Rate and stoichiometry of sulfate-reducing bacteria in suspended and biofilm cultures

The accumulation and activity of sulfate reducing bacteria (SRB) are of critical concern in many industrial water systems. For example, SRB cause numerous problems in petroleum production including contamination of petroleum with H{dollar}sb2{dollar}S, injection well plugging, and corrosion. Prediction of SRB behavior in natural and industrial water systems is difficult because microbial activity and growth are strongly dependent on environmental conditions (e.g., nutrient status and physical constraints). Attachment of cells on surfaces may influence their activity and growth due to change in local environment and/or cell metabolism itself. Thus, it is essential to determine effects of these environmental factors on the activity and growth of SRB to develop a comprehensive model and use this model to predict the SRB behavior.; Mono-population Desulfovibrio desulfuricans was grown on lactate and sulfate in a chemostat and in a RotoTorque biofilm reactor. Effects of temperature, limiting nutrients (e.g., phosphorous, nitrogen, and sulfate), and sulfide product on rate and stoichiometry of microbial sulfate reduction were determined in the chemostat experiment. Biofilm kinetics and stoichiometry were determined in the RotoTorque reactor and compared with planktonic (chemostat) data.; The Monod kinetic coefficients ({dollar}musb{lcub}rm max{rcub}{dollar}, K{dollar}sb{lcub}rm s{rcub}{dollar}, and Y{dollar}sb{lcub}rm x/s{rcub}{dollar}) were dependent on temperature, but stoichiometry for catabolic reactions was not. The limiting C:P and C:N ratios (w/w) were found to be in the rage of 400:1 to 800:1 and 45:1 to 120:1, respectively. Production of extracellular polymeric substance (EPS) increased with increasing both C:P and C:N ratios in the medium. A non-competitive inhibition model adequately described sulfide product inhibition kinetics. Anabolic reactions (cell production), but not the catabolic reactions (energy production), were strongly inhibited by high sulfide concentrations. Maximum biofilm specific growth rate ({dollar}musb{lcub}rm b{rcub}sp{lcub}rm max{rcub}{dollar}) was essentially the same as {dollar}musb{lcub}rm max{rcub}{dollar} for planktonic cells. {dollar}musb{lcub}rm b{rcub}{dollar} as biofilm grew even though the biofilm was not substrate-limited. Stoichiometry of the catabolic reactions was the same for biofilm and planktonic cells, but a low cellular yield and a high EPS yield were determined in biofilms. These results suggested that D. desulfuricans behave differently in biofilms than in suspension. Thus, rate and stoichiometric data determined from planktonic cells must be used cautiously in developing a model to predict growth and activity in biofilms.