Abstract The influence of a defined trace metal solution and additionally Ni 2+ on anaerobic digestion of biomass was investigated. A novel synthetic model substrate was designed consisting of cellulose, starch and urea as carbon and nitrogen source in a ratio mimicking the basic composition of maize silage. Two independent batch fermentations were carried out over 21 d with the synthetic model substrate in the presence of the trace metal solution. Particularly an increase in nickel concentrations (17 and 34 μM) enhanced methane formation by up to 20%. This increased activity was also corroborated by fluorescence microscopy measurements based on cofactor F 420. The eubacterial and methanogenic population was characterized with the single strand conformational polymorphism analysis and the amplified 16S rDNA restriction analysis of 16S rRNA genes amplified by different primer systems. Nearly the half of the analyzed bacteria were identified as Firmicutes while 70% in this phylum belonged to the class of Clostridiales and 30% to the class of Bacilli. Bacteroides and uncultured bacteria represented each a quarter of the analyzed community. Methanogenic archaea were investigated with ARDRA, too. The hydrogenotrophic Methanoculleus sp. was the dominant genus which is commonly described for maize digestion thus confirming the value of the model substrate.