Catalyzes the transfer of myristate from myristoyl-acyl carrier protein (ACP) to Kdo(2)-(lauroyl)-lipid IV(A) to form Kdo(2)-lipid A. dodecanoyl-(Kdo)2-lipid IVA + tetradecanoyl-[ACP] = alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid A + holo-[ACP] Glycolipid biosynthesis; KDO(2)-lipid A biosynthesis; KDO(2)-lipid A from CMP-3-deoxy-D-manno-octulosonate and lipid IV(A): step 4/4. Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis. Belongs to the LpxL/LpxM/LpxP family. LpxM subfamily.