Maxwell's Demon Constant (Information-Energy equivalence)

You're looking for this:

http://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_information_theory#Information_is_physical

So, one bit of information allows an amount of work equal to $kT\ln2$. Where $k$ is Boltzmann's constant and $T$ is the thermodynamic temperature.

I've seen the article in Nature and I think it is horrible. They do a very bad service in explaining what's happening. The way they do it, it sounds like they invented a perpetuum mobile, which is not true. How was the information uncovered in the first place? That involved energy. And as thermodynamics will have it, more energy than the information provided you to perform work with the bead.

To supplement, the answer for your final question. As Raskolnikov pointed out, this article lies about the fact that this process can be a source of energy, and indeed all known biological mechanisms of gathering energy satisfy energy conservation; photosynthesis gathers the energy from light and various kinds of respiration from chemical energy of various substances available in environment (that mostly also originated in photosynthesis, with exception of some esoteric ecosystems).