Observations of metabolite formation and variable yield in thiodiglycol biodegradation process

Abstract

The complete microbial degradation of thiodiglycol (TDG), the primary hydrolysis product of sulfur mustard, byAlcaligenes xylosoxydans ssp.xylosoxydans (SH91) was accomplished in laboratory-scale stirredtank reactors. An Andrews substrate inhibition model was used to describe the cell growth. The yield factor was not constant, but a relationship with initial substrate concentration has been developed. Using a substrate-inhibition and variable-yield kinetic model, we can describe the cell growth and substrate consumption in batch and repeated batch fermentations. Several reactor-operating modes successfully degrade TDG concentration to below 0.5 g/L. According to the experimental results, the two-stage repeated batch operation has the best degradation efficiency, and it also can degrade 500 mM TDG (≈60 g/L) to 5 mM (≈0.7 g/L) in <5 d. A hypothesis for explaining variable-yield and byproduct formation based on the capacity and utilization of metabolic loads is presented.