Disassembly and reassembly of polyhydroxyalkanoates: Recycling through abiotic depolymerization and biotic repolymerization

Abstract

An abiotic-biotic strategy for recycling of polyhydroxyalkanoates (PHAs) is evaluated. Base-catalyzed PHA depolymerization yields hydroxyacids, such as 3-hydroxybutyrate (3HB), and alkenoates, such as crotonate; catalytic thermal depolymerization yields alkenoates. Cyclic pulse addition of 3HB to triplicate bioreactors selected for an enrichment of Comamonas, Brachymonas and Acinetobacter. After each pulse, poly(3-hydroxybutyrate) (P3HB) transiently appeared: accumulation of P3HB correlated with hydrolysis of polyphosphate; consumption of P3HB correlated with polyphosphate synthesis. Cells removed from the cyclic regime and incubated with 3HB under nitrogen-limited conditions produced P3HB (molecular weight>1,000,000Da) at 50% of the cell dry weight (<8h). P3HB also resulted from incubation with acetate, crotonate, or a mixture of hydrolytic depolymerization products. Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) resulted from incubation with valerate or 2-pentenoate. A recycling strategy where abiotic depolymerization of waste PHAs yields feedstock for customized PHA re-synthesis appears feasible, without the need for energy-intensive feedstock purification.

Expanding the range of polyhydroxyalkanoates synthesized by methanotrophic bacteria through the utilization of omega-hydroxyalkanoate co-substrates

“…The M n of all PHAs tested were above 1.0 × 10 6 Da, indicating production of PHAs with high molecular weights. These values are comparable to those of heterotrophic enrichments and to commercial P3HB and PHBV powders (Table 2, Sigma-Aldrich, St Louis, MO, USA) (Myung et al 2014), but are more uniform, with higher M n and lower M w /M n .…”

“…PHAs are biodegradable, biocompatible, and renewable bioplastics (Myung et al 2014) that could substitute for petrochemical-derived plastics in many applications. Accumulation of PHAs occurs when bacterial cells grow under conditions where substrates other than the electron donor (typically the carbon source), such as nitrogen or phosphorus, limit growth.…”

Polyhydroxyalkanoates: Properties and chemical modification approaches for their functionalization

“…Upon the addition of tetrabutylammonium hydroxide, BCA first polymerizes to a high molecular mass monomer followed by the depolymerization and formation of TBAOH, which initiated low molecular mass daughter polymer formation. Later on, it was demonstrated that the base is not vital for this depolymerization–repolymerization reaction and polymer degradation was observed in the solid state of polymer . Moon et al studied the degradation behavior of poly(ethyl‐cyanoacrylate) (PECA) in basic solution.…”

“…Later on, it was demonstrated that the base is not vital for this depolymerization-repolymerization reaction and polymer degradation was observed in the solid state of polymer. 91 Moon et al 92 studied the degradation behavior of poly(ethyl-cyanoacrylate) (PECA) in basic solution. They concluded that this degradation behavior is because of an open depolymerization progression originated from the chain terminus of the polymer.…”

Pretreatment and Anaerobic Co-digestion of Selected PHB and PLA Bioplastics

“…Treatment of PHB in acidic solutions of sulfuric acid (0.05-2 M) at 70 • C for up to 14 h did not result in abiotic degradation (Yu et al, 2005). Near complete abiotic degradation of poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV) was shown at 60 • C in 0.1 M sodium hydroxide after 18 h of treatment (Myung et al, 2014). Thus, pretreatment in alkaline media at elevated temperatures induced polyester backbone hydrolysis resulting in release of water soluble breakdown products such as 3-hydroxybutyrate and crotonate, which have both been shown to support growth of strictly anaerobic microbes (Dörner and Schink, 1990;Janssen and Harfoot, 1990).…”