This invention relates to recombinant microorganisms capable of producing isoprene and isoprene production with the use of such recombinant microorganism with good efficiency. In this invention, functional activity of the ispA gene is altered to reduce the production of isoprenoid molecules in recombinant cells engineered to produce isoprene or in cells otherwise susceptible to isoprenoid accumulation during fermentation. This decreased ispA gene functional activity enables enhanced synthesis of isoprene in a host microorganism.