NOVELTY - The single-step operation of a biogas plant for the production of biogas by anaerobic wet fermentation of a substrate composition supplied to a biogas fermenter (1) of the biogas plant, comprises culturing substrate-specific methane bacteria independent of the biogas plant in a cell-culture reactor (4) and metering of the specific bacteria. The composition is a substrate mixture from a mixture of commercial fertilizers, as liquid manure and/or muck, and/or of regenerating raw materials and/or of organic substrates of the agricultural industry and/or of organic residues.    USE - For the production of biogas by anaerobic wet fermentation of a substrate composition supplied to the biogas fermenter of the biogas plant.    ADVANTAGE - Ensures stable, fast, more economical and controlled operating procedure of the biogas plant as well as enables to produce optimally high yield of the biogas.    DETAILED DESCRIPTION - The single-step operation of a biogas plant for the production of biogas by anaerobic wet fermentation of a substrate composition supplied to a biogas fermenter (1) of the biogas plant, comprises culturing a substrate-specific methane bacteria independent of the biogas plant in a cell-culture reactor (4) and metering of the specific bacteria. The culturing of the substrate-specific bacteria comprises production/procurement of a culture substrate composition, loading a part of the culture substrate into the cell-culture reactor, adjusting the reactor temperature in the interior of the reactor to a mesophilic or a thermophilic temperature range for the anaerobic wet fermentation, step-wise, slow increases the quantity of the culture substrate in the cell-culture reactor, removing a part of the substrate feed (DS1) from the cell-culture reactor, and transporting the substrate feed to the biogas fermenter of the biogas plant and metering the feed into the biogas fermenter for the anaerobic wet fermentation. The composition corresponds to the substrate, and the biogas plant is operated in a starting phase with a time lapse. The reactor temperature is adjusted according to the starting phase with a time lapse. The space load of the substrate is increased within a processing time for the growth of substrate-specific bacteria up to a stable and initiated fermentative decomposition of the culture substrate containing a substrate feed, which contains the large quantity of the specific bacteria. Feeding of the different substrates to each of the reactors takes place in a column of cell-culture reactors, so that the respectively assigned different feed substrates with substrate-specific bacteria are produced and kept ready for use. The substrate-specific bacteria present in a pumpable liquid feed substrate are metered in a thermally insulated tank maintained in the mesophilic or thermophilic temperature range. The cell-culture reactor is arranged at the proximity to the biogas fermenter and is connected with the biogas fermenter by a lockable pumping line (5) for the requirement. A control mechanism of the biogas plant is used for its cell-culture reactor. The feed substrate is kept in a storage vessel at the biogas fermenter, is metered batch-wise and stirred by an agitation mechanism (2). The cell-culture reactor is small with respect to the biogas fermenter. The substrate composition is substrate mixture from a mixture of commercial fertilizers, as liquid manure and/or muck, and/or of regenerating raw materials and/or of organic substrates of the processing agricultural industry and/or of organic residual substances from municipalities and/or of residues from slaughterhouses.    DESCRIPTION OF DRAWING(S) - The figure shows an arrangement of culture reactor and a biogas plant;    Biogas fermenter; (1)    Agitation mechanism; (2)    Cell-culture reactor; (4)    Lockable pumping line; (5)    Substrate feed. (DS1)