Biology subjects

Blanc, G.

Publications and source records attributed to Blanc, G..

5 recordsLinked to original sources

bioRxiv2026

in silico Analysis of Phycodnaviridae Tetrapyrrole Enzymes: Subcellular Localization and Functional Divergence from Host Homologs

RationaleRecent viral metagenomic studies have identified a plethora of enzyme-encoding genes in Phycodnaviridae viruses that are not strictly required for viral replication. These enzymes hold an unexpected metabolic potential during the infection process with their specific green algae host. As neither their role in the infection process nor the subcellular localization of these proteins has been experimentally characterized, comparative sequences, structural and biochemical in silico analyses can help generate functional and localization hypotheses. MethodsIn a recent viral metagenomic dataset, we identified a collection of viral homologs involved in bilin biosynthesis: heme oxygenase (vHMOX1) and Phycocyanobilin:Ferredoxin oxidoreductase (vPcyA). Viral and algal homologues were compared through sequence analyses and AlphaFold3 structural predictions. Predicted biochemical properties were analyzed for their compatibility with subcellular compartments. Active site architecture and putative substrate binding were compared between viral and algal proteins using AlphaFold3 and experimentally resolved structures. ResultsViral HMOX1 and PcyA sequences are truncated compared to algal homologs, lacking the N-terminal extension associated with chloroplast targeting. However biochemical properties, including isoelectric point and surface charge distribution, are compatible with localization in chloroplast stroma. Structural comparisons reveal modifications in the viral HMOX1 active site, including partial substrate reorientation and substitutions of key residues, consistent with modified heme-binding properties. In contrast, vPcyA models show no significant differences to their algal counterparts. ConclusionsActive site remodeling in vHMOX1 protein models suggests that these viral homologues may have evolved distinct heme-binding properties. Unlike vPcyA, vHMOX1 homologs appear to have diverged more substantially from their algal counterparts, potentially reflecting functional specialization in the viral infection context. One sentence summary of key findingsOur bioinformatic analyses expand the repertoire of auxiliary metabolic genes in Phycodnaviridae by identifying a conserved heme degradation pathway, non-canonical vHMOX1/PcyA targeting and structural rearrangements surrounding the catalytic sites of viral HMOX1.

biochemistry↗

bioRxiv2025

A giant virus awakens virophage-like PLVs in the green alga Tetraselmis

Giant double-stranded DNA viruses profoundly influence algal population dynamics, yet their interactions with co-infecting mobile elements remain poorly understood. Here, we describe a natural tripartite infection system in the marine unicellular alga Tetraselmis striata, where a newly isolated giant virus, Oceanusvirus lionense (TetV-2), triggers the productive replication of multiple polinton-like viruses (PLVs). One PLV (Tsv-S2b) was co-isolated from the same seawater sample, while two others (Tsv-S2a and Tsv-S3b) derive from endogenous elements integrated in the algal genome. These PLVs depend strictly on TetV-2 for propagation and exert a virophage-like effect, reducing TetV-2 yields in a dose-dependent manner. Comparative genomics shows that virophagic PLVs retain a conserved structural module but harbor divergent replication and integration genes, supporting modular evolution of the PLV lineage. The reactivation of integrated PLVs mirrors the behavior of endogenous virophages in Cafeteria burkhardae, suggesting that specific Oceanusvirus-PLV compatibilities govern reactivation. This work provides direct evidence that integrated PLVs in green algae can transition to a virophage lifestyle upon infection by a giant virus, highlighting an inducible antiviral defense mechanism within photosynthetic protists. Author SummaryMarine microalgae are frequently infected by giant viruses, but how these infections are regulated is poorly understood. In the green alga Tetraselmis striata, we discovered that a giant virus can "wake up" small DNA viruses known as polinton-like viruses (PLVs) that are normally integrated and silent within the algal genome. Once activated, these PLVs multiply using the giant viruss replication machinery and, in turn, reduce its production. This helper-dependent relationship mirrors the behavior of virophages previously known only in non-photosynthetic protists. Our results reveal that microalgae possess an inducible antiviral system based on the reactivation of endogenous viral elements, suggesting that such interactions may be widespread in the oceans and play an important role in controlling algal virus epidemics.

microbiology↗

bioRxiv2022

"Quasigenus" among Phycodnaviridae: A diversity of chlorophyte-infecting viruses in response to a dense algal culture in a high-rate algal pond.

This study approaches a high rate algal pond (HRAP) culture by metagenomic sequencing of the viral DNA fraction, this includes the so-called giant virus fraction (phylum Nucleocytoviricota), with the goal of revealing viruses coexisting within an intensified algal culture. A wealth of interesting novel viruses is revealed, including members of Nucleocytoviricota, Lavidaviridae, and polinton-like viruses, which are taxa containing previously characterized algal viruses. Our sequencing results are coupled with a virus targeted qPCR study and 18S rDNA metabarcoding to elucidate potential virus-host interactions. Several species of green algae are identified (Chlorophyta), likely representing the alternating dominant populations during the year of study. Finally, we observe a bloom of viral diversity within the family Phycodnaviridae (Nucleocytoviricota), including highly related but non-identical genotypes, appearing in the HRAP in September and October 2018. This bloom is most likely the cause of a mass mortality event of the cultured algae that occurred during these same months. We hypothesize that these related Phycodnaviridae lineages selectively infect different strains of the same algal species of the Genus Picochlorum that have been identified in the HRAP by metabarcoding and coined this phenomenon a "quasigenus" by analogy to the RNA virus quasispecies concept.

evolutionary biology↗

bioRxiv2022

Integrated viral elements unveil the dual lifestyle of Tetraselmis spp. polinton-like viruses

In this study, we aimed at exploring horizontal gene transfer between viruses and Chlorodendraceae green algae (Chlorophyta) using available genomic and transcriptomic sequences for 20 algal strains. We identified a significant number of genes sharing a higher sequence similarity with viral homologues, thus signaling their possible involvement in HGTs with viruses. Further characterization showed that many of these genes were clustered in DNA regions of several tens to hundreds of kilobases in size, originally belonging to viruses related to known Tetraselmis spp. viruses (TetV and TsV). In contrast, the remaining candidate HGT genes were randomly dispersed in the algal genomes, more frequently transcribed and belonged to large multigene families. The presence of homologs in Viridiplantae suggested that these latter were more likely of algal rather than viral origin. We found a remarkable diversity Polinton- like virus (PLV) elements inserted in Tetraselmis genomes, all of which were most similar to the Tetrasemis striata virus TsV. The genes of PLV elements are transcriptionally inactive with the notable exception of the homologue of the TVSG_00024 gene of TsV whose function is unknown. We suggest that this gene may be involved in a sentinel process to trigger virus reactivation and excision in response to an environmental stimulus. Altogether, these results provide evidence that TsV- related viruses have a dual lifestyle, alternating between a free viral phase (i.e., virion) and a phase integrated into host genomes.

microbiology↗

bioRxiv2019

Long-read only assembly of Drechmeria coniospora genomes reveals widespread chromosome plasticity and illustrates the limitations of current nanopore methods

Long read sequencing is increasingly being used to determine eukaryotic genomes. We used nanopore technology to generate chromosome-level assemblies for 3 different strains of Drechmeria coniospora, a nematophagous fungus used extensively in the study of innate immunity in Caenorhabditis elegans. One natural geographical isolate demonstrated high stability over decades, whereas a second isolate, not only had a profoundly altered genome structure, but exhibited extensive instability. We conducted an in-depth analysis of sequence errors within the 3 genomes and established that even with state-of-the-art tools, nanopore methods alone are insufficient to generate eukaryotic genome sequences of sufficient accuracy to merit inclusion in public databases.

genomics↗