Biorefinery concept is a new concept in which renewable resources such as biomass are converted to fuel and chemicals. In the U.S., where this concept was developed, the government takes initiative in replacement of oil refinery, processing crude oil, with biorefinery (Fig. 1). The development of biorefinery technology is anticipated to play an important role in establishing a sustainable society in the 21st century. We have developed an efficient biomass utilization technology "Growth-arrested bioprocess" based on Corynebacterium glutamicum which has been widely used for industrial production of amino acids. The key to achieving high efficiency and high productivity is the effective separation of the microbial growth phase from the production phase of the target compound. This manner of using bacterial cells as if they were simple chemical catalysts enables one to produce large amounts of chemicals in short periods of time, and unlike conventional bioprocesses, the productivities reached, expressed as space-time-yield (STY), are comparable to those of chemical processes (Fig. 2). We are constantly expanding the range of product options that the growth-arrested bioprocess can support. To this end, we implement global analysis tools including system biology based on metabolome analysis, metabolic pathway design, and genome engineering based on the genome database of C. glutamicum. We are making full use of these methods to optimize production strains (Fig. 3).

We are establishing a fundamental technology using the growth-arrested bioprocess which produces bioethanol from non-food agricultural feedstock such as rice straw and corn stover. We are collaborating with NREL (National Renewable Energy Laboratory) founded by U.S. Department of Energy to achieve actualization of an economically efficient production process for ethanol using non-food biomass. We are also working on the production of biobutanol which is one of expected materials for biojet fuels and green chemicals such as organic acids which can be polymer materials, alcohol, and aromatic compounds.

Development of bioprocess based on metabolic engineering requires not only introduction of biosynthesis pathway and/or expression enhancement of promoter activities, but also optimal adaptation to changes of intracellular and extracellular environment such as engineering of redox balance and improving tolerance against fermentation inhibitors. Therefore, comprehensive understanding of several stress responses (oxidative, acid, alkaline, heat shock, osmotic stress etc.) and regulations of carbon catabolism such as carbohydrate utilization, energy metabolism and cofactor regeneration are subject to intensive studies. We are analyzing functions and regulations of several metabolic- and cell division-related genes based on C. glutamicum whole genome sequencing performed by us. We are studying mechanisms of gene expressions and regulations of regulatory elements. Comprehensive analysis of regulatory elements in C. glutamicum has been revealing unique gene regulatory networks in this bacterium. The understanding of the genome-wide regulatory networks is indispensable for basic information to develop a technology to optimize gene expressions by metabolic engineering.