Involved in lipopolysaccharide (LPS) biosynthesis. Catalyzes the transfer of three 3-deoxy-D-manno-octulosonate (Kdo) residues from CMP-Kdo to lipid IV(A), the tetraacyldisaccharide-1,4'-bisphosphate precursor of lipid A. Thus generates the genus-specific LPS epitope of Chlamydia, composed of the trisaccharide alpha-Kdo-(2->8)-alpha-Kdo-(2->4)-alpha-Kdo. CMP-3-deoxy-beta-D-manno-octulosonate + lipid IVA (E. coli) = alpha-Kdo-(2->6)-lipid IVA + CMP + H(+) alpha-Kdo-(2->6)-lipid IVA + CMP-3-deoxy-beta-D-manno-octulosonate = alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid IVA + CMP + H(+) alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid IVA + CMP-3-deoxy-beta-D-manno-octulosonate = alpha-Kdo-(2->8)-alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid IVA + CMP + H(+) Bacterial outer membrane biogenesis; LPS core biosynthesis. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 30 subfamily.