Submitted to: Journal of Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2018
Publication Date: 1/3/2019
Citation: Ashby, R.D., Solaiman, D., Strahan, G.D. 2019. The use of Azohydromonas lata DSM 1122 to produce 4-hydroxyvalerate-containing polyhydroxyalkanoate terpolymers, and unique polymer blends from mixed-cultures with Burkholderia sacchari DSM 17165. Journal of Polymers and the Environment. 27:198-209.
Interpretive Summary: Plastics represent a huge portion of waste materials and while a small fraction is recycled, the vast majority end up in the environment. Pollution, in all forms but especially from plastics, is becoming more distressing as it is directly affecting wildlife and is also indirectly effecting human existence. Polyhydroxyalkanoates (PHAs) are bacterial polyesters that have been documented to be biodegradable in microbially-active environments but also can mimic the properties of many petroleum-based plastics. These materials are much more environmentally friendly than currently-used plastics and can be easily broken down into carbon dioxide and water. In this study compositionally-unique PHAs were produced using two strains of harmless bacteria (Azohydromonas lata and Burkholderia sacchari) using both single- and mixed-culture procedures Most importantly, the source of these syntheses was levulinic acid, which is easily produced from the sugars in plant biomass and is a comparably inexpensive molecule. The PHA polymers that were produced in this study have improved properties over some of the other more well-known PHA polymers and because of the use of the inexpensive feedstock, can be produced more cheaply than previously reported. These results will help stimulate the use of these eco-friendly plastics and help to reduce the rate of recalcitrant petroleum-based plastics being released into the environment.
Technical Abstract: Azohydromonas lata DSM 1122 was utilized to synthesize short-chain-length (scl-) polyhydroxyalkanoate (PHA) terpolymers containing 3-hydroxybutyric (3HB) acid, 3-hydroxyvaleric (3HV) acid, and 4-hydroxyvaleric (4HV) acid from mixtures of glucose (GLC; 1 wt%) and levulinic acid (LevA; 0-0.4 wt%). LevA media concentrations greater than 0.4% were toxic resulting in complete inhibition of cellular growth. At LevA concentrations of 0.4% or less the 3HV polymer content remained constant (3 to 5 mol%), but the 4HV content was slightly elevated (max. 9 mol%) when the bacterial strain was grown with 0.2% LevA for 72 h. Polymer molecular weights (based on number-average molecular weight, Mn) were smallest (Mn = 240,000 g/mol) when synthesized in the presence of 0.2% LevA. At 0.4% LevA and at 1% GLC the average Mn values were 43% and 87% larger than the polymers synthesized in the presence of 0.2% LevA, respectively. Mixed-cultures containing A. lata and Burkholderia sacchari DSM 17165, a known poly-3-hydroxybutyrate-block-3-hydroxyvalerate (P3HB-block-3HV) producer, using LevA media concentrations = 0.4% and staggered inoculations resulted in scl-PHA polymer mixtures with improved tensile properties. The results of this study show that LevA can be utilized in combination with simple sugars to produce unique scl-PHA terpolyesters and scl-PHA mixtures with enhanced properties.