Viruses : Conductors of aquatic ecosystems ? Stéphan JACQUET Thonon-les-Bains
Outline The Group of Aquatic Microbial Ecology The Importance of Aquatic Ecosystems The Importance of Aquatic Micro-organisms The Importance of Aquatic Viruses The Key Roles played by Aquatic Viruses The Uncharacterized Viral Diversity The Phage Therapy in Aquatic Environments Take Home Messages
GAME Group of Aquatic Microbial Ecology
Evaluate and study the diversity, the dynamics and the functioning of aquatic microbial communities, from viruses to protozoan
The French Aquatic Viral Network
AQUAPHAGE
Relationships between prokaryotic and viral diversity in different aquatic environments
Genomics & Ecology of Aquatic Viruses Banyuls-sur-Mer, France 11-13 February, 2008
A meeting in the context of the Marine Genomics Europe Network and
RAVAGE Réseau frAnçais de Virologie Aquatique de la Génomique à l'Ecologie
Aquatic Ecosystems
Aquatic habitats represent >70% of the Earth’ surface >50% of the ocean is >3,000 m depth (V=1.3 x 109 km3) Freshwater ecosystems represent 0.02% of the total water volume The oceans control the climate, produce half of the Earth’s oxygen
Aquatic Microorganisms Microorganisms constitute >90% of living biomass in the sea Prokaryotes dominate over unicellular eukaryotes by a factor of 2-3 orders of magnitude in the pelagic environment Total number of prokaryotes in aquatic habitats : 1.2 x 1029 cells ~ similar to soils. Freshwater : 2.3 x 1026 cells Total biomass of prokaryotes in aquatic habitats and oceanic sub-surfaces : ~ 60-100% of the total C found in plants The higher cellular production of prokaryotes is found in aquatic ecosystems : >1030 cells/year Photosynthetic and heterotrophic microorganisms play a key role in ecosystem functioning and the global biogeochemical cycles. Phytopk fix up to 50 GtC/year vs. BP averages 50% of the PP
Aquatic Microorganisms Abundance In 1 ml of water samples (oceans, lakes, estuaries, etc) : Heterotrophic prokaryotes Photosynthetic prokaryotes Protozoan (Flagellates, Ciliates) Microalgae Zooplankton Fishes
Quid of Viruses ?
1 000 000 cells 100 000 cells < 10 000 cells < 5 000 cells 1030 viruses in aquatic habitats The viral string of pearls is ~10 million light years long
Phages are probably the most abundant life forms on Earth
Aquatic Viruses Abundance In 1 ml of water samples (oceans, lakes, estuaries, etc) : Viruses
Heterotrophic prokaryotes Photosynthetic prokaryotes Protozoan (Flagellates, Ciliates) Microalgae
10 000 000 particles
1 000 000 cells 100 000 cells < 10 000 cells < 5 000 cells
High viral numbers are found in surface waters, in near-shore waters, in eutrophic waters, during productive seasons Low values are found during unproductive seasons, in deep waters, in offshore and oligotrophic waters Viral abundance is typically higher in fresh than in marine waters
Aquatic Viruses Abundance
Viruses represent 5% of the prokaryotic biomass Viruses contain more carbon than 75 million blue whales (~280 Mt)
From Suttle 2007
Aquatic Viruses The main domains of phage research
The environment (ecology and pollution) The bacterial pathogenicity The food industry The evolution The genomic aspect The phagotheraphy
Aquatic Viruses Virus life cycle
Diet
Lysogenic cycle
Insertion Induction UV, nutriments, mutagens, environmental stress
Nutriments, Temperature, host physiology
Lytic cycle Diversity, population control, nutrient fluxes
Character acquisition
Aquatic Viruses Virus life cycle From Weinbauer 2004
Aquatic Viruses Virus life cycle The most important life cycle is still not known in aquatic habitats Contradictory results dealing with lytic vs. lysogenic processes: - important spatial and time variability - important shifts from one to another (environmental factors) Viral-induced cell lysis has been the most studied to date 25-80% of viruses in a community are likely to be infectious There are ~1023 viral infections per second in the ocean 20 to 60% of member species are lysogens (i.e. contain prophages) The frequency of lysogeny varies among taxonomic groups
Aquatic Viruses Virus life cycle Chronic infection has been only reported once in an alpine lake Lytic phages have been reported everywhere FIC vary between 0 to 45% in aquatic ecosystems 20 to 60% of member species are lysogens (i.e. contain prophages) 35% of bacteria contain a functional viral genome The frequency of lysogeny varies among taxonomic groups Lysogenic hosts may gain new phenotypic characteristics, including superinfection immunity, antibiotic resistance, antigenic changes, enterotoxin production and virulence factors
Aquatic Viruses Virus life cycle
•
Important strategy for ‘extreme’ environments (Lisle et al. 2004; Weinbauer et al. 2003), less important for productive ecosystems (Weinbauer et al. 1996; Wilcox and Fuhrman 1994).
•
Major strategy when low host abundance and/or altered physiological state (Jiang and Paul 1994; Weinbauer et al. 2003)
•
Lysogeny = refuge hypothesis for the viral community (Weinbauer 2004, Wommack and Colwell 2000)
Aquatic Viruses Assessing the role of livings in the functioning of aquatic ecosystems require to be able to give answers to 3 basic questions :
Which organisms are there and in which proportion ? What are organism metabolic and reproduction rates ? What kind of players are they in the functioning of ecosystems ?
Aquatic Viruses
Profondeur (m)
Abundance, distribution, dynamics
Geneva Lake
Lake Bourget
2004
2005
2006
Aquatic Viruses 10
Cell ml-1 1e+6 2e+6 3e+6 4e+6 5e+6 6e+6 7e+6
Depth (m)
20 30 40
Heterotrophic Bacteria 50
10
Part ml-1
Depth (m)
20
2.0e+7 4.0e+7 6.0e+7 8.0e+7 1.0e+8 1.2e+8
r= 0.48
30
p= 0.03 40
Viruses
n= 21
50 Mar
May
Jul
Sep
Nov
Aquatic Viruses 10
Cells. ml-1
20
0 2e+4 4e+4 6e+4 8e+4 1e+5
30 40
Picocyanobacteria
50
r= 0.49
10
P
