From Building Better Worlds:
"Different strains of the Engineers' black pathogen were developed to create variations on genetic acceleration. Stored at different planetary facilities, many were used to bioengineer entire worlds and species. Others were weaponized, transforming the Engineers and their genetic offshoots into abominations, anathemas, neomorphic, protomorphic, and xenomorphic mutations, as well as other abhorrent creatures - including the Engineers' worst enemy - the Perfected".