Transcription of fdh and hyd in Syntrophobacter spp. and Methanospirillum spp. as a diagnostic tool for monitoring anaerobic sludge deprived of molybdenum, tungsten and selenium.

Formate dehydrogenases and hydrogenases contain molybdenum or tungsten and/or selenium. These enzymes are crucial for interspecies formate and hydrogen transfer between propionate degrading Syntrophobacter spp. and methanogenic Methanospirillum spp. Here we used reverse transcription of total RNA followed by quantitative PCR (RT-qPCR) with specific primers to get insight into interspecies formate and hydrogen transfer. Transcriptional regulation of formate dehydrogenases and hydrogenases in Syntrophobacter and Methanospirillum spp. in a propionate-fed up-flow anaerobic sludge bed (UASB) reactor was examined. In both microorganisms formate dehydrogenase and hydrogenase coding genes (fdh and hyd respectively) were transcribed simultaneously. During 249 days in which molybdenum, tungsten and selenium were not supplied to the reactor feed, the microbial activity and transcription of fdh and hyd in Syntrophobacter spp. decreased. Transcription of fdh and hyd in Methanospirillum spp. did not decrease, but transcription of fdh increased when after 249 days molybdenum, tungsten and selenium were supplied to the reactor feed. The developed RT-qPCR is a technique that can give rapid information about active processes in methanogenic granular sludge and may contribute to predict metal limitation and failure in UASB reactors.