Abstract: The present invention relates to a device for the isolation and/or purification of nucleic acid molecules suitable to bind and/or inactivate inhibitors of the activity of reagents or enzymes used for DNA manipulation and to separate a plurality of nucleic acid molecules with respect to their size. Moreover, the invention relates to a method for the isolation of a nucleic acid molecule comprising applying a sample to the device of the invention wherein said nucleic acid molecule preferably represents a fraction of the metagenome of a given habitat. Furthermore, the invention relates to a method for the generation of at least one gene library comprising nucleic acid molecules isolated by the method of the invention and to a nucleic acid molecule isolated by the method of the invention.