Polyhydroxyalkanoate synthesis by mixed microbial consortia cultured on fermented dairy manure: Effect of aeration on process rates/yields and the associated microbial ecology

Abstract

Polyhydroxyalkanoates (PHAs) are biodegradable polymers that can substitute for petroleum-based plastics in a variety of applications. One avenue to commercial PHA production involves coupling waste-based synthesis with the use of mixed microbial consortia (MMC). In this regard, production requires maximizing the enrichment of a MMC capable of feast-famine PHA synthesis, with the metabolic response induced through imposition of aerobic-dynamic feeding (ADF) conditions. However, the concept of PHA production in complex matrices remains unrefined; process operational improvements are needed, along with an enhanced understanding of the MMC. Research presented herein investigated the effect of aeration on feast-famine PHA synthesis, with four independent aeration state systems studied; MMC were fed volatile fatty acid (VFA)-rich fermented dairy manure. Regardless of the aeration state, all MMC exhibited a feast-famine response based on observed carbon cycling. Moreover, there was no statistical difference in PHA synthesis rates, with qPHA ranging from 0.10–0.19 CmmolPHA gVSS−1 min−1; VFA uptake rates exhibited similar statistical indifferences. PHA production assessments on the enriched MMC resulted in maximum intracellular concentrations ranging from 22.5–90.7% (mgPHA mgVSS−1); at maximum concentration, the mean hydroxyvalerate mol content was 73±0.6%. While a typical feast-famine dissolved oxygen (DO) pattern was observed at maximum aeration, less resolution was observed at decreasing aeration rates, suggesting that DO may not be an optimal process monitoring parameter. At lower aeration states, nitrogen cycling patterns, supported by molecular investigations targeting AOBs and NOBs, indicate that NO2 and NO3 sustained feast-famine PHA synthesis. Next-generation sequencing analysis of the respective MMC revealed numerous and diverse genera exhibiting the potential to achieve PHA synthesis, suggesting functional redundancy embedded in the diverse MMC. Ultimately, results demonstrate that aeration can be controlled in waste-based ADF systems to sustain PHA production potential, while enriching for a diverse MMC that exhibits potential functional redundancy. Reduced aeration could also enhance cost competitiveness of waste-based PHA production, with potential further benefits associated with nitrogen treatment.

Microbiome dynamics and phaC synthase genes selected in a pilot plant producing polyhydroxyalkanoate from the organic fraction of urban waste

“…The 16S rRNA gene sequencing data showed the occurrence of different putative PHA-accumulating bacteria mainly represented by members of Gammaproteobacteria, Alphaproteobacteria and Bacteroidetes. This finding is in line with previous studies that have indicated the occurrence of functional redundancy in microbial consortia inhabiting PHAproducing systems (Coats et al, 2016;Huang et al, 2018;Inoue et al, 2016). This peculiarity may imply that the eventual species loss can be compensated by other microorganisms contributing similarly to functioning and to the stability of the biological process if perturbations or drastic changes occur.…”

“…Nowadays, the information about PHA-accumulating MMC in pilotscale systems is lacking and derives almost entirely from the application of cultivation-dependent and in situ hybridization techniques (Queirós et al, 2015). Recently, the application of 16S rRNA gene highthroughput sequencing has revealed the occurrence of high biodiversity along with functional redundancy in PHA-accumulating MMC (Coats et al, 2016;Huang et al, 2018). In this study, the concomitant use of in situ detection assays and sequencing techniques was applied in order to investigate microbial community composition and phaC genes diversity during the SBR operation.…”

Rheological Behavior of High Cell Density Pseudomonas putida LS46 Cultures during Production of Medium Chain Length Polyhydroxyalkanoate (PHA) Polymers

“…However, with increasing scale the required power consumption for mixing and aeration becomes significant [79], and so the bioreactor operation parameters must be carefully managed in order to save aeration costs. This aspect is emphasized in PHA production/waste treatment operations using enriched mixed cultures [80].…”

Polyhydroxyalkanoates (PHAs): Biopolymers for Biofuel and Biorefineries

“…Industry focused on two polyesters: polylactic acid (PLA) and PHAs, where PLA is economical and available in bulk but PHAs are expensive. However, the applications and properties of PHAs can be tailored by varying the co-monomer and the content of the copolyesters [ 26 , 27 , 28 , 29 ]. The advantages and disadvantages of both PLA and PHAs are compiled in Table 1 .…”