The production of polyhydroxyalkanoates from Paracoccus haeundaensis

Abstract

Long-persistence of petroleum-based plastics in natural environments and their unintentional release to soil and marine environments are continuously causing microplastic pollutants and threatening all living organisms in the global ecosystem including human beings. To solve this problem, various biodegradable and eco-friendly bioplastics have been proposed. One of the potential alternative materials is polyhydroxyalkanoate (PHA). Many microorganisms can produce PHA, a biodegradable bioplastic material, and store them within cells as carbon and energy sources when the carbon source is in excess with nutrient limited conditions such as nitrogen, phosphorus, oxygen, sulfur, magnesium, and others. Paracoccus haeundaensis has been relatively well-documented for the production of astaxanthin. The objective of this study was to further investigate its industrial values for the production of PHA such as polyhydroxybutyrate [P(3HB)] and/or poly-3-hydoxybutyrate-co-3-hydroxyvalerate [P(3HB-co-3HV)]. In this respect, several batch fermentation studies using this strain were carried out to evaluate its potential production of PHA under excess carbon source concentrations with limited nitrogen concentrations. When P. haeundaensis was cultured in M9MV medium supplemented with 12 g∙L-1 glucose, it was able to produce copolymer of poly (hydroxybutyrate-co-hydroxyvelerate) with HV composition of 3 mol %. The amount of PHA was increased up to 1.03 g∙L-1 (64.38 % of dry cell weight) and the cell biomass concentration was increased up to 1.63 g∙L-1 after 168 h of culture. To promote cell growth and PHA accumulation of P. haeundaensis, 1 g∙L-1 of yeast extract and 0.5 g∙L-1 of tryptone were additionally supplemented. Increasing organic nitrogen increased PHA amount to 1.71 g∙L-1 (32.26 % of DCW) at a maximum cell biomass of 5.3 g∙L-1. However, the PHA content was decreased by 29 %, indicating that increasing organic nitrogen concentration could negatively affect PHA content. The most effective carbon source for PHA production of P. haeundaensis was fructose. At a maximum cell biomass of 2.8 g∙L-1, PHA amount was 1.29 g∙L-1 (46.07 % of DCW) in a batch fermentation. To improve the HV ratio of PHA produced from P. haeundaensis, propionic acid was supplemented to M9MV with glucose as carbon source and 0.05 g∙L-1 of P(3HB-co-HV) was produced with a maximum HV of 50 mol %. In conclusion, P. hauendaensis can produce short chain length PHA including P(3HB) and P(3HB-co-HV) under carbon excess and nitrogen limited conditions.