Abstract
Polyhydroxyalkanoate (PHA) bioplastic was synthesized by Burkholderia glumae MA13 from carbon sources and industrial byproducts related to sugarcane biorefineries: sucrose, xylose, molasses, vinasse, bagasse hydrolysate, yeast extract, yeast autolysate, and inactivated dry yeast besides different inorganic nitrogen sources. Sugarcane molasses free of pre-treatment was the best carbon source, even compared to pure sucrose, with intracellular polymer accumulation values of 41.1–46.6% cell dry weight. Whereas, xylose and bagasse hydrolysate were poor inducers of microbial growth and polymer synthesis, the addition of 25% (v/v) sugarcane vinasse to the culture media containing molasses was not deleterious and resulted in a statistically similar maximum polymer content of 44.8% and a maximum PHA yield of 0.18 g/g, at 34°C and initial pH of 6.5, which is economic and ecologically interesting to save water required for the industrial processes and especially to offer a fermentative recycling for this final byproduct from bioethanol industry, as an alternative to its inappropriate disposal in water bodies and soil contamination. Ammonium sulfate was better even than tested organic nitrogen sources to trigger the PHA synthesis with polymer content ranging from 29.7 to 44.8%. GC-MS analysis showed a biopolymer constituted mainly of poly(3-hydroxybutyrate) although low fractions of 3-hydroxyvalerate monomer were achieved, which were not higher than 1.5 mol% free of copolymer precursors. B. glumae MA13 has been demonstrated to be adapted to synthesize bioplastics from different sugarcane feedstocks and corroborates to support a biorefinery concept with value-added green chemicals for the sugarcane productive chain with additional ecologic benefits into a sustainable model.
Highlights
Polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized by representatives of Bacteria and Archaea domains as intracellular granules
Industrial byproducts are complex carbon sources and many times they are constituted of impurities which may impair the microbial growth, such as salts and residual methanol regarding crude glycerol from biodiesel production (Cavalheiro et al, 2009) or phenolic compounds and additional contaminants from raw cane juice, when sugarcane molasses is used as a complex carbon source (Sen et al, 2019)
Sugarcane vinasse is generally a low sugar, nitrogen, and phosphorus byproduct though high levels of organic matter and cations such as potassium, calcium, and magnesium are present in this low pH effluent (Christofoletti et al, 2013)
Summary
Polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized by representatives of Bacteria and Archaea domains as intracellular granules. PHAs are a family of bioplastics which are fully bio-based and biodegradable These both characteristics are especially interesting since the term “bioplastics” have commonly been used to make a distinction from petrochemical and non-environmentally friendly polymers, which is partially misleading. PHAs are bio-based and biodegradable but they are compostable resulting in humus-rich soil (Chanprateep, 2010; Lackner, 2015; de Paula et al, 2018a; European Bioplastics, 2018). These microbial biopolymers are biocompatible, which is attractive for pharmaceutical and medical applications such as nanobeads for drug delivery systems and nanofiber scaffolds for tissue engineering (Rodriguez-Contreras, 2019). All these mentioned features make PHAs promising candidates for short-lived and disposable applications (de Paula et al, 2018b)
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