No abstract

Type II methanotrophic bacteria are a promising production platform for PHA biopolymers. These bacteria are known to produce pure poly-3-hydroxybutyrate homopolymer (PHB). We isolated a strain, Methylocystis sp. WRRC1, that was capable of producing a wide range of polyhydroxybutyrate-co-hydroxyvalerate copolymers (PHB-co-HV) when co-fed methane and valerate or n-pentanol. The ratio of HB to HV monomer was directly related to the concentration of valeric acid in the PHA accumulation media. We observed increased incorporation of HV and total polymer under copper-free growth conditions. The PHB-co-HV copolymers produced had decreased melting temperatures and crystallinity compared with methanotroph-produced PHB.

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Many studies have been conducted to produce microbial polyhydroxyalkanoates (PHA), a biopolymer, from Pseudomonas sp. fed with various alkanoic acids. Because this previous data was collected using methodologies that varied in critical aspects, such as culture media and size range of alkanoic acids, it has been difficult to compare the results for a thorough understanding of the relationship between feedstock and PHA production. Therefore, this study utilized consistent culture media with a wide range of alkanoic acids (C7-C14) to produce medium chain length PHAs. Three strains of Pseudomonas putida (NRRL B-14875, KT2440, and GN112) were used, and growth, cell dry weight, PHA titer, monomer distribution, and molecular weights were all examined. It was determined that although all the strains produced similar PHA titers using C7-C9 alkanoic acids, significant differences were observed with the use of longer chain feedstocks. Specifically, KT2440 and its derivative GN112 produced higher PHA titers compared to B-14875 when fed longer chain alkanoates. We also compared several analytical techniques for determining amounts of PHA and found they produced different results. In addition, the use of an internal standard had a higher risk of calculating inaccurate concentrations compared to an external standard. These observations highlight the importance of considering this aspect of analysis when evaluating different studies.

Poly-3-hydroxybutyrate (PHB) is a widely distributed carbon storage molecule in prokaryotes and can serve as a biodegradable plastic replacement. However, the handling and material properties of virgin PHB are not as robust as some traditional petroleumbased plastics. Additives can be added to PHB to improve its qualities, but these additives are themselves often not biobased. A strategy was developed to utilize lower molecular weight PHB fragments derived from the recycling process as biobased additives. To simulate recycling, PHB was thermolyzed at elevated temperatures, and this degraded PHB (dPHB) was reactively processed with virgin PHB. Incorporation of dPHB nucleated and plasticized the virgin PHB as evidenced by increased crystallization temperature and crystallinity as well as decreased melt viscosity, stiffness, and melting temperature. Additionally, samples containing dPHB had increased toughness. Processing with dPHB decreased M n , had little effect on M w , and increased the Z-average molecular weight, indicating branching. These results demonstrate a route for nucleating, plasticizing, and toughening virgin PHB by using recycled PHB.