Production Of Acetone Research Articles

Assembly-Line Catalysis in Bifunctional Terpene Synthases.

The magnificent chemodiversity of more than 95 000 terpenoid natural products identified to date largely originates from catalysis by two types of terpene synthases, prenyltransferases and cyclases. Prenyltransferases utilize 5-carbon building blocks in processive chain elongation reactions to generate linear C5n isoprenoid diphosphates (n ≥ 2), which in turn serve as substrates for terpene cyclases that convert these linear precursors into structurally complex hydrocarbon products containing multiple rings and stereocenters. Terpene cyclization reactions are the most complex organic transformations found in nature in that more than half of the substrate carbon atoms undergo changes in chemical bonding during a multistep reaction sequence proceeding through several carbocation intermediates. Two general classes of cyclases are established on the basis of the chemistry of initial carbocation formation, and structural studies from our laboratory and others show that three fundamental protein folds designated α, β, and γ govern this chemistry. Catalysis by a class I cyclase occurs in an α domain, where a trinuclear metal cluster activates the substrate diphosphate leaving group to generate an allylic cation. Catalysis by a class II cyclase occurs in a β domain or at the interface of β and γ domains, where an aspartic acid protonates the terminal π bond of the substrate to yield a tertiary carbocation. Crystal structures reveal domain architectures of α, αβ, αβγ, βγ, and β.In some terpene synthases, these domains are combined to yield bifunctional enzymes that catalyze successive biosynthetic steps in assembly line fashion. Structurally characterized examples include bacterial geosmin synthase, an αα domain enzyme that catalyzes a class I cyclization reaction of C15 farnesyl diphosphate in one active site and a transannulation-fragmentation reaction in the other to yield C12 geosmin and C3 acetone products. In comparison, plant abietadiene synthase is an αβγ domain enzyme in which C20 geranylgeranyl diphosphate undergoes tandem class II-class I cyclization reactions to yield the tricyclic product. Recent structural studies from our laboratory show that bifunctional fungal cyclases form oligomeric complexes for assembly line catalysis. Bifunctional (+)-copalyl diphosphate synthase adopts (αβγ)6 architecture in which the α domain generates geranylgeranyl diphosphate, which then undergoes class II cyclization in the βγ domains to yield the bicyclic product. Bifunctional fusicoccadiene synthase adopts (αα)6 or (αα)8 architecture in which one α domain generates geranylgeranyl diphosphate, which then undergoes class I cyclization in the other α domain to yield the tricyclic product. The prenyltransferase α domain mediates oligomerization in these systems. Attached by flexible polypeptide linkers, cyclase domains splay out from oligomeric prenyltransferase cores.In this Account, we review structure-function relationships for these bifunctional terpene synthases, with a focus on the oligomeric systems studied in our laboratory. The observation of substrate channeling for fusicoccadiene synthase suggests a model for dynamic cluster channeling in catalysis by oligomeric assembly line terpenoid synthases. Resulting efficiencies in carbon management suggest that such systems could be particularly attractive for use in synthetic biology approaches to generate high-value terpenoid natural products.

Metabolic engineering of Moorella thermoacetica for thermophilic bioconversion of gaseous substrates to a volatile chemical

Gas fermentation is one of the promising bioprocesses to convert CO2 or syngas to important chemicals. Thermophilic gas fermentation of volatile chemicals has the potential for the development of consolidated bioprocesses that can simultaneously separate products during fermentation. This study reports the production of acetone from CO2 and H2, CO, or syngas by introducing the acetone production pathway using acetyl–coenzyme A (Ac-CoA) and acetate produced via the Wood–Ljungdahl pathway in Moorella thermoacetica. Reducing the carbon flux from Ac-CoA to acetate through genetic engineering successfully enhanced acetone productivity, which varied on the basis of the gas composition. The highest acetone productivity was obtained with CO–H2, while autotrophic growth collapsed with CO2–H2. By adding H2 to CO, the acetone productivity from the same amount of carbon source increased compared to CO gas only, and the maximum specific acetone production rate also increased from 0.04 to 0.09 g-acetone/g-dry cell/h. Our development of the engineered thermophilic acetogen M. thermoacetica, which grows at a temperature higher than the boiling point of acetone (58 °C), would pave the way for developing a consolidated process with simplified and cost-effective recovery via condensation following gas fermentation.

Disruption of hydrogenase gene for enhancing butanol selectivity and production in Clostridium acetobutylicum

Butanol production by solventogenic clostridia has long been complicated with the formation of acetone as a main byproduct, which causes a low product yield. Here, although some recent attempts failed to engineer the hydrogenase gene hydA in wild-type Clostridium, we successfully disrupted hydA with a plasmid pSY6 in C. acetobutylicum ATCC 55025. The hydA disrupted strain was able to produce 18.3 % more butanol with by-product acetone decreased by 31.2 %, indicating the inactivation of hydrogenase regulated redox balance for selective inhibition of acetone production. Exogenous supplementation of methyl viologen altered the carbon flux and further reduced acetone formation, with the maximum butanol yield of 0.28 g/g and butanol ratio of 84.0 %, respectively. The similar improvements of butanol yield and ratio were observed with corn stover as carbon source, indicating hydA disrupted strain had the potential for biobutanol production using lignocellulosic biomass. This study provides valuable understanding for regulation of redox and solventogenesis by engineering hydrogenase in Clostridium species towards the advanced production of butanol.

Process Engineering of the Acetone-Ethanol-Butanol (ABE) Fermentation in a Linear and Feedback Loop Cascade of Continuous Stirred Tank Reactors: Experiments, Modeling and Optimization

The production of butanol, acetone and ethanol by Clostridium acetobutylicum is a biphasic fermentation process. In the first phase the carbohydrate substrate is metabolized to acetic and butyric acid, in the following second phase the product spectrum is shifted towards the economically interesting solvents. Here we present a cascade of six continuous stirred tank reactors (CCSTR), which allows performing the time dependent metabolic phases of an acetone-butanol-ethanol (ABE) batch fermentation in a spatial domain. Experimental data of steady states under four operating conditions—with variations of the pH in the first bioreactor between 4.3 and 5.6 as well as the total dilution rate between 0.042 h−1 and 0.092 h−1—were used to optimize and validate a corresponding mathematical model. Beyond a residence time distribution representation and substrate, biomass and product kinetics this model also includes the differentiation of cells between the metabolic states. Model simulations predict a final product concentration of 8.2 g butanol L−1 and a productivity of 0.75 g butanol L−1 h−1 in the CCSTR operated at pHbr1 of 4.3 and D = 0.092 h−1, while 31% of the cells are differentiated to the solventogenic state. Aiming at an enrichment of solvent-producing cells, a feedback loop was introduced into the cascade, sending cells from a later state of the process (bioreactor 4) back to an early stage of the process (bioreactor 2). In agreement with the experimental observations, the model accurately predicted an increase in butanol formation rate in bioreactor stages 2 and 3, resulting in an overall butanol productivity of 0.76 g L−1 h−1 for the feedback loop cascade. The here presented CCSTR and the validated model will serve to investigate further ABE fermentation strategies for a controlled metabolic switch.

Direct conversion of dimethyl ether and CO to acetone via coupling carbonylation and ketonization

Acetone is currently produced by large amount of propylene and benzene, and its synthesis from a cheap and non-petroleum material has not yet been reported. Here, we present a new method for acetone production, which involves the carbonylation of dimethyl ether (DME) to methyl acetate and its subsequent ketonization to acetone over pyridine-modified H-mordenite. This convenient approach offers an acetone selectivity of 73% (CO2 excluded) and a DME conversion of 100% at 553 K. Spectral and isotopic studies revealed that the ketonization of methyl acetate was promoted by carbonylation, while the formation of a ketene intermediate was demonstrated by the formation of CH2DCOOD and two types of pyrones. A ketene-based ketonization mechanism was also proposed based on the kinetic isotope effect of CH2=13CO, indicating that the acetyl moiety contributed to the acyl part of acetone, while the ketene moiety was responsible for the alkyl part of acetone and the generation of CO2.

Transition Metal B-Site Substitutions in LaAlO3 Perovskites Reorient Bio-Ethanol Conversion Reactions

LaAlO3 perovskites, as such and with 25% molar Al substitution by Cu, Co, or Ga, have been prepared by sol-gel methods and tested as heterogeneous catalysts in the gas-phase conversion of ethanol. LaAlO3 presented a significant acidic character, with high formation of ethylene by ethanol dehydration. B-site substitutions increased the basicity of the catalysts, favoring the dehydrogenation of ethanol to acetaldehyde. The most reducible Cu- and Co-substituted materials, characterized by easier formation of surface oxygen vacancies, promoted the self-condensation of acetaldehyde by the Tishchenko mechanism, with formation of acetone and odd-carbon number products. Aldol coupling of acetaldehyde, favored on pure and Ga-substituted LaAlO3, led to the formation of butadiene and hexadiene. The role of Ga insertion, favoring both dehydrogenation of ethylene and dehydration of higher alcohols, corresponds to an amphoteric character. The formation of olefins and diolefins on all catalysts suggests that LaAl-based materials present the most acidic character among La-perovskites.

Eggshells as a sustainable source for acetone production

Everyday, tons of food wastes are thrown to the environment constantly by people in the cities, which contain many beneficial substances. One of these beneficial wastes of unknown value is eggshells. Although the eggshells are considered negligible and not valuable material, however, the many researches that dealt with this substance proved its high potential to turn into many useful substances such as a catalyst in biodiesel preparation or as a media for adsorption of heavy metals and dyes or soil fertilizer and others. The current study highlighted the benefit possibility of white chicken eggshells (WCES) from another side, considering it as a raw material for preparing acetone one of the most important industrial solvents. The results obtained showed that this worthless raw material has a high effectiveness for acetone production by containing 94.519% by weight of calcium carbonate. The process of converting WCES to acetone was carried out in two steps, the first one were producing calcium acetate by treating it with glacial acetic acid in a batch mode reaction unit at room temperature and agitation speed, acid % excess and contact time of 200 rpm, 20% and 2 h respectively. Whereas, the next step involved conducting the process of thermal decomposition of the prepared calcium acetate at 380 °C to produce acetone in a stainless steel reactor. The results of testing the samples by the gas chromatography (GC) showed that the maximum yield of acetone is 96.395%. With these experimental results, this study presents a new idea in food waste management as one of the solid waste types by utilizing it in a useful manner to produce important materials in an economical, beneficial and environmentally friendly way, reaching to the concept of zero residue level (ZRL).

Acetone, Butanol, Ethanol and, Xylitol Production Through a Biorefinery Platform: An Experimental & Simulation Approach

Butanol is an interesting biofuel and a product precursor, that could be obtained with acetone and ethanol via fermentation. The biofuels production has been identified as not economically competitive, thus, the parallel production of high value-added products, such as xylitol, could be an alternative to improve the profit. Xylitol can be produced from xylose, which might be considered as a coproduct in a second generation biorefinery. This study presents a systematic biorefinery process design for the simultaneous acetone, butanol, ethanol (ABE) and xylitol production, based on experimental and simulation approaches. Experiments were performed for the pretreatment of sugarcane bagasse and ABE fermentation. The simulation part used the experimental results and experimental data from literature, to perform rigorous calculations of the ABE and xylitol production process. The economic analysis (EA) was performed relying on some indicators such as, the net present value (NPV) and payback period (PBP); EA includes several scenarios for producing only ABE and some scenarios for simultaneous ABE and xylitol production. The results showed that the combined butanol and xylitol production could reduce by 17% the selling price of butanol, compared with only producing butanol. The study also included the combustion of residual solids and carbon dioxide depletion analyses. This approach illustrates the opportunity to perform a rigorous techno-economic analysis, to identify the feasibility of the process at industrial scale, based on realistic data. This approach was implemented for ABE and xylitol production, but it can be used to any other bioproduct.

Liquid-phase synthesis of methyl isobutyl ketone over bifunctional heterogeneous catalysts comprising cross-linked perfluorinated sulfonic acid Aquivion polymers and supported Pd nanoparticles

The solvent-free hydrogenation reaction of acetone over bifunctional heterogeneous catalysts, comprising cross-linked perfluorosulfonic acid (PFSA) resins and supported Pd nanoparticles, was investigated in the liquid phase under batch conditions. A systematic study was performed by analyzing separately the effect of the main reaction parameters on the reaction outputs. Acetone conversion, selectivity and productivity to methyl isobutyl ketone (MIBK) were measured as a function of the reaction temperature, the amount of catalyst, the Pd loading, the H2 pressure, the reaction time and the cross-linkage of the polymeric support. Reproducible trends were observed that could be explained in terms of properties of the catalyst, conversion path and kinetics. Best compromise results between selectivity (92 %) and productivity (37.0 mmolMIBK gcat−1 h-1) at 19.7 % acetone conversion were obtained for the 0.26Pd@X-link-08-PW79 catalyst, based on 0.8 % cross-linked PFSA support and 0.26 % wt Pd content.

Influence of composition and morphology of the active phase on the catalytic properties of cobalt-nickel catalysts in the steam reforming of ethanol

Potassium promoted monometallic and bimetallic cobalt-nickel catalysts with CeO2 support were characterized in the fresh, reduced and after steam reforming of ethanol (SRE) form. TEM studies of reduced catalysts showed the formation of Co0 or Ni0 forms of active phase with fcc structure in the monometallic catalysts and Co–Ni alloys (fcc) with different proportion Co and Ni in the bimetallic catalysts.Among all tested catalysts, the nickel catalyst indicated the smallest crystallites of active phase (8.4 nm), while the cobalt catalyst indicated the largest crystallites of active phase (12.2 nm). The more cobalt in the active phase of catalysts was, the larger the crystallite size of active phase were.The catalytic studies showed that the increase in the content of nickel in the active phase of catalysts increased the selectivity of the SRE to methane, while the increase in the content of cobalt in the active phase caused an increase in the production of acetaldehyde and acetone. Furthermore, the more nickel in the active phase was, the more stable catalysts were.After 24 h work of catalysts in the SRE, nickel and Co–Ni (fcc) active phases were stable forms under SRE conditions, while the cobalt active phase was observed in two forms: metallic cobalt (fcc) and cobalt oxide (CoO). Moreover, on the cobalt catalyst dominated the encapsulating carbon deposit, whereas on the nickel catalyst the fibrous deposit was dominated. Encapsulating carbon deposit cause faster deactivation of the catalyst than fibrous deposit which explained the various stability of both catalysts in the SRE.

Biological production of hydrogen and acetone- butanol-ethanol from sugarcane bagasse and rice straw using co-culture of Enterobacter aerogenes and Clostridium acetobutylicum

Production of hydrogen and acetone-butanol-ethanol (ABE) from hydrolysates of sugarcane bagasse (SCB) and rice-straw (RS) was carried out via dark fermentation using co-culture of Enterobacter aerogenes and Clostridium acetobutylicum. The best improvement in the yield of hydrogen and total ABE production were observed for alkaline pretreated RS at 100 °C for 60 min obtained from the highest total reducing sugars concentration of 40.7 g L−1 after the enzymatic hydrolysis. The hydrolysates of alkaline pretreated samples at 100 °C were efficiently converted to H2 by co-culture of Enterobacter aerogenes and Clostridium acetobutylicum with the highest hydrogen yield of 136.3 and 149.9 mL H2 g−1-VS of SCB and RS, representing 3.4 and 1.5-fold enhancement in the hydrogen production yield over that obtained from the pure cultures of Enterobacter aerogenes and Clostridium acetobutylicum, respectively. Mass balance and energy generation analysis indicate that the highest specific ABE and total energy production yields per gram untreated feedstock reached 0.12 g ABE and 5.5 kJ for SCB and 0.08 g ABE and 6.6 kJ for RS.

Computer-Aided Environmental Assessment Applied for Estimation of Ecological Impacts Derived from Topological Pathways Based on Lignocellulosic Biomass Transformation

The growing awareness to include sustainability goals in the chemical process design has been making palpable since many governments and research institutions have made many efforts precisely to progress new ways to transform available resources into valuable chemicals. In this sense, this work is presenting a computer-aided evaluation based on environmental impact assessment and comparison of technical parameters for estimating the potential effects of two biorefinery designs. The first process involved a multiproduct production of acetone, butanol, and ethanol from cassava waste, while the second biorefinery comprised of succinic acid and bioethanol production from a mixture of cassava waste and banana rachis. These residues are highly available in the North Colombia region due to the agroindustrial activities of that zone. The developed environmental analysis employed the waste reduction algorithm (WAR) for estimating impact generation and output rates considering atmospheric and toxicological categories. Otherwise, process simulation of biorefineries showed production of 546.3 kg/h of acetone, 280.0 kg/h of ethanol, and 1305 kg/h of butanol for topology 1, while topology 2 delivered a synthesis of 13,865.7 kg/h of acetic acid and 2277.9 kg/h of ethanol. Data generated from process simulation allowed performing a technical comparison between evaluated biorefineries, showing a higher performance of evaluated indicators for topology 2. These evaluated variables included resource energy efficiency, and production yield, among others. The environmental analysis provided relevant information, indicating that topology 2 is a better alternative from an ecological viewpoint since this design would emit substances with lower effects than topology 1.

Localized surface plasmonic resonance role of silver nanoparticles in the enhancement of long-chain hydrocarbons of the CO2 reduction over Ag-gC3N4/ZnO nanorods photocatalysts

The conversion of CO2 into hydrocarbon fuels via the photocatalytic reaction route is considered a potential strategy to concurrently address serious energy crisis and greenhouse gas emission problems. Nevertheless, the generation of long-chain hydrocarbon products (Cn, n ≥ 2) from the visible-light-reactive photocatalytic CO2 reduction has also been considering a contemporary challenge. Herein, we indicate that Ag nanoparticles (Ag NPs) loaded gC3N4/ZnO nanorods heterojunction (Ag-gC3N4/ZnO NRs abbreviation) has extended photoactive range and enhanced specific surface area. The combination of Ag NPs and gC3N4/ZnO NRs significantly enhances photocatalytic CO2 reduction efficiency to form the acetone product. Detail, the acetone production efficiency of Ag-gC3N4/ZnO NRs is 8.4 and 7.5 times higher than pure ZnO NRs and gC3N4/ZnO NRs at the same condition, respectively. This study represents a potential approach toward higher-energy-value hydrocarbons production and greenhouse gas emission mitigation.

Recent advances in n-butanol and butyrate production using engineered Clostridium tyrobutyricum.

Acidogenic clostridia naturally producing acetic and butyric acids has attracted high interest as a novel host for butyrate and n-butanol production. Among them, Clostridium tyrobutyricum is a hyper butyrate-producing bacterium, which re-assimilates acetate for butyrate biosynthesis by butyryl-CoA/acetate CoA transferase (CoAT), rather than the phosphotransbutyrylase-butyrate kinase (PTB-BK) pathway widely found in clostridia and other microbial species. To date, C. tyrobutyricum has been engineered to overexpress a heterologous alcohol/aldehyde dehydrogenase, which converts butyryl-CoA to n-butanol. Compared to conventional solventogenic clostridia, which produce acetone, ethanol, and butanol in a biphasic fermentation process, the engineered C. tyrobutyricum with a high metabolic flux toward butyryl-CoA produced n-butanol at a high yield of > 0.30g/g and titer of > 20g/L in glucose fermentation. With no acetone production and a high C4/C2 ratio, butanol was the only major fermentation product by the recombinant C. tyrobutyricum, allowing simplified downstream processing for product purification. In this review, novel metabolic engineering strategies to improve n-butanol and butyrate production by C. tyrobutyricum from various substrates, including glucose, xylose, galactose, sucrose, and cellulosic hydrolysates containing the mixture of glucose and xylose, are discussed. Compared to other recombinant hosts such as Clostridium acetobutylicum and Escherichia coli, the engineered C. tyrobutyricum strains with higher butyrate and butanol titers, yields and productivities are the most promising hosts for potential industrial applications.

Optimisation of solvent recovery in two batch distillation columns of different size

The recovery of acetone from an aqueous industrial waste solvent mixture containing a small amount of dichloromethane is studied. This separation can be performed in a single, large enough batch distillation column. When the amount of the waste solvent mixture increases and exceeds the processing capacity of this column, either the excess of solvent must be incinerated, or the processing capacity must be increased. The incineration is very disadvantageous from both economic and environmental points of view. It is investigated whether capacity can be efficiently increased by applying an additional, much smaller column, which is already available in the plant. Dichloromethane is removed in fore-cuts from both columns. The charge of the larger column (Column2) consists of two main cuts obtained from two consecutive batches of Column1. High purity acetone is obtained in the main cut of Column2. The optimisation of both the single- and two-column processes is performed by a genetic algorithm coupled with a professional flow-sheet simulator. The objective function minimised is the specific energy demand of the production of acetone. The effects of the composition of the fresh feed on the optimal values of the parameters and of the objective function are studied: the specific energy demand changes favourably on the increase of water and the decrease of dichloromethane concentration. A response surface method is used to successfully predict the optimal operating parameters in the space of compositions studied. Each optimised case is evaluated from economic and environmental points of view, as well. For an average charge composition, also by considering recycling of the residues of both columns, the weekly profit is by 12% higher and the CO2 emission is by more than 20% lower compared to the single-column process. Moreover, the processing capacity is increased by about 30%. It is shown in our work that it is worth applying a second, possibly smaller batch distillation column available in the plant before a larger one in order to increase the processing capacity.

Secondary Alcohols as Rechargeable Electrofuels: Electrooxidation of Isopropyl Alcohol at Pt Electrodes

Fuel cells can be operated directly by oxidation of isopropyl alcohol (IPA) to acetone (ACE). If the product ACE is hydrogenated, IPA is formed again. In this way, IPA serves as a rechargeable elec...

RRNPP-type quorum sensing affects solvent formation and sporulation in Clostridium acetobutylicum.

The strictly anaerobic bacterium Clostridium acetobutylicum is well known for its ability to convert sugars into organic acids and solvents, most notably the potential biofuel butanol. However, the regulation of its fermentation metabolism, in particular the shift from acid to solvent production, remains poorly understood. The aim of this study was to investigate whether cell–cell communication plays a role in controlling the timing of this shift or the extent of solvent formation. Analysis of the available C. acetobutylicum genome sequences revealed the presence of eight putative RRNPP-type quorum-sensing systems, here designated qssA to qssH, each consisting of an RRNPP-type regulator gene followed by a small open reading frame encoding a putative signalling peptide precursor. The identified regulator and signal peptide precursor genes were designated qsrA to qsrH and qspA to qspH, respectively. Triplicate regulator mutants were generated in strain ATCC 824 for each of the eight systems and screened for phenotypic changes. The qsrB mutants showed increased solvent formation during early solventogenesis and hence the QssB system was selected for further characterization. Overexpression of qsrB severely reduced solvent and endospore formation and this effect could be overcome by adding short synthetic peptides to the culture medium representing a specific region of the QspB signalling peptide precursor. In addition, overexpression of qspB increased the production of acetone and butanol and the initial (48 h) titre of heat-resistant endospores. Together, these findings establish a role for QssB quorum sensing in the regulation of early solventogenesis and sporulation in C. acetobutylicum .

CATALYTIC SYNTHESIS OF A LINE BY ACETYLENE HYDRATION

Acetone is a valuable chemical product. It can be obtained by oxidative dehydrogenation of isopropyl alcohol, oxidation of propylene, decomposition of acetic acid and ethyl alcohol, oxidation of cymene and others. Among the known processes for the production of acetone, the most promising is the synthesis by hydration of acetylene in the presence of catalysts. The advantage of this method is the possibility of carrying out the process in existing plants for the production of acetic aldehyde. On the other hand, the process of simultaneously producing acetaldehyde and acetone under the influence of multifunctional catalysts and carrying out the process using flexible technology is promising. The vapor-phase hydration of acetylene with the formation of acetone on polyfunctional catalysts was studied. Process parameters are found that provide acetone with high selectivity and acetylene conversion. At present, acetic aldehyde is mainly obtained by two methods - hydration of acetylene and oxidation of ethylene. The process of hydration of acetylene to acetic aldehyde in the presence of catalysts has been studied quite well. Numerous catalysts have been proposed for this process. Among the known catalysts for hydration of acetylene to acetic aldehyde, the most active was the cadmium calcium phosphate catalyst (CCF), which is recommended for industrial use. However, cadmium calcium phosphate catalyst is not without drawbacks. The average yield of acetaldehyde in one pass of acetylene does not exceed 7.0%. The CCF catalyst is very sensitive to temperature changes, its service life before regeneration does not exceed 72-76 hours. Keywords: acetone, propylene, hydration process, catalyst, crosslinking, multifunctional properties.

Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the southwest Pacific Ocean

Abstract. Atmospheric methanethiol (MeSHa), dimethyl sulfide (DMSa) and acetone (acetonea) were measured over biologically productive frontal waters in the remote southwest Pacific Ocean in summertime 2012 during the Surface Ocean Aerosol Production (SOAP) voyage. MeSHa mixing ratios varied from below the detection limit (< 10 ppt) up to 65 ppt and were 3 %–36 % of parallel DMSa mixing ratios. MeSHa and DMSa were correlated over the voyage (R2=0.3, slope = 0.07) with a stronger correlation over a coccolithophore-dominated phytoplankton bloom (R2=0.5, slope 0.13). The diurnal cycle for MeSHa shows similar behaviour to DMSa with mixing ratios varying by a factor of ∼ 2 according to time of day with the minimum levels of both MeSHa and DMSa occurring at around 16:00 LT (local time, all times in this paper are in local time). A positive flux of MeSH out of the ocean was calculated for three different nights and ranged from 3.5 to 5.8 µmol m−2 d−1, corresponding to 14 %–24 % of the DMS flux (MeSH ∕ (MeSH + DMS)). Spearman rank correlations with ocean biogeochemical parameters showed a moderate-to-strong positive, highly significant relationship between both MeSHa and DMSa with seawater DMS (DMSsw) and a moderate correlation with total dimethylsulfoniopropionate (total DMSP). A positive correlation of acetonea with water temperature and negative correlation with nutrient concentrations are consistent with reports of acetone production in warmer subtropical waters. Positive correlations of acetonea with cryptophyte and eukaryotic phytoplankton numbers, and high-molecular-weight sugars and chromophoric dissolved organic matter (CDOM), suggest an organic source. This work points to a significant ocean source of MeSH, highlighting the need for further studies into the distribution and fate of MeSH, and it suggests links between atmospheric acetone levels and biogeochemistry over the mid-latitude ocean. In addition, an intercalibration of DMSa at ambient levels using three independently calibrated instruments showed ∼ 15 %–25 % higher mixing ratios from an atmospheric pressure ionisation chemical ionisation mass spectrometer (mesoCIMS) compared to a gas chromatograph with a sulfur chemiluminescence detector (GC-SCD) and proton transfer reaction mass spectrometer (PTR-MS). Some differences were attributed to the DMSa gradient above the sea surface and differing approaches of integrated versus discrete measurements. Remaining discrepancies were likely due to different calibration scales, suggesting that further investigation of the stability and/or absolute calibration of DMS standards used at sea is warranted.

Engineering Escherichia coli for methanol-dependent growth on glucose for metabolite production

Synthetic methylotrophy aims to engineer methane and methanol utilization pathways in platform hosts like Escherichia coli for industrial bioprocessing of natural gas and biogas. While recent attempts to engineer synthetic methanol auxotrophs have proved successful, these studies focused on scarce and expensive co-substrates. Here, we engineered E. coli for methanol-dependent growth on glucose, an abundant and inexpensive co-substrate, via deletion of glucose 6-phosphate isomerase (pgi), phosphogluconate dehydratase (edd), and ribose 5-phosphate isomerases (rpiAB). Since the parental strain did not exhibit methanol-dependent growth on glucose in minimal medium, we first achieved methanol-dependent growth via amino acid supplementation and used this medium to evolve the strain for methanol-dependent growth in glucose minimal medium. The evolved strain exhibited a maximum growth rate of 0.15 h−1 in glucose minimal medium with methanol, which is comparable to that of other synthetic methanol auxotrophs. Whole genome sequencing and 13C-metabolic flux analysis revealed the causative mutations in the evolved strain. A mutation in the phosphotransferase system enzyme I gene (ptsI) resulted in a reduced glucose uptake rate to maintain a one-to-one molar ratio of substrate utilization. Deletion of the e14 prophage DNA region resulted in two non-synonymous mutations in the isocitrate dehydrogenase (icd) gene, which reduced TCA cycle carbon flux to maintain the internal redox state. In high cell density glucose fed-batch fermentation, methanol-dependent acetone production resulted in 22% average carbon labeling of acetone from 13C-methanol, which far surpasses that of the previous best (2.4%) found with methylotrophic E. coli Δpgi. This study addresses the need to identify appropriate co-substrates for engineering synthetic methanol auxotrophs and provides a basis for the next steps toward industrial one-carbon bioprocessing.