Abstract
Poly-β-hydroxybutyrate (PHB) production from CO2 has the potential to reduce the production cost of this biodegradable polyesters, and also to make the material more sustainable compared to utilization of sugar feedstocks. In this study the unicellular cyanobacterium, Synechocystis sp. PCC 6714 has been identified as an unexplored potential organism for production of PHB. Synechocystis sp. PCC 6714 was studied under various cultivation conditions and nutritional limitations. Combined effects of nitrogen and phosphorus deficiency led to highest PHB accumulation under photoautotrophic conditions. Multivariate experimental design and quantitative bioprocess development methodologies were used to identify the key cultivation parameters for PHB accumulation. Biomass growth and PHB accumulation were studied under controlled defined conditions in a lab-scale photobioreactor. Specific growth rates were fourfold higher in photobioreactor experiments when cultivation conditions were controlled. After 14 days of cultivation in nitrogen and phosphorus, limited media intracellular PHB levels reached up to 16.4% from CO2. The highest volumetric production rate of PHB was 59 ± 6 mg L−1 day−1. Scanning electron microscopy of isolated PHB granules of Synechocystis sp. PCC 6714 cultivated under nitrogen and phosphorus limitations showed an average diameter of 0.7 µm. The results of this study might contribute towards a better understanding of photoautotrophic PHB production from cyanobacteria.
Highlights
Today, petroleum-based plastics are an essential part across all industries and have replaced glass and paper in packaging (Khanna and Srivastava 2005)
Strain characterization Impact of carbon sources on biomass formation Initial characterization by shake flask experiments was done to gain a better understanding of cyanobacterial strain Synechocystis sp
Growth on glucose occurred with a μaverage of 0.107 ± 0.01 day−1 and a μmax of 0.28 ± 0.02 day−1 which is higher when compared to growth on carbonate and acetate
Summary
Petroleum-based plastics are an essential part across all industries and have replaced glass and paper in packaging (Khanna and Srivastava 2005). Global plastics production reached around 322 million tonnes in 2015 (Plastics Europe 2016) Accumulation of these non-biodegradable plastics in the environment is a worldwide concern (Thompson et al 2009), e.g. as microplastics in the marine environment. In this context, attention has been focused on research for the production of biodegradable plastics (Samantaray and Mallick 2015). PHB could be an attractive alternative to petroleum-based plastics (Samantaray and Mallick 2015). It resembles the commodity polymer polypropylene in its properties (Lackner 2015). Despite relatively high yields of PHB, production from bacterial fermentation requires sugar supplementation and continuous oxygen
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