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

One-pot polyhydroxyalkanoate (PHA) production from Cerbera odollam (sea mango) oil using Pseudomonas resinovorans: Optimal fermentation design and mechanism

With growing environmental concerns over plastic pollution, polyhydroxyalkanoates (PHAs) have recently gained significant attention as promising biodegradable polymers to substitute petroleum-based plastics. In this work, non-edible Cerbera odollam oil was employed as a renewable carbon source for PHA production to improve the economic competitiveness and environmental sustainability of the process. The optimization and mechanism of PHA production from C. odollam oil using Pseudomonas resinovorans DSM 21078 were presented. Through response surface methodology, the optimal condition for PHA production was 0.3 g/L urea concentration, 17.52 g/L oil concentration, and 10.46% (v/v) inoculum size. Results showed that a maximum PHA concentration of 0.50 g/L (with a polymer content of 26.0%) was attained at this optimal condition. The product was composed of 1.3% 3-hydroxybutyrate (3HB), 9.2% 3-hydroxyhexanoate (3HHx), 43.3% 3-hydroxyoctanoate (3HO), 32.0% 3-hydroxydecanoate (3HD), 11.9% 3-hydroxydodecanoate (3HDD), and 2.2% 3-hydroxytetradecanoate (3HTD). The PHA polymers exhibited adhesive, soft, and amorphous properties at room temperature, with high thermal stability, making them desirable for polymer processing. From the mechanism proposed, it was inferred that P. resinovorans DSM 21078 produces longer-chain PHA monomers mainly through the direct β-oxidation of long-chain fatty acids and shorter-chain monomers via the de novo fatty acid synthesis pathway when oil-based substrates are utilized. The findings from this work could pave the way for new paradigms that significantly enhance future research in the development of highly efficient oil resource valorization technologies to produce PHAs with intriguing properties, thereby contributing to the commercial success of sustainable bioplastics as an effective environmental management solution.

Lignocellulosic biomass as promising substrate for polyhydroxyalkanoate production: Advances and perspectives

The depletion of fossil resources, coupled with global warming and adverse environmental impact of traditional petroleum-based plastics, have necessitated the discovery of renewable resources and innovative biodegradable materials. Lignocellulosic biomass (LB) emerges as a highly promising, sustainable and eco-friendly approach for accumulating polyhydroxyalkanoate (PHA), as it completely bypasses the problem of "competition for food". This sustainable and economically efficient feedstock has the potential to lower PHA production costs and facilitate its competitive commercialization, and support the principles of circular bioeconomy. LB predominantly comprises cellulose, hemicellulose, and lignin, which can be converted into high-quality substrates for PHA production by various means. Future efforts should focus on maximizing the value derived from LB. This review highlights the momentous and valuable research breakthroughs in recent years, showcasing the biosynthesis of PHA using low-cost LB as a potential feedstock. The metabolic mechanism and pathways of PHA synthesis by microbes, as well as the key enzymes involved, are summarized, offering insights into improving microbial production capacity and fermentation metabolic engineering. Life cycle assessment and techno-economic analysis for sustainable and economical PHA production are introduced. Technological hurdles such as LB pretreatment, and performance limitations are highlighted for their impact on enhancing the sustainable production and application of PHA. Meanwhile, the development direction of co-substrate fermentation of LB and with other carbon sources, integrated processes development, and co-production strategies were also proposed to reduce the cost of PHA and effectively valorize wastes.

Anaerobic acidification membrane bioreactor operating at acidic condition for treating concentrated municipal wastewater: Performance and implication

To address the low-carbon treatment requirements for municipal wastewater, a novel anaerobic acidification membrane bioreactor (AAMBR) was developed for recovering organic matter in terms of volatile fatty acids (VFAs). While the AAMBR successfully generated VFAs from municipal wastewater through forward osmosis (FO) membrane concentration, its operation was limited to a single pH value of 10.0. Here, performance of the AAMBR operating at acidic condition was evaluated and compared with that at alkaline condition. The findings revealed that the AAMBR with pH 5.0 efficiently transformed organic matter into acetic acid, propionic acid, and butyric acid, resulting in a VFAs yield of 0.48 g/g-CODfeed. In comparison with the AAMBR at pH 10.0, this study achieved a similar VFAs yield, a lower fouling tendency, a lower loss of nutrients and a lower controlling cost. In conclusion, this study demonstrated that a pH of 5.0 is optimal for the AAMBR treating municipal wastewater.

Pseudomonas umsongensis GO16 as a platform for the in vivo synthesis of short and medium chain length polyhydroxyalkanoate blends

Polyhydroxyalkanoates (PHAs) are biological polyesters, viewed as a replacement for petrochemical plastic. However, they suffer from suboptimal physical and mechanical properties. Here, it was shown that a metabolically versatile Pseudomonas umsongensis GO16 can synthesise a blend of short chain length (scl) and medium chain length (mcl)-PHA. A defined mix of butyric (BA) and octanoic acid (OA) in different ratios was used. The PHA monomer composition varied depending on the feeding strategy. When OA and BA were fed at 80:20 ratio it showed 14, 8, 77 and 1 mol% of (R)-3-hydroxybutyrate, (R)-3-hydroxyhexanoate, (R)-3-hydroxyoctanoate and (R)-3-hydroxydecanoate respectively. The polymer characterisation clearly shows that polyhydroxybutyrate (PHB) and mcl-PHA are produced individually. The two polymers are blended on the PHA granule level, as demonstrated by fluorescence microscopy and yeast two-hybrid assay. The resulting blend has a specific viscoelasticity compared to PHB and PHO. Mcl-PHA acts as a plasticiser and reduces PHB brittleness.

Production of medium-chain-length PHA in octanoate-fed enrichments dominated by Sphaerotilus sp

Medium-chain-length polyhydroxyalkanoate (mcl-PHA) production by using microbial enrichments is a promising but largely unexplored approach to obtain elastomeric biomaterials from secondary resources. In this study, several enrichment strategies were tested to select a community with a high mcl-PHA storage capacity when feeding octanoate. On the basis of analysis of the metabolic pathways, the hypothesis was formulated that mcl-PHA production is more favorable under oxygen-limited conditions than short-chain-length PHA (scl-PHA). This hypothesis was confirmed by bioreactor experiments showing that oxygen limitation during the PHA accumulation experiments resulted in a higher fraction of mcl-PHA over scl-PHA (i.e., a PHA content of 76 wt% with an mcl fraction of 0.79 with oxygen limitation, compared to a PHA content of 72 wt% with an mcl-fraction of 0.62 without oxygen limitation). Physicochemical analysis revealed that the extracted PHA could be separated efficiently into a hydroxybutyrate-rich fraction with a higher M_w and a hydroxyhexanoate/hydroxyoctanoate-rich fraction with a lower M_w . The ratio between the two fractions could be adjusted by changing the environmental conditions, such as oxygen availability and pH. Almost all enrichments were dominated by Sphaerotilus sp. This is the first scientific report that links this genus to mcl-PHA production, demonstrating that microbial enrichments can be a powerful tool to explore mcl-PHA biodiversity and to discover novel industrially relevant strains.

Evaluation of polyhydroxyalkanoate (PHA) synthesis by Pichia sp. TSLS24 yeast isolated in Vietnam

Following the rising concern on environmental issues caused by conventional fossil-based plastics and depleting crude oil resources, polyhydroxyalkanoates (PHAs) are of great interest by scientists and biodegradable polymer market due to their outstanding properties which include high biodegradability in various conditions and processing flexibility. Many polyhydroxyalkanoate-synthesizing microorganisms, including normal and halophilic bacteria, as well as algae, have been investigated for their performance in polyhydroxyalkanoate production. However, to the best of our knowledge, there is still limited studies on PHAs-producing marine yeast. In the present study, a halophilic yeast strain isolated from Spratly Island in Vietnam were investigated for its potential in polyhydroxyalkanoate biosynthesis by growing the yeast in Zobell marine agar medium (ZMA) containing Nile red dye. The strain was identified by 26S rDNA analysis as Pichia kudriavzevii TSLS24 and registered at Genbank database under code OL757724. The amount of polyhydroxyalkanoates synthesized was quantified by measuring the intracellular materials (predicted as poly(3-hydroxybutyrate) -PHB) by gravimetric method and subsequently confirmed by Fourier transform infrared (FTIR) spectroscopic and nuclear magnetic resonance (NMR) spectroscopic analyses. Under optimal growth conditions of 35 °C and pH 7 with supplementation of glucose and yeast extract at 20 and 10 gL^-1, the isolated strain achieved poly(3-hydroxybutyrate) content and concentration of 43.4% and 1.8 gL^-1 after 7 days of cultivation. The poly(3-hydroxybutyrate) produced demonstrated excellent biodegradability with degradation rate of 28% after 28 days of incubation in sea water.

Strategy for economical and enhanced polyhydroxyalkanoate production from synergistic utilization of palm oil and derived wastewater by activated sludge

The potential of palm oil and derived wastewater pretreated by enzyme as co-substrates to accumulate polyhydroxyalkanoate (PHA) rich in short and medium-chain-length monomers under two feeding strategies was evaluated batchwise through mixed microbial cultures (MMCs) in activated sludge. A terpolymer with the maximum PHA content of 30.5 wt%, volumetric yield of 0.372 g COD/g COD and composition of ca. 84.7 ∼ 97.4/0.5 ∼ 1.6/2.1 ∼ 13.7 (3-hydroxybutyrate/ 3-hydroxyvalerate/ 3-hydroxyoctanoate, %) was achieved as a result of co-substrate incorporation. From the perspective of economic benefits, PHA accumulated via adopting strategy of supplementing carbon source to the same initial concentration per cycle saved 42.7 % of carbon consumption, along with a reduction in culture time (72 h). The above discoveries signify that the combination of palm oil and derived wastewater plus MMCs provides an alternative to the plastics industries for a more sustainable and efficient utilization of biological resources and an economic PHA accumulation approach.

The 3D Printability and Mechanical Properties of Polyhydroxybutyrate (PHB) as Additives in Urethane Dimethacrylate (UDMA) Blends Polymer for Medical Application

The integration of additive manufacturing (3D printing) in the biomedical sector required material to portray a holistic characteristic in terms of printability, biocompatibility, degradability, and mechanical properties. This research aims to evaluate the 3D printability and mechanical properties of polyhydroxybutyrate (PHB) as additives in the urethane dimethacrylate (UDMA) based resin and its potential for medical applications. The printability of the PHB/UDMA resin blends was limited to 11 wt.% as it reached the maximum viscosity value at 2188 cP. Two-way analysis of variance (ANOVA) was also conducted to assess the significant effect of the varied PHB (wt.%) incorporation within UDMA resin, and the aging duration of 3D printed PHB/UDMA on mechanical properties in terms of tensile and impact properties. Meanwhile, the increasing crystallinity index (CI) of X-ray diffraction (XRD) in the 3D printed PHB/UDMA as the PHB loading increased, indicating that there is a strong correlation with the lower tensile and impact strength. FESEM images also proved that the agglomerations that occurred within the UDMA matrix had affected the mechanical performance of 3D printed PHB/UDMA. Nonetheless, the thermal stability of the 3D printed PHB/UDMA had only a slight deviation from the 3D printed UDMA since it had better thermal processability.

Efficient and economical production of polyhydroxyalkanoate from sustainable rubber wood hydrolysate and xylose as co-substrate by mixed microbial cultures

Using co-substrate to accumulate polyhydroxyalkanoate (PHA) is an efficient approach to reduce production cost and improve yield of PHA. In the study, PHA was biosynthesized under full aerobic mode by using rubber wood hydrolysate and xylose co-substrate as the carbon source. The effects of co-substrate on PHA production, microbial community and carbon conversion were explored. The results showed that proper addition of xylose was beneficial for the synthesis of PHA and monomer 3-hydroxyvalerate (3HV). Higher conversion yield of substrate-to-PHA (Y_PHA/S) of 0.933 g COD PHA/g COD S and PHA content of 43.6 g PHA/100 g VSS were gained at co-substrate ratio of 1:1. Likewise, under this condition, PHA production also reached the highest value of 1849 mg COD/L (1088 mg/L). Moreover, the addition of xylose created a favorable screening of PHA dominant strains, improved the conversion of carbon source, and saved 72.3% of feedstock consumption.

Amino Acid Configuration Affects Volatile Fatty Acid Production during Proteinaceous Waste Valorization: Chemotaxis, Quorum Sensing, and Metabolism

During proteinaceous waste valorization to produce volatile fatty acids (VFAs), protein needs to be hydrolyzed to amino acids (AAs), but the effects of the configuration of AAs on their biotransformation and VFA production have not been investigated. In this study, more residual d-AAs than their corresponding l-AAs were observed after VFAs were produced from kitchen waste in a pilot-scale bioreactor. For all AAs investigated, the VFA production from d-AAs was lower than that from corresponding l-AAs. The metagenomics and metaproteomics analyses revealed that the l-AA fermentation system exhibited greater bacterial chemotaxis and quorum sensing (QS) than d-AAs, which benefited the establishment of functional microorganisms (such as Clostridium, Sedimentibacter, and Peptoclostridium) and expression of functional proteins (e.g., substrate transportation cofactors, l-AA dehydrogenase, and acidogenic proteins). In addition, d-AAs need to be racemized to l-AAs before being metabolized, and the difference of VFA production between d-AAs and l-AAs decreased with the increase of racemization activity. The findings of the AA configuration affecting bacterial chemotaxis and QS, which altered microorganism communities and functional protein expression, provided a new insight into the reasons for higher l-AA metabolism than d-AAs and more d-AAs left during VFA production from proteinaceous wastes.

Applications of synthetic light-driven microbial consortia for biochemicals production

Synthetic microbial consortia provide a versatile and efficient platform for biochemicals production through the labor division. Especially, microbial communities composed of phototrophs and heterotrophs offer a promising alternative, as they can directly convert carbon dioxide (CO₂) into chemicals. Within this system, photoautotrophic microbes can convert CO₂ into organic carbon for microbial growth and metabolites synthesis by the heterotrophic partners. In return, heterotrophs can provide additional CO₂ to support the growth of photoautotrophic microbes. However, the unmatched growing conditions, low stability and production efficiency of synthetic microbial consortia hinder their further applications. Thus, design and construction of mutualistic and stable synthetic light-driven microbial consortia are urgently needed. In this review, the progress of synthetic light-driven microbial consortia for chemicals production was comprehensively summarized. In addition, space-efficient synthetic light-driven microbial consortia in hydrogel system were reviewed. Perspectives on orderly distribution of light-driven microbial consortia associated with 3D printing technology in biomanufacturing were also addressed.