Rate and stoichiometry of microbial sulfate reduction by Desulfovibrio desulfuricans in biofilms

The kinetics and stoichiometry of Desulfovibrio desulfuricans attached to a polycarbonate surface were determined in RotoTorque™ reactors and compared with those of suspended cells. Biofilm specific cellular growth rate (μ_b ) and detachment rate (q_dx) were determined from unsteady state biofilm experiments. In the initial biofilm accumulation phase, the specific cellular growth rate was the same as the maximum specific growth rate for D. desulfuricans in suspension (μ_max = 0.37‐h^‐1); thereafter μ_b decreased and approached a steady state value of about 0.1‐h^‐1. The decrease in average cellular specific growth rate could be attributed to substrate (lactate) limitation in some experiments, but in others there was no evidence of this. Biofilm‐specific cellular detachment rate decreased similarly to biofilm‐specific cellular growth rate. In biofilms, cellular yield at μ_b= 0.1.h^‐1 was approximately 18% of planktonic cellular yield partly due to the production of extensive extracellular polymeric substance. A linear relationship between μ_b and specific lactate utilization rate (q_s) in the biofilm did not exist. During the steady state biofilm accumulation phase (μ_b =.0.1.h^‐1), specific lactate utilization by biofilm cells was about 2–3 times greater than by planktonic cells, whereas it was essentially the same during the initial biofilm accumulation phase. These results suggest that kinetic and stoichiometric data derived from suspended cells must be cautiously incorporated into biofilm accumulation models.

Key words:

• Desulfovibrio desulfuricans
• sulfate reduction
• growth rate
• detachment rate
• biofilm
• kinetics
• stoichiometry
• planktonic cell
• EPS production

Notes

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