Polyhydroxyalkanoates Production Research Articles

Green alternatives to petroleum-based plastics: production of bioplastic from Pseudomonas neustonica strain NGB15 using waste carbon source.

Polyhydroxyalkanoates have attracted great interest as a suitable alternative to petrochemical based plastics due to their outstanding properties such as biodegradability and biocompatibility. However, the biggest problem in the production of microbial polyhydroxyalkanoates is low cost-effectiveness. In this study, polyhydroxyalkanoate production was carried out using waste substrates with local isolates. Culture conditions were optimized to increase the polyhydroxyalkanoate production potential. The produced polyhydroxyalkanoate was characterized by FTIR analyses, and its metabolic pathway was determined by real-time PCR. According to the results, the best polyhydroxyalkanoate producer bacteria was characterized as Pseudomonas neustonica NGB15. The optimal culture conditions were detected as 30g/L banana peel powder, 25°C temperature, pH 8, and 4-day incubation time. Under the optimized conditions, 3.34g/L PHA production was achieved. As a result of FTIR analyses, major peaks were obtained at 1723, 1277, 1261, 1097, 1054, and 993cm-1. These peaks represent that the type of produced polyhydroxyalkanoate was poly-β-hydroxybutyrate. According to gene expression profile of NGB15, it was determined that Pseudomonas neustonica NGB15 produces PHA using the de novo fatty acid synthesis metabolic pathway. In conclusion, poly-β-hydroxybutyrate production by Pseudomonas neustonica NGB15 using a low-cost fermentation medium has been shown to be biotechnologically promising.

Polyhydroxyalkanoate Production from Eucalyptus Bark’s Enzymatic Hydrolysate

In recent years, polyhydroxyalkanoates (PHAs) have gained notoriety because of their desirable properties that include proven biodegradability, biocompatibility, and thermal stability, which make them suitable alternatives to fossil-based polymers. However, the widespread use of PHAs is still challenging because of their production costs, which are greatly associated with the cultivation medium used for bacterial cultivation. In Portugal, one-quarter of the forest area is covered by Eucalyptus globulus wood, making its residues a cheap, abundant, and sustainable potential carbon source for biotechnological uses. In this work, eucalyptus bark was used as the sole feedstock for PHA production in a circular bioeconomic approach. Eucalyptus bark hydrolysate was obtained after enzymatic saccharification using Cellic® CTec3, resulting in a sugar-rich solution containing glucose and xylose. Although with differing performances, several bacteria were able to grow and produce PHA with distinct compositions, using the enzymatic hydrolysate as the sole carbon source. Pseudomonas citronellolis NRRL B-2504 achieved a high cellular growth rate in bioreactor assays (24.4 ± 0.15 g/L) but presented a low accumulation of a medium-chain-length PHA (mcl-PHA) comprising the monomers hydroxydecanoate (HD, 65%), hydroxydodecanoate (HDd, 25%), and hydroxytetradecanoate (HTd, 14%). Burkholderia thailandensis E264, on the other hand, reached a lower cellular growth rate (8.87 ± 0.34 g/L) but showed a higher biopolymer accumulation, with a polyhydroxybutyrate (PHB) content in the cells of 12.3 wt.%. The new isolate, Pseudomonas sp., revealed that under nitrogen availability, it was able to reach a higher accumulation of the homopolymer PHB (31 wt.%). These results, although preliminary, demonstrate the suitability of eucalyptus bark’s enzymatic hydrolysate as a feedstock for PHA production, thus offering an exciting avenue for achieving sustainable and environmentally responsible plastic products from an undervalued forestry waste.

A sustainable synthesis of polyhydroxyalkanoate from stubble waste as a carbon source using Pseudomonas putida MTCC 2475

Polyhydroxyalkanoates (PHAs) are biodegradable polymers that can be produced from lignocellulosic biomass by microorganisms. Cheap and readily available raw material, such as corn stover waste, has the potential to lessen the cost of PHA synthesis. In this research study, corn stover is pretreated with NaOH under conditions optimized for high cellulose and low lignin with central composite design (CCD) followed by characterization using Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). Design expert software performed further optimization of alkali pretreated corn stover for high total reducing sugar (TRS) enhancement using CCD using response surface methodology (RSM). The optimized condition by RSM produced a TRS yield of 707.19 mg/g. Fermentation using corn stover hydrolysate by Pseudomonas putida MTCC 2475 gave mcl-PHA detected through gaschromatography–tandemmassspectrometry (GC-MS/MS) and characterization of the PHA film by differential scanning calorimetry (DSC), FTIR, and nuclear magnetic resonance (NMR). Thus, this research paper focuses on using agriculture (stubble) waste as an alternative feedstock for PHA production.

Establishment of low-cost production platforms of polyhydroxyalkanoate bioplastics from Halomonas cupida J9.

Microbial production of polyhydroxyalkanoate (PHA) is greatly restricted by high production cost arising from high-temperature sterilization and expensive carbon sources. In this study, a low-cost PHA production platform was established from Halomonas cupida J9. First, a marker-less genome-editing system was developed in H. cupida J9. Subsequently, H. cupida J9 was engineered to efficiently utilize xylose for PHA biosynthesis by introducing a new xylose metabolism module and blocking xylonate production. The engineered strain J9UΔxylD-P8xylA has the highest PHA yield (2.81 g/L) obtained by Halomonas with xylose as the sole carbon source so far. This is the first report on the production of short- and medium-chain-length (SCL-co-MCL) PHA from xylose by Halomonas. Interestingly, J9UΔxylD-P8xylA was capable of efficiently utilizing glucose and xylose as co-carbon sources for PHA production. Furthermore, fed-batch fermentation of J9UΔxylD-P8xylA coupled to a glucose/xylose co-feeding strategy reached up to 12.57 g/L PHA in a 5-L bioreactor under open and unsterile condition. Utilization of corn straw hydrolysate as the carbon source by J9UΔxylD-P8xylA reached 7.0 g/L cell dry weight (CDW) and 2.45 g/L PHA in an open fermentation. In summary, unsterile production in combination with inexpensive feedstock highlights the potential of the engineered strain for the low-cost production of PHA from lignocellulose-rich agriculture waste.

Influence of Aeration Rate on Uncoupled Fed Mixed Microbial Cultures for Polyhydroxybutyrate Production

The use of residual streams as feedstock for the production of polyhydroxyalkanoates (PHAs) is growing steadily, as it allows the valorization of waste and nutrients otherwise disposed of and the potential production of a biodegradable bioplastic. To date, the environmental and economic costs associated with this process limit its scale-up, which is why it is important to identify possible solutions and optimize the costliest steps. With this in mind, a laboratory-scale sequenced batch reactor (SBR, 5 L) was constructed to allow the selection of a mixed microbial culture able to convert volatile fatty acids (VFAs) into PHA. The reactor is fed with synthetic water containing VFAs, ammonium, phosphate, and micronutrients, typical compounds of fermented streams of certain wastes, such as cheese whey, food waste, or wastewater sludge. The biomass selected and produced by this first reactor is sent to an accumulation reactor, which is fed with a solution rich in VFAs, allowing the accumulation of PHAs. The role of aeration and its impacts on the main process parameters were analyzed. Three scenarios corresponding to different aeration rates were analyzed: 0.08, 0.16, and 0.32 vvm. The SBR was operated at an organic load rate of 600 mgCOD L−1d−1, under a dynamic feeding regime (feast–famine) and a short hydraulic retention time (HRT; 1 day). The results obtained showed that a value of 0.32 enabled better selection and better settling of the sludge. Furthermore, a potential correlation between aeration rate and VFA and NH4+ consumption rates was identified. The resulting biomass was able to accumulate up to 0.15 ± 0.02 g PHAgVSS−1.

A model-driven approach to upcycling recalcitrant feedstocks in Pseudomonas putida by decoupling PHA production from nutrient limitation

Bacterial polyhydroxyalkanoates (PHAs) have emerged as promising eco-friendly alternatives to petroleum-based plastics since they are synthesized from renewable resources and offer exceptional properties. However, their production is limited to the stationary growth phase under nutrient-limited conditions, requiring customized strategies and costly two-phase bioprocesses. In this study, we tackle these challenges by employing a model-driven approach to reroute carbon flux and remove regulatory constraints using synthetic biology. We construct a collection of Pseudomonas putida-overproducing strains at the expense of plastics and lignin-related compounds using growth-coupling approaches. PHA production was successfully achieved during growth phase, resulting in the production of up to 46% PHA/cell dry weight while maintaining a balanced carbon-to-nitrogen ratio. Our strains are additionally validated under an upcycling scenario using enzymatically hydrolyzed polyethylene terephthalate as a feedstock. These findings have the potential to revolutionize PHA production and address the global plastic crisis by overcoming the complexities of traditional PHA production bioprocesses.

Polyhydroxyalkanoate Production Using Sulfuric Acid Pre-Treated Wheat Straw (SAPWS) as a Feedstock: RSM (Response Surface Methodology)-Based Optimization Using Bacillus paranthracis RSKS-3

Polyhydroxyalkanoate Production Using Sulfuric Acid Pre-Treated Wheat Straw (SAPWS) as a Feedstock: RSM (Response Surface Methodology)-Based Optimization Using Bacillus paranthracis RSKS-3

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

Polyhydroxyalkanoate involvement in stress-survival of two psychrophilic bacterial strains from the High Arctic

An ever-growing body of literature evidences the protective role of polyhydroxyalkanoates (PHAs) against a plethora of mostly physical stressors in prokaryotic cells. To date, most of the research done involved bacterial strains isolated from habitats not considered to be life-challenging or extremely impacted by abiotic environmental factors. Polar region microorganisms experience a multitude of damaging factors in combinations rarely seen in other of Earth’s environments. Therefore, the main objective of this investigation was to examine the role of PHAs in the adaptation of psychrophilic, Arctic-derived bacteria to stress conditions. Arctic PHA producers: Acidovorax sp. A1169 and Collimonas sp. A2191, were chosen and their genes involved in PHB metabolism were deactivated making them unable to accumulate PHAs (ΔphaC) or to utilize them (Δi-phaZ) as a carbon source. Varying stressors were applied to the wild-type and the prepared mutant strains and their survival rates were assessed based on CFU count. Wild-type strains with a functional PHA metabolism were best suited to survive the freeze–thaw cycle — a common feature of polar region habitats. However, the majority of stresses were best survived by the ΔphaC mutants, suggesting that the biochemical imbalance caused by the lack of PHAs induced a permanent cell-wide stress response thus causing them to better withstand the stressor application. Δi-phaZ mutants were superior in surviving UV irradiation, hinting that PHA granule presence in bacterial cells is beneficial despite it being biologically inaccessible. Obtained data suggests that the ability to metabolize PHA although important for survival, probably is not the most crucial mechanism in the stress-resistance strategies arsenal of cold-loving bacteria.Key points• PHA metabolism helps psychrophiles survive freezing• PHA-lacking psychrophile mutants cope better with oxidative and heat stresses• PHA granule presence enhances the UV resistance of psychrophiles

Production of Polyhydroxyalkanoates for Biodegradable Food Packaging Applications Using Haloferax mediterranei and Agrifood Wastes.

Polyhydroxyalkanoates (PHAs) are high-value biodegradable polyesters with thermoplastic properties used in the manufacturing of different products such as packaging films. PHAs have gained much attention from researchers and industry because of their biobased nature and appropriate features, similar to conventional synthetic plastics. This review aims to discuss some of the recent solutions to challenges associated with PHA production. The implementation of a cost-effective process is presented by following different strategies, such as the use of inexpensive carbon sources, the selection of high-producing microorganisms, and the functionalization of the final materials to make them suitable for food packaging applications, among others. Research efforts are needed to improve the economic viability of PHA production at a large scale. Haloferax mediterranei is a promising producer of PHAs due to its ability to grow in non-sterile conditions and the possibility of using seawater to prepare the growth medium. Additionally, downstream processing for PHA extraction can be simplified by treating the H. mediterranei cells with pure water. Further research should focus on the optimization of the recycling conditions for the effluents and on the economic viability of the side streams reutilization and desalinization as an integrated part of PHA biotechnological production.

Analysis of fatty acid methyl esters and polyhydroxyalkanoates production along with wastewater contaminant removal using sewage sludge bacteria

Analysis of fatty acid methyl esters and polyhydroxyalkanoates production along with wastewater contaminant removal using sewage sludge bacteria

Evaluation of polyhydroxyalkanoate recovery from food waste by sequencing batch biofilm reactor with high mixed microbial biomass

In this study, the enrichment sequencing batch biofilm reactor (SBBR) and conventional enrichment reactor (SBR) were established, and a new strategy was developed to achieve higher biomass yield and polyhydroxyalkanoate (PHA) production from food waste than those achieved through the conventional method. After the 10th day of an expanded cultivation period, the respective active biomass concentrations in SBR and SBBR were 5.16 and 13.92 g/L, indicating a significant improvement in the biomass yield of mixed microbial culture in the SBBR. The PHA accumulation test revealed that maximum PHA concentration in SBR and SBBR reached 6.60 and 12.70 g/L, respectively, after 80 days of enrichment, indicating that compared to SBR, the SBBR could more effectively improve the PHA accumulation capacity. Meganema, Thauera, and Paracoccus were the dominant PHA-accumulating bacteria in the SBR and SBBR. Additionally, the volumetric productivity of the SBBR was 3.22 g COD/L/d, twice that of the SBR. This study provides new strategies and insights for improving PHA production and reducing the costs of PHA production and reactor investment.

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.

Comparison of batch, fed-batch and continuous operation modes for scalable polyhydroxyalkanoate (PHA) production and carbon sequestration from phenol

Polyhydroxyalkanoates (PHA) are biodegradable intracellular polymers, and a renewable alternative to conventional plastics. To reduce PHA's cost, this study combined an unconventional carbon source, i.e. a toxic aromatics phenol, with an acclimated consortium, to develop a scalable PHA production process. The resultant process performance was systematically compared across three operational modes: batch, fed-batch, and continuous. Phenol toxicity caused inhibition in the batch mode, reducing the PHA synthesis rate but resulting in a high PHA content in cells (PHA% > 50 %). Fed-batch feeding alleviated such inhibition, facilitating a high PHA titer and yield from the substrate. Interestingly, a higher feeding rate in the fed-batch reactor improved its performance, probably by providing a suitable food-to-microbe ratio for the biomass. Using a continuous mode also reduced phenol toxicity, but resulted in more synthesis of non-PHA cellular materials (NPCM). The difference might have been caused by different metabolic states and the presence of intermediates in the reactors. Comparing all 14 conditions under the three modes, feeding phenol more gradually tended to channel substrate away from PHA to NPCM synthesis. The volumetric productivity generally ranged from 3 to 12 mg L−1 min−1, while the biomass productivity was between 2 and 11 mg g initial CDW−1 min−1. A 3-stage, production-harvest and starvation-production process was then designed to simulate real industrialized manufacturing, where the operational modes had a long-term effect on biomass' productivity. Fed-batch mode performed the best, as it fixed 1/3 of phenol's organic carbon in PHA product, suggesting high potential for future application.

Production of Medium Chain Length Polyhydroxyalkanoate from Waste Cannabis sativa Biomass

AbstractThis works aims to evaluate a process to convert residual medical Cannabis sativa stalks into medium chain length polyhydroxyalkanoate (mcl-PHA), using chemical pretreatment and enzymatic hydrolysis to obtain sugars as a carbon source for a fermentation process with Pseudomonas aeruginosa. Chemical composition analysis revealed a content of structural polysaccharides of 57.64%. Thermochemical pretreatments with 2% sulfuric acid or 2% sodium hydroxide were capable of partially removing hemicellulose and lignin, as well as increasing cellulose crystallinity. Pretreated biomass was subjected to hydrolysis using commercial cellulase cocktails Celluclast® 1.5 L and Cellic® CTec3. Acid pretreatment showed an adverse effect on hydrolysis yield of holocellulose, decreasing to 39.5%; compared to 44.4% of untreated biomass. Alkaline pretreatment increased degree of hydrolysis up to 73.3%. Shake flask fermentation of hydrolysate with Pseudomonas aeruginosa produced cell growth of 1.65 g/L and a mcl-PHA titer of 0.41 g/L. Extracted polymer presented characteristic FTIR bands for PHAs, glass transition temperature of − 50.8 °C, melting temperature of 48.9 °C, possibly allowing its use in the biomedical industry. The developed process represents a potential way to valorize Cannabis waste stalks, using alkaline pretreatment, enzymatic hydrolysis with Celluclast® 1.5 L and fermentation with Pseudomonas aeruginosa. Further work should focus on improving yield of the obtained polyhydroxyalkanoate in fermentation, in order to improve industrial feasibility of the entire process and, in turn, increasing revenue of the medical Cannabis industry. Graphical Abstract

Polystyrene degradation by bacteria isolated from the larvae of <i>Rhynchophorusphoenicis</i>

The larvae of insects of the order Coleoptera have been reported to biodegrade plastics aided by their chewing mouthparts and the  activities of their gut biota. However, there is no report of this ability by the African palm weevil (Rhynchophorus phoenicis). This study  aims to the ability of R. phoenicis larvae to biodegrade polystyrene (PS). A total of 100 R. phoenicis larvae were fed for 21 days with PS  foam, and afterwards, the gut contents of survivors were investigated for possible PS-degrading bacteria. Bacterial isolates were  screened for PS biodegradation in an Erlenmeyer flask with PS film as the sole carbon source, in a mineral salt medium (MSM) at a temperature of 30oC and a pH of 7, for a period of 28 days. The isolates were used for biodegradation assay under the same conditions,  for 60 days. The weight of PS films was determined before and after the biodegradation assay. Chemical changes in the films were confirmed by Fourier Transform Infrared (FTIR) spectroscopy. Two bacterial isolates were recovered from the gut of the only surviving R.  phoenicis larvae fed with 100% PS. The isolates were identified based on their 16S rRNA sequences as Lysinibacillus macriodes and  Pantoea dispersa with accession numbers OQ652017 and OQ652023 respectively. The isolates caused an 8.8% reduction in the weight of  PS film and FTIR spectroscopy results confirmed the formation of groups suggestive of degradation products with the carbonyl group  showing up as absorption peaks in the range of 1640-1760 cm-1 and the hydroxylic group at 3000-3700 cm-1 . The isolates were able to  produce polyhydroxyalkanoate (PHA) equivalent to 1.4g/L, under PS degradation conditions. Therefore, coupling the biodegradation of  PS with PHAproduction could be useful for the valorization of PS waste. 

Valorisation of Sugarcane Bagasse for the Sustainable Production of Polyhydroxyalkanoates

With the world shifting towards renewable and sustainable resources, polyhydroxyalkanoates (PHAs) have attracted significant interest as an alternative to synthetic plastics. While possessing promising properties suitable for various applications, the production of PHAs has not yet reached a global commercial scale. The main reason is the high cost of production, which represents a major limitation. Sugarcane bagasse (SCB) is an abundant lignocellulosic waste around the world. Its use to produce PHA enhances the feasibility of producing PHAs at commercial scale. However, SCB requires pretreatment and hydrolysis steps to release the sugars prior to the microbial fermentation. The cost associated with these steps poses additional challenges for large-scale production. Another challenge is the release of inhibitors during the pretreatment process which can result in a low PHA yield. The development of a low cost, co-culture strategy for the bioconversion of SCB into PHAs, can represent a pivotal step towards the large-scale production of bioplastics. This review highlights the advancements made in recent years on the microbial production of PHA using SCB as potential feedstock, with a proposed biological strategy and circular economy model.

Sequential recovery of extracellular alginate and intracellular polyhydroxyalkanoate (PHA) from mixed microbial culture PHA production system

Polyhydroxyalkanoate (PHA) is a biodegradable plastic that exhibits properties similar to petroleum-based plastics. The mixed microbial culture (MMC) process utilized a waste carbon source to produce PHA, reducing the raw material costs associated with pure bacterial technology. However, the high cost of PHA recovery and environmental pollution are significant challenges to the sustainable development of MMC technology. In this study, a sequential recovery strategy was proposed. This strategy involved the use of Na2CO3 to break down the structural extracellular polymeric substances and rhamnolipid to digest non-PHA cell material (NPCM). The recovery rate of PHA in this strategy achieved 61.29 ± 5.92% and a purity of 97.55 ± 0.92%. Additionally, the strategy allowed the sequential recovery of the by-product alginate-like extracellular polymers. FT-IR analysis confirmed that the recovered biopolymer was PHA material, possessing mechanical and thermal properties similar to those obtained through CHCl3 extraction. However, it was important to note that this method had the potential to alter the distribution structure of the PHA polymer, although it successfully avoids the issue of reducing the molecular weight of PHA during NPCM digestion. A comprehensive evaluation demonstrates that the cost of PHA production using this method was only 14.61 CNY/kg, with a more positive environmental impact in terms of global warming potential and carbon emission reduction. Therefore, the sequential recovery strategy presents a feasible alternative for the downstream recovery process and overall economy of the MMC PHA process.

Biorefinery design with combined deacetylation and microwave pretreatment for enhanced production of polyhydroxyalkanoates and efficient carbon utilization from lignocellulose

Lignocellulosic biomass has emerged as a sustainable and economically viable feedstock for polyhydroxyalkanoate (PHA) production. However, it has seldom been used as part of an integrated process for effective carbon utilization. An innovative combined deacetylation and microwave pretreatment strategy (DEA-MW) and a wild-type Cupriavidus necator strain with the potential to utilize a lignocellulose-based carbon source and PHA biosynthesis were selected to set up the module needed to enable a new sustainable platform for biomass pretreatment and waste carbon valorization. DEA-MW pretreatment was introduced to mitigate the concentration of inhibitory acetic acid and phenolic compounds in the biomass hydrolysate. This pretreatment enhanced deacetylation and delignification, resulting in 95.50 % deacetylation and 45.30 % delignification. When DEA-MW pretreated rice husk biomass was coupled with microbial fermentation, C. necator promoted the fermentability of the rice husk hydrolysate. With a 3 g/L of levulinic acid from hydrolysis, as the sole carbon source, we achieved a concentration of PHA 440 mg/L with a content of 65 %. We also successfully recovered 72.22 % of lignin using a combined DEA-MW pretreatment. A detailed structural analysis showed that β-O-4, β–β, and β-5 linkages had been preserved in the recovered lignin. This study has shown that DEA-MW pretreatment plays a role in promoting biomass conversion and enhancing PHA production and opens up new possibilities for efficient and cost-effective lignocellulose-based biorefinery processes.

Dynamics in the profile of biopolymers produced by mixed microbial cultures from ethanol-rich feedstocks

The use of agro-industrial wastes as substrates for polyhydroxyalkanoate (PHA) production by mixed microbial cultures is an alternative to lower the price of these biopolymers. However, when submitting these wastes to pre-fermentation, lactate and ethanol can be produced in addition to volatile fatty acids (VFAs). In this study, the impact of ethanol on PHA storage and in the carbon flux of the process were assessed. The co-production of extracellular polymeric substances (EPS) and its impact on PHA production was investigated. PHA production yield showed a decrease from 0.92 ± 0.004–0.63 ± 0.002 Cmol-PHA.Cmol-S−1 with the increase of ethanol content from 5 to 20 Cmmol.L−1. EPS production was directly proportional to the ethanol’s fed, reaching a maximum EPS total content of 6.70 Cmmol for the maximum ethanol supplied. EPS acted as a protection strategy, which benefited PHA specific storage rate for the highest ethanol content tested. These results indicate that ethanol-rich feedstocks can be valorised through the simultaneous production of two value-added biopolymers.