WP1: Phaeoviral diversity and phylogeny in relevant kelp species

There are around 2000 different species of brown algae (class Phaeophyceae), 143 of which belong to the kelp group (order Laminariales).

Ectocarpoids (order Ectocarpales), which count with 772 species, are the hosts of the only well described phaeoviruses. The limited knowledge we have about the known phaeovirus diversity and prevalence (Table 1) illustrates the discovery potential that lies ahead.

Following the recent discovery of phaeoviruses in eight kelp species (Table 1), our main objective for this initial phase (WP1) will be to investigate the phaeoviral diversity on two very common and ecologically relevant kelp species, which also are subjected to a strong commercial interest in Norway:

  • Laminaria hyperborea: which is the most important raw material in alginate industry (used in pharmaand nutra-ceutical products) since 1963 in Norway, due to mechanization of harvest and high volumes.

  • Saccharina latissima: is one of the fastest growing among the European kelp species and has the highest carbohydrate content.

Table 1: Features of Phaeovirus subgroups. Hypothetical for Laminariales phaeoviruses due to missing data indicated by -. Abbreviation key: EC, Ectocarpales; LA, Laminariales; ac, Acinetosporaceae; al, Alariaceae; ch, Chordariaceae; ec, Ectocarpaceae; la, Laminariaceae; le, Lessoniaceae; gam, gametangia; spo, sporangia; veg, vegetative cells

Captura de Pantalla 2020-12-27 a les 17.

Phaeoviruses follow a persistent infection life strategy, co-existing with their hosts without killing them. They can, however, cause disease and transmit through parent to offspring. Despite their likely prevalence, persistent viral life strategies are not well described. Schroeder and colleagues discovered in 2009 that a central core set of genes are maintained when analysing the genome sequences of three phaeoviruses.

 

Five years later, sequence and gene phylogenies for these viruses revealed that that they can be split into two subgroups (A and B), and that member from sub-group B evolved from sub-group A through genome loss. This genome loss has caused phaeoviruses to increase their host-range, a fact more evident after the discovery of viruses in kelp species, which belong to a new sub-group C & D (Table 1).

We will work with natural samples provided by UIB and our industry collaborators. Ocean Forest AS will provide S. latissima cultivated in Austevoll (Hordaland) and DuPont Health & Nutrition L. hyperborea harvested in two different locations (Rogaland and Sør Trøndelag), in order to correlate viral presence with climatic parameters in the natural environment (WP2). We will make use of the sampling ship Brattstrøm as well, to sample around the Bergen area (Hordaland) with UiB, and will screen  already frozen DNA samples from kelp sporophytes from around 20 stations along the Norwegian coast, kept from a previous microsatellite study at UiB.

 

All samples will be screened for viral detection through DNA extraction following Maeda et al. 2013 and Mckeown et al. 2018, and targeting the phaeovirus-encoded major capsid protein (MCP). All PCR products will be sequenced by Sanger sequencing.

In WP1 we will obtain:

  1. Knowledge of the occurrence and frequency of viruses on different kelp species in Norway,

  2. Insight into the diversity of phaeoviruses,

  3. Descriptive information about phaeoviral infection and symptoms.

  4. Comprehensive knowledge about the phylogeny of the possible new viral species/strains on kelp,

  5. Insight into the host-range of phaeoviruses, the analysis of which can reveal some co-evolutionary dynamics between virus-hosts systems, and whose interactions have fundamental effects on ecological dynamics.

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