During the part where you're on planet Gellix rescuing the defected CERBERUS scientists, just after the scene where you talk to Jacob about things and right before you speak to Dr. Brynn, there is one ex-cerberus official (Dr. Brown) mourning to her husband right beside the screen (you can`t miss it). Speak with her and you`ll automatically receive a +2 reputation. After that, pause the game and then save your data. Load it once again and you will notice that you`ll be in the same moment before you saved, and Dr. Brown is in the exact same position. Speak to her again and gain another +2 reputation. Do this as much as you want until you fill your reputation meter.