It is, but the bacteria live off iron already in the water, increasing the amount of bacteria won't extract more iron. More generally though, there is an entir

It is, but the bacteria live off iron already in the water, increasing the amount of bacteria won't extract more iron. More generally though, there is an entire field of bioleaching[0] which does use bacteria to either mine material or more often recover extra minerals from mine waste products. [0] https://en.wikipedia.org/wiki/Bioleaching https://en.wikipedia.org/wiki/Bioleaching