Polyhydroxyalkanoate production in Pseudomonas putida from alkanoic acids of varying lengths

Authors: SIKKEMA, W.DIRK - Former ARS Employee; Cal, Andrew; Hathwaik, Upul; Orts, William; Lee, Charles

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2023
Publication Date: 7/20/2023
Citation: Sikkema, W., Cal, A.J., Hathwaik, U.I., Orts, W.J., Lee, C.C. 2023. Polyhydroxyalkanoate production in Pseudomonas putida from alkanoic acids of varying lengths. PLOS ONE. 18(7). Article e0284377. https://doi.org/10.1371/journal.pone.0284377.
DOI: https://doi.org/10.1371/journal.pone.0284377

Interpretive Summary: Polyhydroxyalkanoates (PHAs) represent a class of sustainable biodegradable plastics that has been commercialized because of their environmental advantages and material properties similarity to commodity plastics such as polyethylene, polypropylene and polyesters. Successful production will be dependent on many factors, such as the environmental impact associated with the production of the fed carbon substrates. PHAs are produced by many bacteria as a carbon storage molecule, similar to starch or glycogen, often when carbon is in excess and other nutrients (especially nitrogen or phosphorus) are limiting. Many studies have been conducted to optimize microbial polyhydroxyalkanoates (PHA), a biopolymer, from Pseudomonas sp. fed with various alkanoic acids. Tthis 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.

Technical Abstract: 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.