The diazotrophic (nitrogen fixing) Bacteria are extraordinarily diverse and apart from a few select groups are very poorly characterized. Diazotrophs associated with the roots of non-crop plant species are particularly understudied. The North Inlet Microbial Observatory (NIMO) focuses on diazotrophs in a salt marsh ecosystem. This system is characterized by strong zonation patterns of a very limited number of plant species growing along distinct environmental gradients. It also harbors a great diversity of plant root-associated diazotrophs, many of which appear to be novel taxa. The zonation patterns and biota of salt marshes provide a unique opportunity to explore the diversity and distribution patterns of this key bacterial group, and to evaluate the underlying environmental parameters that control diversity, and distributions of the active diazotrophs.