Hope someone didn't already post this, but here goes.
May-June 1999's _American Scientist_ has a review of Michael Ray Taylor's _Dark Life: Martian Nanobacteria, Rock-Eating Cave Bugs, and Other Extreme Organisms of Inner Earth and Outer Space_ (Scriber: 1999). The book looks to be too popular level for me, but it is good to see another addition to the literature on nanobacteria. Hopefully, it'll spark more interest in the subject.
And from that might come another path to creating MNT -- i.e., via reengineering nanobacteria.