Abstract
Synthesis of poly-[3-hydroxybutyrate] (PHB) by Cupriavidus necator H16 in batch cultures was evaluated using three biodiesel-derived by-products as the sole carbon sources: waste glycerol (REG-80, refined to 80 % purity with negligible free fatty acids); glycerol bottom (REG-GB, with up to 65 % glycerol and 35 % free fatty acids), and free fatty acids (REG-FFA, with up to 75 % FFA and no glycerol). All the three substrates supported growth and PHB production by C. necator, with polymer accumulation ranging from 9 to 84 % cell dry weight (cdw), depending on the carbon source. To help understand these differences, proteomic analysis indicated that although C. necator H16 was able to accumulate PHB during growth on all three biodiesel by-products, no changes in the levels of PHB synthesis enzymes were observed. However, significant changes in the levels of expression were observed for two Phasin proteins involved with PHB accumulation, and for a number of gene products in the fatty acid β-oxidation pathway, the Glyoxylate Shunt, and the hydrogen (H2) synthesis pathways in C. necator cells cultured with different substrates. The glycerol transport protein (GlpF) was induced in REG-GB and REG-80 glycerol cultures only. Cupriavidus necator cells cultured with REG-GB and REG-FFA showed up-regulation of β-oxidation and Glyoxylate Shunt pathways proteins at 24 h pi, but H2 synthesis pathways enzymes were significantly down-regulated, compared with cells cultured with waste glycerol. Our data confirmed earlier observations of constitutive expression of PHB synthesis proteins, but further suggested that C. necator H16 cells growing on biodiesel-derived glycerol were under oxidative stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0206-z) contains supplementary material, which is available to authorized users.
Highlights
An increasing demand for renewable, bio-based products is driving the global market for bioplastics
Our analyses indicated that medium containing 2 % (v/v) Renewable Energy Group (REG)-80 contained 23.4 mM glycerol, while medium containing 2 % (w/v) REG-glycerol bottoms (REG-GB) contained 10.4 mM glycerol, which was approximately half the glycerol concentration in REG-80 medium
REG-80 consisted of 80 % glycerol, with negligible amounts of free fatty acids (0.08 %)
Summary
An increasing demand for renewable, bio-based products is driving the global market for bioplastics. PHAs are biodegradable, insoluble in water, nontoxic, biocompatible, piezoelectric, thermoplastic and/or elastomeric. These features make PHAs suitable for several applications in the packaging industry, medicine, pharmacy, agriculture, and food industry, as raw materials for the production of enantiomerically pure chemicals, and for the production of paints. Polyhydroxybutyrate (PHB), a polymer of 3-hydroxybutyrate, is a highly biodegradable natural polyester polymer produced for various applications. PHBs have been produced commercially, but their high production costs make them economically unattractive compared to petroleum-based plastics. Carbon substrates used for PHB synthesis account for 40–48 % of the production costs (Choi and Lee 1997) and there is a global effort to decrease production costs by using low cost carbon substrates (Cavalheiro et al 2009; Obruca et al 2010; Povolo et al 2010; Budde et al 2011; Ashby et al 2005; Solaiman et al 2006)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
