The effect of sulfate:reducing bacteria (SRB), on corrosion of carbon steels and interaction between SRB and the.. carbon steel Q235 are investigated in soil-extract solutions (SES). The results show that corrosion rates are smaller in the SES with. SRB during growing period of SRB; but bigger during dying period.:The procedures of interactions of SRB and the Steel are studied :by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). SRB do not aggregate on the surface of the steel until an anaerobic. space is formed. SRB defend themselves,against free oxygen by absorbing substances containing nonfree oxygen.