Enrichment performance and salt tolerance of polyhydroxyalkanoates (PHAs) producing mixed cultures under different saline environments

The key to the resource recycling of saline wastes in form of polyhydroxyalkanoates (PHA) is to enrich mixed cultures with salt tolerance and PHA synthesis ability. However, the comparison of saline sludge from different sources and the salt tolerance mechanisms of salt-tolerant PHA producers need to be clarified. In this study, three kinds of activated sludge from different salinity environments were selected as the inoculum to enrich salt-tolerant PHA producers under aerobic dynamic feeding (ADF) mode with butyric acid dominated mixed volatile fatty acid as the substrate. The maximum PHA content (PHAm) reached 0.62 ± 0.01, 0.62 ± 0.02, and 0.55 ± 0.03 g PHA/g VSS at salinity of 0.5%, 0.8%, and 1.8%, respectively. Microbial community analysis indicated that Thauera, Paracoccus, and Prosthecobacter were dominant salt-tolerant PHA producers at low salinity, Thauera, NS9_marine, and SM1A02 were dominant salt-tolerant PHA producers at high salinity. High salinity and ADF mode had synergistic effects on selection and enrichment of salt-tolerant PHA producers. Combined correlation network with redundancy analysis indicated that trehalose synthesis genes and betaine related genes had positive correlation with PHAm, while extracellular polymeric substances (EPS) content had negative correlation with PHAm. The compatible solutes accumulation and EPS secretion were the main salt tolerance mechanisms of the PHA producers. Therefore, adding compatible solutes is an effective strategy to improve PHA synthesis in saline environment.

Production of polyhydroxyalkanoate (PHA) copolymer from food waste using mixed culture for carboxylate production and Pseudomonas putida for PHA synthesis

Production of polyhydroxyalkanoates (PHAs) with high concentration of carboxylate, that was accumulated from solid state fermentation (SSF) of food waste (FW), was tested using Pseudomonas putida strain KT2440. Mixed-culture SSF of FW supplied in a high concentration of carboxylate, which caused a high PHA production of 0.56 g PHA/g CDM under nutrients control. Interestingly, this high PHA fraction in CDM was almost constant at 0.55 g PHA/g CDM even under high nutrients concentration (25 mM NH₄⁺), probably due to high reducing power maintained by high carboxylate concentration. PHA characterization indicated that the dominant PHA building block produced was 3-hydroxybutyrate, followed by 3-hydroxy-2-methylvalerate and 3-hydroxyhenxanoate. Carboxylate profiles before and after PHA production suggested that acetate, butyrate, and propionate were the main precursors to PHA via several metabolic pathways. Our result support that mixed culture SSF of FW for high concentration carboxylate and P. putida for PHA production enables sustainable production of PHA in cost-effective manners.

Influence of feedstock source on the development of polyhydroxyalkanoates-producing mixed microbial cultures in continuously stirred tank reactors

Polyhydroxyalkanoates (PHAs) are the new frontier of bioplastic production; however, research is needed to develop and characterise efficient mixed microbial communities (MMCs) for their application with a multi-feedstock approach. Here, the performance and composition of six MMCs developed from the same inoculum on different feedstocks were investigated through Illumina sequencing to understand community development and identify possible redundancies in terms of genera and PHA metabolism. High PHA production efficiencies (>80% mg COD_PHA mg^-1 COD_OA-consumed) were seen across all samples, but differences in the organic acids (OAs) composition led to different ratios of the monomers poly(3-hydroxybutyrate) (3HB) to poly(3-hydroxyvalerate) (3HV). Communities differed across all feedstocks, with enrichments in specific PHA-producing genera, but analysis of potential enzymatic activity identified a certain degree of functional redundancy, possibly leading to the general high efficiency seen in PHA production from all feedstocks. Leading PHAs producers across all feedstocks were identified in genera such as Thauera, Leadbetterella, Neomegalonema and Amaricoccus.

Polyhydroxyalkanoates (PHAs) synthesis and degradation by microbes and applications towards a circular economy

Overusing non-degradable plastics causes a series of environmental issues, inferring a switch to biodegradable plastics. Polyhydroxyalkanoates (PHAs) are promising biodegradable plastics that can be produced by many microbes using various substrates from waste feedstock. However, the cost of PHAs production is higher compared to fossil-based plastics, impeding further industrial production and applications. To provide a guideline for reducing costs, the potential cheap waste feedstock for PHAs production have been summarized in this work. Besides, to increase the competitiveness of PHAs in the mainstream plastics economy, the influencing parameters of PHAs production have been discussed. The PHAs degradation has been reviewed related to the type of bacteria, their metabolic pathways/enzymes, and environmental conditions. Finally, the applications of PHAs in different fields have been presented and discussed to induce comprehension on the practical potentials of PHAs.

Recovery of polyhydroxyalkanoates (PHAs) polymers from a mixed microbial culture through combined ultrasonic disruption and alkaline digestion

PHAs are a form of cellular storage polymers with diverse structural and material properties, and their biodegradable and renewable nature makes them a potential green alternative to fossil fuel-based plastics. PHAs are obtained through extraction via various mechanical, physical and chemical processes after their intracellular synthesis. Most studies have until now focused on pure cultures, while information on mixed microbial cultures (MMC) remains limited. In this study, ultrasonic (US) disruption and alkaline digestion by NaOH were applied individually and in combination to obtain PHAs products from an acclimated MMC using phenol as the carbon source. Various parameters were tested, including ultrasonic sound energy density, NaOH concentration, treatment time and temperature, and biomass density. US alone caused limited cell lysis and resulted in high energy consumption and low efficiency. NaOH of 0.05-0.2 M was more efficient in cell disruption, but led to PHAs degradation under elevated temperature and prolonged treatment. Combining US and NaOH significantly improved the overall process efficiency, which could reduce energy consumption by 2/3rds with only minimal PHAs degradation. The most significant factor was identified to be NaOH dosage and treatment time, with US sound energy density playing a minor role. Under the semi-optimized condition (0.2 M NaOH, 1300 W L^-1, 10 min), over 70% recovery and 80% purity were achieved from a 3 g L^-1 MMC slurry of approximately 50% PHAs fraction. The material and thermal properties of the products were analyzed, and the polymers obtained from US + NaOH treatments showed comparable or higher molecular weight to previously reported results. The products also exhibited good thermal stability and rheological properties, compared to the commercial standard. In conclusion, the combined US and NaOH method has the potential in real application as an efficient process to obtain high quality PHAs from MMC, and cost-effectiveness can be further optimized.

Effect of polyhydroxyalkanoates on the microbial reductive dechlorination of polychlorinated biphenyls and competing anaerobic respirations in a marine microbial culture

The effect of polyhydroxyalkanoates (PHAs) with different composition on the reductive dechlorination activity of a polychlorinated biphenyls (PCBs) dechlorinating marine microbial community and on the activity of sulfate-reducing (SRB) and methanogenic bacteria (MB), were investigated in marine sediment microcosms and compared with the main monomer, 3-hydroxybutyric acid (3HB). Despite PHAs were fermented more slowly than 3HB, all electron donors stimulated constantly sulfate-reduction, methanogenesis and, only transiently, PCB reductive dechlorination. No relevant differences were observed with different compositions of PHAs. According to electron balances, the majority of the supplied electrons (50 %) were consumed by SRB and to less extent by MB (9-31 %), while a small percentage (0.01 %) was delivered to OHRB. In the studied conditions PHAs were confirmed as potential slow‑hydrogen releasing compounds in marine environment but their fermentation rate was sufficiently high to mainly stimulate the competitors of organohalide respring bacteria for electron donors.

PHA-Based Bioplastic: a Potential Alternative to Address Microplastic Pollution

Petroleum-derived plastics are linked to a variety of growing environmental issues throughout their lifecycle, including emission of greenhouse gases, accumulation in terrestrial and marine habitats, pollution, among others. There has been a lot of attention over the last decade in industrial and research communities in developing and producing eco-friendly polymers to deal with the current environmental issues. Bioplastics preferably are a fast-developing family of polymeric substances that are frequently promoted as substitutes to petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) have a number of appealing properties that make PHAs a feasible source material for bioplastics, either as a direct replacement of petroleum-derived plastics or as a blend with elements derived from natural origin, fabricated biodegradable polymers, and/or non-biodegradable polymers. Among the most promising PHAs, polyhydroxybutyrates (PHBs) are the most well-known and have a significant potential to replace traditional plastics. These biodegradable plastics decompose faster after decomposing into carbon dioxide, water, and inorganic chemicals. Bioplastics have been extensively utilized in several sectors such as food-processing industry, medical, agriculture, automobile industry, etc. However, it is also associated with disadvantages like high cost, uneconomic feasibility, brittleness, and hydrophilic nature. A variety of tactics have been explored to improve the qualities of bioplastics, with the most prevalent being the development of gas and water barrier properties. The prime objective of this study is to review the current knowledge on PHAs and provide a brief introduction to PHAs, which have drawn attention as a possible potential alternative to conventional plastics due to their biological origin, biocompatibility, and biodegradability, thereby reducing the negative impact of microplastics in the environment. This review may help trigger further scientific interest to thoroughly research on PHAs as a sustainable option to greener bioplastics.

Influent carbon to phosphorus ratio drives the selection of PHA-storing organisms in a single CSTR

Enriching a biomass with a high fraction of polyhydroxyalkanoate-storing organisms (PHA-storers) represents an essential step in the production of PHAs (bioplastics) from municipal wastewater using mixed microbial cultures. A major challenge is however to create selective growth conditions that are favourable to PHA-storers. Our study thus investigates to what extent the influent COD to phosphorus (COD:P) ratio can be used as a tool for the robust selection of PHA-storers in a single continuous-flow stirred-tank reactor (CSTR). Therefore, we operated five CSTRs in parallel, fed with synthetic wastewater (50% acetate - 50% propionate) with different COD:P ratios (200-1000 gCOD gP^-1), and performed a detailed analysis of the microbial communities over long-term (30-70 solid retention times). Our study demonstrates that efficient and robust selection of PHA-storers can be achieved in a single CSTR at high influent COD:P ratios. The selective advantage for PHA-storers increases with the influent COD:P ratio, but only if growth conditions remain limited by both C-substrate and P. In contrast, selection performance deteriorates when COD:P ratios are too high and growth conditions are limited by P only. At an optimal COD:P ratio of 800 gCOD gP^-1, a stable microbial community consisting of >90% PHA-storers and dominated by Pannonibacter sp. was selected in the long-term. Finally, our results suggest that high COD:P ratios provide a selective advantage to microorganisms with low cellular P requirements, explaining why different PHA-storers (i.e., Xanthobacter sp. vs. Pannonibacter sp.) were selected depending on the influent COD:P ratio (i.e., 200 vs. 800 gCOD gP^-1). Overall, our results provide relevant insights for the development of a new approach for selecting PHA-storers, based on the use of a single CSTR and control of the influent COD:P ratio.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting.

Current application of algae derivatives for bioplastic production: A review

Improper use of conventional plastics poses challenges for sustainable energy and environmental protection. Algal derivatives have been considered as a potential renewable biomass source for bioplastic production. Algae derivatives include a multitude of valuable substances, especially starch from microalgae, short-chain length polyhydroxyalkanoates (PHAs) from cyanobacteria, polysaccharides from marine and freshwater macroalgae. The algae derivatives have the potential to be used as key ingredients for bioplastic production, such as starch and PHAs or only as an additive such as sulfated polysaccharides. The presence of distinctive functional groups in algae, such as carboxyl, hydroxyl, and sulfate, can be manipulated or tailored to provide desirable bioplastic quality, especially for food, pharmaceutical, and medical packaging. Standardizing strains, growing conditions, harvesting and extracting algae in an environmentally friendly manner would be a promising strategy for pollution control and bioplastic production.

Diversifying the products from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates from the liquid fraction and biomethane from the residual solid fraction

This study describes the diversification of products obtainable from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates (PHA) from the liquid fraction and biomethane from the residual solid fraction. OFMSW samples were taken during the 2021 season from two full field scale plants treating wastes. After solid/liquid (S/L) separation, 80% of initial organic acids (OAs) were released in the liquid stream. OAs were then used as feed for PHA production and residual solid cakes were tested for biomethane production. Complete mass balance and energy balance were calculated. PHAs production was of 115 ± 23 (n = 6) g kg^{- 1} OFMSW (TS) and residual biomethane of 219 ± 3 g kg^{- 1} OFMSW TS, (n = 6). Energy balance indicated that nearly 40% of OFMSW energy was recovered as products. This value was lower than that obtained previously when AD was performed before OAs separation (i.e. 64%).

Optimization of the phototrophic Cyanobacteria polyhydroxybutyrate (PHB) production by kinetic model simulation

Cyanobacteria can grow using inorganic substrates, such as CO₂ from industrial sources and nutrients from wastewaters, and therefore are promising microorganisms to produce polyhydroxybutyrate in a cleaner circular context. However, this biotechnological production is highly challenging because it involves different interlinked reactions that are affected by environmental conditions, which hinders process optimization. In this study a new biokinetic mechanistic model using novel experimental approaches was developed to optimize polyhydroxybutyrate (PHB) and glycogen production. The model includes, for the first time, the production of glycogen and its conversion into PHB, which has been found as the main pathway to produce PHB. Model was successfully (r²: 0.6-0.99) calibrated and validated with experimental data from photobioreactors inoculated with Synechocystis sp. The developed model was used to determine suitable initial conditions for a lab scale batch reactor (6.4 mgN·L^-1 and 2 mgP·L^-1) and a new configuration for the continuous industrial production of PHB was proposed and optimized using this tool. The maximum productivity (5.1 mgPHB·L^-1·d^-1) and the optimal configuration and operation of the serial reactors to produce PHB in an industrial scale was achieved using a hydraulic retention time of 4 days in the growth reactor. Then, this reactor daily fed 20 batch accumulation reactors, which were discharged after 20 days. The optimal influent nutrients concentrations for this configuration was found to be 50 mgN·L^-1 and 10 mgP·L^-1. Results found in this study show the necessity to optimize biopolymers production with Cyanobacteria considering environmental conditions, and demonstrated the potential of this model as a tool to increase PHB productivity.

Sludge retention time impacts on polyhydroxyalkanoate productivity in uncoupled storage/growth processes

The process involving mixed microbial cultures (MMCs) and waste-based substrates emerged as an alternative solution to reduce the market price of polyhydroxyalkanoates (PHAs). The selection of an efficient MMC that displays a significant PHA accumulation potential and a high growth rate is considered a key factor for the MMC PHA production feasibility. This study used a pilot plant to investigate the dynamics of growth vs storage in a mixed culture fed with fermented fruit waste under uncoupled carbon and nitrogen feeding. Varying sludge retention times (SRTs) (2 and 4 d) and organic loading rates (OLRs) (from 2.6 to 14.5 gCOD.L^-1.d^-1) were imposed for this purpose. Results showed that, regardless of the OLR imposed, cultures selected at lower SRT grew faster and more efficiently using stored PHA. However, they had inferior specific storage rates and accumulation capacity, resulting in lower PHA productivity. Additionally, the polymer storage yield was independent of the SRT, and was directly linked with the abundance of putative PHA-storers in the MMC. The high PHA productivity (4.6 ± 0.3 g.L^-1.d^-1) obtained for the culture selected at 4 d of SRT was 80% above that obtained for the lower SRT tested, underlining the importance of achieving a good balance between culture growth and accumulation capacity to increase the viability of the PHA-producing process from wastes.

Co-generation of biohydrogen and biochemicals from co-digestion of Chlorella sp. biomass hydrolysate with sugarcane leaf hydrolysate in an integrated circular biorefinery concept

BACKGROUND

A platform for the utilization of the Chlorella sp. biomass and sugarcane leaves to produce multiple products (biorefinery concept) including hydrogen, methane, polyhydroxyalkanoates (PHAs), lipid, and soil supplement with the goal to achieve the zero waste generation (circular economy) is demonstrated in this study. Microalgal biomass were hydrolyzed by mixed enzymes while sugarcane leaves were pretreated with alkali followed by enzyme. Hydrolysates were used to produce hydrogen and the hydrogenic effluent was used to produce multi-products. Solid residues at the end of hydrogen fermentation and the remaining acidified slurries from methane production were evaluated for the compost properties.

RESULTS

The maximum hydrogen yield of 207.65 mL-H₂/g-volatile solid (VS)_added was obtained from 0.92, 15.27, and 3.82 g-VS/L of Chlorella sp. biomass hydrolysate, sugarcane leaf hydrolysate, and anaerobic sludge, respectively. Hydrogenic effluent produced 321.1 mL/g-VS of methane yield, 2.01 g/L PHAs concentration, and 0.20 g/L of lipid concentration. Solid residues and the acidified slurries at the end of the hydrogen and methane production process were proved to have compost properties.

CONCLUSION

Hydrogen production followed by methane, PHA and lipid productions is a successful integrated circular biorefinery platform to efficiently utilize the hydrolysates of Chlorella sp. biomass and sugarcane leaf. The potential use of the solid residues at the end of hydrogen fermentation and the remaining acidified slurries from methane production as soil supplements demonstrates the zero waste concept. The approach revealed in this study provides a foundation for the optimal use of feedstock, resulting in zero waste.

Biodegradable polyhydroxyalkanoates production from wheat straw by recombinant Halomonas elongata A1

Waste straw bio-transformation of high value-added macromolecule polyhydroxyalkanoates (PHAs) was significance to environmental sustainable development. As a member of the PHA family, poly-β-hydroxybutyrate (PHB) could be synthesized by Halomonas elongata A1 with maximal yields of 22.8% and 11.8% of bacterial weights using glucose and carboxymethyl cellulose as carbon sources, respectively. To improve PHB production, we generated three recombinant strains, the H. elongata P2 with highest PHB biosynthesis ability. When wheat straw, mixed substrate and oleic acid were individually used as single carbon source, the maximal PHA polymer accumulation in the H. elongata P2 reached 5.2%, 16.5% and 27.5%, respectively, after 84 h of cultivation. This hardness, toughness and crystallization properties of the PHA macromolecule altered dependent on starting substrates, when analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). In terms of the hardness and roughness, the PHA produced from mixed substrates was much softer than that from wheat straw but harder than that from oleic acid. The long-chain carbon improved the softness and strength of the produced PHA. Our data indicate that economical substrates, such as straw and waste oil, can be used in the synthesis of multi-functional plastic products with biodegradable properties.

Carbon Source Applied in Enrichment Stage of Mixed Microbial Cultures Limits the Substrate Adaptability for PHA Fermentation Using the Renewable Carbon

Suitability of different substrates for enriched mixed microbial cultures (MMCs) is of importance to the polyhydroxyalkanoate (PHA) fermentation using renewable carbon. In this study, three enriched MMCs were evaluated for their fermentation features and kinetics with different carbon sources (sodium acetate, glucose, or starch). The results showed that the highly specific bacterial community composition was developed depending on the applied carbon source. Correspondence analysis suggested that the genus affiliated in Gammaproteobacteria_unclassified was related to 3-hydroxybutyrate (HB) synthesis in acetate-fed MMC (relative abundance of 38%) and glucose-fed MMC (relative abundance of 76.7%), whereas Vibrio genus was related to 3-hydroxyvalerate (HV) production in glucose-fed MMC (relative abundance of 0.4%) and starch-fed MMC (relative abundance of 94.6%). The acetate-fed MMC could not use glucose and starch as fermentation carbon sources, showing the limitation of microbial species developed with the specific metabolic substrate. Glucose-fed MMC produced the highest PHA cell content of 64.2% cell dry weight when using sodium acetate as the fermentation carbon. Glucose-fed MMC showed wide resilience and adaptation to various carbon sources. When actual landfill leachate was used for fermentation by glucose-fed MMC, maximum PHA cell content of 45.5% cell dry weight and the PHA volumetric productivity of 0.265 g PHA/(L·h) were obtained. This study suggested carbon sources applied in the MMC enrichment stage had a significant influence on utilization of carbon in the fermentation stage.

Additive manufacturing of polyhydroxyalkanoates (PHAs) biopolymers: Materials, printing techniques, and applications

Additive manufacturing (AM) is recently imposing as a fast, reliable, and highly flexible solution to process various materials, that range from metals to polymers, to achieve a broad variety of customized end-goods without involving the injection molding process. The employment of biomaterials is of utmost relevance as the environmental footprint of the process and, consequently, of the end-goods is significantly decreased. Additive manufacturing can provide, in particular, an all-in-one platform to fabricate complex-shaped biobased items such as bone implants or biomedical devices, that would be, otherwise, extremely troublesome and costly to achieve. Polyhydroxyalkanoates (PHAs) is an emerging class of biobased and biodegradable polymeric materials achievable by fermentation from bacteria. There are some promising scientific and technical reports on the manufacturing of several commodities in PHAs by additive manufacturing. However, many challenges must still be faced in order to expand further the use of PHAs. In this framework, the present work reviews and classifies the relevant papers focused on the design and development of PHAs for different 3D printing techniques and overviews the most recent applications of this approach.

Scaling-up microbial community-based polyhydroxyalkanoate production: status and challenges

Conversion of organic waste and wastewater to polyhydroxyalkanoates (PHAs) offers a potential to recover valuable resources from organic waste. Microbial community-based PHA production systems have been successfully applied in the last decade at lab- and pilot-scales, with a total of 19 pilot installations reported in the scientific literature. In this review, research at pilot-scale on microbial community-based PHA production is categorized and subsequently analyzed with focus on feedstocks, enrichment strategies, yields of PHA on substrate, biomass PHA content and polymer characterization. From this assessment, the challenges for further scaling-up of microbial community-based PHA production are identified.

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.

Structure-property interpretation of biological polyhydroxyalkanoates with different monomeric composition: Dielectric spectroscopy investigation

Dielectric spectroscopy is employed to study the relaxation phenomena in natural polyhydroxyalkanoates (PHAs) upon temperature and frequency variations. Effects of PHAs molecular structure on the relaxation, arising from the differences in monomeric composition, are investigated under identical conditions in a frequency range of 10^-2-10⁶ Hz, and at different temperatures. All PHA samples showed different dielectric response at different temperature. Primary α-relaxation signals are observed at temperature corresponding to the glass transition temperature. On the other hand, secondary β- and γ-relaxations are detected at low temperatures, and attributed to local motions of polar groups and small segments of the polymer chain. The dielectric properties of representative PHA samples are compared and discussed.

Implementing polyhydroxyalkanoates production to anaerobic digestion of organic fraction of municipal solid waste to diversify products and increase total energy recovery

A simple biorefinery aimed at producing both biomethane (CH₄) and polyhydroxyalkanoates (PHAs), was proposed to valorize the organic fraction of municipal solid waste (OFMSW). Anaerobic digestion (AD) was tested at different organic loading rates (OLR-I-II-III) (i.e. 3, 4 and 6 g L^-1 d^-1, respectively), producing biomethane and volatile fatty acids (VFAs)-rich digestate, the VFAs were then used to produce PHAs. Specific biogas and CH₄ production remained similar when adopting different OLRs (biogas of 522-600 NL kg^-1 VS and CH₄ of 64-67% v/v). VFAs concentrated with OLR increases and their patterns were modified. PHA production was in the range of 117-199 g kg^-1 OFMSW_TS with the lowest production being associated to different polymer composition. The net energy recovery of this simple biorefinery accounted for 64% of OFMSW energy content, and the PHAs produced represented over 30% of the total energy.

Anabolism of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Cupriavidus necator DSM 545 from spent coffee grounds oil

Oil extracted from spent coffee grounds (SCG) [yield 16.8 % (w/w)] was discovered to be a highly suitable carbon substrate for the biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3 HV)] copolymers by Cupriavidus necator DSM 545 in the absence of any traditional 3 HV precursors. Cells cultivated in a 3 L bioreactor (batch) reached a total biomass concentration of 8.9 g L^-1 with a P(3HB-co-3 HV) (6.8 mol% 3 HV) content of 89.6 % (w/w). In contrast, cells grown on sunflower oil reached a total biomass concentration of 9.4 gL^-1 with a P(3HB-co-3 HV) (0.2 mol% 3 HV) content of 88.1 % (w/w). It is proposed that the organism could synthesize 3 HV monomers from succinyl CoA, an intermediate of the tricarboxylic acid (TCA) cycle, via the succinate-propionate metabolic pathway.

Fermentation liquor of CaO2 treated chemically enhanced primary sedimentation (CEPS) sludge for bioplastic biosynthesis

Chemically enhanced primary sedimentation (CEPS) technology has been widely applied in Hong Kong, exhibiting excellent performance in contaminants removal from sewage. The generated CEPS sludge contains abundance of organics which could be recovered as volatile fatty acids (VFAs) by fermentation for further utilization. In this work, the effect of calcium peroxide (CaO₂) on the fermentation of FeCl₃ based CEPS sludge was investigated. The feasibility of utilizing the fermentation liquor as substrate for polyhydroxyalkanoates (PHAs) biosynthesis was also evaluated. Results demonstrated that CaO₂ addition facilitated the disintegration of CEPS sludge and enhanced VFAs production. The maximum VFAs yield of 455.8 mg COD/g VSS was obtained with the dosage of 0.1 g CaO₂/g SS, improving by 44.7% compared with the control sludge. Acetic and propionic acid were the predominant components of the VFAs. Microbial analysis indicated that CaO₂ induced microbial reduction of Fe(III), accelerating the initial disintegration of FeCl₃ based CEPS sludge. Microbial communities with hydrolysis and acidogenesis functions were enriched effectively. CaO₂ treatment had no significant influence on the release of ammonia nitrogen (NH₄⁺-N), while reduced the concentration of orthophosphate (PO₄^3--P) and ferrous (Fe²⁺) in fermentation liquor, that was beneficial to the further utilization as substrate for PHAs biosynthesis. The VFA-rich fermentation liquor was proved to be a suitable substrate for PHAs biosynthesis. After cultivation, the PHAs content in activated sludge reached 22.3%, which was comparable to those obtained using waste materials as carbon source. This integrated technology could be a superior alternative of realizing sludge disposal and bioplastic production simultaneously.

Purification and characterization of new bio-plastic degrading enzyme from Burkholderia cepacia DP1

Depolymerase is an enzyme that plays an important role in the hydrolysis of polyhydroxyalkanoates [PHAs]. In the current study, Burkholderia cepacia DP1 was obtained from Penang, Malaysia in which the enzyme was purified using ion exchange and gel filtration (Superdex-75) column chromatography. The molecular mass of the enzyme was estimated to be 53.3 kDa using SDS-PAGE. The enzyme activity was increased to 36.8 folds with the recovery of 16.3% after purification. The enzyme activity was detected between pH 6.0-10 and at 35-55 °C with pH 6.0 and 45 °C facilitating the maximum activity. Depolymerase was inactivated by Tween-20, Tween-80, SDS and PMSF, but insensitive to metal ions (Mg²⁺, Ca²⁺, K⁺, Na²⁺, Fe³⁺) and organic solvents (methanol, ethanol, and acetone). The apparent K_m values of the purified P(3HB) depolymerase enzyme for P(3HB) and P(3HB-co-14%3HV) were 0.7 mg/ml and 0.8 mg/ml, respectively. The V_max values of the purified enzyme were 10 mg/min and 8.89 mg/min for P(3HB) and P(3HB-co-14%3HV), respectively. The current study discovered a new extracellular poly(3-hydroxybutyrate) [P(3HB)] depolymerase enzyme from Burkholderia cepacia DP1 isolated and purified to homogeneity from the culture supernatant. To the best of our knowledge, this is the first report demonstrating the purification and biochemical characterization of P(3HB) depolymerase enzyme from genus Burkholderia.

En route to economical eco-friendly solvent system in enhancing sustainable recovery of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer

Separation of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] from bacterial cell matter is a critical step in the downstream process with respect to material quality and eco-balance as P(3HB-co-4HB) is widely used for biomedical applications. Therefore, an efficient and eco-based extraction of P(3HB-co-4HB) using a combination of NaOH and Lysol in digesting the non-polymeric cell material (NPCM) digestion is developed. The NaOH and Lysol show synergistic influence on the copolymer extraction at a high purity and recovery of 97 and 98 wt% respectively. The optimized cell digestion method was found applicable to a vast batch of cells containing copolymers from various 4HB monomer compositions. At the largest extraction volume of 100 L, P(3HB-co-4HB) with a purity of 89 wt% was extracted with a maximum recovery of 90 wt%. The method developed has also eliminated the cell pretreatment step. The extraction method developed in this research has not only produced an economic and efficient copolymer recovery but has also retained the copolymer quality, in term of its molecular weight and thermal properties. It demonstrates a practical and promising downstream processing method in recovering the copolymer effectively from the bacterial biomass.

Enhanced degradation of polyhydroxyalkanoates (PHAs) by newly isolated Burkholderia cepacia DP1 with high depolymerase activity

The contribution of microbial depolymerase has received much attention because of its potential in biopolymer degradation. In this study, the P(3HB) depolymerase enzyme of a newly isolated Burkholderia cepacia DP1 from soil in Penang, Malaysia, was optimized using response surface methodology (RSM). The factors affecting P(3HB) depolymerase enzyme production were studied using one-variable-at-a-time approach prior to optimization. Preliminary experiments revealed that the concentration of nitrogen source, concentration of carbon source, initial pH and incubation time were among the main factors influencing the enzyme productivity. An increase of 9.4 folds in enzyme production with an activity of 5.66 U/mL was obtained using optimal medium containing 0.028% N of di-ammonium hydrogen phosphate and 0.31% P(3HB-co-21%4HB) as carbon source at the initial pH of 6.8 for 38 h of incubation. Moreover, the RSM model showed great similarity between predicted and actual enzyme production indicating a successful model validation. This study warrants the ability of P(3HB) degradation by B. cepacia DP1 in producing higher enzyme activity as compared to other P(3HB) degraders being reported. Interestingly, the production of P(3HB) depolymerase was rarely reported within genus Burkholderia. Therefore, this is considered to be a new discovery in the field of P(3HB) depolymerase production.

The link of feast-phase dissolved oxygen (DO) with substrate competition and microbial selection in PHA production

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable polyesters with the potential to replace conventional plastics. Aeration requires large amounts of energy in PHA production by mixed microbial cultures (MMCs), particularly during the feast phase due to substrate uptake. The objective of this study was to investigate the impact of DO concentrations on microbial selection, substrate competition and PHA production performance by MMCs. This represents the first study investigating DO impact on PHA production while feeding the multiple volatile fatty acids (VFAs) typically encountered in real fermented feedstocks, as well as the substrate preferences at different DO levels. Efficient microbial cultures were enriched under both high (3.47 ± 1.12 mg/L) and low (0.86 ± 0.50 mg/L) DO conditions in the feast phase containing mostly the same populations but with different relative abundance. The most abundant microorganisms in the two MMCs were Plasticicumulans, Zoogloea, Paracoccus, and Flavobacterium. Butyrate and valerate were found to be the preferred substrates as compared to acetate and propionate regardless of DO concentrations. In the accumulation step, the PHA storage capacity and yield were less affected by the change of DO levels when applying the culture selected under low DO in the feast phase (PHA storage capacity >60% and yield > 0.9 Cmol PHA/Cmol VFA). A high DO level is required for maximal PHA accumulation rates with the four VFAs (acetate, propionate, butyrate and valerate) present, due to the lower specific uptake rates of acetate and propionate under low DO conditions. However, butyrate and valerate specific uptake rates were less impacted by DO levels and hence low DO for PHA accumulation may be effective when feed is composed of these substrates only.

Polyhydroxyalkanoates (PHAs) production from fermented cheese whey by using a mixed microbial culture

Two fermented cheese wheys (FCW), FCW1 composed of lactic, acetic and butyric acids in the proportion of 58/16/26 (% CODOrganic Acid (OA)) and FCW2 composed of acetic, propionic, butyric, lactic and valeric acids in the proportion of 58/19/13/6/4 (% CODOA) were used to produce polyhydroxyalkanoates (PHAs) by using a pre-selected mixed microbial culture (MMC). PHA accumulation gave for fermented FCW1 a PHA yield (Ytot) of 0.24±0.02mgCODPHAmgCODSolubleSubstrate(SS)(-1) and a total PHA production, referred to the substrate used, of 60gPHAkgcheesewheyTotalSolids(TS)(-1). For fermented FCW2 results were: PHA yield (Ytot) of 0.42±0.03mgCODPHAmgCODSS(-1) and PHA from a substrate of 70gPHAkgcheesewheyTS(-1). Qualitatively, PHAs from FCW1 was made up exclusively of 3-hydroxybutyrate (HB), while those obtained from FCW2 were composed of 40% of 3-hydroxyvalerate (HV) and 60% of HB.

Community proteomics provides functional insight into polyhydroxyalkanoate production by a mixed microbial culture cultivated on fermented dairy manure

Polyhydroxyalkanoates (PHAs) are bio-based, biodegradable polyesters that can be produced from organic-rich waste streams using mixed microbial cultures (MMCs). To maximize PHA production, MMCs are enriched for bacteria with a high polymer storage capacity through the application of aerobic dynamic feeding (ADF) in a sequencing batch reactor (SBR), which consequently induces a feast-famine metabolic response. Though the feast-famine response is generally understood empirically at a macro-level, the molecular level is less refined. The objective of this study was to investigate the microbial community composition and proteome profile of an enriched MMC cultivated on fermented dairy manure. The enriched MMC exhibited a feast-famine response and was capable of producing up to 40 % (wt. basis) PHA in a fed-batch reactor. High-throughput 16S rRNA gene sequencing revealed a microbial community dominated by Meganema, a known PHA-producing genus not often observed in high abundance in enrichment SBRs. The application of the proteomic methods two-dimensional electrophoresis and LC-MS/MS revealed PHA synthesis, energy generation, and protein synthesis prominently occurring during the feast phase, corroborating bulk solution variable observations and theoretical expectations. During the famine phase, nutrient transport, acyl-CoA metabolism, additional energy generation, and housekeeping functions were more pronounced, informing previously under-determined MMC functionality under famine conditions. During fed-batch PHA production, acetyl-CoA acetyltransferase and PHA granule-bound phasin proteins were in increased abundance relative to the SBR, supporting the higher PHA content observed. Collectively, the results provide unique microbial community structural and functional insight into feast-famine PHA production from waste feedstocks using MMCs.

Production and characterization of poly(3-hydroxy butyrate-co-3 hydroxyvalerate) (PHBV) by a novel halotolerant mangrove isolate

A halophilic mangrove isolate identified by 16S rRNA sequence as a Bacillus spp. was found to be capable of using a broad range of carbon sources including monosaccharides (glucose and fructose), disaccharides (sucrose), pentoses (xylose and arabinose), various organic acids (acetic acid, propionic acid and octanoic acid) and even the acid pre-treated liquor (APL) of sugarcane trash, a lignocellulosic biomass, for growth and the production of polyhydroxyalkanoates (PHAs) such as poly(3-hydroxybutyrate, P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate, PHBV), and 4-hydroxyhexanoate, 4HHX). The study describes the innate ability of a wild-type culture for PHBV production by both propionate dependent and propionate independent pathways. The biopolymer was extracted and characterized physico-chemically. The PHBV yield from glucose was estimated to be 73% of biomass weight with a high 3-hydroxyvalerate fraction of 48mol%. Thereafter, spherical homogenous PHBV nanoparticles of ∼164nm size were prepared for future applications.

Polyhydroxyalkanoate (PHA) storage within a mixed-culture biomass with simultaneous growth as a function of accumulation substrate nitrogen and phosphorus levels

The response of a mixed-microbial-culture (MMC) biomass for PHA accumulation was evaluated over a range of relative nitrogen (N) and phosphorus (P) availabilities with respect to the supply of either complex (fermented whey permeate - FWP) or simpler (acetic acid) organic feedstocks. Fed-batch feed-on-demand PHA accumulation experiments were conducted where the feed N/COD and P/COD ratios were varied ranging from conditions of nutrient starvation to excess. A feast-famine enrichment (activated sludge) biomass, produced in a pilot-scale aerobic sequencing batch reactor on FWP and with a long history of stable PHA accumulation performance, was used for all the experiments as reference material. FWP with N/COD ratios of (2, 5, 15, 70 mg/g all with P/COD = 8 mg/g) as well as simulated FWP with nutrient starvation (N/COD = P/COD = 0) conditions were applied. For the acetic acid accumulations, nutrient starvation as well as N/COD variations (2.5, 5, 50 mg/g all with P/COD = 9 mg/g) and P/COD variations (0.5, 2, 9, 15 mg/g all with N/COD = 10 mg/g) were evaluated. An optimal range of combined N and P limitation with N/COD from 2 to 15 mg/g and P/COD from 0.5 to 3 mg/g was considered to offer consistent improvement of productivity over the case of nutrient starvation. Productivity increased due to active biomass growth of the PHA storing biomass without observed risk for a growth response overtaking PHA storage activity. PHA production with respect to the initial active biomass was significantly higher even in cases of excess nutrient additions when compared to the cases of nutrient starvation. The 24-h PHA productivities were enhanced as much as 4-fold from a base value of 1.35 g-PHA per gram initial active biomass with respect nutrient starvation feedstock. With or without nutrient loading the biomass consistently accumulated similar and significant PHA (nominally 60% g-PHA/g-VSS). Based on results from replicate experiments some variability in the extant biomass maximum PHA content was attributed to interpreted differences in the biomass initial physiological state and not due to changes in feedstock nutrient loading. We found that the accumulation process production rates for mixed cultures can be sustained long after the maximum PHA content of the biomass was reached. Within the specific context of the applied fed-batch feed-on-demand methods, active biomass growth was interpreted to have been largely restricted to the PHA-storing phenotypic fraction of the biomass. This study suggests practical prospects for mixed culture PHA production using a wide range of volatile fatty acid (VFA) rich feedstocks. Such VFA sources derived from residual industrial or municipal organic wastes often naturally contain associated nutrients ranging in levels from limitation to excess.

Polyhydroxyalkanoates from Pseudomonas sp. using synthetic and olive mill wastewater under limiting conditions

The present study aimed at investigating the ability of bacteria isolated from an enriched mixed culture to produce polyhydroxyalkanoates (PHAs) and examining the effect of nitrogen and dual nitrogen-oxygen limitation on PHAs production, by using both synthetic and olive mill wastewater (OMW). PHAs production was performed through batch experiments using both the enriched culture and the isolated strains (belonging to the genus of Pseudomonas) aiming to compare PHAs accumulation capacity, yields and rates. The use of enriched culture and synthetic wastewater under nitrogen limitation resulted in the highest PHA accumulation, i.e. 64.4%gPHAs/g of cell dry mass (CDM). However, when OMW was used, PHAs accumulation significantly decreased, i.e. 8.8%gPHAs/g CDM. The same trend was followed by the isolated strains, nevertheless, their ability to synthesize PHAs was lower. Although, dual nitrogen-oxygen limitation generally slowed down PHAs biosynthesis, in certain strains PHAs production was positively affected.

Production of polyhydroxyalkanoates from spent coffee grounds oil obtained by supercritical fluid extraction technology

Spent coffee grounds (SCG) oil was obtained by supercritical carbon dioxide (scCO2) extraction in a pilot plant apparatus, with an oil extraction yield of 90% at a 35kgkg(-1) CO2/SCG ratio. Cupriavidus necator DSM 428 was cultivated in 2L bioreactor using extracted SCG oil as sole carbon source for production of polyhydroxyalkanoates. The culture reached a cell dry weight of 16.7gL(-1) with a polymer content of 78.4% (w/w). The volumetric polymer productivity and oil yield were 4.7gL(-1)day(-1) and 0.77gg(-1), respectively. The polymer produced was a homopolymer of 3-hydroxybutyrate with an average molecular weight of 2.34×10(5) and a polydispersity index of 1.2. The polymer exhibited brittle behaviour, with very low elongation at break (1.3%), tensile strength at break of 16MPa and Young's Modulus of 1.0GPa. Results show that SCG can be a bioresource for polyhydroxyalkanoates production with interesting properties.

Effect of saturated and unsaturated fatty acid supplementation on bio-plastic production under submerged fermentation

Polyhydroxyalkanoates (PHAs) are intracellular reserve material stored by gram-negative bacteria under nutrient-limited condition. PHAs are utilized in biodegradable plastics (bio-plastics) synthesis due to their similarity with conventional synthetic plastic. In the present study, the effect of addition of saturated and unsaturated fatty acids (palmitic acid, stearic acid, oleic acid and linoleic acid) on the production of PHAs by the soil bacterium Alcaligenes sp. NCIM 5085 was studied. Fatty acid supplementation in basal media produced saturated and unsaturated PHAs of medium and short chain length. Gas chromatography analysis of palmitic acid-supplemented media showed the presence of short chain length (scl) PHAs which could potentially serve as precursors for bio-plastic production. The scl PHA was subsequently characterized as PHB by NMR and FTIR. On the other hand, oleic acid and linoleic acid addition showed both saturated and unsaturated PHAs of different chain lengths. Palmitic acid showed maximum PHB content of 70.8 % at concentration of 15 g l⁻¹ under shake flask cultivation. When shake flask cultivation was scaled up in a 7.5-l bioreactor (working volume 3 l), 7.6 g l⁻¹ PHA was produced with a PHB yield (Y_P/X) and productivity of 75.89 % and 0.14 g l⁻¹ h, respectively.