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. 2017 Dec;11(12):2869-2873.
doi: 10.1038/ismej.2017.130. Epub 2017 Jul 25.

Phaeoviruses discovered in kelp (Laminariales)

Dean A McKeown  1   2 , Kim Stevens  1   2 , Akira F Peters  3 , Peter Bond  4 , Glenn M Harper  4 , Colin Brownlee  1   5 , Murray T Brown  2 , Declan C Schroeder  1   6
Affiliations

Phaeoviruses discovered in kelp (Laminariales)

Dean A McKeown et al. ISME J. 2017 Dec.

Abstract

Phaeoviruses are latent double-stranded DNA viruses that insert their genomes into those of their brown algal (Phaeophyceae) hosts. So far these viruses are known only from members of the Ectocarpales, which are small and short-lived macroalgae. Here we report molecular and morphological evidence for a new Phaeovirus cluster, referred to as sub-group C, infecting kelps (Laminariales) of the genera Laminaria and Saccharina, which are ecologically and commercially important seaweeds. Epifluorescence and TEM observations indicate that the Laminaria digitata Virus (LdigV), the type species of sub-group C, targets the host nucleus for its genome replication, followed by gradual degradation of the chloroplast and assembly of virions in the cytoplasm of both vegetative and reproductive cells. This study is the first to describe phaeoviruses in kelp. In the field, these viruses infected two thirds of their host populations; however, their biological impact remains unknown.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Phylogenetic analysis of sub-group C phaeoviral MCP from Laminariales and Ectocarpales phaeoviral sub-groups A and B. The Coccolithovirus EhV-86 (Schroeder et al., 2002) was used as an outgroup. Topology based on maximum likelihood and decimals are Bayesian posterior probabilities for each sub-group. * denotes sequence variants from gametophyte isolates. Accession numbers are given for each sequence. Scale bar denotes number of nucleotide substitutions per site. Highlighted in green is the strain used for microscopy observations.
Figure 2
Figure 2
Light and epifluorescence (a–d, DAPI stained) and transmission electron (e–n) micrographs of Laminaria digitata gametophyte strain LdigPH10-30 m. (a) Spermatozoid (arrowhead) released from antheridium (white arrow), (b,c). Deformed opaque structures with high DAPI blue fluorescence in contrast to normal nuclei (white arrowheads). (d) High prevalence of DAPI-fluorescent filaments. (e) Cross-section of healthy vegetative cell showing chloroplast (ch), nucleus (n), and mitochondria (m). (f–l) VLP formation in vegetative gametophyte cells. Chloroplasts detached from cell periphery, loss of internal structure, appearance of tubular structures (arrows) and various stages of VLP assembly (arrowheads). (m,n) VLPs isolated from extracellular medium and visualised by negative staining.
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