During oxidative growth, roughly half of the sugar carbons can be diverted into cell mass and CO2 [129,130]. For this reason, bacterial production of commodity chemicals has traditionally focused on generating reduced end — products using anaerobic conditions, in order to minimize the loss of carbon as cell material or CO2. Current biological production of acetate involves complex growth conditions consisting of two separate organisms: an ini­tial fermentation of sugars to ethanol by Saccharomyces and subsequent oxidation to acetate by Acetobacter under aerobic conditions [131-133]. Strain TC36, an E. coli W3110 derivative, was engineered to merge aspects of both fermentative and oxidative metabolism for the production of acetate via a single microbial biocatalyst [77]. TC36 contains multiple chromosomal gene deletions to eliminate production of formate focA-pflB), succinate frdBC), lactate (ldhA), and ethanol (adhE), to disrupt the tricarboxylic acid cycle (sucA) and, most notably, to inactivate oxidative phosphorylation (atpFH) in order to direct the flow of carbons from sugar to acetate with minimal car­bon loss to other fermentation products, CO2, and cell mass. A maximum of 878 mM acetate was produced by TC36 in mineral salts medium. Though this is a lower titer than that achieved during ethanol oxidation by Aceto — bacter, TC36 has a twofold higher production rate, can metabolize a wide range of sugars, and requires a simple, single step process in mineral salts medium.

Pyruvate is used as a food additive, nutriceutical, weight control supple­ment, and starting material for the production of amino acids and acetalde­hyde [15,134]. Pyruvate can be produced by either chemical or biological processes. Chemical synthesis from tartrate entails the use of toxic solvents, requires a great deal of energy, and is very costly [135]. Biological produc­tion involves two auxotrophic microorganisms that require costly nutritional supplements and strict regulation of media composition [134,136], or an E. coli strain that produces pyruvate from glucose and acetate in complex medium [137]. More recently, a microbial biocatalyst has been developed for the efficient synthesis of pyruvate from sugar requiring only inexpen­sive mineral salts medium [138]. Strain TC36, an E. coli W3110 derivative described above, was used as a platform to generate the pyruvate pro­ducer TC44. This strain encompasses two additional chromosomal deletions, ackA and poxB, to allow pyruvate accumulation and eliminate acetate pro­duction. TC44 yields (0.75 g pyruvate per gram of glucose), titer (749 mM maximum) and production rate (1.2 g of pyruvate L-1 h-1) in mineral salts medium were comparable to or better than the previously described bio­catalysts, which required costly nutritional supplements and complex me­dia [138]. This strain improves the cost of pyruvate production by reduc­ing the costs of materials, process controls, product purification, and waste disposal.

5.3