Unlike the other assimilatory pathways, bacteria using the RuBP pathway derive all of their organic carbon from  assimilation.  This pathway was first elucidated in photosynthetic autotrophs and is better known as the Calvin Cycle. Shortly thereafter, methylotrophic bacteria who could grow on reduced  compounds were found using this pathway.
First, 3 molecules of ribulose 5-phosphate are phosphorylated to ribulose 1,5-bisphosphate (RuBP). The enzyme ribulose bisphosphate carboxylase (RuBisCO) carboxylates these RuBP molecules which produces 6 molecules of 3-phosphoglycerate (PGA). The enzyme phosphoglycerate kinase phosphorylates PGA into 1,3-diphosphoglycerate (DPGA). Reduction of 6 DPGA by the enzyme glyceraldehyde phosphate dehydrogenase generates 6 molecules of the  compound glyceraldehyde-3-phosphate (GAP). One GAP molecule is diverted towards biomass while the other 5 molecules regenerate the 3 molecules of ribulose 5-phosphate.