INFLUENCE OF ELECTRON-DONOR ON THE MINIMUM SULFATE CONCENTRATION REQUIRED FOR SULFATE REDUCTION IN A PETROLEUM HYDROCARBON-CONTAMINATED AQUIFER

Fluctuations in the availability of electron donor (petroleum hydrocar bons) affected the competition between sulfate-reducing bacteria (SRB) and methanogenic bacteria (MB) for control of electron flow in a petr oleum hydrocarbon-contaminated aquifer. The data suggest that abundant electron donor availability allowed MB to sequester a portion of the electron flow even when sulfate was present in sufficient concentratio ns to support sulfate reduction. For example, in an area of abundant e lectron-donor availability, SRB appeared to be unable to sequester the electron flow from MB in the presence of 1.4 mg/L sulfate. The data a lso suggest that when electron-donor availability was limited, SRB out competed MB for available substrate at a lower concentration of sulfat e than when electron donor was plentiful. For example, in an area of l imited electron-donor availability, SRB appeared to maintain dominance of electron flow at sulfate concentrations less than 1 mg/L. The pres ence of abundant electron donor and a limited amount of sulfate reduce d competition for available substrate, allowing both SRB and MB to met abolize available substrates concurrently.