Polyhydroxyalkanoates Accumulation Research Articles

Recent advances on food waste pretreatment technology via microalgae for source of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyester which are biosynthesized from the intracellular cells of microalgae through the cultivation of organic food waste medium. Before cultivation process, food waste must undergo several pre-treatment techniques such as chemical, biological, physical or mechanical in order to solubilize complex food waste matter into simpler micro- and macronutrients in which allow bio-valorisation of microalgae and food waste compound during the cultivation process. This work reviews four microalgae genera namely Chlamydomonas, Chlorella, Spirulina, and Botryococcus, are selected as suitable species due to rapid growth rate, minimal nutrient requirement, greater adaptability and flexibility prior to lower the overall production cost and maximized the production of PHAs. This study also focuses on the different mode of cultivation for the accumulation of PHAs followed by cell wall destabilization, extraction, and purification. Nonetheless, this review provides future insights into enhancing the productivity of bioplastic derived from microalgae towards low-cost, large-scale, and higher productivity of PHAs.

Optimization of aerobic dynamic discharge process for very rapid enrichment of polyhydroxyalkanoates-accumulating bacteria from activated sludge

The aerobic dynamic discharge (ADD) process has the potential to reduce the enrichment period of polyhydroxyalkanoates (PHA)-accumulating bacteria in PHA production using mixed microbial cultures (MMCs). This study aimed to efficiently enrich PHA-accumulating bacteria from activated sludge within a fixed period of 2 d by optimizing operating conditions of the ADD process. Based on the results, enrichment with separate feeding of carbon and nutrients in the feast and famine phases, respectively, and a settling duration of 10 min after the feast phase in the sequencing batch cycle for 12 h was found to be optimal. The MMC enriched at optimum conditions could store as much as 68.4 wt% of PHA. Dechloromonas and Zoogloea were identified as potential PHA-accumulating bacteria responsible for enhancing PHA accumulation ability in the enriched MMC. The optimized ADD process will facilitate the consecutive use of daily generated waste activated sludge for PHA production.

In Vivo Characterization and Application of the PHA Synthase from Azotobacter vinelandii for the Biosynthesis of Polyhydroxyalkanoate Containing 4-Hydroxybutyrate.

Polyhydroxyalkanoate (PHA) is a biodegradable thermoplastic naturally synthesized by many microorganisms, and the PHA synthase (PhaC) is known to be the key enzyme involved in determining the material properties and monomer composition of the produced PHA. The ability to exploit widely distributed, commonly found soil microorganisms such as Azotobacter vinelandii to synthesize PHA containing the lipase-degradable 4-hydroxybutyrate (4HB) monomer will allow for convenient production of biocompatible and flexible PHA. Comparisons between the A. vinelandii wild type and mutant strains, with and without a surface layer (S-layer), respectively, in terms of gene or amino acid sequences, synthase activity, granule morphology, and PHA productivity, revealed that the S-layer is the sole factor affecting PHA biosynthesis by A. vinelandii. Based on PHA biosynthesis using different carbon sources, the PhaC of A. vinelandii showed specificity for short-chain-length PHA monomers, making it a member of the Class I PHA synthases. In addition, it was proven that the PhaC of A. vinelandii has the inherent ability to polymerize 4-hydroxybutyrate (4HB) and the mediated accumulation of PHA with 4HB fractions ranging from 10 mol% to as high as 22 mol%. The synthesis of biocompatible PHA containing tailorable amounts of 4HB with an expanded range of elasticity and lipase-degradability will enable a wider range of applications in the biomedical field.

Comprehensive optimization of tropical biomass hydrolysis for nitrogen-limited medium-chain polyhydroxyalkanoate synthesis.

Expanding the use of tropical biomass wastes for nitrogen-limited fermentation was investigated, specifically, the production of medium chain length polyhydroxyalkanoates. Comprehensive central composite design was conducted to assess pH, temperature, biomass solid loading, cellulase loading and amylase loading and their impact on the hydrolysis of palm, coconut and cassava wastes. Glucose yields of 33.3, 31.7 and 79.0% wt. with respect to total glucose were found for palm, coconut and cassava, respectively. Importantly, the impact on the total nitrogen derived during enzymatic hydrolysis of these tropical biomass was described for the first time. The level of nitrogen needs to be properly controlled as high nitrogen would result in low carbon to nitrogen ratio leading to low polyhydroxyalkanoates accumulation, but low nitrogen would hinder growth of the biopolymer producer. Maximum hydrolysate nitrogen, were 1.80, 1.55 and 0.871g/l for palm, coconut and cassava, respectively. Using the surface responses, biomass media designed for high carbon-to-nitrogen were produced and validated using Pseudomonas putida. Low glucose-carbon to nitrogen were found for palm and coconut after scale-up, leading to the majority of their polyhydroxyalkanoates not being biomass-derived. However, cassava-derived biopolymers were successfully accumulated at 9.01 and 7.13% wt. for total medium chain length polyhydroxyalkanoates and 10-carbon polyhydroxyalkanoates, respectively. This study provides an important foundation for the expansion of tropical biomass wastes for biopolymer production and other nitrogen-limited applications in general.

The First Insight into Polyhydroxyalkanoates Accumulation in Multi-Extremophilic Rubrobacter xylanophilus and Rubrobacter spartanus.

Actinobacteria belonging to the genus Rubrobacter are known for their multi-extremophilic growth conditions—they are highly radiation-resistant, halotolerant, thermotolerant or even thermophilic. This work demonstrates that the members of the genus are capable of accumulating polyhydroxyalkanoates (PHA) since PHA-related genes are widely distributed among Rubrobacter spp. whose complete genome sequences are available in public databases. Interestingly, all Rubrobacter strains possess both class I and class III synthases (PhaC). We have experimentally investigated the PHA accumulation in two thermophilic species, R. xylanophilus and R. spartanus. The PHA content in both strains reached up to 50% of the cell dry mass, both bacteria were able to accumulate PHA consisting of 3-hydroxybutyrate and 3-hydroxyvalerate monomeric units, none other monomers were incorporated into the polymer chain. The capability of PHA accumulation likely contributes to the multi-extremophilic characteristics since it is known that PHA substantially enhances the stress robustness of bacteria. Hence, PHA can be considered as extremolytes enabling adaptation to extreme conditions. Furthermore, due to the high PHA content in biomass, a wide range of utilizable substrates, Gram-stain positivity, and thermophilic features, the Rubrobacter species, in particular Rubrobacter xylanophilus, could be also interesting candidates for industrial production of PHA within the concept of Next-Generation Industrial Biotechnology.

Waste as feedstock for polyhydroxyalkanoate production from activated sludge: Implications of aerobic dynamic feeding and acidogenic fermentation

Polyhydroxyalkanoates (PHA) are the ideal substitute for petroleum-derived non-biodegradable plastics. However, the cost of polymer production restricts the large-scale implementation. Waste feedstocks are a perfect carbon source to balance the cost and waste disposal and minimization. The suitability of activated sludge as inoculum for PHA production from potential waste feedstocks was analyzed for an affordable production strategy through waste management in a three-step methodology. The methodology involves a combined acidogenic fermentation and aerobic dynamic feeding strategy to improve PHA accumulation. Firstly, the specificity of waste feedstock for storage response was increased through volatile fatty acid (VFAs) production by tuning the process elements during acidogenic fermentation depending on the type of substrate. Secondly, activated sludge enriched through aerobic dynamic feeding strategy for improved storage response weeds out non-accumulators through various approaches. Finally, PHA accumulation bulks the enriched mix culture with PHA through different routes to enable economic downstream processing. The acidogenic fermentation critically impacts PHA composition and property along with operating conditions during the process. These studies point towards the feasibility of integrating PHA production by three-step methodology to the existing waste treatment facility and its future scope. Further investigations to improve the efficiency of the process and polymer properties can lead to cheaper polymer production more comprehensive market application.

Complete genome sequence of Photobacterium ganghwense C2.2: A new polyhydroxyalkanoate production candidate.

Polyhydroxyalkanoates (PHAs) are biodegradable bioplastics that can be manufactured sustainably and represent a promising green alternative to petrochemical‐based plastics. Here, we describe the complete genome of a new marine PHA‐producing bacterium—Photobacterium ganghwense (strain C2.2), which we have isolated from the Black Sea seashore. This new isolate is psychrotolerant and accumulates PHA when glycerol is provided as the main carbon source. Transmission electron microscopy, specific staining with Nile Red visualized via epifluorescence microscopy and gas chromatography analysis confirmed the accumulation of PHA. This is the only PHA‐producing Photobacterium for which we now have a complete genome sequence, allowing us to investigate the pathways for PHA production and other secondary metabolite synthesis pathways. The de novo assembly genome, obtained using open‐source tools, comprises two chromosomes (3.5, 2 Mbp) and a megaplasmid (202 kbp). We identify the entire PHA synthesis gene cluster that encodes a class I PHA synthase, a phasin, a 3‐ketothiolase, and an acetoacetyl‐CoA reductase. No conventional PHA depolymerase was identified in strain C2.2, but a putative lipase with extracellular amorphous PHA depolymerase activity was annotated, suggesting that C2.2 is unable to degrade intracellular PHA. A complete pathway for the conversion of glycerol to acetyl‐CoA was annotated, in accordance with its ability to convert glycerol to PHA. Several secondary metabolite biosynthetic gene clusters and a low number of genes involved in antibiotic resistance and virulence were also identified, indicating the strain's suitability for biotechnological applications.

Creating biotransformation of volatile fatty acids and octanoate as co-substrate to high yield medium-chain-length polyhydroxyalkanoate

Using mixed microbial consortium (MMC) to accumulate polyhydroxyalkanoate (PHA) is an effective strategy to solve high production cost and reduce the amount of excess sludge. In this study, a process for the production of short-chain-length and medium-chain-length PHA using volatile fatty acids (VFAs) from pretreated wood hydrolysate synergistic with octanoate as co-substrate was proposed. The effects of co-substrate ratios on PHA accumulation ability and physical properties were investigated. The incorporation of co-substrate accelerated the time of PHA and 3-hydroxyoctanoate reaching the maximum production (1834 and 280 mg COD/L). The highest PHA content was 53.0% (w/w), which was equivalent to that reported previously. The biopolymer films possessed high tensile strength, Young's modulus, and could be used in the field of water vapor barrier requirements. The accumulation strategy applied for converting fermentation products VFAs and octanoate co-substrate into high value and yield PHA could potentially demonstrate the valuable for low-cost large-scale production.

Strategies for the valorisation of a protein-rich saline waste stream into polyhydroxyalkanoates (PHA)

Saline Mussels Cooking Wastewater was valorised to produce PHA with Mixed Microbial Cultures (MMC). Due to the high protein content (1.8–5.7 g CODPROT/L), PHA accumulating capacity was below 10%, so several strategies were tested. In the acidification unit, Na(HCO3) was added, increasing protein conversion into Volatile Fatty Acids (VFA) from 10.3% to 69.2% and subsequent PHA accumulation from 6.9 to 14.7%. In the enrichment unit, the incorporation of a settling stage after the feast phase provoked a shift in the proteins’ oxidation from the feast to the famine phase, where the nitrogen released in the famine is used by the MMC for growth. This increased the biomass concentration and the tolerated COD (from 1.6 to 4.2 g VSS/L and from 2.2 to 4.38 g COD/L). Finally, varying the proteins/VFA ratio for MMC acclimation to proteins allowed increasing PHA accumulation from 8.8 to 41.5%.

Effect of C/N ratio on the PHA accumulation capability of microbial mixed culture fed with leachates from the organic fraction of municipal solid waste (OFMSW)

Activated sludge was submitted to the aerobic dynamic feeding strategy in a Sequencing Batch Reactor (SBR) to evaluate the effect of the carbon/nitrogen (C/N) ratio on the polyhydroxyalkanoates (PHA) accumulation capability. The SBR was operated for 233 days using leachates from the stabilization of the organic fraction of municipal solid wastes (OFMSW) as carbon source, with a Volatile Fatty Acids (VFA) content of 13.95 ± 7.81 g COD/L. The influence of the C/N ratio on PHA accumulation capability was evaluated by supplementing the leachates with acetate or ammonium, then applying C/N ratios within the range of 13.3 to 42.1. Low C/N ratios of 13.3 and 23.3 promoted PHA accumulation in form of polyhydroxybutyrate (PHB), reaching a maximum of 16.8 % stored, whereas the application of the highest C/N ratios led to a reduction on the PHA accumulation capacity, this probably due to an inhibition induced by the high carbon concentration. Moreover, during the experimental period it was observed that the reduction on the respiration activity of the culture, reflected in a decreasing on the Specific Oxygen Uptake Rate (SOUR) from 1.67 down to 0.42 mg O2/g VSS min This phenomenon could be the result of the continuous exposure of the microorganisms to long famine periods as well as the inhibitory effect of specific organic compounds commonly found in leachates. Overall, the PHB production is negatively affected when the MMC is submitted to the operation at high C/N ratios along with long famine periods.

Characterization of Polyhydroxyalkanoates Produced at Pilot Scale From Different Organic Wastes.

Polyhydroxyalkanoates (PHAs) production at pilot scale has been recently investigated and carried out exploiting different process configurations and organic wastes. More in detail, three pilot platforms, in Treviso (North-East of Italy), Carbonera (North-East of Italy) and Lisbon, produced PHAs by open mixed microbial cultures (MMCs) and different organic waste streams: organic fraction of municipal solid waste and sewage sludge (OFMSW-WAS), cellulosic primary sludge (CPS), and fruit waste (FW), respectively. In this context, two stabilization methods have been applied, and compared, for preserving the amount of PHA inside the cells: thermal drying and wet acidification of the biomass at the end of PHA accumulation process. Afterward, polymer has been extracted following an optimized method based on aqueous-phase inorganic reagents. Several PHA samples were then characterized to determine PHA purity, chemical composition, molecular weight, and thermal properties. The polymer contained two types of monomers, namely 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) at a relative percentage of 92.6–79.8 and 7.4–20.2 w/w, respectively, for Treviso and Lisbon plants. On the other hand, an opposite range was found for 3HB and 3HV monomers of PHA from Carbonera, which is 44.0–13.0 and 56.0–87.0 w/w, respectively. PHA extracted from wet-acidified biomass had generally higher viscosity average molecular weights (Mv) (on average 424.8 ± 20.6 and 224.9 ± 21.9 KDa, respectively, for Treviso and Lisbon) while PHA recovered from thermally stabilized dried biomass had a three-fold lower Mv.

Polyhydroxyalkanoates and pigments coproduction by Arthrospira (Spirulina) platensis cultivated in crude glycerol

Valorization of industrial waste as an alternative carbon source for microalgae mixotrophic cultivation and co-production of high-value compounds are strategies to enhance the bioprocess revenue and make large-scale production of microalgae polyhydroxyalkanoates (PHAs) feasible, with these biopolymers as potential substitutes to conventional polymers, such as polypropylene (PP) and high-density polyethylene (HDPE). In this sense, the use of crude glycerol, a main byproduct of the biodiesel industry, is an alternative to reduce cultivation costs and, at the same time, to provide a biotechnological solution for the excess of this byproduct produced, approximately 10 wt% per biodiesel batch. Thus, this work evaluated the effect of pure and crude glycerol supplementation and nutrient depletion (N and P) on growth, total carotenoids, phycocyanin and PHAs content in Arthrospira platensis xenic cultures. The highest final biomass concentrations, 1.68 and 1.40 g L-1, and PHAs contents, 1.1 and 0.5 % were achieved by supplying a Zarrouk medium with 6.14 g L-1 of pure or crude glycerol, respectively. In spite of having its content reduced at 6.14 g L-1 of pure glycerol, phycocyanin still presents a reasonable content (4.2 %) in this condition and in crude glycerol at 3.07 g.L-1 attained the highest content (10.8 %). On the other hand, glycerol mixotrophic cultivations with simultaneous nutrient depletion (nitrogen or phosphorus) did not improve the accumulation of PHAs.

Brewer’s spent grain as a no-cost substrate for polyhydroxyalkanoates production: Assessment of pretreatment strategies and different bacterial strains

Polyhydroxyalkanoates (PHAs) are polyesters of significant interest due to their biodegradability and properties similar to petroleum-derived plastics, as well as the fact that they can be produced from renewable sources such as by-product streams. In this study, brewer’s spent grain (BSG), the main by-product of the brewing industry, was subjected to a set of physicochemical pretreatments and their effect on the release of reducing sugars (RS) was evaluated. The RS obtained were used as a substrate for further PHA production in Burkholderia cepacia, Bacillus cereus, and Cupriavidus necator in liquid cultures. Although some pretreatments proved efficient in releasing RS (acid-thermal pretreatment up to 42.1 gRS L−1 and 0.77 gRS g−1 dried BSG), the generation of inhibitors in such scenarios likely affected PHA production compared with the process run without pretreatment (direct enzymatic hydrolysis of BSG). Thus, the maximum PHA accumulation from BSG hydrolysates was found in the reference case with 0.31 ± 0.02 g PHA per g cell dried weight, corresponding to 1.13 ± 0.06 g L-1 and a PHA yield of 23 ± 1 mg g-1 BSG. It was also found that C. necator presented the highest PHA accumulation of the tested strains followed closely by B. cepacia, reaching their maxima at 48 h. Although BSG has been used as a source for other bioproducts, these results show the potential of this by-product as a no-cost raw material for producing PHAs in a waste valorization and circular economy scheme.

Productivity of Pseudomonas putida TISTR 1522 in polyhydroxyalkanoates (PHAs) production from saponified palm oil.

Polyhydroxyalkanoates (PHAs) have attracted attention as an environmentally degradable bioplastic which potentially replaces synthetic polymers used in a wide range of industries. One of most promising microorganisms for the production of PHAs is Pseudomonas putida. In this study, we purpose to develop sustainable processes to convert abundant palm oil available in local market to high value PHAs and optimize PHAs production by Pseudomonas putida TISTR 1522 from saponified palm oil. We found that the highest yield of PHAs production (0.95 g/L, 40.15%) was obtained in culture medium supplemented with 1% (w/v) fatty acid salt by P. putida TISTR 1522 after 24-h cultivation. The intracellular PHAs were located in granules inside the cells, which fluoresced bright yellow by staining with Nile red. The physical appearance of intracellular PHAs investigated by transmission electron microscope (TEM) revealed that PHAs accumulate in granules, about 3-10 granules per cell. These granules are white and roundish-shaped with 0.3-0.5-μm diameter. The 1H NMR spectrum represented the typical characters of medium-chain length-PHAs. This variation of all parameters was successfully demonstrated a good intracellular PHAs accumulation in P. putida TISTR 1522 by fatty acid salt utilization.

Accumulation of PHA in the Microalgae Scenedesmus sp. under Nutrient-Deficient Conditions.

Traditional plastics have undoubted utility and convenience for everyday life; but when they are derived from petroleum and are non-biodegradable, they contribute to two major crises today’s world is facing: fossil resources depletion and environmental degradation. Polyhydroxyalkanoates are a promising alternative to replace them, being biodegradable and suitable for a wide variety of applications. This biopolymer accumulates as energy and carbon storage material in various microorganisms, including microalgae. This study investigated the influence of glucose, N, P, Fe, and salinity over the production of polyhydroxyalkanoate (PHA) by Scenedesmus sp., a freshwater microalga strain not previously explored for this purpose. To assess the effect of the variables, a fractional Taguchi experimental design involving 16 experimental runs was planned and executed. Biopolymer was obtained in all the experiments in a wide range of concentrations (0.83–29.92%, w/w DW), and identified as polyhydroxybutyrate (PHB) by FTIR analysis. The statistical analysis of the response was carried out using Minitab 16, where phosphorus, glucose, and iron were identified as significant factors, together with the P-Fe and glucose-N interactions. The presence of other relevant macromolecules was also quantified. Doing this, this work contributes to the understanding of the critical factors that control PHA production and present Scenedesmus sp. as a promising species to produce bio-resources in commercial systems.

Isolation and characterization of fast-growing green snow bacteria from coastal East Antarctica.

Snow microorganisms play a significant role in climate change and affecting the snow melting rate in the Arctic and Antarctic regions. While research on algae inhabiting green and red snow has been performed extensively, bacteria dwelling in this biotope have been studied to a much lesser extent. In this study, we performed 16S rRNA gene amplicon sequencing of two green snow samples collected from the coastal area of the eastern part of Antarctica and conducted genotypic and phenotypic profiling of 45 fast‐growing bacteria isolated from these samples. 16S rRNA gene amplicon sequencing of two green snow samples showed that bacteria inhabiting these samples are mostly represented by families Burkholderiaceae (46.31%), Flavobacteriaceae (22.98%), and Pseudomonadaceae (17.66%). Identification of 45 fast‐growing bacteria isolated from green snow was performed using 16S rRNA gene sequencing. We demonstrated that they belong to the phyla Actinobacteria and Proteobacteria, and are represented by the genera Arthrobacter, Cryobacterium, Leifsonia, Salinibacterium, Paeniglutamicibacter, Rhodococcus, Polaromonas, Pseudomonas, and Psychrobacter. Nearly all bacterial isolates exhibited various growth temperatures from 4°C to 25°C, and some isolates were characterized by a high level of enzymatic activity. Phenotyping using Fourier transform infrared (FTIR) spectroscopy revealed a possible accumulation of intracellular polymer polyhydroxyalkanoates (PHA) or lipids in some isolates. The bacteria showed different lipids/PHA and protein profiles. It was shown that lipid/PHA and protein spectral regions are the most discriminative for differentiating the isolates.

Polyhydroxyalkanoates production from industrial wastewaters using a mixed culture enriched with Thauera sp.: Inhibitory effect of the wastewater matrix

Industries all over the world generate huge amounts of wastewater, which needs to be treated. The integration of polyhydroxyalkanoates (PHA) production into wastewater treatment is a promising strategy for resource recovery that improves the sustainability of industrial wastewater treatment plants. This study aims to investigate PHA production from several industrial wastewaters using a microbial mixed culture enriched in bacteria of the genus Thauera. The wastewaters were classified based on the volatile fatty acid (VFA) concentration and the presence of ethanol: (W1) wastewater with VFA <12 mM (anaerobically treated dairy, yeast and paper mill wastewaters), (W2) wastewater with VFA >12 mM (acidified sugar, paper mill and brewery wastewaters), and (W3) wastewater with VFA >12 mM and ethanol (acidified starch, distillery and dairy wastewaters). No PHA accumulation was obtained with wastewaters in the category W1 because the VFA concentration was low and was used for biomass growth and maintenance. The maximum PHA accumulation of 46.5% cdw was achieved from acidified paper mill wastewater. For other wastewaters in the categories W2 and W3, PHA accumulation was in the range of 37–45.6% cdw. In the W2 category, PHA accumulation inhibition due to VFA concentration was observed in the case of acidified sugar wastewater, while for wastewaters in the W3 category inhibition was provoked by the wastewater matrix itself. Nevertheless, PHA accumulation inhibition was overcome by wastewater dilution. The presence of ethanol in wastewaters within the category W3 (>27 mM) decreased PHA accumulation circa 20%. The thermal characteristics of the copolymer PHB:PHV obtained in the present study are similar to those of commercial PHAs. Additionally, the produced copolymer was used successfully as a carbon source for nitrate removal (0.72 mg NO3−/mg PHA). This study shows that resource recovery in the form of biopolymers is an option for several industrial wastewaters and that the copolymers obtained are biodegradable.

Analysis of the genome sequencing data of the Marinobacterium genus

The marine genus Marinobacterium was first identified in 1997, and a total of 18 species have been characterized so far, 10 of which have published whole-genome sequencing data. This article summarizes the characteristics of Marinobacterium genus and analyzes the genome sequencing data related to the carbon source utilization, polyhydroxyalkanoate metabolism, and aromatic compounds degradation. The Marinobacterium species possess the complete glycolysis pathway and tricarboxylic acid cycle, yet lack genes involved in xylose utilization. All strains of the Marinobacterium genus contain the genes encoding for the typeⅠand type Ⅲ polyhydroxyalkanoate synthases, suggesting that the genus may have ability of polyhydroxyalkanoate accumulation. The Marinobacterium species contain the degradation pathways of aromatic compounds. Benzene, phenol and benzoic acid can be degraded into catechol via different enzymes, subsequently catechol is converted to 3-ketoadipate through the ortho-cleavage pathway. Alternatively, catechol can be degraded into pyruvate and acetyl-CoA. The analysis of genome sequencing data of the Marinobacterium genus provides in-depth understanding of the metabolic characteristics, indicating that the genus may have certain applications in the synthesis of polyhydroxyalkanoate and the removal of marine aromatic compounds.

Bio-based conversion of volatile fatty acids from waste streams to polyhydroxyalkanoates using mixed microbial cultures

Production of polyhydroxyalkanoates is an important field in the biorefinery as bio-alternative to conventional plastics. However, its commercialization is still limited by high production cost. In this study, a process with the potential to reduce the production cost of polyhydroxyalkanoates was proposed. Mixed cultures accumulated polyhydroxyalkanoates using volatile fatty acid-rich effluents from waste streams, without pH and temperature control. In addition, the impact of two types of carbon sources was investigated by analyzing the microbial community as well as the polyhydroxyalkanoate accumulation capacity. Mixed cultures successfully adapted to different substrates, consuming the volatile fatty acids in their totality. The phyla Proteobacteria, Bacteroidetes and Firmicutes dominated the bacterial community. The highest polyhydroxyalkanoate content was 43.5% w/w, which is comparable to contents reported from mixed cultures using synthetic carbon sources. The biopolymer consisted of (R)-3-hydroxybutyrate 94.8 ± 1.7% w/w and (R)-3-hydroxyvaletare 5.2 ± 1.7% w/w.

Recovery of Polyhydroxyalkanoates from Cooked Mussel Processing Wastewater at High Salinity and Acidic Conditions

Polyhydroxyalkanoates (PHA) are biodegradable polymers that can be intracellularly produced by microorganisms valorizing organic-rich wastes. In the present study, a PHA production system was fed with mussel cooker wastewater after acidogenic fermentation. Besides low pH (4.0 ± 0.3) and high salt (21.7 ± 2.9 g NaCl/L) concentrations, this wastewater also contained nitrogen concentrations (0.8 ± 0.1 g N/L), which were previously reported to be a challenge to the PHA accumulating bacteria enrichment. Bacteria with a PHA storage capacity were selected in an enrichment sequencing batch reactor (SBR) after 60 days of operation. The enriched mixed microbial culture (MMC) was mainly formed by microorganisms from phylum Bacteroidetes, and genera Azoarcus, Comamonas and Thauera from phylum Proteobacteria. The MMC was able to accumulate up to 25 wt% of PHA that was mainly limited by the wastewater nitrogen content, which promoted biomass growth instead of PHA accumulation. Indeed, when the presence of nutrient was limited, PHA stored in the accumulation reactor increased to up to 40.9 wt%. This work demonstrated the feasibility of the enrichment of a MMC with a PHA storage ability valorizing the fish-canning industrial wastewater at low pH, which is generally difficult to treat in wastewater treatment plants.