Evaluation of brown midrib (bmr) sorghum stover as potential renewable biomass feedstock for poly(3-hydroxybutyrate) production employing Paraburkholderia Sacchari and Cupriavidus necator

Abstract

The aim of this work was to evaluate the use of stover from brown midrib (bmr) grain sorghum to produce polyhydroxyalkanoates (PHAs). These mutants produce lignin with novel compositions and/ or reduced lignin content that was hypothesized to result in higher PHA production than when using a wild-type sorghum stover. Five sorghum stover samples [wild-type (control) and four bmr mutants [bmr2, bmr6, and bmr12, and a double bmr mutant: bmr6 and bmr12 (stacked)] were evaluated as substrates for poly(3-hydroxybutyrate) (P(3HB)) production. When the main sugars in non-detoxified alkali-pretreated sorghum stover hydrolysates (SSHs) were metabolized by Paraburkholderia sacchari for P(3HB) production, the SSHs from bmr plants were demonstrated to be promising feedstocks with a maximum P(3HB) concentration of 7.2 g/L from the bmr6 SSH, while a maximum P(3HB) concentration of 4.2 g/L P(3HB) was produced using wild-type SSH. Moreover, the highest maximum Y_{[P(3HB)/sugars]} were achieved using stacked SSH and bmr12 SSH (0.44 g/g and 0.42 g/g, respectively). Furthermore, Cuprivadus necator was utilized to evaluate P(3HB) synthesis from the alkaline pretreated liquor (APL) remaining after sorghum stover pretreatment and an oxidative enzyme-mediator-surfactant system (OEMS) was used to improve P(3HB) production from the APLs. A 28-fold increase in PHB production from the bmr2-APL with OEMS compared to the fermentation of the same APL with no OEMS was observed. This is the first published report to use grain sorghum stover to produce polyhydroxyalkanoates (PHAs). Also, a novel combination of PHA production from both sugars and lignin is reported.

Funding

Agricultural Research Division, Institute of Agriculture and Natural Resources,(Agricultural Research Division, Institute of Agriculture and Natural Resources)

Agricultural Research Service,(Agricultural Research Service)