|Ashby, Richard - Rick
|LIN, XIAOQING - Guangdong University
Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2022
Publication Date: 6/18/2022
Citation: Ashby, R.D., Qureshi, N., Strahan, G.D., Johnston, D., Msanne, J.N., Lin, X. 2022. Corn stover hydrolysate and levulinic acid: mixed substrates for short-chain polyhydroxyalkanoate production. Biocatalysis and Agricultural Biotechnology. 43:102391. https://doi.org/10.1016/j.bcab.2022.102391.
Interpretive Summary: As the plastic disposal problem becomes more urgent, many avenues are being pursued to effectively reduce the number of recalcitrant plastics found in nature. One method that is currently receiving attention is the development of biodegradable substitutes for many of the commonly used petroleum-based plastics. Polyhydroxyalkanoates (PHA) are bacterially-derived molecules that have been documented to exhibit analogous properties to many plastics. They can be produced through fermentation from renewable resources and they can be naturally degraded in microbially active environments. These qualities make PHA an interesting material from a pollution reducing perspective. Unfortunately, producing these PHA materials is more cost prohibitive than their non-degradable counterparts which has thwarted their widespread use. One area that is being pursued to help reduce the production costs of PHA is the the use of low-value, high-volume biobased feedstocks. One such feedstock is residual plant material. Corn stover comprises the leaves, stalks, and cobs left over after corn harvesting and makes up about 50% of the overall corn crop. It is a cheap source of carbon and is produced in large amounts. As such, in this study corn stover was used in combination with levulinic acid (a plentiful biobased organic acid) to produce PHA with varying compositions and properties that may be useful for widespread applications. While additional work is needed to achieve higher productivities and thus further improve production economics, the results of this study show that corn stover and other equivalent plant-based feedstocks can be successfully utilized to produce unique PHA's for a broader application base.
Technical Abstract: The plastic disposal problem has been augmented over the years due to the surge in utilization of single-use plastics, the indiscriminate discarding of plastics, and space limitations associated with landfill sites. Therefore, in this study the biodegradable, biorenewable, and biocompatible plastic substitutes, poly(hydroxyalkanoate) (PHA) biopolymers were synthesized from low-value and high-volume corn stover in combination with levulinic acid (LevA). Acid hydrolysis liberated the fermentable sugars from the cellulosic and hemicellulosic fractions of the corn stover. This hydrolysate was used as a feedstock in combination with LevA to produce a terpolyester composed of 3-hydroxybutyric acid (3-HB), 3-hydroxyvaleric acid (3-HV), and 4-hydroxyvaleric acid (4-HV) by the bacterium Azohydromonas lata, and a copolymer of 3-HB and 3-HV by the bacterium Burkholderia sacchari. Detoxification of the hydrolysate through ‘overliming’ was necessary to induce bacterial growth and PHA production in A. lata, while B. sacchari was able to utilize the hydrolysate without detoxification achieving a maximum PHA titer of 1.2 g PHA/L. The inclusion of higher LevA in the medium affected the monomeric composition of the copolymers produced by B. sacchari resulting in a 3-HB:3-HV ratio of 39:61 when grown in the presence of 0.4% (w/v) LevA. In contrast, the monomeric compositions were relatively unaffected by the LevA media concentration for the PHA biopolymers produced by A. lata. The results of this study should help reduce the overall costs to synthesize bacterially derived PHA biopolymers and increase their applicability, thus reducing our dependence on recalcitrant petroleum-based plastics.