Lot 255, also known as the Protection Bond and the Protector System Plasmid, is a biological modification designed by Yi Suchong used to try condition a Big Daddy to attack anything that physically harms a Little Sister. It is described in the Audio Diary Protection Bond.


After the Pair Bonding method used for the Alpha Series was deemed inadequate, Suchong, under the order of Andrew Ryan, created Lot 255. Suchong attempted to create the formula using the DNA of Elizabeth as he believed her genes contained the secret to the bonding mechanism from her bonding to Songbird. The formula appeared to fail, as the Big Daddies continued to ignore the Little Sisters. The girls were terrified of the hulking semi-mechanical beasts. While recording a failure in his clinic, Suchong became annoyed and struck one of the Little Sisters he was working on. Unbeknownst to him the Big Daddy had in fact bonded with the girl using a different method and quickly dispatched him: empathy.

Burial at Sea - Episode 2Edit

Main article: Burial at Sea - Episode 2

Originally in the first BioShock, it was implied that Suchong's Lot 255 did work to generate the bonding; his physical attack upon the Little Sister finally precipitated the Big Daddy to react. In Burial at Sea - Episode 2, it is revealed that the Big Daddy had actually bonded with the Little Sisters once it learned it needed their ADAM to live.