Plasmid vectors and use of plasmid vectors in methods for producing methane and isoprene using Archaea are disclosed . Particularly, plasmid vectors that express isoprene synthase ( ispS ) are prepared and inserted into methanogens, such as Methanosarcina acetivorans, to allow for co - production of methane and isoprene. In one embodiment , the methods of the present disclosure can be used for wastewater management