Certain eukaryotic Chlorella-like green microalgae are hosts for large (>310 kb), plaque-forming, dsDNA viruses (chlorella viruses or chloroviruses) found in fresh water throughout the world.  Chloroviruses, family Phycodnaviridae, are a rich source of enzymes with unique structural and genetic features.  The prototype of the family, PBCV-1, has a 331 Kb genome, that encodes ~365 proteins and 11 tRNAs.  The algae-virus system is a model for studying DNA virus/algal interactions and has been the focus of our laboratory's research for the past 25+ years. Cell wall degrading enzymes are crucial at two points during PBCV-1 replication.  First, the virus infects its host by attaching specifically to the external surface of the algal cell wall. Attachment results in the release of virion-packaged cell wall digesting enzyme(s) that allow entry of virus DNA, leading to replication and release of progeny virus particles in 6 – 8 hours post infection.  Second, progeny viruses are released from the host by cell wall lysis.  Six viruses have been sequenced and annotated (Fitzgerald at al., 2007a, b, c).  Fifteen genes with cellulose binding domains were identified, nine of which have predicted cellulase/xylanase functions, including a b-1,4-glucuronic lyase, an exo-1,4-b D-glycanase, and a b-1,3-gluconase. These genes were cloned, expressed and determined to be enzymatically active.  The host, Chlorella sp. NC64A, is also predicted to encode its own wall-degrading enzymes to aid in progeny release during cell replication.  The Chlorella sp. NC64A genome was sequenced by the Joint Genome Institute (USDOE) and predicted to encode at least 5 xyloglucan-specific endoglucanases.