Biology subjects

Falk, K.

Publications and source records attributed to Falk, K..

3 recordsLinked to original sources

bioRxiv2026

DNA metabarcoding samples from nest soil and beaks outperform samples from talons and faeces when identifying diversity of white-tailed eagle diet in South Greenland

DNA metabarcoding is an emerging approach to study diets across a broad range of species but requires careful optimisation of the sample collection method and substrate used. The suitability of different sample types to identify the diet of the target species remains under investigated. Here, we address these knowledge gaps by collecting four different sample types - faeces, beak swabs, talon swabs, and soil samples - during nest visits of white-tailed eagles (Haliaeetus albicilla) during the 2025 breeding season in South Greenland. We further investigated whether some eagle dietary taxa could act as vectors for microplastic pollution. Our analyses revealed a broad diet, with 25 dietary taxa for white-tailed eagles. Lumpfish (Cyclopterus lumpus) was the most frequently detected dietary taxon in the diet, which was composed of 75 % fish, 19 % birds, and 7 % mammals. Our findings indicate that diets varied strongly between nesting sites. Although each sample type was efficient in capturing diet, soil and beak swabs were most promising for eagles and gave comparable results. On the other hand, faeces provided a distinct dietary profile with a reduced detection of fish, while requiring an increased sample size, and talon swabs missed rare food items. Finally, we recovered microplastic contamination in 33 % of our samples, but no dietary taxon was associated with microplastic pollution. Taken together our results underline the overlooked value of soil from nests to provide dietary information and highlight the necessity to deepen our knowledge of Arctic food webs and their microplastic contamination.

ecology↗

bioRxiv2026

Common ISAV haemagglutinin esterase variants at residues 229 and 230 influence the efficiency of receptor destruction and erythrocyte release in Atlantic salmon

Sialic acid-binding viruses often encode receptor-destroying enzymes that modulate infection through host glycan alteration. Isavirus salaris (ISAV), the aetiological agent of infectious salmon anaemia, encodes a haemagglutinin esterase with 4-O-acetylesterase activity. The ISAV esterase removes the virus-targeted epitope and causes homologous attachment interference, but its broader biological roles remain poorly understood. Several aspects of ISAV receptor engagement and release remain unresolved: Although ISAV agglutinates erythrocytes from both rainbow trout and Atlantic salmon, only rainbow trout erythrocytes elute from this interaction. By contrast, Atlantic salmon erythrocytes remain persistently bound, despite the presence of an active esterase. Here, we used ISAV-erythrocyte interactions to dissect receptor destruction and dissociation across viral genotypes and strains. We uncovered substantial functional diversity in viral permissiveness for Atlantic salmon erythrocyte elution. Common variants of residues 229 and 230 of the haemagglutinin-esterase, located at the distal rim of the P1 esterase pocket, were key determinants of elution permissiveness. Elution further required an active esterase catalytic triad. In vivo, Atlantic salmon infected with ISAV carrying the elution-permissive 229N variant showed earlier loss of erythrocyte Neu4,5Ac2 than fish infected with an elution-restrictive strain. The loss of Neu4,5Ac2 preceded the reduction in ISAV-bound erythrocytes by several days, indicating that receptor removal alone was insufficient to trigger virion release. Targeted sialic acid analyses revealed similar levels of Neu4,5Ac2 on Atlantic salmon and rainbow trout erythrocytes. Atlantic salmon erythrocytes additionally expressed di-O-acetylated Neu4,5,9Ac3. By contrast, brown trout erythrocytes expressed little or no Neu4,5Ac2, consistent with their reported inability to support ISAV haemagglutination. Together, our findings give insight into viral and host determinants of ISAV receptor interactions. We demonstrate functional diversity within the ISAV esterase and link virion binding and release to salmonid erythrocyte sialic acid composition. The delay between receptor loss and virion dissociation further supports the existence of additional erythrocyte attachment factors.

microbiology↗

bioRxiv2023

The infectious salmon anaemia virus esterase prunes erythrocyte surfaces in infected Atlantic salmon and exposes terminal sialic acids to lectin recognition

Many sialic acid-binding viruses express a receptor-destroying enzyme (RDE) that removes the virus-targeted receptor and limits viral interactions with the host cell surface. Despite a growing appreciation of how the viral RDE promotes viral fitness, little is known about its direct effects on the host. Infectious salmon anaemia virus (ISAV) attaches to 4-O-acetylated sialic acids on the surface of Atlantic salmon epithelial, endothelial, and red blood cells. ISAV receptor binding and destruction are effectuated by the same surface molecule, the haemagglutinin esterase (HE). We recently discovered a global loss of vascular 4-O-acetylated sialic acids in ISAV-infected fish. The loss correlated with the expression of viral proteins, giving rise to the hypothesis that it was mediated by the HE. Here, we report that the capacity to bind new ISAV particles is also progressively lost from circulating erythrocytes in infected fish. Furthermore, salmon erythrocytes exposed to ISAV ex vivo lost their capacity to bind new ISAV particles. The loss of ISAV binding was not associated with receptor saturation. Moreover, upon loss of the ISAV receptor, erythrocyte surfaces became more available to the lectin wheat germ agglutinin, suggesting a potential to alter interactions with endogenous lectins of similar specificity. The pruning of erythrocyte surfaces was inhibited by an antibody that prevented ISAV attachment. Furthermore, recombinant HE, but not an esterase-silenced mutant, was sufficient to induce the observed surface modulation. Our results directly link the ISAV-induced erythrocyte modulation to the hydrolytic activity of the HE and show that the observed effects are not mediated by endogenous esterases. Our findings are the first to directly link a viral esterase to extensive host cell surface modulation in infected individuals. This raises the question of how common the phenomenon is among sialic acid-binding viruses. It is also relevant to ask if the altered sialic acid landscape of the affected cells influences host biological functions with relevance to viral disease.

microbiology↗