Abstract
Using microbial enrichment cultures for the production of waste-derived polyhydroxyalkanoates (PHAs) is a promising technology to recover secondary resources. Volatile fatty acids (VFAs) form the preferred substrate for PHA production. Isobutyrate is a VFA appearing in multiple waste valorization routes, such as anaerobic fermentation, chain elongation, and microbial electrosynthesis, but has never been assessed individually on its PHA production potential. This research investigates isobutyrate as sole carbon source for a microbial enrichment culture in comparison to its structural isomer butyrate. The results reveal that the enrichment of isobutyrate has a very distinct character regarding microbial community development, PHA productivity, and even PHA composition. Although butyrate is a superior substrate in almost every aspect, this research shows that isobutyrate-rich waste streams have a noteworthy PHA-producing potential. The main finding is that the dominant microorganism, a Comamonas sp., is linked to the production of a unique PHA family member, poly(3-hydroxyisobutyrate) (PHiB), up to 37% of the cell dry weight. This is the first scientific report identifying microbial PHiB production, demonstrating that mixed microbial communities can be a powerful tool for discovery of new metabolic pathways and new types of polymers.Key points• PHiB production is a successful storage strategy in an isobutyrate-fed SBR• Isomers isobutyrate and butyrate reveal a very distinct PHA production behavior• Enrichments can be a tool for discovery of new metabolic pathways and polymersGraphical abstract
Highlights
Polyhydroxyalkanoate (PHA) has attracted widespread attention as an alternative to petrochemical-based plastics (Lee 1996)
The pumps for feeding, effluent removal, and pH control, the stirrer, and the airflow were controlled by a hardware abstraction layer (HAL; TU Delft, the Netherlands), which in turn was controlled by a PC using a custom scheduling software (D2I; TU Delft, the Netherlands)
The feast phase was characterized by a high oxygen uptake rate, and its duration could be extracted from the dissolved oxygen (DO) data (Stouten et al 2019)
Summary
Polyhydroxyalkanoate (PHA) has attracted widespread attention as an alternative to petrochemical-based plastics (Lee 1996). PHA is completely biodegradable and biobased, and has thermoplastic properties. The type of PHA monomer produced is determined by the substrate provided, the environmental conditions, and the microorganism, and in its turn will determine the physicochemical properties of the final polymer product. An opportunity to produce PHA cost-effectively is by using mixed microbial communities and organic waste streams as feedstock. These technologies diminish the relatively large costs for sterilization and raw substrates (Kleerebezem and van Loosdrecht 2007), and as a consequence, avoid part of the waste disposal expenses (Fernández-Dacosta et al 2015). The most common type of PHA produced is the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)
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