User blog comment:Flame Knight101/What Did Blackbeard Do to Acquire the Gura Gura no Mi?/@comment-3203286-20140228122709

I'm sure we've been over this before, but very well.

We know he can effect Devil Fruit abilities. That's how he was able to hit Ace, despite him being a Logia. It's not beyond the bounadry of imagination that given time he could remove the Devil Fruit Abilities from someone. I suspect the only reason he needed Whitebeard dead was because he couldn't beat him in a fight and keep him alive, but weaker users might not have to be killed.