Metabolic engineering of Corynebacterium glutamicum aimed at alternative carbon sources and new products

Abstract

Corynebacterium glutamicum is well known as the amino acid-producing workhorse of fermentation industry, being used for multi-million-ton scale production of glutamate and lysine for more than 60 years. However, it is only recently that extensive research has focused on engineering it beyond the scope of amino acids. Meanwhile, a variety of corynebacterial strains allows access to alternative carbon sources and/or allows production of a wide range of industrially relevant compounds. Some of these efforts set new standards in terms of titers and productivities achieved whereas others represent a proof-of-principle. These achievements manifest the position of C. glutamicum as an important industrial microorganism with capabilities far beyond the traditional amino acid production. In this review we focus on the state of the art of metabolic engineering of C. glutamicum for utilization of alternative carbon sources, (e.g. coming from wastes and unprocessed sources), and construction of C. glutamicum strains for production of new products such as diamines, organic acids and alcohols.

Keywords: amino acids; diamines; glycerol; hemicellulose; organic acids.

Figure 1

Carbon source utilization in C. glutamicum. Open boxes: C. glutamicum enzymes, gray shaded boxes: enzymes from other organisms produced in C. glutamicum by heterologous expression. Abbreviations: Ara, arabinose; AraA, arabinose isomerase; AraB, ribulokinase; AraD, ribulose 5-phosphate 4-epimerase; AraE, arabinose transporter; βgal, β-galactosidase; BglA, phospho-β-glucosidase; BglF*, cellobiose specific PTS; Cel-6-P, cellobiose-6-phosphate; DHAP, dihydroxyacetonephosphate; Fba, fructose-bisphosphate aldolase; Fbp, fructose-bisphosphatase; Frc-1-,6-BP, fructose-1,6-bisphosphate; Frc-6-P, fructose-6-phosphate; Frc-1-P, fructose-1-phosphate; GalPW, galactose pathway; GAP, glyceraldehyde-3-phosphate; Glc-6-P, glucose-6-phosphate; Glc, glucose; Glk, ATP dependent glucokinase; GlpD, glycerol-3-phosphate dehydrogenase; GlpF, glycerol facilitator; GlpK, glycerol kinase; Gly-3-P, glycerol-3-phosphate; IolT, inositol transporter, also accepting glucose; LacP, lactose permease; PfkA, 6-phosphofructokinase; PfkB, 1-phosphofructokinase; PpgK, polyphosphate dependent glucokinase; PtsF, fructose specific PTS; PtsG, glucose specific PTS; PtsS, sucrose specific PTS; Rbu-5-P, ribulose-5-phosphate; ScrB, sucrose-6-phosphate hydrolase; Suc-6-P, sucrose-6-phosphate; Tpi, triosephosphate isomerase; Xlu-5-P, xylulose-5-phosphate; XylA, xylose isomerase; XylB, xylulokinase.

Figure 2

Products for which C. glutamicum has been metabolically engineered. The products are depicted in rectangles and the enzymes involved in the biosynthesis pathway (bold arrows) are shown in ovals. The gene names for which the designation is not the same as enzyme name are mentioned separately next to ovals. Broken arrows represent multiple steps. argR (underlined) is a gene-encoding regulator of the arginine pathway. Abbreviations: 2-KIV, 2-Ketoisovaleric acid; 3P-Gly, 3-phosphoglycerate; α-KG, α-Ketoglutaric acid; ADC, Aspartate decarboxylase; ADH, alcohol dehydrogenase; AHAIR, acetohydroxyacid isomeroreductase; AHAS, acetohydroxyacid synthase; AK, acetate kinase; AlaT, alanine aminotransferase; AraE, arabinose transporter; ArgF, L-ornithine carbamoyltransferase; Asp, aspartate, AvtA, valine-pyruvate aminotransferase; CadA, L-lysine decarboxylase; CoAT, acetyl-CoA:CoA transferase; DHAD, dihydroxyacid dehydratase; DHAP, dihydroxyacetonephosphate; Fba, fructose-bisphosphate aldolase; Frc-6-P, fructose-6-phosphate; Frc-1,6-BP, fructose-1,6-bisphosphate; GAD, glutamate decarboxylase; GAP, glyceraldehyde-3-phosphate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GDH, glutamate dehydrogenase; Glc-6-P, glucose-6-phosphate; GLF, glucose/fructose facilitator; GOGAT, glutamate-2-oxoglutarate aminotransferase; HDH, homoserine dehydrogenase; H-ser, homoserine; ICL, isocitrate lyase; IolT1, inositol transporter; KIVD, 2-ketoacid decarboxylase; KPHMT, ketopantoate hydroxymethyltransferase; LDH, lactate dehydrogenase; LeuCD, 3-isopropylmalate dehydratase; LysC, aspartate kinase; MDH, mannitol dehydrogenase; MDH′, malate dehydrogenase; MGS, methylglyoxal synthase; OAA, Oxaloacetate; PCx, pyruvate carboxylase; PDC, pyruvate decarboxylase; PDHC, pyruvate dehydrogenase complex; PEP, phosphoenolpyruvate; PEPC, phosphoenolpyruvate carboxylase; PGDH, 3-phosphoglycerate dehydrogenase; PQO, pyruvate:quinone oxidoreductase; PSAT, phosphoserine aminotransferase; Pgi, glucose-6-phosphate isomerase; PS, pantothenate synsthase; PSP, phosphoserine phosphatase; PTA, phosphotransacetylase; PYR, pyruvate; SDH, succinate dehydrogenase; SerDH, serine dehydratase; SHMT, serine hydroxymethyltransferase; SpeC, ornithine decarboxylase; TA, transaminase; Thr, threonine; ThrB, homoserine kinase; XR, xylose reductase.