Viruses and AlgaeViruses and AlgaeBy Stephanie BooneBy Stephanie Boone

Virus FactsVirus Facts

• Most abundant life form in aquatic systems.• In the ocean the total number exceeds 1029.

• Marine viruses high concentrations up to 10 8 in ml-1

• Play a significant role in the transfer of matter and energy in aquatic microbial food webs.

• Infect at least some members of all the major classes of freshwater and marine algae.– Reported in at least 44 taxa of eukaryotic algae – Includes members 10 of 14 classes of algae

• Virus Interactions range from – true parasitism (chronic infection/cellular release without

death)– to predation (lytic infection resulting in cell death).

Ecological SignificanceEcological Significance• Play a significant role in

the transfer of matter and energy in aquatic microbial food webs.

• Viral lysis of algae effects carbon nutrient flow.– Carbon stored in dissolved

organic matter released into system.

– May influence carbon cycling and climate.

• Significant role in transfer of information through DNA.

• Important role in algae blooms.– effect marine community

structure.

Algal VirusesAlgal Viruses

• Despite the Despite the established ecological established ecological importance of marine importance of marine viruses there have viruses there have been few studies which been few studies which extensively investigate extensively investigate and characterize and characterize viruses of algae. viruses of algae.

• The viruses studied The viruses studied extensively fall into extensively fall into two catagories.two catagories.

Large ds DNA viruses.Large ds DNA viruses.

PBCV-1, Fsv, EsVPBCV-1, Fsv, EsV

Small viruses.Small viruses.

HaRNA, HaNIVHaRNA, HaNIV

Large dsDNA VirusesLarge dsDNA Viruses

• Family Family PhycodnaviridaePhycodnaviridae– Paramecium bursaria chorella

virus (PBCV-1) infect eukaryotic unicellular-like green algae.

– Ectocarpus virus (EsV) Feldmannnia virus (FsV) infect marine brown alga.

• Common characteristicsCommon characteristics

– Found on five continents– tropical, subtropical

seawater, and freshwater – large icosahedral particles

130-190 nm diameter– large dsDNA genomes

160-380 kb– Viral capsid assembly and

DNA packaging occurs in the cytoplasm

PBVC-1/ Chlorella virusPBVC-1/ Chlorella virus

• PBVC-1 infects chlorella algae strain NC64A or Pbi.

• Chlorella algae are small, spherical, unicellular, nonmotile, asexual reproducing green algae.

• Hereditary endosymbionts in protozoan P. bursaria - resistant to viral infection when in symbiotic relationship.

• PBCV-1 - linear nonintegrated genome– 16 classes of virus

• Virus attaches to agal cell wall with hexagonal vertices, digests the wall releases viral DNA into cell.

• Packaging and assembly of virions takes place in cytoplasm virus released by localized cell wall lysis

EsV & FsV- Brown algal EsV & FsV- Brown algal virusesviruses• Ectocarpus virus (EsV) and Ectocarpus virus (EsV) and

Feldmannia virus (FsV) Feldmannia virus (FsV) infect brown algaeinfect brown algae

• densely packed polyhedral densely packed polyhedral viral particles viral particles

• do not infect vegetative do not infect vegetative cellscells

• viral particles displace viral particles displace normal reproductive cells normal reproductive cells producing sterilityproducing sterility

• Viral capsid assembly and Viral capsid assembly and DNA packaging occur in the DNA packaging occur in the cytoplasm after nuclear cytoplasm after nuclear membrane degeneration. membrane degeneration.

Small VirusesSmall Viruses

• Heterosigma akashiwoHeterosigma akashiwo nuclear nuclear inclusion virus (HaNIV) and inclusion virus (HaNIV) and Heterosigma akashiwoHeterosigma akashiwo RNA virus RNA virus (HaRNAV) infect the algae (HaRNAV) infect the algae Heterosigma akashiwo Heterosigma akashiwo (Raphidophyceae(Raphidophyceae) ) a toxic bloom-a toxic bloom-forming microalgaeforming microalgae

• Host specific - simultaneous Host specific - simultaneous coinfection. coinfection.

• HaRNAV 25 nm diameterHaRNAV 25 nm diameter– polyhedral symmetry polyhedral symmetry

• HaNIV 30 nm diameterHaNIV 30 nm diameter• replicates to high copy number replicates to high copy number

(10(1055) before host lysis ) before host lysis – nonenveloped and hexagonal nonenveloped and hexagonal

implying icosahedral symmetry. implying icosahedral symmetry. • Each virus forms a crystalline arrayEach virus forms a crystalline array

– Arrays located in different parts of Arrays located in different parts of cell. cell.

• References:• Van Etten J L, & Meints R H. Giant viruses infecting algae. Annual Review

of Microbiology 1999;53:447-494.• Weinbauer M G, & Rassoulzadegan F. Are viruses driving microbial

diversification and diversity. Envirnmental Microbiology 2004; 6: 1-11.• Lawrence J E. & Chan A M. A novel virus (HaNIV) causes lysis of the toxic

bloom-forming alga Heterosigma akashiwo (Raphidophyceae). Journal of Phycology 2001; 37:216-222.

• Tai V, Lawerence J E, Lang A S, Chan A M, Culley A I, Suttle C A. Characetrization of HaRNAV, a single stranded RNA virus causing lysis of Heterosigma akashiwo (Raphidophyceae). Journal of Phycology 2003; 39: 343-352.

• Conclusion:Conclusion:

• Need more research. Need more research.

• We know very very little about the viruses We know very very little about the viruses that infect algae.that infect algae.