transfer in Cellobiose Dehydrogenase.

The function of cellobiose dehydrogenase (CDH) in biosensors, biofuel cells, and as a physiological redox partner of lytic polysaccharide monooxygenase (LPMO) is based on its role as an electron donor. Before donating electrons to LPMO or electrodes, an interdomain electron transfer from the catalytic FAD-containing dehydrogenase domain to the electron shuttling cytochrome domain of CDH is required. This study investigates the role of two crucial amino acids located at the dehydrogenase domain on domain interaction and interdomain electron transfer by structure-based engineering. The electron transfer kinetics of wild-type Myriococcum thermophilum CDH and its variants M309A, R698S, and M309A/R698S were analyzed by stopped-flow spectrophotometry and structural effects were studied by small-angle X-ray scattering. The data show that R698 is essential to pull the cytochrome domain close to the dehydrogenase domain and orient the heme propionate group towards the FAD, while M309 is an integral part of the electron transfer pathway - its mutation reducing the interdomain electron transfer 10-fold. Structural models and molecular dynamics simulations pinpoint the action of these two residues on the domain interaction and interdomain electron transfer.

Further spread of perch rhabdovirus on European percid farms.

Variants of perch rhabdovirus (PRV) circulate across European percid farms via the fish trade. To trace their circulation, they are usually isolated by cell culture and subsequently identified genetically by sequencing partial or complete genes. Here, a newly developed nested PCR-based method was used to amplify and sequence the complete N and P genes directly from clinical samples obtained during an outbreak on a farm as well as from four batches of fish sampled from two other farms in another country. In an attempt to trace the origin of the five detected viruses, their N and P sequences were concatenated and compared with related viruses. One virus found in pike-perch was highly related to a virus isolated in 2016 in Belgium. Two other viruses detected on a single farm were distinct from one another, with one being almost identical to another virus isolated in 2016 in Belgium and the other being more closely related to a subgroup with different origins, France and Belgium. Two other viruses found in perch from a third farm were identical and were more related to a subgroup of viruses isolated in France. Identifying variants by a direct PCR approach will help to prevent further dissemination in farms.

Novel Filoviruses, Hantavirus, and Rhabdovirus in Freshwater Fish, Switzerland, 2017.

European perch (Perca fluviatilis) are increasingly farmed as a human food source. Viral infections of European perch remain largely unexplored, thereby putting farm populations at incalculable risk for devastating fish epizootics and presenting a potential hazard to consumers. To address these concerns, we applied metatranscriptomics to identify disease-associated viruses in European perch farmed in Switzerland. Unexpectedly, in clinically diseased fish we detected novel freshwater fish filoviruses, a novel freshwater fish hantavirus, and a previously unknown rhabdovirus. Hantavirus titers were high, and we demonstrated virus in macrophages and gill endothelial cells by using in situ hybridization. Rhabdovirus titers in organ samples were low, but virus could be isolated on cell culture. Our data add to the hypothesis that filoviruses, hantaviruses, and rhabdoviruses are globally distributed common fish commensals, pathogens, or both. Our findings shed new light on negative-sense RNA virus diversity and evolution.

Systemic infection in European perch with thermoadapted virulent Aeromonas salmonicida (Perca fluviatilis).

In non-salmonid fish, Aeromonas salmonicidacan cause local infections with severe skin ulcerations, known as atypical furunculosis. In this study, we present a systemic infection by a virulent A. salmonicidain European perch (Perca fluviatilis).This infection was diagnosed in a Swiss warm water recirculation aquaculture system. The isolate of A.  salmonicida encodes a type three secretion system (TTSS) most likely located on a plasmid similar to pAsa5/pASvirA, which is known to specify one of the main virulence attributes of the species A. salmonicida. However, the genes specifying the TTSS of the perch isolate show a higher temperature tolerance than strains isolated from cold-water fish. The function of the TTSS in virulence was verified in a cytotoxicity test using bluegill fry and epithelioma papulosum cyprinid cells.