Virome Analysis of Signal Crayfish (Pacifastacus leniusculus) along Its Invasion Range Reveals Diverse and Divergent RNA Viruses

The diversity, pathogenic spectrum, and ecological significance of arthropod viruses

Research on arthropod viruses initially focused on those associated with diseases in vertebrates, particularly humans, as well as in plants of economic importance. However, the more recent deployment of metatranscriptomic sequencing of diverse arthropod species has facilitated the discovery of a multitude of novel arthropod viruses, in turn revealing that pathogenic viruses represent only a small component of the arthropod virome. In addition, arthropods may play a pivotal role in viral evolution and ecological dynamics, and have the potential to act as reservoirs for pathogens affecting vertebrates or plants. Due to active interactions between arthropod populations and diverse organisms - including fungi, plants, vertebrates, and even other arthropods in both aquatic and terrestrial ecosystems - there is an increased risk of the spillover of arthropod viruses to other organisms, including mammals. Herein, we review our current understanding of the diversity and ecology of arthropod viruses. We outline what is known about pathogenic arthropod viruses in diverse host types and emphasize the unique niche of arthropods as the source of emerging viral infectious diseases. Finally, we describe the evolutionary interactions between arthropod viruses and their hosts in ecosystems, at the same time highlighting their ecological significance with respect to regulating host populations.

Virome analysis unveils a rich array of newly identified viruses in the red swamp crayfish Procambarus clarkii

The red swamp crayfish (Procambarus clarkii) is the second most widely cultured crustacean globally. As a highly invasive species with a worldwide distribution, P. clarkii presents a substantial risk for the transmission of viral pathogens to native aquatic organisms. Recently, the emergence of growth retardation disease (GRD) in P. clarkii has led to significant production declines and economic losses. A comprehensive viromic analysis could offer valuable insights into the potential viral pathogens harbored by P. clarkii. Here we systematically examined the RNA viromes of healthy and GRD-affected P. clarkii collected from Qianjiang, China. Our investigation identified a total of 1729 viral species across 21 known viral taxa, with 1603 species being previously unreported. The orders Picornavirales, Tolivirales, and Nodamuvirales were predominant in both species count and relative abundance. Moreover, seven viruses exhibited higher abundance in GRD-affected P. clarkii compared to healthy individuals. Our work uncovers an unexpectedly diverse RNA viral community within P. clarkii and identifies potential viral pathogens associated with GRD in this species.

Unraveling the genomic landscape of piscine myocarditis virus: mutation frequencies, viral diversity and evolutionary dynamics in Atlantic salmon

Over a decade since its discovery, piscine myocarditis virus (PMCV) remains a significant pathogen in Atlantic salmon aquaculture. Despite this significant impact, the genomic landscape, evolutionary dynamics, and virulence factors of PMCV are poorly understood. This study enhances the existing PMCV sequence dataset by adding 34 genome sequences and 202 new ORF3 sequences from clinical cardiomyopathy syndrome (CMS) cases in Norwegian aquaculture. Phylogenetic analyses, also including sequences from the Faroe Islands and Ireland revealed that PMCV sequences are highly conserved with distinct clustering by country of origin. Still, single CMS outbreaks display multiple PMCV variants, and although some clustering was seen by case origin, occasional grouping of sequences from different cases was also apparent. Temporal data from selected cases indicated increased sequence diversity in the population. We hypothesize that multiple bottlenecks and changing infection dynamics in the host population, with transfer to naïve individuals over time, represent a continuous selection pressure on the virus populations. No clear relation was found between PMCV variants and the severity of heart pathology. However, specific non-synonymous and synonymous mutations that might impact protein function and gene expression efficiency were identified. An additional factor that may impact PMCV replication is the presence of defective viral genomes, a novel finding for viruses of the order Ghabrivirales. This study provides new insights into PMCV genomic characteristics and evolutionary dynamics, highlighting the complex interplay of genetic diversity, virulence markers, and host-pathogen interactions, underscoring the epidemiological complexity of the virus. Keywords: piscine myocarditis virus; evolutionary dynamics; diversity; phylogeny; genomic sequencing; defective viral genomes.

Enormous diversity of RNA viruses in economic crustaceans

Crustaceans are important food sources worldwide and possess significant ecological status in the marine ecosystem. However, our understanding of the diversity and evolution of RNA viruses in crustaceans, especially in economic crustaceans, is still limited. Here, 106 batches of economic crustaceans including 13 species were collected from 24 locations in China during 2016-2021. We identified 90 RNA viruses, 69 of which were divergent from the known viruses. Viral transcripts were assigned to 18 different viral families/clades and three unclassified groups. Among the identified viruses, five were double-stranded RNA viruses, 74 were positive-sense single-stranded RNA (+ssRNA) viruses, nine were negative-sense single-stranded RNA (-ssRNA) viruses, and two belonged to an unclassified RNA virus group. Phylogenetic analyses showed that crustacean viruses were often clustered with viruses identified from invertebrates. Remarkably, most crustacean viruses were closely related to those from different host species along the same food chain or ecological aquatic niche. In addition, the genome structures of the newly discovered picornaviruses exhibited remarkable diversity. Our study significantly expands the diversity of viruses in important economic crustaceans and provides essential data for the risk assessment of the pathogens spreading in the global aquaculture industry.

IMPORTANCE

The study delves into the largely uncharted territory of RNA viruses in crustaceans, which are not only vital for global food supply but also play a pivotal role in marine ecosystems. Focusing on economic crustaceans, the research uncovers 90 RNA viruses, with 69 being potentially new to science, highlighting the vast unknown viral diversity within these marine organisms. The findings reveal that these viruses are often related to those found in other invertebrates and tend to share close relationships with viruses from species within the same food web or habitat. This suggests that viruses may move between different marine species more frequently than previously thought. The discovery of such a wide variety of viruses, particularly the diverse genome structures of newly identified picornaviruses, is a significant leap forward in understanding the crustacean virology. This knowledge is crucial for managing disease risks in aquaculture and maintaining the balance of marine ecosystems.

Detection of novel RNA viruses in wild noble crayfish (Astacus astacus): A virome analysis in Swiss water bodies

European native crayfish populations are undergoing a strong decline due to environmental factors and the introduction of highly competitive non-native species. Pathogens are an additional threat to native crayfish. However, aside from the crayfish plague, other infectious diseases are still widely unknown. This study aimed to investigate viruses present in seven populations of wild noble crayfish (Astacus astacus) in Switzerland, through high-throughput sequencing. Sequence analysis revealed the presence of 11 novel RNA viruses (one bunya-like, four hepe-like, two dicistro-like, three picorna-like, and one permutotetra-like) in the samples. The discovery of a novel bunya-like virus in noble crayfish without associated mortality or macroscopical alterations is of particular interest since it is closely related to the bunya-like brown spot virus, a virus described in 2019 from diseased native white-clawed crayfish (Austropotamobius pallipes) during a mass mortality event in France. It seems that these two closely related viruses have very different impacts on their respective hosts, raising the need for further investigations on virulence factors and host susceptibility towards these viruses. This study provides a basis for future investigations, permitting to gradually fill the knowledge gap in crayfish viral diseases.

Comparison of exoskeleton microbial communities of co-occurring native and invasive crayfish species

Host-associated microbial communities are an important determinant of individual fitness and have recently been highlighted as one of the factors influencing the success of invasive species. Invasive hosts introduce their microbes into the new environment, and then both the host and its associated microbes enter into a series of interactions with the native macroscopic and microscopic biota. As these processes are largely unexplored, we aimed to compare the exoskeletal microbial communities of co-occurring and phylogenetically related crayfish: the native narrow-clawed crayfish Pontastacus leptodactylus and the invasive signal crayfish Pacifastacus leniusculus from the recently invaded Korana River, Croatia. The results of high-throughput 16S rRNA sequencing showed that the exoskeletal microbiome of both species is very diverse, significantly influenced by the local environment and dominated by low abundance bacterial families from the phylum Proteobacteria. Furthermore, the exoskeletal microbiomes of the crayfish species differed significantly in the composition and abundance of Amplicon Sequence Variants (ASVs), suggesting that they are to some extent shaped by species-specific intrinsic factors, despite sharing a common habitat. However, over 95% of the bacterial genera associated with the exoskeleton were detected in the exoskeleton samples of both native and invasive crayfish. We paid particular attention to two known crayfish pathogens, Aphanomyces astaci and Saprolegnia parasitica, and find that both species carry low amounts of both pathogens. On the side, we find that a non-standard ddPCR protocol outperforms standard qPCR test for A. astaci under low concentration conditions. Taken together, our results indicate the possibility of bidirectional mixing and homogenisation of exoskeleton microbiome. As such, they can serve as a baseline in future detangling of the processes that act together to shape the microbiomes of co-occuring native and invasive congeners during biological invasions.

Virome Analysis of Normal and Growth Retardation Disease-Affected Macrobrachium rosenbergii

The giant freshwater prawn, Macrobrachium rosenbergii, is an important aquaculture species in China. Growth retardation disease (GRD) is a common contagious disease in M. rosenbergii, resulting in slow growth and precocious puberty in prawns, and has caused growing economic losses in the M. rosenbergii industry. To investigate the viral diversity of M. rosenbergii and identify potentially high-risk viruses linked to GRD, virome analysis of the GRD-affected and normal M. rosenbergii was carried out using next-generation sequencing (NGS). A total of 327 contigs (>500 bp) were related to viral sequences belonging to 23 families/orders and a group of unclassified viruses. The majority of the viral contigs in M. rosenbergii belonged to the order Picornavirales, with the Solinviviridae family being the most abundant in both the diseased and normal groups. Furthermore, 16 RNA viral sequences with nearly complete genomes were characterized and phylogenetically analyzed, belonging to the families Solinviviridae, Flaviviridae, Polycipiviridae, Marnaviridae, and Dicistroviridae as well as three new clades of the order Picornavirales. Notably, the cross-species transmission of a picorna-like virus was observed between M. rosenbergii and plants. The "core virome" seemed to be present in the diseased and normal prawns. Still, a clear difference in viral abundance was observed between the two groups. These results showed that the broad diversity of viruses is present in M. rosenbergii and that the association between viruses and disease of M. rosenbergii needs to be further investigated. IMPORTANCE Growth retardation disease (GRD) has seriously affected the development and economic growth of the M. rosenbergii aquaculture industry. Our virome analysis showed that diverse viral sequences were present in M. rosenbergii, significantly expanding our knowledge of viral diversity in M. rosenbergii. Some differences in viral composition were noted between the diseased and normal prawns, indicating that some viruses become more abundant in occurrences or outbreaks of diseases. In the future, more research will be needed to determine which viruses pose a risk for M. rosenbergii. Our study provides important baseline information contributing to disease surveillance and risk assessment in M. rosenbergii aquaculture.

Legacy of Plant Virology in Croatia-From Virus Identification to Molecular Epidemiology, Evolution, Genomics and Beyond

This paper showcases the development of plant virology in Croatia at the University of Zagreb, Faculty of Science, from its beginning in the 1950s until today, more than 70 years later. The main achievements of the previous and current group members are highlighted according to various research topics and fields. Expectedly, some of those accomplishments remained within the field of plant virology, but others make part of a much-extended research spectrum exploring subviral pathogens, prokaryotic plant pathogens, fungi and their viruses, as well as their interactions within ecosystems. Thus, the legacy of plant virology in Croatia continues to contribute to the state of the art of microbiology far beyond virology. Research problems pertinent for directing the future research endeavors are also proposed in this review.