Cluster III includes nitrogenase from diverse anaerobic bacteria such as clostridia (lowG+C, Grampositive) and sulfate reducers delta proteobacteria
Both strains fall within the same subgroup of delta Proteobacteria
. They are both gram-negative, nonmotile sulfate reducers, and they both have very long generation times on the order of several days.
In another study, incubation of anaerobic sediments with [C.sup.13]-acetate yielded signature lipids of grampositive bacteria rather than those of the more readily isolated delta Proteobacteria
sulfate-reducing bacteria (Boschker et at., 1998).