In situ immobilization of lysine decarboxylase on a biopolymer by fusion with phasin

ATP is not essential for cadaverine production by Escherichia coli whole-cell bioconversion

ATP plays an essential role in the substrate/product transmembrane transportation during whole-cell bioconversion. This study aimed to address the impact of ATP upon cadaverine synthesis by whole-cell biocatalysts. The results showed no significant change in the ATP content (P = 0.625), and the specific cadaverine yield (P = 0.374) was observed in enzyme-catalyzed cadaverine synthesis with exogenous addition of ATP, indicating that the enzyme-catalyzed process does not require the participation of ATP. Furthermore, a whole-cell biocatalyst co-overexpressed methionine adenosyltransferase (MetK), lysine decarboxylase (CadA), and lysine/cadaverine antiporter (CadB) was constructed and used to investigate the effect of ATP deficiency on the cadaverine production by conversion of L-methionine and L-lysine, simultaneously. The results showed no significant difference (P = 0.585) in the specific cadaverine content between high and low levels of intracellular ATP. In addition, the intra- and extracellular cadaverine concentration and the ratio of ATP/ADP of whole-cell biocatalyst were determined. Results showed that the extracellular cadaverine concentration was much higher than the intracellular concentration, and no significant changes in ATP/ADP ratio during cadaverine synthesis. In contrast, an inhibition effect of the proton motive force (PMF) inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) on cadaverine production was detected. These findings strongly suggest that cadaverine transport in whole-cell biocatalysts was energized by PMF rather than ATP. Finally, a model was proposed to describe cadaverine's PMF-driven transport under different external pHs during whole-cell biocatalysis. This study is the first to experimentally confirm that the cadaverine production by Escherichia coli whole-cell bioconversion is independent of intracellular ATP, which helps guide the subsequent construction of biocatalysts and optimize transformation conditions.

From Enzyme to Preparative Cascade Reactions with Immobilized Enzymes: Tuning Fe(II)/α-Ketoglutarate-Dependent Lysine Hydroxylases for Application in Biotransformations

Fe(II)/α-ketoglutarate-dependent dioxygenases (KDOs) catalyze a broad range of selective C–H oxidation reactions. However, the difficult production of KDOs in recombinant E. coli strains and their instability in purified form have so far limited their application in preparative biotransformations. Here, we investigated the immobilization of three KDOs (CaKDO, CpKDO, FjKDO) that catalyze the stereoselective hydroxylation of the L-lysine side chain using two one-step immobilization techniques (HaloTag®, EziG™). The HaloTag®-based immobilisates reached the best results with respect to residual activity and stability. In preparative lab-scale experiments, we achieved product titers of 16 g L−1 (3S)-hydroxy-L-lysine (CaKDO) and (4R)-hydroxy-L-lysine (FjKDO), respectively, starting from 100 mM L-lysine. Using a HaloTag®-immobilized lysine decarboxylase from Selenomonas ruminantium (SrLDC), the (3S)-hydroxy-L-lysine from the CaKDO-catalyzed reaction was successfully converted to (2S)-hydroxy-cadaverine without intermediate product purification, yielding a product titer of 11.6 g L−1 in a 15 mL consecutive batch reaction. We propose that covalent in situ immobilization is an appropriate tool to access the preparative potential of many other KDOs.

Established and Emerging Producers of PHA: Redefining the Possibility

The polyhydroxyalkanoate was discovered almost around a century ago. Still, all the efforts to replace the traditional non-biodegradable plastic with much more environmentally friendly alternative are not enough. While the petroleum-based plastic is like a parasite, taking over the planet rapidly and without any feasible cure, its perennial presence has made the ocean a floating island of life-threatening debris and has flooded the landfills with toxic towering mountains. It demands for an immediate solution; most resembling answer would be the polyhydroxyalkanoates. The production cost is yet one of the significant challenges that various corporate is facing to replace the petroleum-based plastic. To deal with the economic constrain better strain, better practices, and a better market can be adopted for superior results. It demands for systems for polyhydroxyalkanoate production namely bacteria, yeast, microalgae, and transgenic plants. Solely strains affect more than 40% of overall production cost, playing a significant role in both upstream and downstream processes. The highly modifiable nature of the biopolymer provides the opportunity to replace the petroleum plastic in almost all sectors from food packaging to medical industry. The review will highlight the recent advancements and techno-economic analysis of current commercial models of polyhydroxyalkanoate production. Bio-compatibility and the biodegradability perks to be utilized highly efficient in the medical applications gives ample reason to tilt the scale in the favor of the polyhydroxyalkanoate as the new conventional and sustainable plastic.

Green chemical and biological synthesis of cadaverine: recent development and challenges

Cadaverine has great potential to be used as an important monomer for the development of a series of high value-added products with market prospects. The most promising strategies for cadaverine synthesis involve using green chemical and bioconversion technologies. Herein, the review focuses on the progress and strategies towards the green chemical synthesis and biosynthesis of cadaverine. Specifically, we address the specific biosynthetic pathways of cadaverine from different substrates as well as extensively discussing the origination, structure and catalytic mechanism of the key lysine decarboxylases. The advanced strategies for process intensification, the separation and purification of cadaverine have been summarized. Furthermore, the challenging issues of the environmental, economic, and applicable impact for cadaverine production are also highlighted. This review concludes with the promising outlooks of state-of-the-art applications of cadaverine along with some insights toward their challenges and potential improvements.

Progress and strategies towards the green chemo/bio-synthesis of cadaverine with special attention to their environmental, economic, and applicable impact are reviewed.

Biowaste-to-bioplastic (polyhydroxyalkanoates): Conversion technologies, strategies, challenges, and perspective

Biowaste management is a challenging job as it is high in nutrient content and its disposal in open may cause a serious environmental and health risk. Traditional technologies such as landfill, bio-composting, and incineration are used for biowaste management. To gain revenue from biowaste researchers around the world focusing on the integration of biowaste management with other commercial products such as volatile fatty acids (VFA), biohydrogen, and bioplastic (polyhydroxyalkanoates (PHA)), etc. PHA production from various biowastes such as lignocellulosic biomass, municipal waste, waste cooking oils, biodiesel industry waste, and syngas has been reported successfully. Various nutrient factors i.e., carbon and nitrogen source concentration and availability of dissolved oxygen are crucial factors for PHA production. This review is an attempt to summarize the recent advancements in PHA production from various biowaste, its downstream processing, and other challenges that need to overcome making bioplastic an alternate for synthetic plastic.

Bio-specific immobilization of enzymes on electrospun PHB nanofibers

Enzyme immobilization provides substantial advantages in terms of improving the efficiency of enzymatic process as well as enhancing the reusability of enzymes. Phasins (PhaPs) are naturally occurring polyhydroxyalkanoate (PHA)-binding proteins, and thus can potentially be used as a fusion partner for oriented immobilization of enzymes onto PHA supports. However, presently available granular PHA supports have low surface-area-to-volume ratio and limited configurational flexibility of enzymatic reactions. In this study, we explored the use of electrospun polyhydroxybutyrate (PHB) nanofibers as an alternative support for high density immobilization of a PhaP-fused lipase. As envisioned, the electrospun PHB nanofibers could anchor 120-fold more enzyme than PHB granules of the same weight. Furthermore, the enzymes immobilized onto the PHB nanofibers exhibited markedly higher stability and activity compared to when immobilized on conventional immobilization supports. Our approach combines the advantageous features of nanofibrous material and specificity of biomolecular interaction for the efficient use of enzymes, which can be widely adopted in the development of various enzymatic processes.

Bioengineered Polyhydroxyalkanoates as Immobilized Enzyme Scaffolds for Industrial Applications

Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable fine-tuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.

Cadaverine Production From L-Lysine With Chitin-Binding Protein-Mediated Lysine Decarboxylase Immobilization

Lysine decarboxylase (CadA) can directly convert L-lysine to cadaverine, which is an important platform chemical that can be used to produce polyamides. However, the non-recyclable and the poor pH tolerance of pure CadA hampered its practical application. Herein, a one-step purification and immobilization procedure of CadA was established to investigate the cadaverine production from L-lysine. Renewable biomass chitin was used as a carrier for lysine decarboxylase (CadA) immobilization via fusion of a chitin-binding domain (ChBD). Scanning electron microscopy, laser scanning confocal microscopy, fourier transform infrared spectra, elemental analysis, and thermal gravimetric analysis proved that the fusion protein ChBD-CadA can be adsorbed on chitin effectively. Furthermore, the fusion protein (ChBD-CadA) existed better pH stability compared to wild CadA, and kept over 73% of the highest activity at pH 8.0. Meanwhile, the ChBD-CadA showed high specificity toward chitin and reached 93% immobilization yield within 10 min under the optimum conditions. The immobilized ChBD-CadA (I-ChBD-CadA) could efficiently converted L-lysine at 200.0 g/L to cadaverine at 135.6 g/L in a batch conversion within 120 min, achieving a 97% molar yield of the substrate L-lysine. In addition, the I-ChBD-CadA was able to be reused under a high concentration of L-lysine and retained over 57% of its original activity after four cycles of use without acid addition to maintain pH. These results demonstrate that immobilization of CadA using chitin-binding domain has the potential in cadaverine production on an industrial scale.

Protein-Rich Biomass Waste as a Resource for Future Biorefineries: State of the Art, Challenges, and Opportunities

Protein-rich biomass provides a valuable feedstock for the chemical industry. This Review describes every process step in the value chain from protein waste to chemicals. The first part deals with the physicochemical extraction of proteins from biomass, hydrolytic degradation to peptides and amino acids, and separation of amino acid mixtures. The second part provides an overview of physical and (bio)chemical technologies for the production of polymers, commodity chemicals, pharmaceuticals, and other fine chemicals. This can be achieved by incorporation of oligopeptides into polymers, or by modification and defunctionalization of amino acids, for example, their reduction to amino alcohols, decarboxylation to amines, (cyclic) amides and nitriles, deamination to (di)carboxylic acids, and synthesis of fine chemicals and ionic liquids. Bio- and chemocatalytic approaches are compared in terms of scope, efficiency, and sustainability.

A Novel Process for Cadaverine Bio-Production Using a Consortium of Two Engineered Escherichia coli

Bio-production of cadaverine from cheap carbon sources for synthesizing bio-based polyamides is becoming more common. Here, a novel fermentation process for cadaverine bio-production from glucose was implemented by using a microbial consortium of two engineered Escherichia coli strains to relieve the toxic effect of cadaverine on fermentation efficiency. To achieve controllable growth of strains in the microbial consortium, two engineered E. coli strains grown separately on different carbon sources were first constructed. The strains were, an L-lysine-producing E. coli NT1004 with glucose as carbon source, and a cadaverine-producing E. coli CAD03 with glucose metabolism deficiency generated by modifying the PTS^Glc system with CRISPR-Cas9 technology and inactivating cadaverine degradation pathways. Co-culturing these two engineered E. coli strains with a mixture of glucose and glycerol led to successful production of cadaverine. After optimizing cultivation conditions, a cadaverine titer of 28.5 g/L was achieved with a multi-stage constant-speed feeding strategy.

Catalytically active inclusion bodies of L-lysine decarboxylase from E. coli for 1,5-diaminopentane production

Sustainable and eco-efficient alternatives for the production of platform chemicals, fuels and chemical building blocks require the development of stable, reusable and recyclable biocatalysts. Here we present a novel concept for the biocatalytic production of 1,5-diaminopentane (DAP, trivial name: cadaverine) using catalytically active inclusion bodies (CatIBs) of the constitutive L-lysine decarboxylase from E. coli (EcLDCc-CatIBs) to process L-lysine-containing culture supernatants from Corynebacterium glutamicum. EcLDCc-CatIBs can easily be produced in E. coli followed by a simple purification protocol yielding up to 43% dry CatIBs per dry cell weight. The stability and recyclability of EcLDCc-CatIBs was demonstrated in (repetitive) batch experiments starting from L-lysine concentrations of 0.1 M and 1 M. EcLDC-CatIBs exhibited great stability under reaction conditions with an estimated half-life of about 54 h. High conversions to DAP of 87-100% were obtained in 30-60 ml batch reactions using approx. 180-300 mg EcLDCc-CatIBs, respectively. This resulted in DAP titres of up to 88.4 g l^-1 and space-time yields of up to 660 g_DAP l^-1 d^-1 per gram dry EcLDCc-CatIBs. The new process for DAP production can therefore compete with the currently best fermentative process as described in the literature.