Abstract
A methanotrophic community was enriched in a semi-continuous reactor under non-aseptic conditions with methane and ammonia as carbon and nitrogen source. After a year of operation, Methylosinus sp., accounted for 80% relative abundance of the total sequences identified from potential polyhydroxyalkanoates (PHAs) producers, dominated the methane-fed enrichment. Prior to induction of PHA accumulation, cells harvested from the parent reactor contained low level of PHA at 4.0 ± 0.3 wt%. The cells were later incubated in the absence of ammonia with various combinations of methane, propionic acid, and valeric acid to induce biosynthesis of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Previous studies reported that methanotrophic utilization of odd-chain fatty acids for the production of PHAs requires reducing power from methane oxidation. However, our findings demonstrated that the PHB-containing methanotrophic enrichment does not require methane availability to generate 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV)—when odd-chain fatty acids are presented. The enrichment yielded up to 14 wt% PHA with various mole fractions of 3HV monomer depending on the availability of methane and odd-fatty acids. Overall, the addition of valeric acid resulted in a higher PHA content and a higher 3HV fraction. The highest 3HV fraction (up to 65 mol%) was obtained from the methane–valeric acid experiment, which is higher than those previously reported for PHA-producing methanotrophic mixed microbial cultures.
Highlights
Methane (CH4) gas, which is a cheap, abundant, and widely available carbon source has emerged as a potential feedstock for the production of polyhydroxyalkanoates (PHAs), a group of biodegradable, biocompatible, and renewable bioplastic (Strong et al 2016)
In this study, net PHA production was only observed when valeric acid was used, our result shows that PHA synthesis in the absence of methane may have been driven by the reducing power generated via degradation of stored PHA for the assimilation of organic acids
We conclude that a semi-continuous reactor can facilitate methanotrophic enrichment and yield a community capable of producing PHA
Summary
Methane (CH4) gas, which is a cheap, abundant, and widely available carbon source has emerged as a potential feedstock for the production of polyhydroxyalkanoates (PHAs), a group of biodegradable, biocompatible, and renewable bioplastic (Strong et al 2016). Mixed microbial cultures of methane-utilizing bacteria or methanotrophs, a group of bacteria metabolize methane as their sole carbon and energy source, has a robust and self-regulating nature (Morgan-Sagastume et al 2010), and offers opportunity to operate under nonaseptic conditions, thereby reducing operating costs of large-scale production (Dias et al 2006). Under nutrient-limiting conditions (i.e., nitrogen), methanotrophs can convert methane to poly(3-hydroxybutyrate) (PHB), the most common type of PHA naturally produced in microorganisms (Pfluger et al 2011). One common approach to make PHB with more desirable properties is to incorporate 3-hydroxyvalerate (3HV) into the polymer chain (Laycock et al 2013), so called poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which has higher impact strength and flexibility (Sudesh et al 2000)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
