Public Library of Science (PLoS) is a fairly recent concept for biology publications of making a freely available, open-access journal. General info about PLoS can be found here.
"The Third Age of Phage" is a primer on new doings in phage biology written by Nicholas H. Mann.
By his reckoning, the first two "ages of phage" were early interest in phage as possible antibacterial therapeutics (before the discovery of antibiotics) and then the subsequent use of phage for many, many years in basic biological research. Now...
"The third age of phage has begun only recently with the growing recognition that phages may be major players in the great planetary biogeochemical cycles [1] and also may represent the greatest potential genetic resource in the biosphere."
Some key points from the primer:
Phages are abundant, especially in our oceans.
"It is now widely accepted that phages with a very distinctive morphology, the so-called tailed phages (Figure 2), which dominate the marine virus population, represent the most abundant biological entities on the planet, and total phage abundance in the biosphere has been estimated at 10^30 or more [3]."
...and we don't know much about them:
"Approximately 65% of the sequences obtained in a 2002 study did not have homologues in the nucleotide databases, suggesting that marine viral diversity is largely unsampled."
Phages described in a paper by Sullivan et al contain a substantial set of genes, including a number of genes that code for cellular components. These can, for example, be activated even when the phage shuts down cellular gene expression, thus allowing key cellular functions that are necessary for phage replication for continue (after all, it's hard to replicate if you kill the cell instantly).
Naturally, this suggests that a whole lot of phage-mediated lateral gene transfer is going on in the ocean.
The ocean's full o' bugs.