An endogenous DNA virus in an amphibian-killing fungus associated with pathogen genotype and virulence

The global panzootic lineage (GPL) of the pathogenic fungus Batrachochytrium dendrobatidis (Bd) has caused severe amphibian population declines, yet the drivers underlying the high frequency of GPL in regions of amphibian decline are unclear. Using publicly available Bd genome sequences, we identified multiple non-GPL Bd isolates that contain a circular Rep-encoding single-stranded (CRESS)-like DNA virus, which we named Bd DNA virus 1 (BdDV-1). We further sequenced and constructed genome assemblies with long read sequences to find that the virus is integrated into the nuclear genome in some strains. Attempts to cure virus-positive isolates were unsuccessful; however, phenotypic differences between naturally virus-positive and virus-negative Bd isolates suggested that BdDV-1 decreases the growth of its host in vitro but increases the virulence of its host in vivo. BdDV-1 is the first-described CRESS DNA mycovirus of zoosporic true fungi, with a distribution inversely associated with the emergence of the panzootic lineage.

An Overview of Mycoviral Curing Strategies Used in Evaluating Fungal Host Fitness

The number of novel mycoviruses is increasing at a high pace due to advancements in sequencing technologies. As a result, an uncountable number of mycoviral sequences are available in public sequence repositories. However, only genomic information is not sufficient to understand the impact of mycoviruses on their host biology. Biological characterization is required to determine the nature of mycoviruses (cryptic, hypervirulent, or hypovirulent) and to search for mycoviruses with biocontrol and therapeutic potential. Currently, no particular selective method is used as the gold standard against these mycoviral infections. Given the importance of curing, we present an overview of procedures used in preparation of isogenic lines, along with their benefits and drawbacks. We concluded that a combination of single-spore isolation and hyphal tipping is the best fit for preparation of isogenic lines. Furthermore, recent bioinformatic approaches should be introduced in the field of mycovirology to predict virus-specific antivirals to get robust results.

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses

Mycoviruses (viruses of fungi) are ubiquitous throughout the fungal kingdom and are currently classified into 23 viral families and the genus botybirnavirus by the International Committee on the Taxonomy of Viruses (ICTV). The primary focus of mycoviral research has been on mycoviruses that infect plant pathogenic fungi, due to the ability of some to reduce the virulence of their host and thus act as potential biocontrol against these fungi. However, mycoviruses lack extracellular transmission mechanisms and rely on intercellular transmission through the hyphal anastomosis, which impedes successful transmission between different fungal strains. This review provides a comprehensive overview of mycoviruses, including their origins, host range, taxonomic classification into families, effects on their fungal counterparts, and the techniques employed in their discovery. The application of mycoviruses as biocontrol agents of plant pathogenic fungi is also discussed.

Presence of Virus like Particles in Human Pathogenic Fungi: Chrysosporium sps and Candida albicans

Out of eight isolates of different human pathogenic fungi, four were found to be infected with virus like particles (VLP): Chrysosporium pseudomerdarium, C. xerophillum, C. keratinophillum and Candida albicans through electron microscopy. Frozen mycelium without abrasive was seemingly better disruption method for VLP extraction in Chrysosporium extracts but in Candida albicans disruption with abrasive revealed the presence of considerable amount of VLP. The growth of five isolates of Chrysosporium species associated with VLP was significantly affected by different media tested. Absorption spectra revealed the nucleo protein nature of VLP in C. albicans. Virus like particles in Chrysosporium species reported for the first time and in C. albicans, it is reported for the first time in India.

A novel mycovirus closely related to hypoviruses that infects the plant pathogenic fungus Sclerotinia sclerotiorum

Three dsRNA segments, two similarly sized at 9.5kbp and a third one of approximately 3.6kbp, were extracted from a hypovirulent strain SZ-150 of Sclerotinia sclerotiorum. The complete cDNA sequence of one of the two large dsRNA segment (10398bp, excluding the poly (A) tail) reveals a single ORF that encodes a polyprotein with conserved domains of putative papain-like protease, UDP glucose/sterol glycosyltransferase, RNA-dependent RNA polymerase and viral RNA Helicase. This virus is closely related to Cryphonectria hypovirus (CHV) 3/GH2 and CHV4/SR2 in the family Hypoviridae and designated as Sclerotinia sclerotiorum hypovirus 1 (SsHV1/SZ-150). The satellite-like 3.6kbp dsRNA segment (S-dsRNA) shares high sequence identity with the 5'-UTR of SsHV1/SZ-150. SsHV1/SZ-150 alone is not the primary causal agent for hypovirulence of strain SZ-150 since strains without the S-dsRNA show normal phenotype. This is the first report of a naturally occurring hypovirus that infects a fungus other than Cryphonectria parasitica.