Dimethyl carbonate and switchable anionic surfactants: two effective tools for the extraction of polyhydroxyalkanoates from microbial biomass

Abstract

The availability of green and cheap technologies to recover polyhydroxyalkanoates (PHAs) from microbial biomass is crucial for the development of a reliable and sustainable production chain. Here, two novel protocols are proposed to extract PHAs from Cupravidus necator. The first method is based on PHA-extraction with dimethyl carbonate (DMC), a green solvent that is completely biodegradable and less harmful to humans and the environment than most solvents. The procedure can be applied directly to concentrated microbial slurries or to dry biomass, affording very high polymer recovery (>85%) and excellent purity (>95%). No degradation/decomposition of the polymer is observed in both cases. The second protocol uses fatty acid carboxylates as surfactants, which disrupt cell membranes, providing excellent polymer recovery (>99%) and high purity (>90%). Ammonium laurate can be successfully used and easily recycled (98%) by lowering the pH through CO 2 addition. Therefore, both protocols reported here are effective and sustainable: the recovery and purity of the obtained PHAs are very high, the use of toxic chemicals is avoided, and the recycling of various solvents/surfactants used in the processes is optimal. Extraction of PHB with organic solventsFreeze-dried biomass extraction. C. necator freeze-dried samples (50 mg) were extracted with organic solvents (2 mL) for 1-4 h. The tested solvents and the corresponding temperatures of extraction were: DMC (90°C and 50°C), PC (90°C), DEC (90°C), ethyl acetate (80°C) and CH 2 Cl 2 (50°C). At the end of the extraction, the solutions were centrifuged at 4000 rpm for 1 min and then filtered with polypropylene membrane filters of 0.45 µm porosity. The polymer was recovered by solvent evaporation or by precipitation with EtOH, then dried at 60°C under vacuum overnight.Each extraction was performed in quadruplicate.

The Green Attitude in Art Conservation: Polyhydroxybutyrate–based Gels for the Cleaning of Oil Paintings

“…We have now found that lactones, such as GVL, γ‐butyrolactone and δ‐valerolactone, are able to dissolve up to 20 wt% of PHB in 1 min at temperatures above 100 °C, subsequently thickening to form a gel‐like material when the solution is cooled (seven‐membered ring lactones such as ϵ‐caprolactone did not dissolve PHB even under more severe conditions). This behavior was already described for other solvents such as chloroform, dimethylformamide, dimethyl sulfoxide (DMSO), dimethyl carbonate (DMC) and methyl isobutyl ketone . Since the addition of plasticizers can improve thermal and mechanical properties of the copolymer P(3HB‐3HV), TEC was used to enhance gel handling, increasing the overall greenness; TEC in fact, is a non‐toxic, bio‐based and biodegradable plasticizer, thus its use is highly advantageous respect to the health‐concerning phthalates …”

Polyhydroxyalkanoate (PHA) purification through dilute aqueous ammonia digestion at elevated temperatures

“…13,[17][18][19] To the extent of our knowledge, only two studies have reported the molar mass of PHA after NH 3 digestion. 15,20 Up to date, there has not been a comprehensive evaluation of the potential of NH 3 digestion as a PHA purification method. There is lack of knowledge about the effect of digestion conditions on the PHA purity and polymer degradation.…”

Sophorolipid biosurfactants: Possible uses as antibacterial and antibiofilm agent

“…The extraction of PHAs using organic solvents is the most common used technique [30], however there is a need for using green and cheap technologies to recover polyhydroxyalkanoates (PHAs) from microbial biomass for the development of a reliable and sustainable production chain [31]. The importance of the use of sophorolipids is thought to be as a novel molecule proposed to extract PHAs from Cupriavidus necator.…”