Identification of the microbial community responsible for thiocyanate and thiosulfate degradation in an activated sludge process

An activated sludge reactor fed with thiocyanate and/or thiosulfate was operated to examine the characteristics of its microbial community. Terminal-restriction fragment length polymorphism analyses were conducted to detect shifts in the microbial community structure corresponding to influent conditions. Then, clone library analyses and RNA-based stable-isotope probing were conducted to identify sulfur-oxidizing bacteria (SOB) responsible for the degradation of each substrate. The results suggested that there were two types of SOB: thiocyanate-degrading bacteria (that can utilize both thocyanate and thiosulfate) and thiosulfate-specific bacteria (that cannot utilize thiocyanate). Thiocyanate-degrading SOB, however, were outcompeted by thiosulfate-specific SOB when the influent contained only thiosulfate. Of the sequenced clones, Marinicella-related (with 98.7% identity) and Methylobacter-related (with 91.3% identity) bacteria were identified as thiocyanate-degrading SOB, whereas Thiomicrospira thermophila-related (with 100% identity over 903 bp) bacteria were identified as thiosulfate-specific SOB.