  Giant double-stranded DNA viruses (such as record breaking Acanthamoeba
polyphaga Mimivirus), with particle sizes of 0.2 to 0.6 micron, genomes of 300
kbp to 1.200 kbp, and commensurate complex gene contents, constitute an
evolutionary mystery. They challenge the common vision of viruses,
traditionally seen as highly streamlined genomes optimally fitted to the
smallest possible -filterable- package. Such giant viruses are now discovered
in increasing numbers through the systematic sampling of ocean waters as well
as freshwater aquatic environments, where they play a significant role in
controlling phyto- and bacterio- plankton populations. The 4th algal virus
workshop showed that the study of these ecologically important viruses is now
massively entering the genomic era, promising a better understanding of their
diversity and, hopefully, some insights on their origin and the evolutionary
forces that shaped their genomes.
