My bacterial isolates are capable to grow on 600 ppm concentration of arsenite (III) which is used as a electron acceptor by bacteria.

For the confirmation of transforming ability of arsenite by bacteria, I had done silver nitrate test.

According to existing methods for determining arsinite oxidation, a brownish precipitate should appear while performing silver nitrate test if there is occurrence of arsinite oxidation.

But I did not got any colour changes even after applying the (0.1 M) silver nitrate.

Here I suspect that, naturally the silver nitrate is photoreactive which gives dark brown colour when it is exposed in light.

Even after performing the silver nitrate test done on arsinite reducing bacteria (which was grown on minimal media containing Arsenite) there was no colour change observed till two days incubation.

But when the plates were kept outside (under light) after two days of incubation, it produced brown precipitates within 4 hours of light exposure. Is that implies this is caused by photoreactive nature of silver nitrate or is it due to bacterial arsenite oxidation?