Analysis of Medium-Chain-Length Polyhydroxyalkanoate-Producing Bacteria in Activated Sludge Samples Enriched by Aerobic Periodic Feeding

Evaluation of the production and extraction of polyhydroxybutyrate from volatile fatty acids by means of mixed cultures and B. cepacia

The global consumption of plastics generates accelerated environmental pollution in landfills and marine ecosystems. Biopolymers are the materials with the greatest potential to replace synthetic polymers in the market due to their good biodegradability, however, there are still several disadvantages, mainly related to their production cost. Considering the above, the generation of biodegradable and biocompatible bioplastics stands out as an alternative solution, some of which are made from renewable raw materials, including polyhydroxyalkanoates PHAs. Although much research has been done on bacteria with the capacity for intracellular accumulation of PHAs, among others, it is also possible to produce PHAs using mixed microbial cultures instead of a single microorganism, using natural microbial consortia that have the capacity to store high amounts of PHAs. In this contribution, three methods for the extraction and purification of PHAs produced by fermentation using volatile fatty acids as a carbon source at different concentrations were evaluated, using the pure strain Burkholderia cepacia 2G-57 and the mixed cultures of the activated sludge from the El Salitre WWTP, in order to select the best method from the point of view of environmental sustainability as this will contribute to the scalability of the process. The mixed cultures were identified by sequencing of the 16S gene. A yield of 89% was obtained from the extraction and purification of PHA using acetic acid as a solvent, which according to its properties is "greener" than chloroform. The polymer obtained was identified as polyhydroxybutylated PHB.

Exploring the potential of slaughterhouse waste valorization: Development and scale-up of a new bioprocess for medium-chain length polyhydroxyalkanoates production

The progressive increase of slaughterhouse waste production requires actions for both addressing an environmental issue and creating additional value within a biorefinery concept. In this regard, some of these animal by-products exhibit a significant content of fatty acids that could be efficiently converted into bioplastics such as polyhydroxyalkanoates (PHAs) by adequately performing substrate screening with producing bacterial strains and applying affordable pretreatments. One of the main challenges also relies on the difficulty to emulsify these fat-rich substrates within culture broth and make the fatty acids accessible for the producing bacteria. In this work, the potential of two fat-rich animal by-products, grease trap waste (GTW) and tallow-based jelly (TBJ), as inexpensive carbon sources for microbial growth and PHA production was evaluated for the first time. Upon substrate screening, using different pseudomonadal strains (P. resinovorans, P. putida GPo1, P. putida KT2440) and pretreatment conditions (autoclave-based, thermally-treated or saponified substrates), the highest growth and mcl-PHA production performance was obtained for P. resinovorans, thus producing up to 47% w/w mcl-PHA simply using hygienized GTW. The novel bioprocess described in this study was successfully scaled up to 5 and 15 L, resulting in CDW concentrations of 5.9-12.8 g L^-1, mcl-PHA contents of 33-62% w/w and PHA yields of 0.1-0.4 gPHA g^-1_{fatty acids}, greatly depending on the substrate dosing strategy used and depending on culture conditions. Moreover, process robustness was confirmed along Test Series by the roughly stable monomeric composition of the biopolymer produced, mainly formed by 3-hydroxyoctanoate and 3-hydroxydecanoate. The research here conducted is crucial for the cost-effectiveness of mcl-PHA production along this new slaughterhouse waste-based biorefinery concept.

Valorisation of waste cooking oil using mixed culture into short- and medium-chain length polyhydroxyalkanoates: Effect of concentration, temperature and ammonium

The production of polyhydroxyalkanoates (PHAs) from waste cooking oil (WCO) by a mixed culture was investigated in the present study at increasing WCO concentrations, temperature and ammonium availability. The PHA production was done in two steps: in the first step, a mixed culture was enriched in PHA-accumulating bacteria from activated sludge in a sequencing batch reactor operated in a feast-famine mode and in the second step the PHA accumulation by the enriched mixed culture was assessed in a batch reactor. In the enrichment step, two substrates, WCO and nonanoic acid were used for enrichment and in the PHA accumulation step only WCO was used. It was not possible to enrich a mixed culture in PHA-accumulating bacteria using WCO as substrate due to the development of filamentous bacteria causing foam formation and bulking in the reactor. However, our results showed that the mixed culture continuously fed with nonanoic acid was enriched in PHA-accumulating bacteria. This enriched culture accumulated both scl- and mcl-PHA using WCO as substrate. The maximum PHA accumulation capacity of this mixed culture from WCO was 38.2% cdw. Increasing the temperature (30-40 ℃) or WCO concentrations (5-20 g/l) increased the PHA accumulation capacity of the mixed culture and the ratios of scl-PHA to mcl-PHA. The presence of ammonium increased PHA accumulation (21.9% cdw) compared to the complete absence of ammonium (5.8% cdw). The thermal characterization of the PHA exhibited the advantageous properties of both scl- and mcl-PHA, i.e., higher melting temperature (152-172 ℃) similar to scl-PHA and a lower degree of crystallinity (12%) similar to mcl-PHA. This is the first study to report the potential of open mixed culture to produce scl- and mcl-PHA from WCO and thus contributing to the understanding of sustainable polymer production.

Recent advances in constructing artificial microbial consortia for the production of medium-chain-length polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are a class of high-molecular-weight polyesters made from hydroxy fatty acid monomers. PHAs produced by microorganisms have diverse structures, variable physical properties, and good biodegradability. They exhibit similar physical properties to petroleum-based plastics but are much more environmentally friendly. Medium-chain-length polyhydroxyalkanoates (mcl-PHAs), in particular, have attracted much interest because of their low crystallinity, low glass transition temperature, low tensile strength, high elongation at break, and customizable structure. Nevertheless, high production costs have hindered their practical application. The use of genetically modified organisms can reduce production costs by expanding the scope of substrate utilization, improving the conversion efficiency of substrate to product, and increasing the yield of mcl-PHAs. The yield of mcl-PHAs produced by a pure culture of an engineered microorganism was not high enough because of the limitations of the metabolic capacity of a single microorganism. The construction of artificial microbial consortia and the optimization of microbial co-cultivation have been studied. This type of approach avoids the addition of precursor substances and helps synthesize mcl-PHAs more efficiently. In this paper, we reviewed the design and construction principles and optimized control strategies for artificial microbial consortia that produce mcl-PHAs. We described the metabolic advantages of co-cultivating artificial microbial consortia using low-value substrates and discussed future perspectives on the production of mcl-PHAs using artificial microbial consortia.