Use of a laboratory model system to study bacterial activities and interactions in sulphate-reducing biofilms on metal surfaces
A laboratory model system was developed for the study of the ecology of sulphate-reducing bacteria in biofilms on metal surfaces. The model could be used to generate reproducible biofilms. The model system was used to study biofilm development under aerobic and anaerobic conditions. Under anaerobic conditions, the effect on biofilm development and activity, of varying the nutrient composition and concentration in the bulk phase, was studied. The effect of aeration on biofilm development was also studied, using a modification of the model system. The variations in nutrient regime (using glucose in addition to lactate; reducing the glucose/lactate concentration 2.5-fold) did not have a significant effect on biofilm activity. Sulphate reduction activity in the biofilm was stimulated by addition of glucose, a substrate not generally utilised as an electron donor for sulphate reduction. Glucose respiration activity in the biofilm was partially inhibited in the presence of molybdate, a specific inhibitor of sulphate reduction. There is therfore a close metabolic communication and synergism between glucose oxidisers and sulphate reducers in the biofilm, with glucose oxidisers producing suitable substrates for sulphate reduction; and the sulphate reducers helping to pull over the glucose metabolism by preventing the accumulation of its end products. The model system is not a true mimic of the situation occurring in an offshore water injection system, where the sea-water used will contain much lower numbers of bacteria, and the relative numbers of sulphate reducers to aerobes and anaerobes would be much smaller. The model is controllable, however (to a certain extent) and therefore can potentially reveal more about microbial interactions within biofilms, and the effect of various conditions on biofilm development and activity, than can field studies, and the results obtained are more reproducible. The study has shown that such a model can be used in the study of sulphate-reducing bacteria in biofilms on metal surfaces, and in the future more information about the ecology of these economically important organisms may be gained through the use of such models.