Abstract
Microbial polyhydroxyalkanoate (PHA) production serves as a substitute for petroleum-based plastics. Enriching mixed microbial cultures (MMCs) with the capacity to store PHA is a key precursor for low-cost PHA production. This study investigated the impact of carbon types on enrichment outcomes. Three MMCs were separately fed by acetate sodium, glucose, and starch as an enriching carbon source, and were exposed to long-term aerobic dynamic feeding (ADF) periods. The PHA production capacity, kinetics and stoichiometry of the enrichments, the PHA composition, and the microbial diversity and community composition were explored to determine carbon and enrichment correlations. After 350-cycle enriching periods under feast-famine (F-F) regimes, the MMCs enriched by acetate sodium and glucose contained a maximum PHA content of 64.7% and 60.5% cell dry weight (CDW). The starch-enriched MMC only had 27.3% CDW of PHA. High-throughput sequencing revealed that non-PHA bacteria survived alongside PHA storing bacteria, even under severe F-F selective pressure. Genus of Pseudomonas and Stappia were the possible PHA accumulating bacteria in acetate-enriched MMC. Genus of Oceanicella, Piscicoccus and Vibrio were found as PHA accumulating bacteria in glucose-enriched MMC. Vibrio genus was the only PHA accumulating bacteria in starch-enriched MMC. The community diversity and composition were regulated by the substrate types.
Highlights
The PHA production method using mixed microbial culture (MMC) has two steps
These studies show that volatile fatty acid (VFA) can be directly converted into PHA, facilitating PHA functional bacteria selection by providing a competitive advantage to PHA-storing organisms[8]
Martins et al found that a freshwater MMC accumulated PHA with a similar qs and qPHA as this study found, using acetate as the only carbon[23]
Summary
The PHA production method using MMC has two steps. First, substrates are used to enrich the culture. Another study achieved the development of MMCs capable of producing PHAs by periodically feeding with nonanoic acid in a SBR in a municipal wastewater treatment plant in Daejeon, Korea; this allowed the accumulation of maximum PHA content of 48.6% dry cell weight (CDW)[7] In these studies described above, the single volatile fatty acid (VFA) or mixed VFA produced by acidogenic fermentation was applied as the enrichment substrate. These studies show that VFA can be directly converted into PHA, facilitating PHA functional bacteria selection by providing a competitive advantage to PHA-storing organisms[8]. Applying this three-step strategy, many researchers have tested renewable carbon sources for their use in PHA production, including of waste starch, molasses, lignocellulosic waste, whey from dairy industry, glycerol from biodiesel production, slaughterhouse waste, and waste oils[11,12,13,14]
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