Watch the Minor 9th online guitar lesson by Fareed Haque from 1-2-3 Bossa Nova
Dig on how the 5th in the bass really adds to the deep moody sound. One thing to note, if you go and check out Joao Gilberto's music, you will hear great bass, and it usually takes a minute to realize that it's Joao's guitar. There is no bass player. Just him and a drummer playing on a hi hat and that's it - fat fat fat sound - a big part of that is keeping the bass notes low and deep, and more often than not using the 5th in the bass not the root. Also don't get too carried away with the alternating root-5th basslines; it's a cool sound but moves around more than the typical bossa does, so use the alternating bass lines sparingly.