Merry Youle of Small Things Considered fame has a new post on the site that looks at the Acidianus two-tailed virus.
"Why two tails? Why such long tails? The researchers note that ATV is the only virus of an acidophilic hyperthermophile known to lyse its host, albeit only under stress conditions. Thus, unlike those that stay indoors, ATV is confronted with a hostile environment where host cells are sparse. The tails triple their length, greatly increasing their chances of quickly bumping into a potential host cell.
How the tails are formed remains a mystery. The process is temperature dependent. Tailless newborn particles can be held at 4 ºC for several months, and still sprout no tails. At 75 ºC, they grow tails, but very slowly, taking about 8 days. Given their preferred 85 ºC they complete the job in less than an hour. In the process, the particles shrink to about half their original volume (even allowing for the volume of the tails).
One clue comes from ATV's genome..."
Click source for more.