I have carried out work ...

I have carried out work investigating manganese deposits on stainless steel and copper.  In nearly all of the samples, bacteria were involved in both the deposition and corrosion.  Clear evidence was found of bacteria being present within the deposits and once these were introduced into fresh samples of stainless steel and copper in the presence of water, they grew and produced fresh deposits.  Stainless colonisation is slower than copper but still occurs.  I am sure that there will be exceptions, but so far the presence of manganese bacteria is the reason for deposits and corrosion.