Efficiently unsterile polyhydroxyalkanoate production from lignocellulose by using alkali-halophilic Halomonas alkalicola M2

Techno-economic assessment of polyhydroxyalkanoates production from lignocellulosic biomass employing halophilic and thermophilic microbial platform: Effect of fermentation conditions and downstream operations

This study investigates the techno-economic viability of synthesizing polyhydroxyalkanoates (PHA) from lignocellulosic biomass through the utilization of extremophilic microorganisms, framed within the context of Next-Generation Industrial Biotechnology (NGIB). Microbial platforms characterized by halophilic and thermophilic properties, specifically Halomonas halophila and Caldimonas thermodepolymerans, were utilized to tackle issues related to sterility demands, process efficiency, and sustainability. Scenarios incorporating rice straw and discarded softwood, which are low-cost feedstocks that do not interfere with the human food supply, were modeled as resources for PHA biosynthesis. Additionally, a comparison was conducted between traditional chloroform extraction methods and environmentally friendly hypotonic lysis for the recovery of PHA from extremophilic microbial cultures prone to this treatment. Economic indicators such as net present value, internal rate of return, and payback period, were analyzed to evaluate the economic viability of the process. Findings indicate that the incorporation of extremophilic microorganisms alongside waste valorization techniques could make PHA production economically viable, thereby decreasing dependence on fossil-derived plastics while simultaneously addressing ecological issues. This initial study highlights the necessity for subsequent scale-up investigations to authenticate the proposed methodology, which shows potential for the sustainable production of PHA.

Emerging biotechnological strategies advancing biological lignin valorization towards polyhydroxyalkanoates

Lignin is the largest renewable aromatic resource available for producing high-value products such as biomaterials, biofuels, and chemicals. Polyhydroxyalkanoate (PHA) is a biodegradable and biocompatible polymer synthesized by various microorganisms, offering broad application potential. Microbial conversion of lignin-derived aromatics into PHA promoted both lignin valorization and PHA biosynthesis. However, lignin's recalcitrance and heterogeneity pose significant challenges for its microbial degradation and value-added utilization. This review examines the entire pathway of lignin conversion into high-value products, highlighting the advantages of microbial processes for synthesizing PHA and promoting the biological upgrading of lignin. Additionally, synthetic biology techniques and metabolic regulation strategies can further enhance microbial PHA synthesis. Overall, integrating microbial PHA synthesis with lignin bioconversion not only facilitates lignin valorization but also supports the sustainable production of PHA, making a significant contribution to the utilization and sustainable development of biomass resources.

Production of polyhydroxybutyrate from wheat straw hydrolysate using a low-salt requiring and alkaliphilic Halomonas nigrificans X339 under non-sterile open condition

Utilizing agricultural waste is a sustainable approach to reduce the production cost of bio-based products. Here, we report a novel haloalkaliphilic strain, Halomonas nigrificans X339, which exhibits an exceptional ability to utilize various low-cost carbon sources. Compared to other halophiles, X339 could be cultivated at an optimal salinity as low as 2 % (w/v). X339 accumulated extraordinarily large granules of polyhydroxybutyrate (PHB). In open batch fermentation, X339 produced 5.11 g/L of PHB from wheat straw hydrolysate (WSH) at 3 % salinity and pH 9, with a PHB/carbon source conversion rate of 0.30 g/g. This represents the highest PHB yield reported from straw hydrolysates in shake-flask fermentation by halophiles. Additionally, whole genome of X339 was sequenced to identify candidate genes related to carbon source utilization. Our findings will benefit researchers in developing a suitable chassis for Next Generation Industrial Biotechnology, and offer a sustainable and eco-friendly solution for bio-based products.

Advances and challenges in polyhydroxyalkanoates (PHA) production using Halomonas species: A review

Plastic waste pollution is one of the major threats to sustainable development. Biodegradable polymers and biopolymers such as polyhydroxyalkanoates (PHAs) offer suitable alternatives for replacing synthetic plastics. PHAs are produced by diverse bacteria species and archaea as storage compounds for utilization as carbon and energy sources. Halomonas species have emerged as attractive microbial cell factories for biosynthesis of PHAs due to their metabolic versality, ability to valorize diverse feedstock materials, and tolerance to high salinity and pH that allows fermentation in contamination-resistant conditions. In recent years, there has been great attention to the use of Halomonas species in PHA biosynthesis and genetic engineering efforts for enhanced production. This article provides a discussion of the current state of knowledge on production of polyhydroxyalkanoates by Halomonas species. It includes an overview of PHA biosynthesis mechanisms, fermentation strategies, production with cheap substrates, exploitation of open and unsterile conditions, co-production of PHAs and other products, and advances genetic engineering efforts.

Sustainable polyhydroxybutyrate (PHB) production from biowastes by Halomonas sp. WZQ-1 under non-sterile conditions

Polyhydroxyalkanoates (PHA) are promising candidates for replacing petroleum-derived plastics; however, their high production costs limit their commercialisation. In this study, we successfully isolated an efficient PHA-producing strain from a salt lake, which was subsequently identified as Halomonas sp. WZQ-1. Notably, Halomonas sp. WZQ-1 could serve as a promising cell-factory platform for polyhydroxybutyrate (PHB) production, achieving a comparatively high PHB productivity (7.64 ± 0.4 g L-1) under moderate salt stress (60 g L-1 NaCl). We further realised semi-continuous PHB production in a bench-scale fermenter at a steady state by irregularly replenishing the organic substrate. The maximum PHB concentration reached 12.13 g L-1. Finally, we realised the non-sterile conversion of typical biowastes (e.g. pomelo and cantaloupe residues) to PHB using Halomonas sp. WZQ-1. Encouragingly, 4.36 g L-1 PHB was directly obtained from the hydrolysate of pomelo residues with a characteristic melting temperature of 174.0 °C. Life cycle assessment was employed to systematically evaluate the environmental sustainability and potential challenges of biowaste-driven PHB biorefineries. Overall, our findings could serve as a pivotal step toward the commercialisation of PHB and provide a valuable reference for PHB biorefineries.

Biorefinery of sugarcane molasses for poly(3-hydroxybutyrate) fermentation and genomic elucidation of metabolic mechanism using Paracoccus sp. P2

Biorefining sugarcane molasses to produce polyhydroxyalkanoates (PHAs) is an anticipated paradigm for replacing petroleum-based plastics. Nevertheless, there exists a deficiency in excellent chassis and genome resolution for the synthesis of poly(3-hydroxybutyrate) (PHB), which is a typical representative of PHAs. In this study, successive enrichment domestication was employed to screen PHB producers. The isolated species was defined as Paracoccus sp. P2 through taxonomic analysis. Then, a variety of nutrient substrates and physicochemical parameters were tailored to enhance the fermentation capacity. The maximum production of bio-polyester was 4.4 g·L-1, corresponding to a yield of 0.37 g-PHB·g-1-glucose. The concentration of PHB produced from 30 g·L-1 sugarcane molasses was 3.9 g·L-1, indicating a comparable fermentation performance. Furthermore, three-step condensation of acetyl-CoA and de novo synthesis of fatty acids were identified as the primary PHB accumulation pathways. The fermentation performance and genome investigation were compared with Paracoccus genus. The effective production of Paracoccus sp. P2 might be attributed to its efficient substrate conversion capacity and abundant PHB metabolic network. This study broadened the germplasm resources available for the bioconversion of sugarcane molasses, providing theoretical references for the valorization of high-concentration waste carbon sources.

Production, isolation, optimization, and characterization of microbial PHA from Bacillus australimaris

Population explosion in recent years has driven the environment to overuse nondegradable substances. Microbial polyesters known as polyhydroxyalkanoates (PHAs) are generated and retained as cytoplasmic granules in microorganisms with restricted nutritional availability and can be used to manufacture bioplastics. The current study attempts to screen soil isolates for PHA production and optimize their media parameters. Among all the isolates, 17 were identified and confirmed by Sudan black staining, as they are screening for PHA production and are identified by their colony characteristics. The isolation of the most promising strain, GS-14, was achieved through the sodium hypochlorite method, and subsequent quantification involved establishing a standard curve of crotonic acid. Notably, isolate GS-14 presented the highest yield, which was determined by extrapolating its data onto the standard curve. Characterization of the PHA polymer was subsequently performed, and the results were used to discern its properties. FTIR confirmed characteristic PHA absorption bands, with a prominent C = O stretching peak at 1732 cm⁻¹. LC-MS detected a molecular mass of 641.6 g/mol, indicative of an oligomeric species, while the actual polymer molecular weight is estimated between 5,000 and 20,000 Da. DSC revealed an exothermic peak at 174 °C, allowing the calculation of crystallinity, a key determinant of mechanical properties. Furthermore, the PHA-producing organism was identified as Bacillus australimaris through the sequencing of 16 S ribosomal RNA. The media optimization was performed via Minitab software, with statistical analyses employed to interpret the resulting data comprehensively.

Advances in polyhydroxyalkanoate (PHA) production from renewable waste materials using halophilic microorganisms: A comprehensive review

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polymers that can replace conventional plastics in different sectors. However, PHA commercialization is hampered due to their high production cost resulting from the use of high purity substrates, their low conversion into PHAs by using conventional microbial chassis and the high downstream processing cost. Taking these challenges into account, researchers are focusing on the use of waste by-products as alternative low-cost feedstocks for fast-growing and contamination-resistant halophilic microorganisms (Bacteria, Archaea…). This is of great importance since these extremophiles can use low-cost substrates, produce high PHA content of copolymers or different PHA monomer compositions. They can present high potential for reducing the costs of PHA fermentation and recovery processes, making their use in commercial applications easier. However, little is known about the potential of halophiles in advancing the PHA production from renewable waste materials at lab-scale and their successful implementation at industrial-scale. This review presents actual advances in PHA production by halophilic pure/engineered species (e.g. Haloferax mediterranei, Halomonas spp.) and mixed microbial consortia (MMC) using organic waste streams. The development of optimal PHA production process involves robust genetic engineering strategies, advanced fermentation processes using mixed microbial consortia versus pure/engineered strains as well as algal biomass as feedstocks.

Enhanced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from volatile fatty acids by Halomonas sp. YJ01 with 2-methylcitrate cycle

Volatile fatty acids (VFAs) are suitable substrates for synthesizing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), wherein propionate is a precursor of PHBV biosynthesis; however, high concentrations are toxic to bacteria. Therefore, VFAs with suitable ratio are needed. Here, with the ratio of acetate: propionate: butyrate being 1:4:2, the maximum PHBV content and the 3HV content were 46.77 wt% and 19.24 mol%, respectively, by Halomonas sp. YJ01. The optimal C/P and C/N ratios for PHBV synthesis were controlled at 800-1000 and 70-90. The carbon source uptake by the strain at higher C/N ratios was mainly used to synthesize PHBV. The metabolic pathway for PHBV biosynthesis with mixed VFAs showed that the 2-methylcitrate cycle (2-MCC) pathway converted propionyl-CoA to pyruvate, which reduced the toxicity of propionate to the strain. Moreover, the strain utilized acetate and butyrate without producing pyruvate, which did not affect the detoxification of the 2-MCC pathway. Real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) results showed that when the 2-MCC pathway was inhibited, phaC expression decreased 2.74-fold, and the expression of prpB and prpC was down-regulated 2-fold and 6.88-fold, respectively; therefore, propionate toxicity exposure resulted in a significant decrease in PHBV content.

New model compounds for the efficient colorimetric screening of medium chain length polyhydroxyalkanoate (mcl-PHA) depolymerases reveal mechanism of activity

Plastic pollution presents a significant environmental problem contributing to increased CO2 emissions and persistently accumulation in ecosystems. Biobased polymers, like polyhydroxyalkanoates (PHAs), offer a part of a solution with their biodegradability and reduced carbon footprint. However, effective end-of-life strategies, such as controlled enzymatic depolymerization, are crucial for sustainability, relying on efficient PHA depolymerases (PHAases). Here we describe the synthesis of two new chromogenic compounds derived from polyhydroxyoctanoate (PHO) and their application in a continuous, quantitative spectrophotometric assay for PHO depolymerase and other medium chain lengths PHAase activity within 10 min. These substrates allow activity measurement at temperatures above 45 °C, simplifying the comparison of PHAases and aiding enzymatic degradation progress. The study also explores enzyme specificity and identifies key amino acids involved in PHO recognition by PfPHOase. The 3-hydroxyoctanoyl moieties of both compounds were found to bind specifically to a groove formed by the amino acids Phe96, Phe125, Ile171, and Val230, which are highly conserved in known mcl-PHA depolymerases.

Effects of magnetic field exposure patterns on polyhydroxyalkanoates synthesis by Haloferax mediterranei at extreme hypersaline context: Carbon distribution and salt tolerance

The synthesis of polyhydroxyalkanoates (PHAs) by extremophiles presents a promising alternative to mitigate pollution originating from the use of petroleum-based plastics. This study focuses on the impact of different magnetic field (MF) exposure patterns on PHA production and carbon metabolism, aiming to enhance PHA productivity by Haloferax mediterranei within the extreme hypersaline environment and subsequently reducing production costs. Results indicated that under 300 g/L salinity, the highest PHA productivity (1.45 ± 0.06 g/(L d)) and PHA content (65.91 % PHA/cell dry weight) were achieved with 50 mT MF exposure throughout the fermentation period. Continuous exposure to 50 mT MF proved vital for maximizing cell biomass and PHA productivity. Continuous exposure to 50 mT MF enabled Haloferax mediterranei to channel acetyl-CoA towards the PHA synthesis pathway while maintaining growth and proliferation. Correlation analysis further proved the principal role of carbon flux on PHA accumulation. Due to the demand for balancing osmotic pressure, cellular substances were sacrificed to ensure PHA synthesis as anti-salinity substance. Meanwhile, the observed promotion of MF on PHA production, betaine aldehyde dehydrogenase activity, and K+ uptake contributed to sustaining cellular activity at 300 g/L salinity. This study provides a non-gene editing approach to enhance PHA productivity.

Copolymers as a turning point for large scale polyhydroxyalkanoates applications

Traditional plastics reshaped the society thanks to their brilliant properties and cut-price manufacturing costs. However, their protracted durability and limited recycling threaten the environment. Worthy alternatives seem to be polyhydroxyalkanoates, compostable biopolymers produced by several microbes. The most common 3-hydroxybutyrate homopolymer has limited applications calling for copolymers biosynthesis to enhance material properties. As a growing number of researches assess the discovery of novel comonomers, great endeavors are dedicated as well to copolymers production scale-up, where the choice of the microbial carbon source significantly affects the overall economic feasibility. Diving into novel metabolic pathways, engineered strains, and cutting-edge bioprocess strategies, this review aims to survey up-to-date publications about copolymers production, focusing primarily on precursors origins. Specifically, in the core of the review, copolymers precursors have been divided into three categories based on their economic value: the costliest structurally related ones, the structurally unrelated ones, and finally various low-cost waste streams. The combination of cheap biomasses, efficient pretreatment strategies, and robust microorganisms paths the way towards the development of versatile and circular polymers. Conceived to researchers and industries interested in tackling polyhydroxyalkanoates production, this review explores an angle often underestimated yet of prime importance: if PHAs copolymers offer advanced properties and sustainable end-of-life, the feedstock choice for their upstream becomes a major factor in the development of plastic substitutes.

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.

Nonsterile microbial production of chemicals based on Halomonas spp

The use of extremophile organisms such as Halomomas spp. can eliminate the need for fermentation sterilization, significantly reducing process costs. Microbial fermentation is considered a pivotal strategy to reduce reliance on fossil fuel resources; however, sustainable processes continue to incur higher costs than their chemical industry counterparts. Most organisms require equipment sterilization to prevent contamination, a practice that introduces complexity and financial strain. Fermentations involving extremophile organisms can eliminate the sterilization process, relying instead on conditions that are conductive solely to the growth of the desired organism. This review discusses current challenges in pilot- and industrial-scale bioproduction when using the extremophile bacteria Halomomas spp. under nonsterile conditions.

Production and characterization of polyhydroxyalkanoates by Halomonas alkaliantarctica utilizing dairy waste as feedstock

Currently, the global demand for polyhydroxyalkanoates (PHAs) is significantly increasing. PHAs are produced by several bacteria that are an alternative source of synthetic polymers derived from petrochemical refineries. This study established a simple and more feasible process of PHA production by Halomonas alkaliantarctica using dairy waste as the only carbon source. The data confirmed that the analyzed halophile could metabolize cheese whey (CW) and cheese whey mother liquor (CWML) into biopolyesters. The highest yield of PHAs was 0.42 g/L in the cultivation supplemented with CWML. Furthermore, it was proved that PHA structure depended on the type of by-product from cheese manufacturing, its concentration, and the culture time. The results revealed that H. alkaliantarctica could produce P(3HB-co-3HV) copolymer in the cultivations with CW at 48 h and 72 h without adding of any precursors. Based on the data obtained from physicochemical and thermal analyses, the extracted copolymer was reported to have properties suitable for various applications. Overall, this study described a promising approach for valorizing of dairy waste as a future strategy of industrial waste management to produce high value microbial biopolymers.

Recent Challenges and Trends of Polyhydroxyalkanoate Production by Extremophilic Bacteria Using Renewable Feedstocks

Polyhydroxyalkanoates (PHAs) are biodegradable polymers with immense potential in addressing the global plastic pollution crisis and advancing sustainable bioplastics production. Among the various microbes known for PHA production, extremophilic bacteria possess unique capabilities to thrive under extreme conditions, making them attractive candidates for PHA synthesis. Furthermore, the utilization of renewable feedstocks for PHA production aligns with the growing demand for sustainable bioplastic alternatives. A diverse range of extremophilic bacteria, especially halophiles and thermophiles, has provided cost-competitive platforms for producing customized PHA polymers. Extremophilic bacteria offer unique advantages over mesophiles due to their contamination resistance, high cell density growth, and unique culture conditions. The current status of Halomonas spp. as a chassis further allows exploration of metabolic engineering approaches to overcome the challenges associated with current industrial biotechnology. This article especially focuses on extremophilic bacteria and explores recent advances in utilizing renewable feedstocks such as lignocellulosic biomass, agro-industrial residues, and waste streams for PHA production. The integration of biorefinery concepts and circular economy principles in PHA manufacturing is also examined. This review is an attempt to provide an understanding of renewable substrates as feedstocks and emerging trends in PHA production by extremophilic bacteria. It underscores the pivotal role of extremophiles and sustainable feedstock sources in advancing the feasibility and eco-friendliness of PHAs as a promising biopolymer alternative.

Biofuneling lignin-derived compounds into lipids using a newly isolated Citricoccus sp. P2

Lignin-derived compounds (LDCs) bioconversion into lipids is a promising yet challenging task. This study focuses on the isolation of the ligninolytic bacterium Citricoccus sp. P2 and investigates its mechanism for producing lipids from LDCs. Although strain P2 exhibits a relatively low lignin degradation rate of 44.63%, it efficiently degrades various concentrations of LDCs. The highest degradation rate is observed when incubated with 0.6 g/L vanillic acid, 0.6 g/L syringic acid, 0.8 g/L p-coumaric acid, and 0.4 g/L phenol, resulting in respective lipid yields of 0.16 g/L, 0.13 g/L, 0.24 g/L, and 0.13 g/L. The genome of strain P2 provides insights into LDCs bioconversion into lipids and stress tolerance. Moreover, Citricoccus sp. P2 has been successfully developed a non-sterilized lipid production using its native alkali-halophilic characteristics, which significantly enhances the lipid yield. This study presents a promising platform for lipids production from LDCs and has potential to promote valorization of lignin.

Enhanced poly(3-hydroxybutyrateco-3-hydroxyvalerate) production from high-concentration propionate by a novel halophile Halomonas sp. YJ01: Detoxification of the 2-methylcitrate cycle

As a carbon substrate, propionate can be used to synthesize poly(3-hydroxybutyrateco-3-hydroxyvalerate) [PHBV] biopolymer, but high concentrations can inhibit PHBV production. Therefore, novel PHBV producers that can utilize high propionate concentrations are needed. Here, a novel halophile, Halomonas sp. YJ01 was applied to PHBV production via a propionate-dependent pathway, and optimal culture growth conditions were determined. The maximum poly(3-hydroxybutyrate) [PHB] content and yield in the presence of glucose were 89.5 wt% and 5.7 g/L, respectively. This strain utilizes propionate and volatile fatty acids (VFAs) for PHBV accumulation. Multiple genes related to polyhydroxyalkanoate (PHA) synthesis were identified using whole-genome annotation. The PHBV yield and 3HV fraction obtained by strain YJ01 utilizing 15 g/L propionate were 0.86 g/L and 29 mol%, respectively, but in cultures with glucose-propionate, it decreased its copolymer dry weight. This indicates that propionyl-CoA was converted to pyruvate through the 2-methylcitrate cycle (2MCC), which reduced propionate detoxification for the strain.

Biosynthesis of poly(3-hydroxybutyrate) by N,N-dimethylformamide degrading strain Paracoccus sp. PXZ: A strategy for resource utilization of pollutants

N,N-dimethylformamide is a toxic chemical solvent, which widely exists in industrial wastewater. Nevertheless, the relevant methods merely achieved non-hazardous treatment of N,N-dimethylformamide. In this study, one efficient N,N-dimethylformamide degrading strain was isolated and developed for pollutant removal coupling with poly(3-hydroxybutyrate) (PHB) accumulation. The functional host was characterized as Paracoccus sp. PXZ, which could consume N,N-dimethylformamide as the nutrient substrate for cell reproduction. Whole-genome sequencing analysis confirmed that PXZ simultaneously possesses the essential genes for poly(3-hydroxybutyrate) synthesis. Subsequently, the approaches of nutrient supplementation and various physicochemical variables to strengthen poly(3-hydroxybutyrate) production were investigated. The optimal biopolymer concentration was 2.74 g·L^-1 with a poly(3-hydroxybutyrate) proportion of 61%, showing a yield of 0.29 g-PHB·g^-1-fructose. Furthermore, N,N-dimethylformamide served as the special nitrogen matter that could realize a similar poly(3-hydroxybutyrate) accumulation. This study provided a fermentation technology coupling with N,N-dimethylformamide degradation, offering a new strategy for resource utilization of specific pollutants and wastewater treatment.

Recent updates to microbial production and recovery of polyhydroxyalkanoates

The increasing use of synthetic polymers and their disposal has raised concern due to their adverse effects on the environment. Thus, other sustainable alternatives to synthetic plastics have been sought, such as polyhydroxyalkanoates (PHAs), which are promising microbial polyesters, mainly due to their compostable nature, biocompatibility, thermostability, and resilience, making this biopolymer acceptable in several applications in the global market. The large-scale production of PHAs by microorganisms is still limited by the high cost of production compared to conventional plastics. This review reports some strategies mentioned in the literature aimed at production and recovery, paving the way for the bio-based economy. For this, some aspects of PHAs are addressed, such as synthesis, production systems, process control using by-products from industries, and advances and challenges in the downstream. The bioplastics properties made them a prime candidate for food, pharmaceutical, and chemical industrial applications. With this paper, it is possible to see that biodegradable polymers are promising materials, mainly for reducing the pollution produced by polymers derived from petroleum.

Non-sterilized conversion of whole lignocellulosic components into polyhydroxybutyrate by Halomonas sp. Y3 with a dual anti-microbial contamination system

Polyhydroxybutyrate (PHB) production from lignocellulosic biomass is challenging due to the need for whole components and energy-effective conversion. Herein, Halomonas sp. Y3, a ligninolytic bacterium with the capacity to produce PHB from lignin and cellulose- and hemicellulose-derived sugars, is employed to explore its feasibility. This strain shows high sugar tolerance up to 200 g/L of glucose and 120 g/L of xylose. A dual anti-microbial contamination system (DACS) containing alkali-halophilic system (AHS) and phosphite-urea system (PUS) is presented, successfully achieving a completely aseptic effect and resulting in a total of 8.2 g of PHB production from 100 g bamboo biomass. We further develop a stage-fed-batch fermentation to promote the complete utilization of xylose. Approximately 69.99 g of dry cell weight (DCW) and 46.45 g of PHB with 66.35 % are obtained from a total of 296.58 g of sugars and 5.70 g of lignin, showing a significant advancement for LCB bioconversion. We then delete the native phosphate transporters, rendering the strain unable to grow on phosphate-loaded media, effectively improving the strain biosafety without compromising its ability to produce PHB. Overall, our findings demonstrate the potential of Y3 as a classic bacterium strain for PHB production with potential uses in industry.

Co-conversion of lignocellulose-derived glucose, xylose, and aromatics to polyhydroxybutyrate by metabolically engineered Cupriavidus necator

Utilization of all major components of lignocellulose is essential for biomass biorefining. Glucose, xylose, and lignin-derived aromatics can be generated from cellulose, hemicellulose, and lignin of lignocellulose degradation through pretreatment and hydrolysis. In present work, Cupriavidus necator H16 was engineered to utilize glucose, xylose, p-coumaric acid, and ferulic acid simultaneously by multi-step genetic engineering. Firstly, genetic modification and adaptive laboratory evolution were performed to promote glucose transmembrane transport and metabolism. Xylose metabolism was then engineered by integrating genes xylAB (xylose isomerase and xylulokinase) and xylE (proton-coupled symporter) in the locus of ldh (lactate dehydrogenase) and ackA (acetate kinase) on the genome, respectively. Thirdly, p-coumaric acid and ferulic acid metabolism was achieved by constructing an exogenous CoA-dependent non-β-oxidation pathway. Using corn stover hydrolysates as carbon sources, the resulting engineered strain Reh06 simultaneously converted all components of glucose, xylose, p-coumaric acid, and ferulic acid to produce 11.51 g/L polyhydroxybutyrate.

Biotransformation of toxic lignin and aromatic compounds of lignocellulosic feedstock into eco-friendly biopolymers by Pseudomonas putida KT2440

Lignin and its derivatives are the most neglected compounds in bio-processing industry due to their toxic and recalcitrant nature. Considering this, the present study aimed at valorizing these toxic compounds by employing Pseudomonas putida KT2440. Acclimatization resulted in improved tolerance with considerable lag phase reduction and aromatics degradation. Glucose as co-substrate enhanced growth and degradation in the toxic environment. The strain was able to degrade 30 % (1.60 g·L^-1) lignin, 45 mM benzoate, 40 mM p-coumarate, 35 mM ferulate, 10 mM phenol, 10 mM pyrocatechol and 8 mM aromatics mixture. The strain synthesized biopolymers using these compounds under feast and famine conditions. Characterization using GC-MS, FT-IR, H¹ NMR revealed them to be Polyhydroxyalkanoate (PHA) heteropolymers. All the analyzed PHAs contained versatile monomers with Hexadecanoic acid being the major one. This is a novel attempt towards lignin and aromatics degradation coupled with biopolymers synthesis without any genetic manipulation of the strain.

Funneling lignin-derived compounds into polyhydroxyalkanoate by Halomonas sp. Y3

Lignin-derived compounds (LDCs) biological funneling for polyhydroxyalkanoate (PHA) synthesis has been attractive but elusive. Herein, the Halomonas sp. Y3 is isolated and developed for PHA production from LDCs. Of the tested 13 LDCs, 4-hydroxybenzoic acid (4-HBA), protocatechuate (PA), catechol (CAT), and vanillic acid (VA) exhibit a hyper-degradation and production with 87.2 %, 85.8 %, 84.7 %, and 83.4 % TOC removal rate and 535.2 mg/L, 506.5 mg/L, 435.6 mg/L, and 440.8 mg/L PHA concentration, respectively. The Halomonas sp. Y3 genome is sequenced by identifying numerous genes responsible for LDCs funneling, stress response, and PHA biosynthesis. An open unsterilized fermentation with optimal conditions of pH 9.0 and NaCl 60 g/L is investigated, achieving a completely aseptic effect and significantly improved PHA production from LDCs. Overall, the results indicate that the Halomonas sp. Y3 is an ideal candidate for LDC bioconversion and exhibits a great potential to realize black liquor valorization.

Coproduction of exopolysaccharide and polyhydroxyalkanoates from Sphingobium yanoikuyae BBL01 using biochar pretreated plant biomass hydrolysate

Sphingobium yanoikuyae BBL01 can produce exopolysaccharides (EPS) and polyhydroxyalkanoates (PHAs). The effect of side products (furfural, hydroxymethylfurfural (HMF), vanillin, and acetate) produced during pretreatment of biomass was evaluated on S. yanoikuyae BBL01. It was observed that a certain concentration range (0.01-0.03 %) of these compounds can improve growth, EPS production, and polyhydroxybutyrate (PHB) accumulation. The addition of HMF increases glucose and xylose utilization while other side products have a negative effect. The C/N of 5 favors EPS production (3.24 ± 0.05 g/L), while a higher C/N ratio of 30 promotes PHB accumulation (38.7 ± 0.08 % w/w), when commercial sugar is used as a carbon source. Pine biomass-derived biochar was able to remove 40 ± 2.1 % of total phenolic. Various biomass hydrolysates were evaluated and the use of detoxified pine biomass hydrolysate (DPH) as a carbon source resulted in the higher coproduction of EPS (2.83 ± 0.03 g/L) and PHB (40.8 ± 2.4 % w/w).

Valorization of lignocellulosic biomass for polyhydroxyalkanoate production: Status and perspectives

With the increasing concerns regarding climate, energy, and plastic crises, bio-based production of biodegradable polymers has become a dire necessity. Significant progress has been made in biotechnology for the production of biodegradable polymers from renewable resources to achieve the goal of zero plastic waste and a net-zero carbon bioeconomy. In this review, an overview of polyhydroxyalkanoate (PHA) production from lignocellulosic biomass (LCB) was presented. Having established LCB-based biorefinery with proper pretreatment techniques, various PHAs could be produced from LCB-derived sugars, hydrolysates, and/or aromatic mixtures employing microorganisms. This provides a clue for addressing the current environmental crises because "biodegradable polymers" could be produced from one of the most abundant resources that are renewable and sustainable in a "carbon-neutral process". Furthermore, the potential future of LCB-to-non-natural PHA production was discussed with particular reference to non-natural PHA biosynthesis methods and LCB-derived aromatic mixture biofunnelling systems.