Abstract
Polyhydroxyalkanoate (PHA) is a biopolyester/bioplastic that is produced by a variety of microorganisms to store carbon and increase reducing redox potential. Photosynthetic bacteria convert carbon dioxide into organic compounds using light energy and are known to accumulate PHA. We analyzed PHAs synthesized by 3 purple sulfur bacteria and 9 purple non-sulfur bacteria strains. These 12 purple bacteria were cultured in nitrogen-limited medium containing acetate and/or sodium bicarbonate as carbon sources. PHA production in the purple sulfur bacteria was induced by nitrogen-limited conditions. Purple non-sulfur bacteria accumulated PHA even under normal growth conditions, and PHA production in 3 strains was enhanced by nitrogen-limited conditions. Gel permeation chromatography analysis revealed that 5 photosynthetic purple bacteria synthesized high-molecular-weight PHAs, which are useful for industrial applications. Quantitative reverse transcription polymerase chain reaction analysis revealed that mRNA levels of phaC and PhaZ genes were low under nitrogen-limited conditions, resulting in production of high-molecular-weight PHAs. We conclude that all 12 tested strains are able to synthesize PHA to some degree, and we identify 5 photosynthetic purple bacteria that accumulate high-molecular-weight PHA molecules. Furthermore, the photosynthetic purple bacteria synthesized PHA when they were cultured in seawater supplemented with acetate. The photosynthetic purple bacteria strains characterized in this study should be useful as host microorganisms for large-scale PHA production utilizing abundant marine resources and carbon dioxide.
Highlights
Polyhydroxyalkanoate (PHA) is a biopolyester that functions both as an intracellular carbon and energy storage molecule as well as a sink for reducing redox potential [1, 2]
We found that all photosynthetic purple bacteria tested were able to accumulate PHAs
PHA production had been previously reported in Rdv. sulfidophilum [13], whereas this is the first report of PHA production in the other 11 photosynthetic purple bacteria
Summary
Polyhydroxyalkanoate (PHA) is a biopolyester that functions both as an intracellular carbon and energy storage molecule as well as a sink for reducing redox potential [1, 2]. PHA has garnered attention as an alternative to petroleum-derived plastics due to its biodegradability and biocompatibility [3]. Efforts have been made to reduce the price of PHA, the cost of the necessary carbon sources, such as sugars or plant oils, is still high compared with petroleum-derived plastics. To solve this problem, some researchers have focused on direct fixation of CO2 to PHAs via photosynthesis in an attempt to reduce the price of PHA production. High PHA productivity in higher plants or cyanobacteria has yet to be achieved
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