ViroBlogy

Euglena cells in pondwater. Image copyright Russell Kightley, http://www.rkm.com.au

Thanks to AJ Cann’s MicrobiologyBytes, and The Scientist:

Decoding the Genome of Chlorella Microalgae, a Promising Genus for Biofuel Production

ScienceDaily (Oct. 13, 2010)
“…the analysis of the Chlorella genome has also revealed numerous genes governing the synthesis of flagellar proteins, which suggests that this species could have a sexual cycle that has gone unnoticed until now. Last but not least, the ability of Chlorella algae to synthesize chitin could have been inherited from a virus (itself endowed with chitinase activity) having secured exclusive use of its host against other viruses incapable of piercing through its protective shell. This “monopoly” scenario illustrates a new mode of co-evolution between viruses and their hosts.”

Gotta love ’em – because maybe we and many other things couldn’t be here without ’em.  This builds on previous evidence that retroviruses probably helped in the evolution of placental mammals, that much of the planet’s oxygen may be due to viruses, and that viruses often aid hosts in developing resistance against them.

However, the parent paper is always preferable to a commentary – and I am indebted to Guillaume Blanc – the corresponding author – for a copy of the paper; our otherwise reliable library service fell down on access to the Plant Cell!  This allows me to quote the following (bold text my emphases):

The Chlorella variabilis NC64A Genome Reveals Adaptation to Photosymbiosis, Coevolution with Viruses, and Cryptic Sex

Guillaume Blanc et al., Plant Cell Advance Online Publication
Published on September 17, 2010; 10.1105/tpc.110.076406

With 233 predicted enzymes involved in carbohydrate metabolism, NC64A appears much better equipped for synthesizing and modifying polysaccharides than the other sequenced chlorophytes that have between 92 (O. tauri) and 168 (C. reinhardtii) of such predicted enzymes…. However, we did not find homologs of the Arabidopsis proteins involved in the synthesis of cellulose (cellulose synthase CesA) or hemicellulose (hemicellulose syn- thase CLS), the major components of the primary cell wall of land plants. Instead, experimental evidence suggests that the cell wall of Chlorella species, including NC64A, contain glucosamine polymers such as chitin and chitosan….

Chitin is a natural component of fungal cell walls and of the exoskeleton of arthropods but is not normally present in green algae. The origin of chitin and its derivatives in the Chlorella genus has long been an enigma. Except for the plant-type chitinase gene, which is found in land plants (but not in chlorophytes apart from Chlorella), the four gene classes involved in forming and remodeling chitin cell walls (i.e., chitin synthase, chitin deacetylase, chitinase, and chitosanase) are absent in all the other fully sequenced Viridiplantae species. By contrast, homologs for each of these families exist in genomes of Chlorella viruses. The viral genes are presumably involved in degradation of the Chlorella cell wall (chitinase and chitosanase)… and production of chitinous fibers on the external surface of virus-infected cells (chitin synthase and chitin deacetylase) …. Phylogenetic analysis suggests that the Chlorella ancestor exchanged the bacterial-type chitinase and chitin-deacetylase genes with the chloroviruses.

And as I have often said (well, mostly to myself, but also in MicrobiologyBytes) – “Profound Insight (No. 4): in order to understand viruses, we should all be working on seawater…. That is where the diversity is, after all; that is where the gene pool that gave rise to all viruses came from originally – and who knows what else is being cooked up down there?”.

Amen.  But let’s add ponds to that.

Tags: chitin, Chlorella, Evolution, virus

This entry was posted on 21 October, 2010 at 12:23 and is filed under Evolution, General, Viruses. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.