> That seems to indicate that they wouldn't be able to compete with
     >  their cousins outside of a controlled environment.

Not clear. They only grew more slowly when in a less friendly environment than they're used to. It's conceivable that the new environment selected for bacteria who can process AsO4 more quickly than the control strain, but it's not clear how well suited these new bacteria are to the original concentrations of AsO4 and PO4. Perhaps they'd do better, perhaps worse.