For quite some time , it was thought that Geobacter species lacked c - cytochromes that can be utilized to reduce metal ions , .
It was assumed that species required direct physical contact in order to use metal ions as terminal electron acceptors .
For quite some time , it was thought that Geobacter species lacked c - cytochromes that can be utilized to reduce metal ions , hence it was assumed that they required direct physical contact in order to use metal ions as terminal electron acceptors .