phyloseq is a set of classes, wrappers, and tools (in R) to make it easier to import, store, and analyze phylogenetic sequencing data; and to reproducibly share that data and analysis with others. See the phyloseq front page:
MG-RAST has not released an official R package as an API, and they do export to BIOM format. For now it would seem this issue is moot, unless someone can point out a specific unsupported step that would be useful.
Although in preliminary stage and no official release,
KbaseKit
will provide a way to import data directly from MG-RAST in R.MG-RAST: http://metagenomics.anl.gov/
The development repository is on GitHub. I also forked a version, but this should probably be re-forked as it is under heavy development.
https://github.com/MG-RAST/matR
Installation of
KbaseKit
: