Main By-product Research Articles

Nutrition promotion of brewer's spent grain by symbiotic fermentation adding Bacillus velezensis and Levilactobacillus brevis

Brewer's spent grain (BSG) is the main byproduct of the beer industry and is commonly used as a low-value animal feed or food ingredient. This study investigated the role of symbiotic fermentation with Bacillus velezensis and Levilactobacillus brevis in improving the nutritional value of BSG. The addition of B. velezensis increased the cell growth of L. brevis by over thirty-fold higher than that in the single-strain system. Simultaneously, cellulase and protease activities were substantially increased, and more soluble sugars were produced. Total amino acid, glutamic acid, and γ-aminobutyric acid (GABA) levels increased by 52.2%, 155.1%, and 144.1%, respectively. Conversely, lactic acid production decreased. Genetic analysis showed that the glycolysis-related gene pykA, pentose phosphate pathway gene gnd, and GABA-related gene gad were upregulated, while the heterolactin-related gene xpkA was downregulated, explaining that B. velezensis might inhibit heterolactin fermentation while enhancing GABA biosynthesis. This study provides a potential strategy for the high-value utilization of BSG in the food or feed industry.

Effect of La/Ce modification over Cu based Y zeolite catalysts on high temperature selectivity for selective catalytic reduction with ammonia

CuY zeolite catalyst is considered to be one of most promising catalysts for selective catalytic reduction with ammonia (NH3-SCR), but its main byproduct is the greenhouse gas N2O. To increase N2 selectivity, the modification mode and promotion mechanism of La/Ce doping with two-step ion exchange method were investigated. Impressively, CuLaY achieved above 90% efficiency from 140 °C to 380 °C and less N2O production especially at the temperature above 250 °C. The characterization results showed La/Ce doping increased the content of surface Cu2+ species and improved the oxidation ability of Cu ions in catalysts. However, the formation of La/Ce oxides on the zeolite surface had an adverse impact on the SCR activity, while Ce oxides were more easily formed than La oxides. In addition, more abundant adsorbed NOx species and stronger NH3 adsorption on the surfaces enhanced L-H mechanism for CuLaY with high N2 selectivity above 250 °C.

Promotional effects of calcination temperature and H2O on the catalytic activity of Al-substituted MnAlO catalysts for low-temperature acetone oxidation.

In order to enhance the role of Al in the materials, Al-substituted MnAlO catalysts were synthesized via the hydrothermal-redox method at different calcination temperatures for acetone oxidation. There were Al-substituted α-MnO2 and amorphous aluminum oxide existed with homogeneous dispersion of elements in the catalysts. The surface property, reaction rate, CO2 yield and water resistance of MnAlO catalysts were greatly affected by calcination temperatures. MnAlO-450 catalyst exhibited the best catalytic performance (acetone conversion of 90% at 165°C) with CO2 yield higher than 99.7%, which was mainly related to the weaker Mn-O bond strength, lower temperature reducibility and abundant Lewis acid sites. The acetone conversion of MnAlO-450 increased by as much as 16% in the presence of 1vol% H2O compared to that in the absence of H2O at T50 (the temperature for 50% conversion of acetone). The acceleration consumption of ethanol as the main by-product by H2O improved the catalytic performance. This work would shed light on the Al substitution based catalysts for OVOC oxidation with highly efficient and water resistance.

Simultaneous removal of toluene and chlorobenzene in a nonthermal plasma-catalysis reactor packed with Fe1-Mn1/γ-Al2O3

Toluene and chlorobenzene are the representative aromatic VOCs and chlorinated VOCs coexisted in the exhaust gases. In this study, the removal of the single pollutant (toluene or chlorobenzene) and the multipollutants (toluene and chlorobenzene) were studied in a nonthermal plasma reactor packed with Fe 1 –Mn 1 /γ-Al 2 O 3 . Meanwhile, the toxic by-products, reaction kinetic and degradation pathway were also discussed. The results indicated that the multipollutants removal had a negative impact on toluene and chlorobenzene conversion. Meanwhile, O 3 and NOx generated from simultaneous removal were also higher than that obtained from single pollutant (toluene or chlorobenzene) removal in the nonthermal plasma reactor packed with the Fe 1 –Mn 1 /γ-Al 2 O 3 . The reaction rates for toluene or chlorobenzene removal were 0.00168 s −1 and 0.00134 s −1 , respectively. While the reaction rates of toluene and chlorobenzene during the simultaneous removal were respectively reduced to 0.00111 s −1 and 0.00099 s −1 due to the interaction between toluene and chlorobenzene. Finally, the possible removal pathway of simultaneous removal of toluene and chlorobenzene in the plasma reactor coupled with Fe 1 –Mn 1 /γ-Al 2 O 3 was also proposed based on the organic intermediates identified by GC/MS. • Simultaneous removal had negative impact on conversion. • Interaction between toluene and chlorobenzene reduced the reaction rates. • Ethylacetate was the main organic byproducts in a plasma-catalysis sysytem. • The simultaneous removal route in a plasma-catalysis system was proposed.

Enhanced solar inactivation of fungal spores by addition of low-dose chlorine: Efficiency and mechanism

This work demonstrated that the solar inactivation of fungal spores was enhanced by addition of low-dose chlorine. Although the effect of low-dose chlorine alone (2.0 mg/L) on culturability of fungal spores was negligible, the solar/chlorine inactivation on fungal spores performed better than solar alone inactivation, with a lower shoulder length and a higher maximum inactivation rate constant. The enhanced inactivation of Aspergillus niger can be ascribed to the membrane oxidation by chlorine, and the enhanced inactivation of Penicillium polonicum can be ascribed to the membrane oxidation by chlorine and ·OH (·OH plays a major role). The oxidization by chlorine and ·OH led to an increase in membrane permeability of fungal spores, which enhanced the solar inactivation, resulting in an increase in intracellular ROS and more serious morphological damage. Due to the presence of background substances such as dissolved organic matter and metal ions (Fe2+, Mn2+, etc.), the inactivation efficiency in real water matrices was decreased. The main disinfection by-products (DBPs) produced in the inactivation of fungal spores in chlorine alone and solar/chlorine treatments were dichloroacetic acid, trichloroacetic acid, trichloroacetone and trichloromethane. Generally, DBPs formation in solar/chlorine treatment was lower than those in chlorine alone treatment. Moreover, the regrowth potential of the two genera of fungal spores in R2A medium could be inhibited by adding low-dose chlorine.

Enhancing Free Cyanide Photocatalytic Oxidation by rGO/TiO2 P25 Composites.

Graphene-TiO2 composites have been investigated in various photocatalytic reactions showing successful synergy compared to pristine TiO2. In the present work, graphene oxide (GO) was synthesized by the Hummers method and then reduced graphene oxide-TiO2 composites (rGO/TiO2) were obtained by an in situ GO photoreduction route. X-ray diffraction, FTIR, Raman, UV–vis DRS, and photoluminescence were the main characterization techniques. The obtained composites containing 1 and 3 wt.% rGO were evaluated in the cyanide (50 mg/L) oxidation and Au-cyanide complex (300 mg/L) degradation under UV-A light. The composites showed higher photocatalytic activity than TiO2, mainly with the 1% rGO content. Cyanate and gold nanoparticles, deposited on the photocatalyst’s surface, were the main byproducts during the photocatalyst assessment. The improved photocatalytic activity of the composites was attributed to a higher rate of electron transfer and a lower rate of charge recombination due to the chemical interaction of rGO with TiO2.

Impact of Anode Materials on Electrochemical Degradation of Carbamazepine: A Case Study of Producing the Main By-Product 10,11-Epoxycarbamazepine after Electrochemical Degradation of Carbamazepine

Copper (Cu), nickel (Ni), platinum (Pt), and graphite (G)” have been applied to the electrochemical degradation of carbamazepine (CBZ) from its aqueous solution. The optimum results were observed with graphite anode as follows: fully complete removal of CBZ, 0.0758 min−1 rates constant, and 0.59 Wh/mg consumption energy under these conditions: 5 V, 0.5 g NaCl, and a graphite anode. Kinetics was also considered in the present study, in which rate constants ranged between 0.0023 and 0.0886 min−1. It was observed that applied voltage has an effect on consumption energy giving 0.34, 0.59, and 1.08 Wh/mg using 3, 5, and 7 V, respectively. Field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscope (EDS) were used to characterize the organo-metallic precipitates which were formed using Ni and Cu anodes. The main by-product of 10,11-epoxycarbamazepine (EPX-CBZ) was elucidated and monitored using liquid chromatography-time of flight/mass spectrometry (LC-ToF/MS). Therefore, graphite is suggested to be a promising electrode in which it is exhibited good performance compared to other electrodes in terms of removal and consumption of energy.

Hybrid model to predict the effect of complex media changes in mammalian cell cultures

This work presents a modelling approach to account for the contribution of minor elements in cell culture media for mammalian cell cultures. The effect of minor elements is captured through an empirical PLS (Partial Least Squares) based correction that is incorporated into a dynamic mechanistic model composed of mass balances of major components in the media: amino acids, main by-products, biomass and product. The combination of the empirical correction based on PLS and the mechanistic model results in a hybrid model that was calibrated and validated with industrial experimental data. The goal is to develop a comprehensive model that can be used in the future to optimize batch, fed-batch and perfusion operations with respect to the media formulation. Based on the application of t-test to the sum of square errors (SSE) of the models it is shown that the re-calibrated hybrid model accounting for minor components interactions performed better predictions as compared to mechanistic or hybrid models that do not account for the minor components. Furthermore, the hybrid model is shown to remove dynamic auto-correlation error which is another indicator of reduced model error.

Metabolic engineering of Corynebacterium glutamicum for efficient production of optically pure (2R,3R)-2,3-butanediol

Background2,3-butanediol is an important platform compound which has a wide range of applications, involving in medicine, chemical industry, food and other fields. Especially the optically pure (2R,3R)-2,3-butanediol can be employed as an antifreeze agent and as the precursor for producing chiral compounds. However, some (2R,3R)-2,3-butanediol overproducing strains are pathogenic such as Enterobacter cloacae and Klebsiella oxytoca.ResultsIn this study, a (3R)-acetoin overproducing C. glutamicum strain, CGS9, was engineered to produce optically pure (2R,3R)-2,3-butanediol efficiently. Firstly, the gene bdhA from B. subtilis 168 was integrated into strain CGS9 and its expression level was further enhanced by using a strong promoter Psod and ribosome binding site (RBS) with high translation initiation rate, and the (2R,3R)-2,3-butanediol titer of the resulting strain was increased by 33.9%. Then the transhydrogenase gene udhA from E. coli was expressed to provide more NADH for 2,3-butanediol synthesis, which reduced the accumulation of the main byproduct acetoin by 57.2%. Next, a mutant atpG was integrated into strain CGK3, which increased the glucose consumption rate by 10.5% and the 2,3-butanediol productivity by 10.9% in shake-flask fermentation. Through fermentation engineering, the most promising strain CGK4 produced a titer of 144.9 g/L (2R,3R)-2,3-butanediol with a yield of 0.429 g/g glucose and a productivity of 1.10 g/L/h in fed-batch fermentation. The optical purity of the resulting (2R,3R)-2,3-butanediol surpassed 98%.ConclusionsTo the best of our knowledge, this is the highest titer of optically pure (2R,3R)-2,3-butanediol achieved by GRAS strains, and the result has demonstrated that C. glutamicum is a competitive candidate for (2R,3R)-2,3-butanediol production.

Thermomechanically micronized sugar beet pulp: Dissociation mechanism, physicochemical characteristics, and emulsifying properties

Sugar beet pulp (SBP), the main by-product of the beet sugar industry, has gained increasing attention due to its potential functional properties as a clean-label food ingredient. The aim of the present work was to optimize a food-grade approach for SBP micronization via harsh thermal pretreatment and ultrasonication, after which the micronized SBP was used as an emulsifier. Harsh thermal pretreatment substantially softened the compact particle structure of SBP, thereby improving breakage efficiency by reducing the ultrasonication time to 10 min (suspension stability of ∼100%). During ultrasonication, the particle size of SBP declined from ∼34 to ∼25 μm, which showed long and tangled morphology as fibers (diameter of 50–300 nm). The increased solubility enlarged the specific surface area of SBP from ∼0.6 to ∼3.5 g/m2, endowing it with a porous structure for improved ultrasonic energy adsorption, thereby preventing the degradation of the dissolved pectic polymers. The dissociation of SBP particles contributed to the enhancement of emulsification and was correlated with an increase in suspension stability. These findings provide a feasible strategy for the high added-value utilization of SBP.

Alkali treatment–acid leaching of rare earth elements from phosphogypsum fertilizer: insight for additional resource of valuable components

Phosphogypsum (PG) is the main by-product of phosphoric acid, which is produced by the sulfuric acid attack of phosphate rocks, wet process. This by-product, which contains around 2.0% phosphoric acid, is used as a low-cost soil fertilizer, PGF. PGF consists mainly of gypsum (CaSO4·2H2O), P2O5, SiO2, and other impurities, including a minor amount of rare earth elements, REEs. In general, phosphate rocks contain from about 0.04 to 1.0% REE, which are precipitated with PG. Now, REEs are considered as strategic elements. Therefore, PG is now regarded as a secondary source of REE. This paper address a process for the separation of REEs and sodium sulphate as a product from PGF. This paper is based on the metathesis of the bulk of PGF with sodium carbonate to obtain calcium carbonate precipitated contain REEs. Furthermore, sodium sulphate was obtained as a product. Calcium carbonate containing REEs was leached out by citric acid as a green acid or nitric acid. At optimum conditions, maximum leaching of REEs from CaCO3 after one cycle of leaching by 3.0 mol/L nitric acid at L/S = 3/1, agitation time of 180.0 min., and at a temperature of 25 °C is 75.1%, 361.10 mg/kg from the total REEs present in PGF. While, the maximum leaching of 87.4%, 420.2 mg/kg of REEs from CaCO3 after one cycle of leaching by 1.0 mol/L citric acid, L/S = 5/1, agitation time of 15.0 min., and 85 °C. The REEs that were obtained in the leaching citrate solutions were purified by solvent extraction using 10% of di-2-ethyl hexyl phosphoric acid, HDEHP, in kerosene. The extracted REEs were stripped by 0.5 mol/L H2SO4. The stripped solutions were further treated with 10.0% oxalic acid to precipitate the REEs. The developed procedure can recover REEs from PGF with an efficiency of 85.2% and a purity of 97.7%.

The Non-solventogenic Clostridium beijerinckii Br21 Produces 1,3-Propanediol From Glycerol With Butyrate as the Main By-Product

Ever-increasing biofuel production has raised the supply of glycerol, an abundant waste from ethanolic fermentation and transesterification, for biodiesel production. Glycerol can be a starting material for sustainable production of 1,3-propanediol (1,3 PD), a valued polymer subunit. Here, we compare how Clostridium pasteurianum DSMZ 525, a well-known 1,3-PD-producer, and the non-solventogenic Clostridium beijerinckii Br21 perform during glycerol fermentation. Fermentative assays in 80-, 390-, or 1,100-mM glycerol revealed higher 1,3-PD productivity by DSMZ 525 compared to Br21. The highest 1,3-PD productivities by DSMZ 525 and Br21 were obtained in 390 mM glycerol: 3.01 and 1.70 mM h−1, respectively. Glycerol uptake by the microorganisms differed significantly: C. beijerinckii Br21 consumed 41.1, 22.3, and 16.3%, while C. pasteurianum consumed 93, 44.5, and 14% of the initial glycerol concentration in 80, 390, and 1,100 mM glycerol, respectively. In 1,100 mM glycerol, C. beijerinckii Br21 growth was delayed. Besides 1,3-PD, we detected butyrate and acetate during glycerol fermentation by both strains. However, at 80 mM glycerol, C. beijerinckii Br21 formed only butyrate as the by-product, which could help downstream processing of the 1,3-PD fermentation broth. Therefore, C. beijerinckii Br21, an unexplored biocatalyst so far, can be used to convert glycerol to 1,3-PD and can be applied in biofuel biorefineries.

(Invited) Photoelectrochemical Glycerol Oxidation to Value-Added Commodity Chemicals Using BiVO4-Based Photoanodes

To create a functional photoelectrochemical cell (PEC) for solar fuels production, a cathode and anode reaction must both be chosen and optimized. In order to generate clean energy, a renewable resource such as water, nitrogen, or biomass, is typically reduced at the photocathode to generate H2, ammonia, or carbon-based fuel. In aqueous media, the anode reaction is typically water oxidation, as water is renewable and available in the cell. However, the product of water oxidation, O2, is not very valuable. As such, in recent years attention has been directed to finding a more attractive oxidation reaction that forms a value-added product that can be paired with reduction reactions of interest. Ideally, this reaction would consist of renewable, abundant, and affordable feedstock, such as biomass, that can be readily oxidized to a more valuable compound. The photoelectrochemical oxidation of glycerol to value-added commodity chemicals fits these criteria. Glycerol is the main byproduct of biodiesel production, and as such is cheap and abundant. As investment in clean fuels increases, the production of biodiesel will continue to increase, leading to an overabundance of glycerol, which can create storage and environmental issues. Developing systems to valorize glycerol will ensure sustainable biodiesel production and advance the transition to renewable fuels. Glycerol consists of three alcohol groups, and many oxidation pathways are possible, with the most profitable being the selective oxidation of the secondary alcohol to a ketone to make dihydroxyacetone (DHA). This conversion yields an over 200-fold value increase from $0.66 to $150 per kilogram. Thus, photoelectrochemical DHA production can provide an opportunity to make PEC operation more profitable while improving the sustainability of the biodiesel industry. BiVO4 is a good candidate for photoelectrochemical glycerol oxidation as it has a favorable band gap (2.4eV), excellent charge separation, and low water oxidation selectivity. In this presentation, we report our recent results obtained for photoelectrochemical glycerol oxidation using a BiVO4 photoanode. We will discuss various surface modifications of BiVO4 that we employed to elucidate the reaction mechanisms and to maximize the efficiency and selectivity for DHA production.

Pt/Au Nanoparticles@Co3O4 Cataluminescence Sensor for Rapid Analysis of Methyl Sec-Butyl Ether Impurity in Methyl Tert-Butyl Ether Gasoline Additive

High purity methyl tert-butyl ether (MTBE) can be used to adjust gasoline octane values. However, an isomer, methyl sec-butyl ether (MSBE), is the main by-product of its industrial production, and this affects the purity of MTBE. Pt/Au NPs@Co3O4 composites with a hollow dodecahedron three-dimensional structure were synthesized using ZIF-67 as a template, with Pt and Au nanoparticles (NPs) evenly distributed on the shell of the hollow structure. A CTL sensor was established for the determination of MSBE based on the specificity of Pt/Au NPs@Co3O4. The experimental results showed that Pt/Au NPs@Co3O4 had a strong specific cataluminescence (CTL) response to MSBE, with no interference from MTBE. The linear range was 0.10–90 mg/L, the limit of detection was 0.031 mg/L (S/N = 3), the RSD was 2.5% (n = 9), and a complete sample test could be completed in five minutes. The sensor was used to detect MSBE in MTBE of different purity grades, with recoveries ranging from 92.0% to 109.2%, and the analytical results were consistent with those determined by gas chromatography. These results indicate that the established method was accurate and reliable, and could be used for rapid analysis of MTBE gasoline additive.

A conceptual study on understanding Ama concept with special reference to free radical theory

Ayurveda speaks the main cause of diseases is rooted in the impairment of the body's main fire, called Agni, the fire of digestion. Ayurveda views the health of the body as the functioning of a biological fire-governing metabolism. If this essential part is functioning effectively, the whole body will be nourished, full of life and vibrancy. Altered digestive functioning can lead to the production of Ama, a toxic material that initiates and promotes disease processes throughout the body. In the same way, free radicals are also found to be the root cause of many diseases. The majority of free radicals that dAmage biological systems are oxygen-free radicals, and these are more generally known as “Reactive Oxygen Species” (ROS). These are the main by-products formed in the cells of aerobic organisms, and can initiate autocatalytic reactions so that molecules to which they react are themselves converted into free radicals to propagate the chain of dAmage. Here we shall discuss about properties of both Ama and Free Radicals. The present article attempts to correlate the concept of Free radical with the concept of Ama.

Scenario-based techno-economics and heat integration feasibility assessment of integrated multiproduct biorefineries with biosuccinic acid as the main product and various byproduct options

Scenario-based techno-economics and heat integration feasibility assessment of integrated multiproduct biorefineries with biosuccinic acid as the main product and various byproduct options

Photocatalytic Carboxylation with CO2: A Review of Recent Studies

AbstractCarbon dioxide (CO2) is the main byproduct from the combustion of fossil fuels, the excessive emission into the atmosphere is regarded as primary causes for global warming and climate change. On the other hand, CO2 is also a readily available, non‐toxic, low‐cost C1 source, and widely used in synthetic chemistry to afford value carboxylic acids and derivatives by photocatalysis CO2 transformation under light irradiation. Herein, we present a summarization for the recent advances and achievements in the area of photocatalytic carboxylation of unsaturated hydrocarbons, organo(pseudo)halides, carbonyl compounds, tetraalkyl ammonium salt, and C(sp3) C−O bonds with CO2. We also discuss the mechanisms of such reactions, which will help us to comprehend the specific process of carboxylation. We hope the summary of these methods will further stimulate future research in this sought‐after area.

The beneficial effects of citrus peel waste and its extract on fish performance and health status: A review

Food production and processing in developing countries produce a huge amount of fruit waste by-products, which is costly and pose detrimental effects on the environment. Proteins, lipids, starch, micronutrients, bioactive compounds and dietary fibres are found in many of these fruit wastes. Among fruit wastes, citrus fruits play an important role in generating a wide range of health benefits. Citrus L. of the Rutaceae family are common fruits cultivated and consumed globally both as fresh fruits and as a juice. Citrus peel wastes (CPW) are considered the main by-products, with an average of 60% of processed fruits; hence, CPW have a promising role in the food production industry. CPW contain high concentrations of polyphenol and essential oils, which have nutritional importance and pharmaceutical usage. There is a concern on the increasing prevalence and incidence of different fish infections and a growing interest in shifting from synthetic to natural antimicrobial agents, leading to the use of citrus peel wastes for identification of novel compounds for use as fish feed additives. Although the antimicrobial properties of EOs have been reviewed extensively, the antimicrobial properties of citrus peels oil have not been extensively discussed. In fish farming, feeding strategies that employ phytochemicals as modulators of immunological and physiological responses such as growth, antioxidant activity and gene expression have received attention. In the past years, several studies have reported positive results of using citrus peel extracts as a nutritional additive in aquafeeds. Recently, these dietary functional feed additives have been evaluated and reported to increase disease resistance and improve fish growth, animal welfare and feed utilization. This review elucidates the global production, bioactive compounds, natural sources, chemical structures, physical properties, practical applications of citrus peel wastes and extracts as a desirable and sustainable route in fish nutrition.

Comprehensive kinetic model of a three-way catalyst for stoichiometric natural gas engines: Experiments and simulation

BackgroundKinetic modeling is an important technique for designing and optimizing automotive exhaust gas aftertreatment systems. However, few kinetic models can simultaneously predict the main pollutant removal and byproduct formation on three-way catalysts for stoichiometric natural gas engines. Therefore, further development of the TWC model was needed to address such issues. MethodsIn this study, a detailed global kinetic model for natural gas engines was developed by extending the classic TWC model by combining the investigation of reaction pathways and light-off experiments over a wide range of conditions. Significant findingsWith the help of a gradually simplified light-off experiment, the main side reactions between NO and CO/H2/O2 to form NH3/N2O/NO2 were well defined. Adding all observed reactions into the classic model, the extended kinetic model can capture all the experimental phenomena under a wide range of operating conditions in laboratory light-off tests. Importantly, this model can also describe the light-off phenomena of aged samples when aging factors are used. Apart from predicting reactor-scale phenomena, the extended model above describes and predicts the cold start emission under cold WHTC. This study provides a feasible and straightforward method to build a global kinetic model covering full-scale laboratory conditions to actual operating conditions.

Mutation of rpoS is Beneficial for Suppressing Organic Acid Secretion During 1,3-Propandiol Biosynthesis in Klebsiella pneumoniae

In this study, to reduce the formation of organic acid during 1,3-propanediol biosynthesis in Klebsiella pneumoniae, a method combining UV mutagenesis and high-throughput screening with pH color plates was employed to obtain K. pneumoniae mutants. When compared with the parent strain, the total organic acid formation by the mutant decreased, whereas 1,3-propanediol biosynthesis increased after 24h anaerobic shake flask culture. Subsequently, genetic changes in the mutant were analyzed by whole-genome sequencing and verified by signal gene deletion. Mutation of the rpoS gene was confirmed to contribute to the regulation of organic acid synthesis in K. pneumoniae. Besides, rpoS deletion eliminated the formation of 2,3-butanediol, the main byproduct produced during 1,3-propanediol fermentation, indicating the role of rpoS in metabolic regulation in K. pneumoniae. Thus, a K. pneumoniae mutant was developed, which could produce lower organic acid during 1,3-propanediol fermentation due to an rpoS mutation in this study.