The Future: Bacteria Produced Hot Pants?
Scientists from the company Genomica have genetically engineered E.Coli to produce 1,4-Butanediol (BDO), a key chemical in the production of Spandex, clothing of choice for superheroes, glam rockers and 80’s disco enthusiasts.
The work, published in the journal Nature Chemical Biology, has the potential to drastically change the way BDO is produced. Currently one million metric tons are produced per year and all of this is derived from oil and natural gas. Almost half of the BDO produced globally is dehydrated to produce Tetrahydrofuran. This can then be polymerised to polytetramethylene oxide, the primary use of which is in fibres such as spandex.
The researchers faced several challenges whilst trying to produce their engineered bacteria. The first of which being identifying a synthesis mechanism, as there is no known naturally occurring biological synthesis pathway for BDO. Instead they had to compute all potential pathways from the typical E. coli metabolites to BDO. The computer algorithm they used identified over 10,000 four-six step pathways that could result in synthesis of BDO from common metabolites, including acetyl-CoA, succinyl-CoA and glutamate.
These methods were then narrowed down based on theoretical yield, pathway length and thermodynamic feasibility. After this they picked out the following pathway as the best way for E.Coli to produce BDO:
The BDO synthesis pathway. Each number indicates an enzyme: (1) 2-oxoglutarate decarboxylase; (2) succinyl-CoA synthetase; (3) CoA-dependent succinate semialdehyde dehydrogenase; (4) 4-hydroxybutyrate dehydrogenase; (5) 4-hydroxybutyryl-CoA transferase; (6) 4-hydroxybutyryl-CoA reductase; (7) alcohol dehydrogenase. Steps 2 and 7 occur naturally in E. coli, whereas the others are encoded by heterologous genes introduced in this work.
With an elucidated pathway, then came the challenge of how to get a bacterium to carry it out. Not all the enzymes required for the pathway are present in the wildtype E.Coli. As a result of this, the group identified several different mechanisms for generating the intermediate 4-Hydroxybulymate (4HB) settling on; the addition of three genes sucCD (E. coli), sucD and 4hbd (P. gingivalis).
The final stage in the process, 4HB to BDO, also required some manipulation. The change requires two reduction steps, catalyzed by dehydrogenases. This can occur by the addition of exogenous 4HB to wild-type Clostridium acetobutylicum. However, for efficient production they needed to have the process contained within E.Coli. So instead they expressed the 4-hydroxybutyryl-CoA transferase (cat2) gene from P. gingivalis for the conversion of 4HB to 4HB-CoA. The final stages then involved the action of 4-hydroxybutyryl-CoA reductase and the native alcohol dehydrogenase, finally resulting in a viable BDO product.
Whilst this discovery does not directly result in the production of spandex or other useful fibres by bacteria. This could prove to be an efficient and environmentally friendly way to produce crime-fighting and disco outfits at some point in the future!