Medium chain length polyhydroxyalkanoate produced from ethanol by Pseudomonas putida grown in liquid obtained from acidogenic digestion of organic municipal solid waste

One-Pot lignin bioconversion to polyhydroxyalkanoates based on hierarchical utilization of heterogeneous compounds

Pseudomonas putida degraded 35 % of compounds in alkali-pretreated lignin liquor under nitrogen-replete conditions but with low polyhydroxyalkanoates (PHA) production, while limiting nitrogen supplement improved PHA content (PHA/dry cell weight) to 43 % at the expense of decreased lignin degradation of 22 %. Increase of initial cell biomass (0.1-1.5 g/L) monotonically improved the lignin degradation from 22 % to 33 % under nitrogen-limited conditions. Hierarchical utilization of heterogenous compounds under cell growth restricted conditions has been unveiled - simple carbon sources were prioritized for valorization, followed by aromatic compounds bioconversion. Based on the results of hierarchy and leveraging the initial bacterial biomass, acetate was augmented to facilitate one-pot lignin bioconversion under nitrogen-limited conditions. This approach improved lignin bioconversion closer to its upper degradation limit of 35 %, concomitant with PHA yield of 39 mg/g-lignin. Anaerobic digestion of lignocellulose was redesigned to favor acetate-type fermentation, with acetate constituting 91 wt%, providing an economic source of acetate.

Cold Plasma Treatment Facilitated the Conversion of Lignin-Derived Aldehyde for Pseudomonas putida

Syringaldehyde derived from lignin is one of the essential intermediates for the production of basic chemicals. However, it was poorly understood for the direct microbial conversion of syringaldehyde. Here, this study tried to use cold plasma technique to enhance syringaldehyde conversion for the bacterium Pseudomonas putida. It illustrated that cell growth and syringaldehyde conversion were separately increased by 1.49 times at 3 h and 1.60 times at 6 h for 35 s, 1.16 and 3.44 times for 140 W, and 1.63 and 4.02 times for 105 Pa for P. putida through single factor assays of cold plasma treatment. To be sure, cell growth and syringaldehyde conversion were enhanced by 1.14 and 5.54 times at 3 h under the optimum parameters (35 s, 140 W, and 105 Pa) for P. putida. Furthermore, genome re-sequencing further discovered single-nucleotide polymorphisms of P. putida, such as PP_2589 (A428V), PP_5651 (V82F), and PP_0545 (W335R), and thus indicated that the potential genetic changes derived from cold plasma treatment would be responsible for the acceleration of syringaldehyde conversion. This work would provide a robust strain catalyst and the potential candidate mutation sites for genetic manipulation for microbial bioconversion of the value-added and lignin-based biochemicals.

Microbial conversion of ethanol to high-value products: progress and challenges

Industrial biotechnology heavily relies on the microbial conversion of carbohydrate substrates derived from sugar- or starch-rich crops. This dependency poses significant challenges in the face of a rising population and food scarcity. Consequently, exploring renewable, non-competing carbon sources for sustainable bioprocessing becomes increasingly important. Ethanol, a key C2 feedstock, presents a promising alternative, especially for producing acetyl-CoA derivatives. In this review, we offer an in-depth analysis of ethanol's potential as an alternative carbon source, summarizing its distinctive characteristics when utilized by microbes, microbial ethanol metabolism pathway, and microbial responses and tolerance mechanisms to ethanol stress. We provide an update on recent progress in ethanol-based biomanufacturing and ethanol biosynthesis, discuss current challenges, and outline potential research directions to guide future advancements in this field. The insights presented here could serve as valuable theoretical support for researchers and industry professionals seeking to harness ethanol's potential for the production of high-value products.

A Review of Current Achievements and Recent Challenges in Bacterial Medium-Chain-Length Polyhydroxyalkanoates: Production and Potential Applications

Using petroleum-derived plastics has contributed significantly to environmental issues, such as greenhouse gas emissions and the accumulation of plastic waste in ecosystems. Researchers have focused on developing ecofriendly polymers as alternatives to traditional plastics to address these concerns. This review provides a comprehensive overview of medium-chain-length polyhydroxyalkanoates (mcl-PHAs), biodegradable biopolymers produced by microorganisms that show promise in replacing conventional plastics. The review discusses the classification, properties, and potential substrates of less studied mcl-PHAs, highlighting their greater ductility and flexibility compared to poly(3-hydroxybutyrate), a well-known but brittle PHA. The authors summarize existing research to emphasize the potential applications of mcl-PHAs in biomedicine, packaging, biocomposites, water treatment, and energy. Future research should focus on improving production techniques, ensuring economic viability, and addressing challenges associated with industrial implementation. Investigating the biodegradability, stability, mechanical properties, durability, and cost-effectiveness of mcl-PHA-based products compared to petroleum-based counterparts is crucial. The future of mcl-PHAs looks promising, with continued research expected to optimize production techniques, enhance material properties, and expand applications. Interdisciplinary collaborations among microbiologists, engineers, chemists, and materials scientists will drive progress in this field. In conclusion, this review serves as a valuable resource to understand mcl-PHAs as sustainable alternatives to conventional plastics. However, further research is needed to optimize production methods, evaluate long-term ecological impacts, and assess the feasibility and viability in various industries.

Acid hydrolysis of Solanum tuberosum periderm for accumulation of polyhydroxyalkanoates in Pseudomonas putida MTCC 2475

Polyhydroxyalkanoates are a class of biodegradable, biocompatible polymers composed of polyesters of R-hydroxyalkanoic acids and deposited intracellularly by a variety of microorganisms which have potential to serve as alternative to commercial plastic. Bioplastics are gaining attention due to sustainability, biodegradability, biocompatibility, and lower carbon footprint. Nevertheless, the commercialization of PHA is predominantly hindered by the elevated production expenses arising primarily from the use of a pure sugar substrate. Our study has established a feasible method for bioplastic formation applying Pseudomonas putida MTCC 2475 and Solanum tuberosum periderm as a carbon source. To optimize the sugar yield response surface methodology was used, which released 69.34% ± 0.25% reducing sugar. PHA production experiments were performed in hydrolysate containing media as well as commercial sugar containing mineral salt media. After 48 h of fermentation of using this sugar, a biomass concentration of 2.19 gL-1, with a PHA production of 0.60 gL-1 (28.71% ± 0.55%) was obtained which was comparatively similar with synthetic media (2.56 gL-1 cell dry weight and 29.97% ± 0.45% PHA). Furthermore, the monomers of PHA produced by hydrolysate were characterized using Gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance. This investigation has identified three distinct monomers of medium-chain PHAs, namely, methyl 3-Hydroxydodecanoate, 3-Hydroxytetradecanoate, and Hexadecanoic acid 3-Hydroxy methyl esters. Hence this study concludes a sustainable production of bioplastics from S. tuberosum periderm waste.

Carbon dioxide and methane as carbon source for the production of polyhydroxyalkanoates and concomitant carbon fixation

The currently used plastics are non-biodegradable, and cause greenhouse gases (GHGs) emission as they are petroleum-based. Polyhydroxyalkanoates (PHAs) are biopolymers with excellent biodegradability and biocompatibility, which can be used to replace petroleum-based plastics. A variety of microorganisms have been found to synthesize PHAs by using typical GHGs: carbon dioxide and methane as carbon sources. Converting carbon dioxide (CO2) and methane (CH4) to PHAs is an attractive option for carbon capture and biodegradable plastic production. In this review, the microorganisms capable of using CO2 and CH4 to produce PHAs were summarized. The metabolic mechanism, PHAs production process, and the factors influencing the production process are illustrated. The currently used optimization techniques to improve the yield of PHAs are discussed. The challenges and future prospects for developing economically viable PHAs production using GHGs as carbon source are identified. This work provides an insight for achieving carbon sequestration and bioplastics based circular economy.

Synthesis and commercialization of bioplastics: Organic waste as a sustainable feedstock

Substituting synthetic plastics with bioplastics, primarily due to their inherent biodegradable properties, represents a highly effective strategy to address the current global issue of plastic waste accumulation in the environment. Advances in bioplastic research have led to the development of materials with improved properties, enabling their use in a wide range of applications in major commercial sectors. Bioplastics are derived from various natural sources such as plants, animals, and microorganisms. Polyhydroxyalkanoate (PHA), a biopolymer synthesized by bacteria through microbial fermentation, exhibits physicochemical and mechanical characteristics comparable to those of synthetic plastics. In response to the growing demand for these environmentally friendly plastics, researchers are actively investigating various cleaner production methods, including modification or derivatization of existing molecules for enhanced properties and new-generation applications to expand their market share in the coming decades. By 2026, the commercial manufacturing capacity of bioplastics is projected to reach 7.6 million tonnes, with Europe currently holding a significant market share of 43.5 %. Bioplastics are predominantly utilized in the packaging industry, indicating a strong focus of their application in the sector. With the anticipated rise in bioplastic waste volume over the next few decades, it is crucial to comprehend their fate in various environments to evaluate the overall environmental impact. Ensuring their complete biodegradation involves optimizing waste management strategies and appropriate disposal within these facilities. Future research efforts should prioritize exploration of their end-of-life management and toxicity assessment of degradation products. These efforts are crucial to ensure the economic viability and environmental sustainability of bioplastics as alternatives to synthetic plastics.