Shifts in microbial community structure at Co and Ni nutrient deficiency in biogas tank reactors digesting grain stillage

• From previous studies in our laboratory it was concluded that Co- and Ni-amendment was necessary for stable biogas process operation during anaerobic digestion of grain stillage. In the present study, shifts in microbial community structure were investigated in relation to omission of Co or Ni from the stable biogas processes. The first effect of the stopped Co- or Ni-additions was an increase in volatile fatty acid (VFA) concentrations. Eventually, the methane production ceased in the reactor without Niaddition. Quantitative polymerase chain reaction (qPCR) revealed that Methanosarcinales was the dominating order of methanogens during stable process performance (both Co and Ni supplied) while Methanomicrobiales increased with increasing VFA-concentrations at both Co- and Ni-deficiency. The increase was however more pronounced at Co-limitation. The qPCR results agreed with sequencing data obtained by 454-pyrosequencing, where the dominating sequences belonged to Methanosaeta sp (order Methanosarcinales) at stable conditions, while the proportion of sequences belonging to Methanoculleus sp. (order Methanomicrobiales) increased at reactor instability as a result of decreasing concentration of Co or Ni.

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