Table 2.
Summary of genetically modified acetogens.
| Organism | Genetic modifications | Results | References |
|---|---|---|---|
| EXPANDED PRODUCT SPECTRUM | |||
| A. woodii | Plasmid based expression of C. acetobutylicum acetone biosynthetic genes (thlA-ctfAB-adc) using different combinations of promoter (ackA, pta-ack) and plasmid origin (pIP404, pBP1, pCB102, and pCD6) | Continuous production of 26.4 mg/L/h acetone from synthetic syngas in CSTR | Hoffmeister et al., 2016 |
| C. aceticum | Plasmid based expression of C. acetobutylicum acetone biosynthetic genes (thlA-ctfAB-adc) | Production of up to 9 mg/L acetone from synthetic syngas in bottles | Schiel-Bengelsdorf and Dürre, 2012 |
| C. aceticum | Plasmid based expression of synthetic acetone operon of C. acetobutylicum thiolase and acetoacetate decarboxylase genes (thl-adc) and genes for B. subtilis thioesterase (teII) or H. influenzae acyl-CoA thioesterase (ybgC) | Production of up to 59 mg/L acetone a H2/CO2 gas mix | Becker et al., 2012 |
| C. autoethanogenum, C. ljungdahlii | Plasmid based expression of C. acetobutylicum butanol biosynthetic genes (thlA-crt-hbd-bcd-etfAB) | Production of up to 1.93 g/L butanol from steel mill gas and syngas in bottles; Butanol as major product | Köpke and Liew, 2011 |
| C. autoethanogenum, C. ljungdahlii | Plasmid based expression of acetone and isopropanol biosynthetic genes thlA (from C. acetobutylicum) and ctfA-ctfB-adc (from C. beijerinckii) | Production of up to 300 mg/L acetone and 25 mg/L isopropanol from steel mill gas and syngas in bottles; Continuous production of 700 mg/L/d isopropanol from steel mill gas in CSTR | Köpke et al., 2012 |
| C. autoethanogenum | Plasmid based expression of Chloroflexus aurantiacus malonyl-coenzyme A reductase | Production of low levels of 3-hydroxypropionate from steel mill gas and H2/CO2 | Köpke and Chen, 2013 |
| C. autoethanogenum | Plasmid based expression of Klebsiella pneumoniae (S)-specific butanediol dehydrogenase and Klebsiella oxytoca diol dehydratase pddABC in C. autoethanogenum with inactivated native 2,3-butanediol dehydrogenase | Production of up to 370 mg/L meso-2,3-butanediol, MEK and 2-butanol from steel mill gas in bottles | Mueller et al., 2013 |
| C. autoethanogenum | Plasmid base expression of unspecific acyltransferase from Acinetobacter baylyi | Production of low levels of butanoic acid butyl ester from steel mill gas | Liew and Köpke, 2012 |
| C. autoethanogenum | Plasmid based over-expression of DOXP synthase, expression of mevalonate pathway, C. beijerinckii isopentenyl diphosphate isomerase, and either Poplar isoprene synthase or farnesene synthase | Production of low levels of mevalonate, isoprene and franesene from steel mill gas and syngas | Chen et al., 2013a |
| C. ljungdahlii | Plasmid based expression of C. acetobutylicum butanol biosynthetic genes (thlA-crt-hbd-bcd, adhE-bdhA) | Production of up to 148 mg/L n-butanol from synthetic syngas in bottles; Conversion to butyrate at end of growth | Köpke et al., 2010 |
| C. ljungdahlii | Plasmid expression of C. acetobutylicum acetone biosynthetic genes (thlA-ctfAB-adc) under lactose inducible promoter | Production of up to 871 mg/L acetone from CO in bottles | Banerjee et al., 2014 |
| C. ljungdahlii | Chromosomal integration (single crossover recombination) of C. acetobutylicum butyrate biosynthetic genes (thl-crt-bcd-etfB-etfA-hbd-ptb-buk) into pta promoter region | Production of up to 881 mg/L butyrate under H2/CO2 in bottles | Ueki et al., 2014 |
| C. ljungdahlii | Plasmid based expression of mevalonate pathway, E. coli isopentenyl diphosphate isomerase, and Poplar isoprene synthase | Production of up to 68 mg/L mevalonate and low levels of isoprene from syngas in bottles | Beck et al., 2014 |
| C. ljungdahlii | Plasmid based expression of mevalonate pathway, yeast isopentenyl diphosphate isomerase, and Poplar isoprene synthase | Production of up to 68 low levels of isoprene from syngas in bottles | Beck et al., 2014 |
| M. thermoacetica | Genome insertion of ldh from Thermoanaerobacter pseudethanolicus into pyrF locus | Heterotrophic production of up to 613 mg/L lactate from glucose in bottles; Autotrophic production not reported | Kita et al., 2013 |
| ENHANCED PROCESS | |||
| A. woodii | Plasmid based expression of formyl-THF-synthetase, methenyl-THF-cyclohydrolase, methylene-THF-dehydrogenase, and methylene-THF-reductase of C. ljungdahlii | Increase in volumetric acetate production rate by 14% under H2/CO2 conditions in CSTR | Straub et al., 2014 |
| C. autoethanogenum | Inactivation of acetolactate decarboxylase gene budA | Abolishment of 2,3-butanediol production along with enhanced ethanol production by 79%; Small levels of succinate and lactate produced during growth on steel mill gas | Köpke et al., 2013a |
| C. autoethanogenum | Inactivation of lactate dehydrogenase gene ldhA | Abolishment of lactate production | Nagaraju et al., 2015 |
| C. autoethanogenum | Plasmid expression of vitamin biosynthetic genes thiC of “C. ragsdalei” and panBCD of C. beijerinckii | Successful complementation of thiamine and panthothenate biosynthesis pathways; Strains independent of vitamin B1 and B5 supplementation during growth on steel mill gas | Köpke and Al-Sinawi, 2013 |
| C. autoethanogenum | Plasmid expression of native groES and groEL | Increased cell viability when challenged with ethanol during growth on steel mill gas | Simpson et al., 2011 |
| C. difficile | Generation of more than 70,000 unique mutants via transposon mutagenesis, coupled with transposon-directed insertion site sequencing | Identification of 404 essential genes for growth; Identification of 798 genes that are likely to affect sporulation | Dembek et al., 2015 |
| C. ljungdahlii | Chromosomal deletion of adhE1 and/or adhE2 | 6-fold reduction in ethanol concentration of ΔadhE1 mutant (but not ΔadhE2 mutant) under heterotrophic conditions | Leang et al., 2013 |
| C. ljungdahlii | Plasmid expression of formate dehydrogenase from E. coli | 4.3-fold increase in intracellular NADH concentration; 2.3-fold improvement in maximum power density in a sodium formate fed microbial fuel cell | Han et al., 2016 |