This is not that important as it sounds. It would not be able to solve NP-complete problems for large inputs, because it enumerates all possibilities in DNA base-pair combinations. This has actually been done before with pure DNA and their manipulation (now they use bacteria for color-marking and thus selection of the right solution's DNA sequence).
Anyways, this does not scale well, having only a few hundred cities would require DNA, that would weight cca the mass of our earth.
So this result is nice as a genetic manipulation excercise, I like that they contribute to the "standard biological components database", but it has no implication for computational complexity.
And it won't solve complex problems better than sillicon, because instead of time, you need mass. There's simply not enough material and space on this small planet for DNA solution of hamiltonian path for >500 cities.