Optimizing microbial electrolysis cell performance: strategies to mitigate electron mediator degradation on membranes.

This investigation probes the role of the electron mediator, neutral red (NR), in the electrosynthesis process, specifically examining its effect on the production of succinic acid by Actinobacillus succinogenes. Our findings reveal that NR, when integrated into the cell membrane, is pivotal for sustaining MEC efficiency. Nevertheless, it is susceptible to both intrinsic and MECs-induced degradation. Notably, during the exponential growth phase of the bacteria, NR is readily incorporated into the cell membrane. However, the supplemental addition of NR fails to significantly enhance the MEC's capacity for succinic acid synthesis, no matter what stage of bacterial growth. And significant depletion of membrane-associated NR is not adequately compensated by the NR present in the fermentation liquid. The ORP feedback-regulated MECs adeptly conserve the NR on the cell membrane, which is essential for maintaining the efficiency of long-term electrosynthesis. The presence of NR on the cell membrane is essential for the functionality of MECs, yet its external replenishment hard. Implementing precise electro-potential regulation strategies can effectively diminish the degradation of NR, thus maintaining the system's efficiency.

Enhanced direct gaseous CO2 fixation into higher bio-succinic acid production and selectivity.

Utilizing CO2 for bio-succinic acid production is an attractive approach to achieve carbon capture and recycling (CCR) with simultaneous production of a useful platform chemical. Actinobacillus succinogenes and Basfia succiniciproducens were selected and investigated as microbial catalysts. Firstly, the type and concentration of inorganic carbon concentration and glucose concentration were evaluated. 6 g C/L MgCO3 and 24 g C/L glucose were found to be the optimal basic operational conditions, with succinic acid production and carbon yield of over 30 g/L and over 40%, respectively. Then, for maximum gaseous CO2 fixation, carbonate was replaced with CO2 at different ratios. The "less carbonate more CO2" condition of the inorganic carbon source was set as carbonate: CO2 = 1:9 (based on the mass of carbon). This condition presented the highest availability of CO2 by well-balanced chemical reaction equilibrium and phase equilibrium, showing the best performance with regarding CO2 fixation (about 15 mg C/(L·hr)), with suppressed lactic acid accumulation. According to key enzymes analysis, the ratio of phosphoenolpyruvate carboxykinase to lactic dehydrogenase was enhanced at high ratios of gaseous CO2, which could promote glucose conversion through the succinic acid path. To further increase gaseous CO2 fixation and succinic acid production and selectivity, stepwise CO2 addition was evaluated. 50%-65% increase in inorganic carbon utilization was obtained coupled with 20%-30% increase in succinic acid selectivity. This was due to the promotion of the succinic acid branch of the glucose metabolism, while suppressing the pyruvate branch, along with the inhibition on the conversion from glucose to lactic acid.

Mutation breeding of high-stress resistant strains for succinic acid production from corn straw.

The production of succinic acid from corn stover is a promising and sustainable route; however, during the pretreatment stage, byproducts such as organic acids, furan-based compounds, and phenolic compounds generated from corn stover inhibit the microbial fermentation process. Selecting strains that are resistant to stress and utilizing nondetoxified corn stover hydrolysate as a feedstock for succinic acid production could be effective. In this study, A. succinogenes CICC11014 was selected as the original strain, and the stress-resistant strain A. succinogenes M4 was obtained by atmospheric and room temperature plasma (ARTP) mutagenesis and further screening. Compared to the original strain, A. succinogenes M4 exhibited a twofold increase in stress resistance and a 113% increase in succinic acid production when hydrolysate was used as the substrate. By conducting whole-genome resequencing of A. succinogenes M4 and comparing it with the original strain, four nonsynonymous gene mutations and two upstream regions with base losses were identified. KEY POINTS: • A high-stress-resistant strain A. succinogenes M4 was obtained by ARTP mutation •  The production of succinic acid increased by 113% • The mutated genes of A. succinogenes M4 were detected and analyzed.

Development of highly efficient and specific base editors in Actinobacillus succinogenes for enhancing succinic acid production.

The production of bio-succinic acid (SA) from renewable feedstocks is a promising and sustainable approach to mitigating the high carbon emissions associated with the current energy crisis. Actinobacillus succinogenes was recognized as one of the most promising SA producers; however, lack of genetic background and the scarcity of genetic manipulation tools hinder the improvement in A. succinogenes by metabolic engineering. Here, for the first time, we successfully developed a series of A. succinogenes base editors (BEs) mediated by the fusion of Cas9 nickase and deaminase, including CBE, ABE, Td-GABE, and Td-CBE. Among these, ABE and Td-CBE based on a fusion of Cas9 nickase and TadA-8e variant (Escherichia coli TadA) can efficiently convert A to G and C to T, respectively, with editing efficiencies of up to 100%. We also investigated the multiplex base editing of ABE and Td-CBE, and the results showed that the editing efficiency of ABE reached 100% for six sites and 10% editing efficiency of Td-CBE for two sites. In addition, cytosine base editors were applied to inactivate hypothetical sugar and SA transporters of A. succinogenes. We found that the inactivation of Asuc_0914 encoding sucrose-specific IIBC subunit enhanced SA production, while the inactivation of hypothetical SA transporters Asuc_0715 and Asuc_0716 significantly reduced SA production. Therefore, the tools have great application potential in the metabolic engineering of A. succinogenes.

Comparative Transcriptome Analysis Reveals the Molecular Mechanisms of Acetic Acid Reduction by Adding NaHSO3 in Actinobacillus succinogenes GXAS137.

Acetic acid (AC) is a major by-product from fermentation processes for producing succinic acid (SA) using Actinobacillus succinogenes. Previous experiments have demonstrated that sodium bisulfate (NaHSO3) can significantly decrease AC production by A. succinogenes GXAS137 during SA fermentation. However, the mechanism of AC reduction is poorly understood. In this study, the transcriptional profiles of the strain were compared through Illumina RNA-seq to identify differentially expressed genes (DEGs). A total of 210 DEGs were identified by expression analysis: 83 and 127 genes up-regulated and down-regulated, respectively, in response to NaHSO3 treatment. The functional annotation analysis of DEGs showed that the genes were mainly involved in carbohydrates, inorganic ions, amino acid transport, metabolism, and energy production and conversion. The mechanisms of AC reduction might be related to two aspects: (i) the lipoic acid synthesis pathway (LipA, LipB) was significantly down-regulated, which blocked the pathway catalyzed by pyruvate dehydrogenase complex to synthesize acetyl-coenzyme A (acetyl-CoA) from pyruvate; (ii) the expression level of the gene encoding bifunctional acetaldehyde-alcohol dehydrogenase was significantly up-regulated, and this effect facilitated the synthesis of ethanol from acetyl-CoA. However, the reaction of NaHSO3 with the intermediate metabolite acetaldehyde blocked the production of ethanol and consumed acetyl-CoA, thereby decreasing AC production. Thus, our study provides new insights into the molecular mechanism of AC decreased underlying the treatment of NaHSO3 and will deepen the understanding of the complex regulatory mechanisms of A. succinogenes.

Asuc_0142 of Actinobacillus succinogenes 130Z is the l-aspartate/C4-dicarboxylate exchanger DcuA.

Anaerobic bacteria often use antiporters DcuB (malate/succinate antiport) or DcuA (l-aspartate/succinate antiport) for the excretion of succinate during fumarate respiration. The rumen bacterium Actinobacillus succinogenes is able to produce large amounts of succinate by fumarate respiration, using the DcuB-type transporter DcuE for l-malate/succinate antiport. Asuc_0142 was annotated as a second DcuB-type transporter. Deletion of Asuc_0142 decreased the uptake rate for l-[14C]aspartate into A. succinogenes cells. Properties of transport by heterologously expressed Asuc_0142 were investigated in an Escherichia coli mutant deficient of anaerobic C4DC transporters. Expression of Asuc_0142 resulted in high uptake activity for l-[14C]fumarate or l-[14C]aspartate, but the former showed a strong competitive inhibition by l-aspartate. In E. coli loaded with l-[14C]aspartate, [14C]succinate or [14C]fumarate, extracellular C4DCs initiated excretion of the intracellular substrates, with a preference for l-aspartateex/succinatein or l-aspartateex/fumaratein antiport. These findings indicate that Asuc_0142 represents a DcuA-type transporter for l-aspartate uptake and l-aspartateex/C4DCin antiport, differentiating it from the DcuB-type transporter DcuE for l-malateex/succinatein antiport. Sequence analysis and predicted structural characteristics confirm structural similarity of Asuc_0142 to DcuA, and Asuc_0142 was thus re-named as DcuAAs. The bovine rumen fluid contains l-aspartate (99.6 µM), whereas fumarate and l-malate are absent. Therefore, bovine rumen colonisers depend on l-aspartate as an exogenous substrate for fumarate respiration. A. succinogenes encodes HemG (protoporphyrinogen oxidase) and PyrD (dihydroorotate dehydrogenase) for haem and pyrimidine biosynthesis. The enzymes require fumarate as an electron acceptor, suggesting an essential role for l-aspartate, DcuAAs, and fumarate respiration for A. succinogenes growing in the bovine rumen.

Simultaneous biosuccinic production and biogas upgrading: Exploring the potential of sugar-based confectionery waste within a biorefinery concept.

The imminent need for fossil fuel independence in EU countries has led to an increased development of organic waste valorisation technologies for the production of biomethane and chemical building blocks, such as bio-succinic acid (SA). In this work, the potential of two confectionery waste, in the form of wastewater (SCWW) or a side-stream rejection (SSCW), as inexpensive carbon sources for simultaneous SA production and biogas upgrading was evaluated for the first time. Both substrates were tested batchwise with evolved Actinobacillus succinogenes cultures at different nutrient conditions, SSCW at 100 g L-1 resulting in the highest titres/productivities (∼80 g L-1 and 1.3 g L-1h-1, respectively). Then, simultaneous biogas upgrading under continuous gas feeding was studied at bioreactor-scale, higher gas residence times and pressurization leading to desirable biomethane purities (>98%). The research here conducted is crucial for the cost-effectiveness and scale-up of the technology along this new waste-based biorefinery concept.

Reduced acetic acid formation using NaHSO3 as a steering agent by Actinobacillus succinogenes GXAS137.

The high production of acetic acid (AC) as a by-product leads to difficult separation and purification of succinic acid (SA) and increases production costs in SA fermentation by Actinobacillus succinogenes. NaHSO3 as a steering agent was used to reduce AC production. Herein, the optimum fermentation conditions were achieved by single-factor and orthogonal tests as follows: glucose 60 g/L; MgCO3 60 g/L; NaHSO3 0.15% (w/v); and NaHSO3 addition time, 8 h after inoculation. After optimization, the SA and AC contents were 44.42 and 5.73 g/L. The SA improved by 100.72%, the AC decreased by 21.18% compared with the unfermented. The acetate kinase activity decreased by 14.36% and acetyl-CoA content improved by 97.55% in the group of NaHSO3 addition compared with control check (CK). The mechanism of NaHSO3 is formation acetaldehyde-sodium bisulfite compound and reduction the activity of acetate kinase. These findings indicated a new way of using NaHSO3 as a steering agent to reduce AC generation and may help promote the development of SA industrial production.

Transcriptional regulation in key metabolic pathways of Actinobacillus succinogenes in the presence of electricity.

The potential of renewable energy application via direct electrode interaction for the production of bio-based chemicals is a promising technology. The utilization of extracellular energy in pure culture fermentations aims in intracellular redox balance regulation in order to improve fermentation efficiency. This work evaluates the impact of a bioelectrochemical system in succinic acid fermentation and the metabolic response of Actinobacillus succinogenes. The metabolic pathway regulation of A. succinogenes was evaluated via RNA expression of the key enzymes that participate in TCA cycle, pyruvate metabolism and oxidative phosphorylation. The genes that were significantly overexpressed in BES compared to non-BES were phosphoenolpyruvate carboxykinase (0.4-fold change), inorganic pyrophosphatase (2.3-fold change) and hydrogenase (2.2-fold change) and the genes that were significantly underexpressed were fumarase (-0.94-fold change), pyruvate kinase (-6.9-fold change), all subunits of fumarate reductase (-2.1 to -1.17-fold change), cytochromes I and II (-1.25 and -1.02-fold change, respectively) and two C4-carboxylic acid transporters.

Effects of down-regulation of ackA expression by CRISPR-dCpf1 on succinic acid production in Actinobacillus succinogenes.

Succinic acid (SA), a key intermediate in the cellular tricarboxylic acid cycle (TCA), is a 4-carbon dicarboxylic acid of great industrial value. Actinobacillus succinogenes can ferment various carbon sources and accumulate relatively high concentrations of SA, but few reliable genetic engineering tools exist for A. succinogenes and this has hindered strain improvement to increase SA production for industrial application. Two different repressors, endonuclease-deactivated Cas9 (dCas9) from Streptococcus pyogenes and Cpf1 (dCpf1) from Francisella tularensis, were applied to construct a CRISPRi system in A. succinogenes. Codon-optimized Cas9 and native Cpf1 were successfully expressed in A. succinogenes, and the corresponding sgRNA and crRNA expression elements, promoted by the fumarate reductase promoter, frd, were introduced into the CRISPRi plasmid. The highest repression of the ackA gene (encoding acetate kinase) and thereby acetic acid production (~ eightfold) was achieved by the dCpf1-based CRISPRi system, in which the mutation site, E1006A acted at the start of the coding region of ackA, the gene which regulates acetic acid biosynthesis. Compared with the ackA gene knockout mutant, cell growth was moderately improved and SA production increased by 6.3%. Further, the SA titer and productivity in a 3 L fermenter reached 57.06 g/L and 1.87 g/L/h, and there was less acetic acid production. A dCpf1-based CRISPRi-mediated gene repression system was successfully established for the first time, providing a simple and effective tool for studying functional genomics in A. succinogenes and optimizing SA production.

Process optimisation for production and recovery of succinic acid using xylose-rich hydrolysates by Actinobacillus succinogenes.

Succinic acid (SA) is a top platform chemical obtainable from biomass. The current study evaluated the potential of Actinobacillus succinogenes for SA production using xylose-rich hemicellulosic fractions of two important lignocellulosic feedstocks, olive pits (OP) and sugarcane bagasse (SCB) and the results were compared with pure xylose. Initial experiments were conducted in shake flask followed by batch and fed-batch cultivation in bioreactor. Further separation of SA from the fermented broth was carried out by adapting direct crystallisation method. During fed-batch culture, maximum SA titers of 36.7, 33.6, and 28.7 g/L was achieved on pure xylose, OP and SCB hydrolysates, respectively, with same conversion yield of 0.27 g/g. The recovery yield of SA accumulated on pure xylose, OP and SCB hydrolysates was 79.1, 76.5, and 75.2%, respectively. The results obtained are of substantial value and pave the way for development of sustainable SA biomanufacturing in an integrated biorefinery.

Succinic acid fermentation with immobilized Actinobacillus succinogenes using hydrolysate of carbohydrate-rich microalgal biomass.

This work aimed to study the efficiency of polyvinyl-alcohol-immobilized Actinobacillus succinogenes ATCC55618 for succinic acid (SA) production. Batch fermentation (pH 7, 45% CO2 gas at 0.04 vvm) using glucose (40 g L-1) resulted in SA titer, 26.7 g L-1; productivity, 3.33 g L-1h-1; yield, 0.621 g g-1. Fed-batch mode with cyclic extrication of SA from the medium markedly enhanced the yield to 0.699 g g-1 and concentration to 59.5 g L-1. Batch fermentation using sugars derived from Chlorella vulgaris ESP-31 without yeast extract gave a SA productivity, concentration, and yield of 1.82 g L-1h-1, 36.1 g L-1, and 0.720 g g-1, respectively. Furthermore, continuous fermentation (at 6 h HRT) with microalgal sugar improved the productivity and yield to 3.53 g L-1h-1 and 0.62 g g-1, respectively, which is comparable to those obtained by using glucose. This study reports the highest productivity for SA fermentation using microalgae-derived sugars.

Batch fermentation of succinic acid from cheese whey by Actinobacillus succinogenes under variant medium composition.

Bio-based succinic acid production has attracted global attention since its consideration as a potential replacement to petroleum-based platform chemicals. This study used three different CO2 sources, namely NaHCO3, K2CO3 and MgCO3 for fermentation of succinic acid (SA) by Actinobacillus succinogenes under three distinct substrate conditions i.e. lactose, whey and whey devoid of any supplements. Batch experiments were performed in both anaerobic flasks and 5L benchtop fermenter. SA fermentation in anaerobic flasks was unfettered by supplementary nutrients. However, fermentation in the benchtop fermenter devoid of supplementary nutrients resulted into 42% reduction in SA yield as well as lower SA productivities. Furthermore, a significant reduction of cell growth occurred in anerobic flasks at pH < 6.0, and complete termination of bacterial activity was noted at pH < 5.3. The highest SA titer, yield and productivity of 15.67 g/L, 0.54 g/g and 0.33 g/L/h, respectively, was recorded from whey fermentation with MgCO3. The present study further highlights significant inhibitory effect of K2CO3 buffered medium on Actinobacillus succinogenes. Thus, we can claim that environmental pollution as well as costs of SA production from whey can be reduced by leveraging on whey residual nutrients to support the activity of Actinobacillus succinogenes.

Microbial fuel cell-assisted utilization of glycerol for succinate production by mutant of Actinobacillus succinogenes.

BACKGROUND: The global production of glycerol is increasing year by year since the demands of biodiesel is rising. It is benefit for high-yield succinate synthesis due to its high reducing property. A. succinogenes, a succinate-producing candidate, cannot grow on glycerol anaerobically, as it needs a terminal electron acceptor to maintain the balance of intracellular NADH and NAD+. Microbial fuel cell (MFC) has been widely used to release extra intracellular electrons. However, A. succinogenes is a non-electroactive strain which need the support of electron shuttle in MFC, and pervious research showed that acid-tolerant A. succinogenes has higher content of unsaturated fatty acids, which may be beneficial for the transmembrane transport of lipophilic electron shuttle. RESULTS: MFC-assisted succinate production was evaluated using neutral red as an electron shuttle to recover the glycerol utilization. First, an acid-tolerant mutant JF1315 was selected by atmospheric and room temperature plasma (ARTP) mutagenesis aiming to improve transmembrane transport of neutral red (NR). Additionally, MFC was established to increase the ratio of oxidized NR to reduced NR. By combining these two strategies, ability of JF1315 for glycerol utilization was significantly enhanced, and 23.92 g/L succinate was accumulated with a yield of 0.88 g/g from around 30 g/L initial glycerol, along with an output voltage above 300 mV. CONCLUSIONS: A novel MFC-assisted system was established to improve glycerol utilization by A. succinogenes for succinate and electricity production, making this system as a platform for chemicals production and electrical supply simultaneously.

Succinic acid production from pulp and paper industry waste: A transcriptomic approach.

The fermentative production of biobased chemicals and polymers using crude lignocellulose hydrolysates is challenging due to the presence of various inhibitory compounds and multiple sugars. This study evaluates the metabolic response of Actinobacillus succinogenes for the production of succinic acid using spent sulphite liquor (SSL) as feedstock derived from industrial acidic sulphite pulping of Eucalyptus globulus hardwood. A transcriptomic approach led to significant insights on gene regulation of the major metabolic pathways (glycolysis, pentose phosphate pathway, TCA cycle, pyruvate metabolism and oxidative phosphorylation) in batch cultures carried out on SSL and compared with glucose and xylose. Significantly overexpressed genes in SSL compared to glucose and xylose were fructose biphosphate aldolase (> 1.18-fold change) in the catabolism, phosphoenolpyruvate carboxykinase (> 1.59-fold change) and malate dehydrogenase (> 1.49-fold change) in the TCA cycle, citrate lyase (> 1.7-fold change), dihydrolipoamide dehydrogenase (> 0.88-fold change), pyruvate dehydrogenase E2 (> 1.63-fold change) and pyruvate formate lyase (> 0.61-fold change), involved in acetyl-CoA pathways. Finally, C4 tricarboxylic transporters were overexpressed (DCU (> 1.61-fold change) and 0079 (> 4.19-fold change). SSL was responsible for the upregulation of genes involved in the TCA cycle and oxidative phosphorylation, while xylose showed similar results with SSL in the oxidative phosphorylation.

Succinic acid production from whey and lactose by Actinobacillus succinogenes 130Z in batch fermentation.

This study focuses on succinic acid production by Actinobacillus succinogenes in batch fermentation from whey and lactose widely encountered in dairy effluents. The effects of initial whey and lactose concentration, CO2 rate on succinic acid production were investigated. The optimal succinic acid production was obtained with 25 g L-1 of lactose and 35 g L-1 of whey with yields and productivities respectively of 65% and 0.9 g L-1 h-1 for lactose and 62.1%, 0.81 g L-1 h-1 for whey. The maximum yield and productivity of succinic acid was obtained with lactose in comparison with whey. Productivity and yield decreased when the amount of initial lactose was increased. Biomass, acetic acid and formic acid increased when whey was used as a substrate compared to lactose. Succinic acid production by anaerobic fermentation is a green biotechnology alternative to valorize whey and lactose from dairy effluent and to reduce their impact on the environment.

Evaluation of organic fractions of municipal solid waste as renewable feedstock for succinic acid production.

BACKGROUND: Despite its high market potential, bio-based succinic acid production experienced recently a declining trend because the initial investments did not meet the expectations for rapid market growth. Thus, reducing the succinic acid production cost is imperative to ensure industrial implementation. RESULTS: Succinic acid production has been evaluated using hydrolysates from the organic fraction of municipal solid waste (OFMSW) collected from MSW treatment plants. A tailor-made enzymatic cocktail was used for OFMSW hydrolysate production containing up to 107.3 g/L carbon sources and up to 638.7 mg/L free amino nitrogen. The bacterial strains Actinobacillus succinogenes and Basfia succiniciproducens were evaluated for succinic acid production with the latter strain being less efficient due to high lactic acid production. Batch A. succinogenes cultures supplemented with 5 g/L yeast extract and 5 g/L MgCO3 reached 29.4 g/L succinic acid with productivity of 0.89 g/L/h and yield of 0.56 g/g. Continuous cultures at dilution rate of 0.06 h-1 reached 21.2 g/L succinic acid with yield of 0.47 g/g and productivity of 1.27 g/L/h. Downstream separation and purification of succinic acid was achieved by centrifugation, treatment with activated carbon, acidification with cation exchange resins, evaporation and drying, reaching more than 99% purity. Preliminary techno-economic evaluation has been employed to evaluate the profitability potential of bio-based succinic acid production. CONCLUSIONS: The use of OFMSW hydrolysate in continuous cultures could lead to a minimum selling price of 2.5 $/kg at annual production capacity of 40,000 t succinic acid and OFMSW hydrolysate production cost of 25 $/t sugars.

Effect of shear on morphology, viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms.

Two custom-designed bioreactors were used to evaluate the effect of shear on biofilms of a succinic acid producer, Actinobacillus succinogenes. The first bioreactor allowed for in situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. The smooth, low porosity biofilms obtained under high shear conditions had an average cell viability of 79% compared to 57% at the lowest shear used. The maximum cell-based succinic acid productivity for high shear biofilm was 2.4 g g-1DCW h-1 compared to the 0.8 g g-1DCW h-1 of the low shear biofilm. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays confirmed higher cell metabolic activities for high shear developed biofilm compared to biofilm developed at low shear conditions. Results clearly indicated that high shear biofilm cultivation has beneficial morphological, viability, and cell-based productivity characteristics.

Adaptation of Methanosarcina barkeri 227 as acetate scavenger for succinate fermentation by Actinobacillus succinogenes.

Acetate is the main by-product from microbial succinate production. In this study, we performed acetate removal by Methanosarcina barkeri 227 for succinate fermentation by Actinobacillus succinogenes 130Z. The acetoclastic methanogen M. barkeri requires similar environmental factors to A. succinogenes, and the conditions required for co-cultivation were optimized in this study: gas used for anaerobicization, strain adaptation, medium composition, pH adjustment, and inoculation time points. M. barkeri 227 was adapted to acetate for 150 days, which accelerated the acetate consumption to 9-fold (from 190 to 1726 mmol gDW-1 day-1). In the acetate-adapted strain, there was a noticeable increase in transcription of genes required for acetoclastic pathway-satP (acetate transporter), ackA (acetate kinase), cdhA (carbon monoxide dehydrogenase/acetyl-CoA synthase complex), and mtrH (methyl-H4STP:CoM methyltransferase), which was not induced before the adaptation process. The activities of two energy-consuming steps in the pathway-acetate uptake and acetate kinase-increased about 3-fold. This acetate-adapted M. barkeri could be successfully applied to succinate fermentation culture of A. succinogenes, but only after pH adjustment following completion of fermentation. This study suggests the utility of M. barkeri as an acetate scavenger during fermentation for further steps towards genetic and process engineering.

An evaluation of thermal characteristics of bacterium Actinobacillus succinogenes for energy use and circular bioeconomy.

The thermal characteristics of Actinobacillus succinogenes (AS) from pyrolysis, torrefaction, and combustion are analyzed to evaluate the potential of this biomass as a renewable fuel. AS pyrolysis can be classified into four stages, and its main decomposition zone is at 200-500 °C. The solid yield of AS after 60 min torrefaction is over 60 wt%, and the torrefaction severity index map indicates that a high torrefaction temperature with a short duration has a more profound influence on its decomposition. The Py-GC/MS analysis of AS suggests that the volatile products from 500 °C pyrolysis are similar to microalgae-derived pyrolysis bio-oils. The combustibility index (S) of AS is 4.07 × 10-7 which is much higher than that of lignite coal (0.39 × 10-7) and bituminous coal (0.18 × 10-7), and close to those of biochar and bio-oil. The obtained results are conducive to the development of microorganisms as fuel to achieve a circular bioeconomy.