Inexpensive Carbon Feedstocks Research Articles

Enzymatic CO2 reduction catalyzed by natural and artificial Metalloenzymes

The continuously increasing level of atmospheric CO2 in the atmosphere has led to global warming. Converting CO2 into other carbon compounds could mitigate its atmospheric levels and produce valuable products, as CO2 also serves as a plentiful and inexpensive carbon feedstock. However, the inert nature of CO2 poses a major challenge for its reduction. To meet the challenge, nature has evolved metalloenzymes using transition metal ions like Fe, Ni, Mo, and W, as well as electron-transfer partners for their functions. Mimicking these enzymes, artificial metalloenzymes (ArMs) have been designed using alternative protein scaffolds and various metallocofactors like Ni, Co, Re, Rh, and FeS clusters. Both the catalytic efficiency and the scope of CO2-reduction product of these ArMs have been improved over the past decade. This review first focuses on the natural metalloenzymes that directly reduce CO2 by discussing their structures and active sites, as well as the proposed reaction mechanisms. It then introduces the common strategies for electrochemical, photochemical, or photoelectrochemical utilization of these native enzymes for CO2 reduction and highlights the most recent advancements from the past five years. We also summarize principles of protein design for bio-inspired ArMs, comparing them with native enzymatic systems and outlining challenges and opportunities in enzymatic CO2 reduction.

Sustainable biosynthesis of chemicals from methane and glycerol via reconstruction of multi-carbon utilizing pathway in obligate methanotrophic bacteria.

SummaryObligate methanotrophic bacteria can utilize methane, an inexpensive carbon feedstock, as a sole energy and carbon substrate, thus are considered as the only nature‐provided biocatalyst for sustainable biomanufacturing of fuels and chemicals from methane. To address the limitation of native C1 metabolism of obligate type I methanotrophs, we proposed a novel platform strain that can utilize methane and multi‐carbon substrates, such as glycerol, simultaneously to boost growth rates and chemical production in Methylotuvimicrobium alcaliphilum 20Z. To demonstrate the uses of this concept, we reconstructed a 2,3‐butanediol biosynthetic pathway and achieved a fourfold higher titer of 2,3‐butanediol production by co‐utilizing methane and glycerol compared with that of methanotrophic growth. In addition, we reported the creation of a methanotrophic biocatalyst for one‐step bioconversion of methane to methanol in which glycerol was used for cell growth, and methane was mainly used for methanol production. After the deletion of genes encoding methanol dehydrogenase (MDH), 11.6 mM methanol was obtained after 72 h using living cells in the absence of any chemical inhibitors of MDH and exogenous NADH source. A further improvement of this bioconversion was attained by using resting cells with a significantly increased titre of 76 mM methanol after 3.5 h with the supply of 40 mM formate. The work presented here provides a novel framework for a variety of approaches in methane‐based biomanufacturing.

Improvement of the Production and Characterisation of Polyhydroxyalkanoate by Bacillus endophyticus Using Inexpensive Carbon Feedstock

The study aimed at the production and characterization of biopolymer polyhydroxyalkanoate (PHA) by Bacillus endophyticus. The usage of refined (sucrose 2–4%) and inexpensive unrefined (sugar cane molasses 2–4%) carbon source was evaluated by varying the media components via shake flask method and batch cultivation in bioreactor. The optimal PHA production of 10.7 g/L of PHA from 15.37 g/L of cell density was obtained using 4% sugarcane molasses (SCM) at 250 rpm using optimized medium obtained through statistical experimental design. Batch cultivation with increased agitation rate and addition of feeding nutrients provided by SCM significantly lead to enhanced PHA production by the test organism by increasing the overall cell density. According to the statistical model, the increase in the sugar concentration (>4%) by SCM had a negative effect on PHA production. Characterization by FTIR and 1 H NMR was performed to confirm the biopolymer that has been produced by Bacillus spp.

Polyhydroxyalkanoates production with Ralstonia eutropha from low quality waste animal fats

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters considered as alternatives to petroleum-based plastics. Ralstonia eutropha is a model organism for PHA production. Utilizing industrially rendered waste animal fats as inexpensive carbon feedstocks for PHA production is demonstrated here. An emulsification strategy, without any mechanical or chemical pre-treatment, was developed to increase the bioavailability of solid, poorly-consumable fats. Wild type R. eutropha strain H16 produced 79–82% (w/w) polyhydroxybutyrate (PHB) per cell dry weight (CDW) when cultivated on various fats. A productivity of 0.3g PHB/(L×h) with a total PHB production of 24g/L was achieved using tallow as carbon source. Using a recombinant strain of R. eutropha that produces poly(hydroxybutyrate-co-hydroxyhexanoate) [P(HB-co-HHx)], 49–72% (w/w) of PHA per CDW with a HHx content of 16–27mol% were produced in shaking flask experiments. The recombinant strain was grown on waste animal fat of the lowest quality available at lab fermenter scale, resulting in 45g/L CDW with 60% (w/w) PHA per CDW and a productivity of 0.4g PHA/(L×h). The final HHx content of the polymer was 19mol%. The use of low quality waste animal fats as an inexpensive carbon feedstock exhibits a high potential to accelerate the commercialization of PHAs.

Potential and Prospects of Continuous Polyhydroxyalkanoate (PHA) Production

Together with other so-called “bio-plastics”, Polyhydroxyalkanoates (PHAs) are expected to soon replace established polymers on the plastic market. As a prerequisite, optimized process design is needed to make PHAs attractive in terms of costs and quality. Nowadays, large-scale PHA production relies on discontinuous fed-batch cultivation in huge bioreactors. Such processes presuppose numerous shortcomings such as nonproductive time for reactor revamping, irregular product quality, limited possibility for supply of certain carbon substrates, and, most of all, insufficient productivity. Therefore, single- and multistage continuous PHA biosynthesis is increasingly investigated for production of different types of microbial PHAs; this goes for rather crystalline, thermoplastic PHA homopolyesters as well as for highly flexible PHA copolyesters, and even blocky-structured PHAs consisting of alternating soft and hard segments. Apart from enhanced productivity and constant product quality, chemostat processes can be used to elucidate kinetics of cell growth and PHA formation under constant process conditions. Furthermore, continuous enrichment processes constitute a tool to isolate novel powerful PHA-producing microbial strains adapted to special environmental conditions. The article discusses challenges, potential and case studies for continuous PHA production, and shows up new strategies to further enhance such processes economically by developing unsterile open continuous processes combined with the application of inexpensive carbon feedstocks.

Biomediated production of structurally diverse poly(hydroxyalkanoates) from surplus streams of the animal processing industry

For commercial success, enhanced poly(hydroxyalkanoate) (PHA) production must address both material performance and economic aspects. Conventional PHA production consumes expensive feedstocks dedicated to nutrition. Switching to carbon-rich (agro)industrial side-streams alleviates industrial disposal problems, preserves food resources, and can be economically superior. Processes developed in the recently performed EU-FP7 project ANIMPOL resort to lipid-rich surplus streams from slaughterhouses and the ren- dering industry; these materials undergo chemical transformation to crude glycerol phase (CGP) and bio- diesel. The saturated biodiesel share (SFAE) counteracts its applicability as a biofuel but, in addition to CGP, can be converted biotechnologically to PHAs. Depending on the applied microbial production strain and the selected carbon source (SFAE or CGP), thermoplastic short chain length PHA (scl-PHA), as well as elastome- ric to latex-like medium chain length PHA (mcl-PHA), can be produced from these inexpensive feed stocks. The article illustrates the biotechnological conversion of animal-based CGP and SFAE towards poly(3-hyd- roxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), respectively, by Cupriavi- dus necator strain DSM 545. SFAE conversion towards mcl-PHAs consisting of various saturated and unsatu- rated building blocks by two pseudomonades, Ps. citronellolis DSM 50332 and Ps. chlororaphis DSM 50083, are also shown. Together with the kinetics of the bioprocesses, the results from the characterization of isolated samples of these structurally diverse biopolyesters are compared; data demonstrate the high versatility of biopolymer properties making them applicable in various fields of the plastic market. In addition to the need for inexpensive carbon feed stocks, the article points to further hot spots of the PHA-production chain that must be considered in order to lower the overall PHA production costs, and to enhance product quality. The benefits arising from multistage continuous cultivation production set-ups, namely high-throughput pro- duction of PHA of predefined composition and constant quality, are especially discussed. Finally, contempo- rary approaches towards environmentally and ecologically sustainable PHA recovery from biomass are summarized.

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

AbstractThe efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe3)2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.

Towards a practical development of light-driven acceptorless alkane dehydrogenation.

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3)2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.

Novel Description of mcl-PHA Biosynthesis by Pseudomonas chlororaphis from Animal-Derived Waste

A novel description of mcl-PHA biosynthesis by Ps. chlororaphis from tallow-based biodiesel as an inexpensive carbon feed stock is presented. Fermentation protocols, kinetic analysis, an efficient product recovery strategy, and product characterization are included. Maximum specific growth rates (μmax.) of 0.08 h−1, 0.10 h−1 and 0.13 h−1, respectively, were achieved in three different fermentation set-ups. Volumetric productivity for mcl-PHA amounted to 0.071g/L h, 0.094g/L h and 0.138g/L h, final intracellular PHA contents calculated from the sum of active biomass and PHA from 22.1 to 29.4wt.-%, respectively. GC-FID analysis showed that the obtained biopolyester predominantly consists of 3-hydroxyoctanoate and 3-hydroxydecanoate, and, to a minor extent, 3-hydroxydodecanoate, 3-hydroxynonanoate, 3-hydroxyhexanoate, and 3-hydroxyheptanoate monomers. The overall distribution of the monomers remained similar, regardless to working volumes, biodiesel concentrations and pre-treatment of the inoculum.

Biodegradable latexes from animal-derived waste: Biosynthesis and characterization of mcl-PHA accumulated by Ps. citronellolis

Backgroundmcl-PHA biosynthesis by Pseudomonas citronellolis from tallow-based biodiesel as inexpensive carbon feed stock was accomplished. Fermentation protocols, kinetic analysis, an efficient product recovery strategy, and a detailed product characterization are presented. ResultsA maximum specific growth rate, μmax. of 0.10 and 0.08h−1, respectively, was achieved in two different fermentation set-ups. Volumetric productivity for mcl-PHA amounted to 0.036g/Lh and 0.050g/Lh, final intracellular PHA contents calculated from the sum of active biomass and PHA to 20.1 and 26.6wt.%, respectively. GC-FID analysis showed that the obtained biopolyester predominantly consists of 3-hydroxyoctanoate and 3-hydroxydecanoate, and, to a minor extent, 3-hydroxydodecanoate, 3-hydroxynonanoate, 3-hydroxyhexanoate, and 3-hydroxyheptanoate monomers. This was confirmed by 1H- and 13C NMR, also evidencing the occurrence of low quantities of unsaturated and 3-hydroxyvalerate building blocks. High purity of the recovered materials was proofed by elemental analysis. Regarding the results from thermogravimetric analysis, differential scanning calorimetry and molecular mass determination, results were in a range typical for this type of PHA (1st fermentation: decomposition temperature Td=296°C, peak of melting range Tm=48.6°C; glass transition temperature Tg=−46.9°C, degree of crystallinity Xc=12.3%, Mw=66,000, Mn=35,000, dispersity index Pi=1.9; 2nd fermentation: Td=295°C, Tm=53.6°C, Tg=-43.5°C, Xc=10.4%, Mw=78,000, Mn=196,000, Pi=2.5).