Enzyme cost is an interest topic. In my personal view, the market is the most determinant drive force for its costs. Take cellulase an example, cellulase is produced by Trichoderma species for more than 20 years. After the discovery of Rut-30 (a super cellulase-producing strain), enzyme companies produce a lot of cellulases for some real applications. About 10 years ago, the cellulase production costs were $50-60 dollars per kg because of limited application. After DOE gave > 22 millions to Genencor and Novozymes for reducing enzyme cost for cellulosic ethanol production, current cellulose costs ranges 1-2 dollars/kg. They decrease cost through several factors: change carbon source from lactose to glucose (cheaper), increase fermentation titer (100 g proterin /L), adjust enzyme composition, etc.

About recombinant protein, should we purify it before use? The answer may be not. If we express a thermophilic recombinant protein E. coli, after expression we can increase temperature to denature the E. coli that we do not need. If we need protein purification, we are developing a new ultra-low-cost recombinnat protern purification method (lower than all existing method). Surely, high cell-density fermentation will be very important for protein production. I think that most of them are well-known industrial skills. Markets and money will drive the enzyme cost greatly. Thank of computer, DVD player, digital camera, etc.