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Succinoglycan is an industrially important exopolysaccharide biosynthesized by bacteria. In this study, mutant strain 18052 N-11 was obtained from the wild type strain Rhizobium radiobacter ATCC 19358 by NTG mutagenesis. It has a high yield succinoglycan of 32.5 g/L cultured in a 15 L-fementer for 72 h. Succinoglycan SG-A from the wild type strain has two components, and the molecular weights were 1.55 × 107 Da and 1.26 × 106 Da, respectively. While, succinoglycan SG-N from the mutant strain was a homogeneous polysaccharide, and the molecular weight was 1.01 × 107 Da. The molecular weight of both succinoglycan was higher than those reported in literatures. DSC thermogram of SG-A showed a higher endothermic peak than that of SG-N due to the higher crystallinity of SG-A. The dynamic frequency sweep test of SG-A and SG-N showed that the elastic modulus G' and viscosity modulus G" curves intersected at 65 °C, indicating the thermally induced order-disorder conformation. The results of effect of concentrations (2.5–15%) and temperatures (25–75 °C) on apparent viscosity of SG-A and SG-N showed that the succinoglycan solutions exhibited non-Newtonian, shear-thinning behavior. Both SG-A and SG-N showed an excellent emulsification activity. The characterizations and rheological properties make SG-A and SG-N prominent candidates in food, cosmetics, pharmaceutical and petroleum industries.

Curdlan is a neutral linear exopolysaccharide produced by Agrobacterium spp. under nitrogen-limiting conditions. In this study, we explored the role of glnA in curdlan biosynthesis in Agrobacterium sp. CGMCC 11546. The curdlan production of the ΔglnA strain was impaired, decreasing by 93% compared with that of the wild-type strain after 96 h fermentation. Analysis of fermentation profiles revealed that cell growth and utilization of carbon and nitrogen sources were impaired in the ΔglnA strain. Transcriptome analysis indicated that various of genes involved in curdlan biosynthesis were downregulated after 24 h fermentation in the ΔglnA strain, particularly genes involved in heme synthesis and the electron transport chain, which are essential for energy generation. Metabolomics analysis revealed flavin adenine dinucleotide (FAD) and adenosine diphosphate (ADP) accumulation in the ΔglnA strain, suggesting insufficient energy supply. Furthermore, glnA overexpression led to an 18% increase in the curdlan yield of the ΔglnA mutant compared with that of the wild-type strain after 96 h fermentation. Taken together, the findings demonstrate that glnA plays a vital role in curdlan biosynthesis by supplying ATP via regulating the expression of genes involved in heme synthesis and the electron transport chain.

The recovery of low-molecular-weight γ-polyglutamic acid (γ-PGA) by metal ion precipitation from the fermentation broth was explored. The broth containing 20 g/L γ-PGA was firstly adjusted to a low pH (2 or 3) to remove the bacteria cells easily, and then Cu2+ was chosen to recover γ-PGA in the diluted cell-free broth, resulting in the precipitation of a Cu2+-γ-PGA complex. The optimum concentration of copper sulfate for maximum γ-PGA precipitation was 0.08 M, and 0.64 M EDTA solution could completely redissolve the Cu2+-γ-PGA complex pellet. The recovery of γ-PGA from the original culture broth by this method was more than 90%. The redissolved γ-PGA was dialyzed against deionized water to obtain the purified γ-PGA biopolymer. As detected by infrared spectroscopy and GPC, the purified γ-PGA recovered by low pH and Cu2+ was characterized as γ-PGA biopolymer with a low molecular weight of 50.5 kDa and narrow polydispersity. The total metal content and Cu2+ concentration of the purified γ-PGA were found to be below the US FDA permissible limits. Therefore, the method combining low pH with the metal cation-induced precipitation offered an option to recover γ-PGA with low molecular weight and narrow polydispersity from the fermentation broth.

Curdlan is a water-insoluble exopolysaccharide produced by Agrobacterium species under nitrogen starvation. The curdlan production in the ΔmdeA, ΔmetA, ΔmetH, and ΔmetZ mutants of methionine biosynthesis pathway of Agrobacterium sp. CGMCC 11546 were significantly impaired. Fermentation profiles of four mutants showed that the consumption of ammonia and sucrose was impaired. Transcriptome analysis of the ΔmetH and ΔmetZ mutants showed that numerous differentially expressed genes involved in the electron transfer chain (ETC) were significantly down-regulated, suggesting that methionine biosynthesis pathway affected the production of energy ATP during the curdlan biosynthesis. Furthermore, metabolomics analysis of the ΔmetH and ΔmetZ mutants showed that ADP and FAD were significantly accumulated, while acetyl-CoA was diminished, suggesting that the impaired curdlan production in the ΔmetH and ΔmetZ mutants might be caused by the insufficient supply of energy ATP. Finally, the addition of both dibasic sodium succinate as a substrate of FAD recycling and methionine significantly restored the curdlan production of four mutants. In conclusion, methionine biosynthesis pathway plays an important role in curdlan biosynthesis in Agrobacterium sp. CGMCC 11546, which affected the sufficient supply of energy ATP from the ETC during the curdlan biosynthesis.

In this study, 15 strains of Lactic acid bacteria (Allata et al.) and 6 strains of propionic acid bacteria (PAB) were firstly tested for their antifungal activity against three spoilage fungi, Aspergillus niger, Penicillium crustosum and Aspergillus flavus. Two strains of LAB and PAB were selected and assessed, alone or paired, for their abilities to inhibit the most resistant mold, Aspergillus niger. A mixed culture of P. freudenreichii D6 and L. plantarum L9 was found to be the most active and their optimal inoculum was 1×108 and 1 × 106 CFU/mL, respectively. Furthermore, the in situ antifungal effect of the mixed culture was evaluated against bakery product spoilage fungi. It was found that the growth of airborne fungi was delayed for up to 7 days. The cell number of L. plantarum L9 was slightly increased by the presence of P. freudenreichii D6. Quantification of three main acids (propionic, lactic and acetic acid) produced by the protective cultures suggested that acetic acid was mainly responsible for the antifungal activity. In conclusion, the mixed culture of P. freudenreichii and L. plantarum may be exploited as biopreservatives in bakery products.

Microbial transglutaminase (MTGase) derived from Streptomyces mobaraensis has been widely used in the food, biotechnology and medicine fields. The lot-to-lot consistency and product stability of MTGase must be ensured. The structure and charge variants of MTGase can influence its bioactivity. In this study, MTGase isomers (MTG I1 and MTG I2) were found during the separation of MTGase by pH-mediated cation-exchange chromatography. MTG I1 and MTG I2 had the same molecular weight and N-terminal amino acid sequences, but they showed charge heterogeneity. The affinity of MTG I2 for substrates was higher than that of MTG I1, and the thermal stability and the acid-base tolerance of MTG I1 were significantly higher than that of MTG I2. Therefore, the ratio of MTG I1/MTG I2 was positively correlated with the stability of MTGase. The buffer pH and the ionic strength of the eluent had significant effects on the separation of MTG I1 and MTG I2, and the elution gradient steepness and column load showed little effect on the separation of the MTG I1 and MTG I2 peaks. We built a stable and repeatable separation method for MTG I1 and MTG I2. MTG I1 could transform into MTG I2, but MTG I2 was unable to transform into MTG I1, making the transformation of MTG I1 to MTG I2 was irreversible. When MTG I2 was removed from the MTGase, a portion of the MTG I1 could transform into MTG I2. Therefore, one way to increase the stability of MTGase was to reduce the transformation of MTG I1 to MTG I2.

This paper presents a new topology of switched reluctance motor (SRM) drive for plug-in hybrid electric vehicles (PHEVs). Six operating modes can be achieved as a result. Three of those modes are applied for driving and the others for charging. During the driving mode, the topology can be converted to a four-level one. During the charging mode, two battery packs are charged in parallel with the boost circuit by the external AC source or generators. The main contributions of the proposed topology are as follows: 1) A four-level converter is formed by adopting different ways of connection (series or parallel) of the two battery packs (or the two capacitors), which can accelerate the excitation and demagnetization procedures of SRMs. Moreover, the topology contributes to decreasing the switching losses and extending the constant torque region to improve the drive performance as well. 2) The state of charge (SOC) of the two battery packs (or the voltages of two capacitors) can keep balance on their own by parallel operation of the two battery packs. Furthermore, a detailed comparison between two drive modes of the proposed topology and asymmetric half bridge inverters is undertaken with simulation and experimental studies, the results of which demonstrate the validity of the proposed topology.

Bacterial nanocellulose (BNC) has many advantages over plant cellulose, which make it widely used in many fields, especially in the food industry. In this study, three strains including BCA263, BCC529, and P1 were selected for characteristics analysis of BNCs under static and agitated culture conditions. The BNCs produced under static culture condition were in the shape of uniform membrane, while BNCs produced under agitated culture were in form of small agglomerates and fragments. BCA263 and BCC529 strains were more suitable for static culture, while P1 strain was more suitable for agitated culture. BNCs produced under static culture condition exhibited higher crystallinity, stronger tensile strength, denser network structure, higher temperature resistance and good flame retardancy; while BNCs produced under agitated culture condition exhibited larger porous and lower crystallinity. Furthermore, BNCs produced under agitated culture condition were more suitable as a stabilizer of coffee milk beverage.

A novel microbial transglutaminase (MTG-TX) was obtained from Streptomyces mobaraensis by fermentation and purification. The enzyme was purified by ethanol precipitation via a two-step purification method, with a 44.0% yield and a specific activity of 39.2 U mg −1 . The purified enzyme exhibited stable performance over a range of pH 5.0–pH 10.0 and displayed maximal activity at pH 6 and 48 °C. We verified through biochemical analyses that the enzyme is a novel MTG variant possessing the same zymogen characteristics as that of another reported MTG from Streptoverticillium ladakanum B1. Furthermore, the loss of enzyme activity by MTG-TX in the presence of high salt was only 79.8% that observed in a control MTG from S. mobaraensis DSM40847. On the basis of salt resistance, the novel MTG-TX presented here also performed well in food-related applications by successfully crosslinking proteins in high-salt environments, thereby enhancing the cohesiveness of bacon.

Curdlan is a bacterial, water-insoluble, linear homopolysaccharide that has been widely used in the food industry. In this study, genome information of strain CGMCC 11546, a UV-induced high-yield mutant of the model curdlan-producing strain Agrobacterium sp. ATCC 31749, was used to investigate the molecular mechanism of curdlan biosynthesis. The maximum curdlan yield of 47.97 ± 0.57 g/L was obtained from strain CGMCC 11546 by using optimal media containing 60 g/L sucrose, 6 g/L yeast, 2 g/L KH2PO4, 0.4 g/L MgSO4·7H2O, 2 g/L CaCO3, 0.1 g/L FeSO4·7H2O, 0.04 g/L MnSO4, and 0.02 g/L ZnCl2 at 30 °C and 280 rpm after 96 h of fermentation. The gel strength of curdlan was improved by 41 % by knocking out the β-1,3-glucanase genes exoK and exsH of strain CGMCC 11546. Furthermore, the application of curdlan from the ΔexoK-exsH strain in noodles significantly improved the eating quality of both raw and cooked noodles.

Bacterial cellulose (BC) has received considerable attention as an environment-friendly, biodegradable nanomaterial. In this study, the strain Komagataeibacter sp. nov. CGMCC 17276, which showed rapid cell growth and high BC-production ability, was isolated and classified into a novel species in the Komagataeibacter genus. Four BC synthase operons were annotated using whole-genome analysis, partially explaining the high BC yield of strain CGMCC 17276. Operons bcs Ⅱ and bcs Ⅲ showed high transcriptional levels under static and agitated culture conditions, indicating their importance in BC synthesis. Of the eight suitable carbon sources identified by whole-genome analysis, the highest BC production was achieved using glycerol as a single carbon source. Finally, waste glycerol was successfully used as an eco-friendly and sustainable strategy for BC production. This study provides valuable insights into the mechanism of BC synthesis, genetic structure of BC-producing strains, and industrialization of BC production using an eco-friendly and low-cost strategy.

Comparison of different torque control methods is presented in this paper, including current chopping control (CCC), torque sharing function (TSF) control and direct instantaneous torque control (DITC). These control methods play different roles in reducing torque ripples, increasing total output torque and getting maximum efficiency in different speed range.For example, DITC can reduce torque ripples at low speed obviously while it does not work out at high speed. TSF can reduce torque ripples efficiently at high speed but, in the meantime, it leads to total output torque decrease. CCC can output higher torque compared with previous two control methods, however its torque ripples is higher at high speed . In this paper, these three control methods are introduced and their performances are compared in terms of torque ripples and maximum output torque in order to further understand their inherent characteristics. Torque ripple-speed performance and the maximum output torque-speed performance of these control methods are obtained based on simulation results. Theoretical comparison and analysis brings us the guideline of how to select optimal control methods of SR drive system in different speed range for getting better output performance.

This paper presents a novel 4-level converter with switch capacitor and boost circuit, meanwhile, introduces its control strategy for a three-phase switched reluctance (SR) drive. The proposed 4-level converter adds one switch, two diodes, one capacitor and one inductance to the front end of a conventional asymmetric converter. The added capacitor and original dc-link capacitor could be connected both in series and in parallel. The performance of SRM is closely related to the supply voltage. High voltage can reduce the time that current flows within the commutation period, and improve the output torque. However, high voltage is not always favorable. For example, higher voltage in the range of low rotational speeds will improve transistors switching frequency, and that causes rise of switching losses. Therefore, the converter having variable output voltage is very useful. The terminal voltage of the converter side is at general dc-link capacitor voltage. Meanwhile, the voltage also could be up to a double dc-link capacitor voltage level to adapt different operation conditions. In this paper, a detailed analysis of current-overlap modes is also presented. The compared simulation and experiments are done. The results verify the performance of the proposed converter.

A direct instantaneous torque control (DITC) of switched reluctance motor (SRM) with a three-bridge five-level converter is presented in this paper. Compared with conventional asymmetric half bridge converter, the proposed converter has more switching states, which can contribute significantly to reducing torque ripples and smoothing the total output torque. Additionally, in consideration of the unbalance of dc-link capacitor voltages, appropriate switching states are selected to achieve dynamic balance of the dc-link capacitor voltages. The validity of proposed DITC method applied with the five-level converter is verified by comparing its simulation and experimental results with the ones of traditional DITC method under a three-phase asymmetric half bridge converter.