Production of polyhydroxyalkanoate copolymers containing 4-hydroxybutyrate in engineered Bacillus megaterium

Authors: Cal, Andrew; Kibblewhite, Rena; SIKKEMA, DIRK - US Department Of Agriculture (USDA); Torres, Lennard; Hart-Cooper, William; Orts, William; Lee, Charles

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2020
Publication Date: 12/5/2020
Citation: Cal, A.J., Kibblewhite, R.E., Sikkema, D.W., Torres, L.F., Hart-Cooper, W.M., Orts, W.J., Lee, C.C. 2020. Production of polyhydroxyalkanoate copolymers containing 4-hydroxybutyrate in engineered Bacillus megaterium. International Journal of Biological Macromolecules. 168:86-92. https://doi.org/10.1016/j.ijbiomac.2020.12.015.
DOI: https://doi.org/10.1016/j.ijbiomac.2020.12.015

Interpretive Summary: There is a major dependency on plastic due to the tremendous functional characteristics of the material. Unfortunately, the vast majority of plastic is composed of non-biodegradable polymers, such as such as PET (polyethylene terephthalate), which will continue to pollute the environment long after their utility. Thus, there is a great demand for biodegradable plastic replacements. Polyhydroxyalkanoates (PHAs) are biopolymers that are slowly being commercialized as biodegradable plastics. The majority of PHAs are produced from gram-negative bacteria which have lipopolysaccharides that must be removed due to their endotoxicity. In this work, we have produced PHAs from a gram-positive bacterium that does not have lipopolysaccharides. We engineered the bacteria to express a copolymer which has improved toughness. The copolymer was produced without the use of expensive precursors in the fermentation media.

Technical Abstract: Despite being used as a common platform for the production of many industrial biochemicals, Bacilli are often overlooked as a source of polyhydroxyalkanoates (PHAs), biodegradable plastic replacements. In addition to having a robust expression system, the lack of lipopolysaccharides and ease of lysis make Bacilli an attractive host for the production of PHAs. In this work, a Bacillus megaterium strain was engineered to generate poly(3-hydroxybutyrate-co-4-hydroxybutryate) [P(3HB-co-4HB)] copolymers, which are among the among the most useful and industrially-relevant copolymers. These copolymers had lower modulus and increased toughness, thus making the copolymer suitable for a broader range of applications. Due to high metabolic flux through succinate, the engineered B. megaterium strain produced P(3HB-co-4HB) with >10% mol fraction 4HB from glucose, without the use of highly regulated and expensive precursors or potentially damaging truncation of central biochemical pathways.