Production of d-malate and d-citramalate by Arthrobacter pascens DMDC12 having stable citraconase

Efficient bio-production of citramalate using an engineered Escherichia coli strain

Citramalic acid is a central intermediate in a combined biocatalytic and chemocatalytic route to produce bio-based methylmethacrylate, the monomer used to manufacture Perspex and other high performance materials. We developed an engineered E. coli strain and a fed-batch bioprocess to produce citramalate at concentrations in excess of 80 g l⁻¹ in only 65 h. This exceptional efficiency was achieved by designing the production strain and the fermentation system to operate synergistically. Thus, a single gene encoding a mesophilic variant of citramalate synthase from Methanococcus jannaschii, CimA3.7, was expressed in E. coli to convert acetyl-CoA and pyruvate to citramalate, and the ldhA and pflB genes were deleted. By using a bioprocess with a continuous, growth-limiting feed of glucose, these simple interventions diverted substrate flux directly from central metabolism towards formation of citramalate, without problematic accumulation of acetate. Furthermore, the nutritional requirements of the production strain could be satisfied through the use of a mineral salts medium supplemented only with glucose (172 g l⁻¹ in total) and 1.4 g l⁻¹ yeast extract. Using this system, citramalate accumulated to 82±1.5 g l⁻¹, with a productivity of 1.85 g l⁻¹ h⁻¹ and a conversion efficiency of 0.48 g_citramalate g⁻¹_glucose. The new bioprocess forms a practical first step for integrated bio- and chemocatalytic production of methylmethacrylate.

Stereochemistry of enzymatic water addition to C=C bonds

Water addition to carbon-carbon double bonds using hydratases is attracting great interest in biochemistry. Most of the known hydratases are involved in primary metabolism and to a lesser extent in secondary metabolism. New hydratases have recently been added to the toolbox, both from natural sources or artificial metalloenzymes. In order to comprehensively understand how the hydratases are able to catalyse the water addition to carbon-carbon double bonds, this review will highlight the mechanistic and stereochemical studies of the enzymatic water addition to carbon-carbon double bonds, focusing on the syn/anti-addition and stereochemistry of the reaction.

The selective addition of water

Water is omnipresent and unreactive. How to speed up water addition and even make it selective are highlighted in this perspective.

Past, present, and future industrial biotechnology in China

Fossil resources, i.e. concentrated carbon from biomass, have been irrecoverably exhausted through modern industrial civilization in the last two hundred years. Serious consequences including crises in resources, environment and energy, as well as the pressing need for direct and indirect exploitation of solar energy, pose challenges to the science and technology community of today. Bioenergy, bulk chemicals, and biomaterials could be produced from renewable biomass in a biorefinery via biocatalysis. These sustainable industries will match the global mass cycle, creating a new form of civilization with new industries and agriculture driven by solar energy. Industrial biotechnology is the dynamo of a bioeconomy, leading to a new protocol for production of energy, bulk chemicals, and materials. This new mode of innovation will place the industry at center stage supported by universities and research institutes. Creativity in industrial biotechnology will be promoted and China will successfully follow the road to green modernization. China's rapid economic development and its traditional capacity in fermentation will place it in an advantageous position in the industrial biotechnology revolution. The development and current status of industrial biotechnology in China are summarized herein.