[Effects of Combined Stress of High Density Polyethylene Microplastics and Chlorimuron-ethyl on Soybean Growth and Rhizosphere Bacterial Community].

With the vigorous development of agriculture in China， plastic mulch film and pesticides are widely used in agricultural production. However， the accumulation of microplastics （formed by the degradation of plastic mulch film） and pesticides in soil has also caused many environmental problems. At present， the environmental biological effects of microplastics or pesticides have been reported， but there are few studies on the combined effects on crop growth and the rhizosphere soil bacterial community. Therefore， in this study， the high density polyethylene microplastics （HDPE， 500 mesh） were designed to be co-treated with sulfonylurea herbicide chlorimuron-ethyl to study their effects on soybean growth. In addition， the effects of the combined stress of HDPE and chlorimuron-ethyl on soybean rhizosphere soil bacterial community diversity， structure composition， microbial community network， and soil function were investigated using high-throughput sequencing technology， interaction network， and PICRUSt2 function analysis to clarify the combined toxicity of HDPE and chlorimuron-ethyl to soybean. The results showed that the half-life of chlorimuron-ethyl in soil was prolonged by the 1% HDPE treatment （from 11.5 d to 14.3 d）， and the combined stress of HDPE and chlorimuron-ethyl had more obvious inhibition effects on soybean growth than that of the single pollutant or control. The HiSeq 2 500 sequencing showed that the rhizosphere bacterial community of soybean was composed of 20 phyla and 312 genera under combined stress， the number of phyla and genera was significantly less than that of the control and single pollutant treatment， and the relative abundances of bacteria with potential biological control and plant growth-promoting characteristics （such as Nocardioides and Sphingomonas） were reduced. Alpha diversity analysis showed that the combined stress significantly reduced the richness and diversity of the soybean rhizosphere bacterial community， and Beta diversity analysis showed that the combined stress significantly changed the structure of the bacterial community. The dominant flora of the rhizosphere bacterial community were regulated， and the abundances of secondary functional layers such as amino acid metabolism， energy metabolism， and lipid metabolism were reduced under combined stress by the analysis of LEfSe and PICRUSt2. It was inferred from the network analysis that the combined stress of HDPE and chlorimuron-ethyl reduced the total number of connections and network density of soil bacteria， simplified the network structure， and changed the important flora species to maintain the stability of the network. The results above indicated that the combined stress of HDPE and chlorimuron-ethyl significantly affected the growth of soybean and changed the rhizosphere bacterial community structure， soil function， and network structure. Compared with that of the single pollutant treatment， the potential risk of combined stress was greater. The results of this study can provide guidance for evaluating the ecological risks of polyethylene microplastics and chlorimuron-ethyl and for the remediation of contaminated soil.

Engineering Escherichia coli for high-yielding 2,5-Dimethylpyrazine synthesis from L-Threonine by reconstructing metabolic pathways and enhancing cofactors regeneration.

2,5-Dimethylpyrazine (2,5-DMP) is important pharmaceutical raw material and food flavoring agent. Recently, engineering microbes to produce 2,5-DMP has become an attractive alternative to chemical synthesis approach. In this study, metabolic engineering strategies were used to optimize the modified Escherichia coli BL21 (DE3) strain for efficient synthesis of 2,5-DMP using L-threonine dehydrogenase (EcTDH) from Escherichia coli BL21, NADH oxidase (EhNOX) from Enterococcus hirae, aminoacetone oxidase (ScAAO) from Streptococcus cristatus and L-threonine transporter protein (EcSstT) from Escherichia coli BL21, respectively. We further optimized the reaction conditions for synthesizing 2,5-DMP. In optimized conditions, the modified strain can convert L-threonine to obtain 2,5-DMP with a yield of 2897.30 mg/L. Therefore, the strategies used in this study contribute to the development of high-level cell factories for 2,5-DMP.

Dopamine D2 receptors in the dorsomedial prefrontal cortex modulate social hierarchy in male mice.

Social hierarchy greatly influences behavior and health. Both human and animal studies have signaled the medial prefrontal cortex (mPFC) as specifically related to social hierarchy. Dopamine D1 receptors (D1Rs) and D2 receptors (D2Rs) are abundantly expressed in the mPFC, modulating its functions. However, it is unclear how DR-expressing neurons in the mPFC regulate social hierarchy. Here, using a confrontation tube test, we found that most adult C57BL/6J male mice could establish a linear social rank after 1 week of cohabitation. Lower rank individuals showed social anxiety together with decreased serum testosterone levels. D2R expression was significantly downregulated in the dorsal part of mPFC (dmPFC) in lower rank individuals, whereas D1R expression showed no significant difference among the rank groups in the whole mPFC. Virus knockdown of D2Rs in the dmPFC led to mice being particularly prone to lose the contests in the confrontation tube test. Finally, simultaneous D2R activation in the subordinates and D2R inhibition in the dominants in a pair switched their dominant-subordinate relationship. The above results indicate that D2Rs in the dmPFC play an important role in social dominance. Our findings provide novel insights into the divergent functions of prefrontal D1Rs and D2Rs in social dominance, which may contribute to ameliorating social dysfunctions along with abnormal social hierarchy.

Engineering of formate dehydrogenase for improving conversion potential of carbon dioxide to formate.

Formate dehydrogenase (FDH) is a D-2-hydroxy acid dehydrogenase, which can reversibly reduce CO2 to formate and thus act as non-photosynthetic CO2 reductase. In order to increase catalytic efficiency of formate dehydrogenase for CO2 reduction, two mutants V328I/F285W and V354G/F285W were obtained of which reduction activity was about two times more than the parent CbFDHM2, and the formate production from CO2 catalyzed by mutants were 2.9 and 2.7-fold higher than that of the parent CbFDHM2. The mutants had greater potential in CO2 reduction. The optimal temperature for V328I/F285W and V354G/F285W was 55 °C, and they showed increasement of relative activity under 45 °C to 55 °C compared with parent. The optimal pH for the mutants was 9.0, and they showed excellent stability in pH 4.0-11.5. The kcat/Km values of mutants were 1.75 times higher than that of the parent. Then the molecular basis for its improvement of biochemical characteristics were preliminarily elucidated by computer-aided methods. All of these results further established a solid foundation for molecular modification of formate dehydrogenase and CO2 reduction.

High level expression of nicotinamide nucleoside kinase from Saccharomyces cerevisiae and its purification and immobilization by one-step method.

Nicotinamide riboside kinase (NRK) plays an important role in the synthesis of ß -nicotinamide nucleotide (NMN). NMN is a key intermediate of NAD+ synthesis, and it actually contribute to the well-being of our health. In this study, gene mining technology was used to clone nicotinamide nucleoside kinase gene fragments from S. cerevisiae, and the ScNRK1 was achieved a high level of soluble expression in E. coli BL21. Then, the reScNRK1 was immobilized by metal affinity label to optimize the enzyme performance. The results showed that the enzyme activity in the fermentation broth was 14.75 IU/mL, and the specific enzyme activity after purification was 2252.59 IU/mg. After immobilization, the optimum temperature of the immobilized enzyme was increased by 10°C compared with the free enzyme, and the temperature stability was improved with little change in pH. Moreover, the activity of the immobilized enzyme remained above 80% after four cycles of immobilized reScNRK1, which makes the enzyme more advantageous in the enzymatic synthesis of NMN.

Gene cloning of a highly active phytase from Lactobacillus plantarum and further improving its catalytic activity and thermostability through protein engineering.

Phytase belongs to orthophosphate monoester hydrolase, which can catalyze the gradual hydrolysis of phytic acid to inositol phosphate. It can be added to animal feed to reduce the anti-nutritional factor of phytic acid in feed. The thermostability and specific activity of phytases are two key factors determining their potential applications. In this study, a highly active 233-aa phytase gene (LpPHY233) from Lactobacillus plantarum was cloned and expressed in Escherichia coli (E. coli), achieving 800 times higher activity than that expressed in L. plantarum. Next, the temperature characteristic and catalytic performance of LpPHY233 was improved by disulfide bond engineering and C-terminal truncation, respectively. Surprisingly, the specific activity of the C-terminal truncated mutant LpPHY200 was about 5.6 times higher than that of LpPHY233, and the optimal temperature for the mutant LpPHY233S58C/K61C introduced disulfide bond was 15 °C higher than that of LpPHY233. Moreover, these phytase mutants displayed excellent pH property and kinetic parameters, and have great application prospect in feed additives field. The molecular basis for its catalytic performance was preliminarily explained by in silico design methods. Our results provided a solid theoretical foundation for further molecular modification and industrial application of phytases.

[Polyamine-producing Bacteria Regulated the Community Structure of Rhizosphere Bacteria and Reduced the Absorption of Cd in Wheat].

Some functional microorganisms in the soil immobilize heavy metals by adsorption and precipitation, prevent the absorption of heavy metals by crops, and play an important role in the passivation and remediation of medium and mild heavy metal-contaminated soil. A pot experiment was conducted to study the effects of the exogenous polyamine-producing bacterium Bacillus sp. N3 on Cd uptake and the bacterial community composition and function in the rhizosphere soil. The results showed that strain N3 significantly reduced the contents of Cd (64.7%) in wheat grain and DTPA-Cd (50.1%) in rhizosphere soil and increased the pH (from 6.84 to 6.97) and polyamine content. High-throughput sequencing results showed that inoculation of strain N3 reduced the diversity of the bacterial community; however, it increased the relative abundances of ß-Proteobacteria, Bacteroidetes, and Firmicutes in wheat rhizosphere soil. Meanwhile, strain N3 also increased the relative abundances of heavy metal-immobilizing bacteria and plant growth-promoting bacteria (Bacillus, Arthrobacter, Brevundimonas, Ensifer, Pedobacter, Rhizobium, Pseudomonas, Enterobacter, and Serratia) in wheat rhizosphere soil. The PICRUSt function prediction showed that strain N3 increased the copy number of genes involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil. These results indicated that the polyamine-producing bacteria N3 reduced the DTPA-Cd content by increasing the pH; the polyamine contents; the abundances of bacteria with heavy metal-immobilizing or plant growth-promoting traits; and the metabolic pathway involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil, thus inhibiting the absorption of Cd by wheat. The results provide theoretical basis and technical support for restoring farmland with excessive heavy metals and ensuring the safe production of wheat.

Expression of Novel L-Leucine Dehydrogenase and High-Level Production of L-Tert-Leucine Catalyzed by Engineered Escherichia coli.

Leucine dehydrogenase (LDH) is a NAD+-dependent oxidoreductase, which can selectively catalyze α-keto acids to obtain α-amino acids and their derivatives. It plays a key role in the biosynthesis of L-tert-leucine (L-Tle). As a non-naturally chiral amino acid, L-Tle can be used as an animal feed additive, nutrition fortifier, which is a perspective and important building block in the pharmaceutical, cosmetic, and food additive industry. In this study, four hypothetical leucine dehydrogenases were discovered by using genome mining technology, using the highly active leucine dehydrogenase LsLeuDH as a probe. These four leucine dehydrogenases were expressed in Escherichia coli BL21(DE3), respectively, and purified to homogeneity and characterized. Compared with the other enzymes, the specific activity of PfLeuDH also shows stronger advantage. In addition, the highly selective biosynthesis of L-Tle from trimethylpyruvic acid (TMP) was successfully carried out by whole-cell catalysis using engineered E. coli cells as biocatalyst, which can efficiently coexpress leucine dehydrogenase and formate dehydrogenase. One hundred-millimolar TMP was catalyzed for 25 h, and the yield and space-time yield of L-Tle reached 87.38% (e.e. >99.99%) and 10.90 g L-1 day-1. In short, this research has initially achieved the biosynthesis of L-Tle, laying a solid foundation for the realization of low-cost and large-scale biosynthesis of L-Tle.

[Functional Stability and Applicability of Heavy Metal Passivators in Reducing Cd Uptake by Lettuce].

The use of heavy metal passivators to prevent vegetables from absorbing heavy metals is an important measure to control heavy metal-polluted vegetable fields and to ensure the safe production of vegetables. A pot experiment of planting three times in succession was conducted to study the effects of Bacillus megaterium N3 (N3), rice husk biochar (BC), sheep manure organic fertilizer (SM), strain N3 combined with biochar (BC+N3), and strain N3 combined with sheep manure (SM+N3) on Cd uptake and the functional stability of lettuce using a heavy metal passivator only at the first planting. The comprehensive applicability of the passivation materials was evaluated by the dynamic weighted comprehensive function. The results showed that when lettuce was planted for the first time, compared with the control, all the heavy metal passivators could significantly reduce (61.2%-81%) the Cd content in the edible part of the lettuce. However, in the third cultivation of lettuce, only SM+N3 could significantly reduce the Cd uptake by lettuce, which indicated that SM+N3 had the best functional stability. The dynamic weighted comprehensive function was used to evaluate the Cd content in the edible part of fresh lettuce, available Cd content in the soil, yield, and remediation cost. The results showed that the comprehensive applicability of SM+N3 was the best, followed by that of SM, BC+N3, and BC, and the comprehensive evaluation effect of strain N3 was the worst. The results of this study provide a theoretical basis and technical support for remediation of heavy metal-contaminated vegetable fields.

Phytotoxic mechanism of allelochemical liquiritin on root growth of lettuce seedlings.

As the main active ingredient of the traditional Chinese medicine Glycyrrhiza uralensis Fisch, liquiritin has multiple biological activities, including anti-inflammatory, antihepatotoxicity, immune regulation, anti-virus and anti-cancer. In addition, liquiritin has been recognized as an allelochemical that displays markedly inhibitory effects on the growth of target plants, G. uralensis and lettuce. However, its phytotoxic mechanism remains unknown. In the present study, the mode of action of liquiritin against root growth of lettuce seedling was researched. After treatments with liquiritin, the cell division in root tips of lettuce seedlings was partly arrested, and the cell viability and root vitality were obviously lost. At the same time, overproduction of reactive oxygen species (ROS), malondialdehyde (MDA) and proline (Pro) in lettuce seedlings were induced by liquiritin. The results indicated that the phytotoxic effects of liquiritin was probably dependent on the induction of ROS overproduction, resulting in membrane lipids peroxidation following with cell death and mitosis process disorder.

[Bacterial Community Composition in Cadmium-Contaminated Soils in Xinxiang City and Its Ability to Reduce Cadmium Bioaccumulation in Pak Choi (Brassica chinensis L.)].

There are many types of bacteria in heavy metal-contaminated soils, including plant growth-promoting bacteria and heavy metal-immobilizing bacteria, which may potentially be used for the bioremediation of contaminated soil. In this study, the Cd-contaminated soil around a battery factory in Xinxiang City was collected and its bacterial community composition was analyzed using high-throughput sequencing (HTS) and the plate lineation separation method. The traditional culture method showed that bacteria isolated from contaminated soil belonged to four phyla (Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes) and 30 genera including Bacillus, Arthrobacter, and Rhizobium. HTS showed that the soil contained 25 phyla including Proteobacteria, Actinobacteria, and Acidobacteria and 400 genera. The HTS analysis revealed a greater diversity of the bacterial community than the traditional culture method. Network analysis was performed using the relative abundances of bacteria based on the phylogenetic molecular ecological network (pMEN) method. Network analysis showed that the key bacteria included Arthrobacter, Marmoricola, Nocardioides, Ferruginibacter, Flavitalea, Nitrospira, and Lysobacter. The Cd fixation and adsorption abilities of the 159 cultivable strains were determined. The results showed that 30 strains from 11 genera, including Aneurinibacillus, Arthrobacter, and Bacillus, were highly efficient. Six high-efficiency strains were shown to increase the biomass of pak choi (Brassica chinensis L.) and reduce the content of Cd in different pak choi tissues. This study provides candidate bacterial species for the remediation of heavy metal-contaminated soil in Xinxiang City and provides references for the bacterial community and its function in heavy metal-contaminated soil.

Efficient expression of novel glutamate decarboxylases and high level production of γ-aminobutyric acid catalyzed by engineered Escherichia coli.

Glutamate decarboxylase (GAD) has the potential of converting L-glutamate to gamma-aminobutyric acid (GABA), which is an important non-proteinogenic amino acid that has a potential use as food additive or dietary supplement for its physiological functions. A novel pyridoxal 5'-phosphate (PLP)-dependent glutamate decarboxylase (LsGAD) was cloned from GRAS (generally recognized as safe) Lactobacillus senmaizukei by genome mining and efficiently expressed in Escherichia coli BL21. The LsGAD displayed excellent temperature property, pH property and kinetic parameters compared with the probe LbGAD and the other GADs. By increasing the copy number of the LsGAD encoding gene, the expression level of LsGAD and the biosynthesis yield of GABA were increased, which was near to 2 times of that was expressed in single copy. These results established a solid foundation for increasing the added value of L-glutamate and the biosynthesis of GABA.

High level and enantioselective production of L-phenylglycine from racemic mandelic acid by engineered Escherichia coli using response surface methodology.

L-Phenylglycine (L-PHG) is a member of unnatural amino acids, and becoming more and more important as intermediate for pharmaceuticals, food additives and agrochemicals. However, the existing synthetic methods for L-PHG mainly rely on toxic cyanide chemistry and multistep processes. To provide green, safe and high enantioselective alternatives, we envisaged cascade biocatalysis for the one-pot synthesis of L-PHG from racemic mandelic acid. A engineered E. coli strain was established to co-express mandelate racemase, D-mandelate dehydrogenase and L-leucine dehydrogenase and catalyze a 3-step reaction in one pot, enantioselectively transforming racemic mandelic acid to give L-PHG (e.e. >99 %). After the conditions for biosynthesis of L-PHG optimized by response surface methodology, the yield and space-time yield of L-PHG can reach 87.89 % and 79.70 g·L-1·d-1, which was obviously improved. The high-yielding and enantioselective synthetic methods use cheap and green reagents, and E. coli whole-cell catalysts, thus providing green and useful alternative methods for manufacturing L-PHG.

[Endogenous Release of Nitrogen and Phosphorus in the Danjiangkou Reservoir].

In situ sediments were collected at different sites of the Danjiangkou Reservoir using a columnar sediment sampler, and the release rate of N and P at the sediment-water interface was determined through static incubation experiments and the diffusion model of interstitial water molecules. The results showed that there was a significant difference in the release rate for N and P from sediments collected at five sampling sites. The release rates of NH4+-N and PO43--P under static incubation conditions were 13.07-24.88 mg·(m2·d)-1 and 3.06-6.02 mg·(m2·d)-1, whereas those estimated by Fick's Fist Law were 2.67-7.25 mg·(m2·d)-1 and 0.04-0.18 mg·(m2·d)-1, respectively. Overall, the release rates of N and P in the tributaries were 1.48 and 1.57 times higher than that in the reservoir, respectively, and they tended to decrease from the north to the south. The R/F values of NH4+-N and PO43--P were 3.43-4.98 and 29.67-72.88, respectively. The highest release rates of N and P were observed in the Guojiashan tributary for both methods. However, it was found that the release rates of N and P estimated by Fick's Fist Law were significantly lower than those obtained by the simulation method, indicating that the static incubation experiment with intact sediments allowed the release rates of N and P to be closer to the actual situation compared to the interstitial water molecule diffusion model.

[Community Structure of Heavy Metal Immobilized Bacteria in the Lettuce (Lactuca sativa L.) Rhizosphere in Soil Polluted by Heavy Metals and Its Effects on Reducing Heavy Metal Accumulation in Lettuce].

To investigate the diversity of culturable bacteria and heavy metal-immobilizing bacteria in vegetable rhizosphere soil with high concentrations of heavy metals and explore these microbial resources, two samples of Italian lettuce rhizosphere soil with high heavy metal concentration (HY) and low heavy metal concentration (DK) were collected from Xinxiang, Henan Province. The diversity of culturable bacteria and heavy metal-immobilizing bacteria in the rhizosphere soil of lettuce was compared by culturable separation technology and a solution adsorption experiment. The enhancement of Cd and Pb immobilization and lettuce growth by the strains was also investigated in a hydroponic experiment. The results showed that 400 strains belonging to 3 phyla and 14 genera were isolated from the HY sample, with ß-Proteobacteria being the dominant phylum. Meanwhile, 400 strains belonging to 4 phyla and 30 genera were isolated from the DK sample, with Firmicutes being the dominant phylum. A total of 146 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the HY sample; Brevundimonas, Serratia, Arthrobacter, and Pseudarthrobacter were the main genera. However, 44 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the DK sample, with Bacillus being the main genus. Compared with the control, inoculation with Serratia liquefaciens HY-22, Bacillus thuringiensis HY-53, and Acinetobacter lwoffii HY-157 significantly increased the dry weight of roots (7.5%-77.6%) and shoots (15.4%-67.2%) of the Italian lettuce and cauliflower lettuce and reduced the contents of Cd (38.7%-66.6%) and Pb (34.7%-62.5%) in roots and shoots of Italian lettuce. In addition, the contents of Cd and Pb in the fresh shoots of Italian lettuce and cauliflower lettuce in the presence of Bacillus thuringiensis HY-53 were lower than the Cd and Pb limits set by national food safety standards. Thus, the results provided strain resources and a theoretical basis for the remediation of Cd-and Pb-contaminated farmlands for the safe production of crops.

[Isolation of Heavy Metal Immobilizing and Plant Growth-Promoting Bacteria and Its Effects on Reducing Heavy Metal Accumulation in Wheat].

The effects of heavy metal contamination on farmland continues to worsen progressively with an increase in anthropogenic activities such as industrial pollution and mining. Excess Cd and Pb in agricultural soils enter the food chain and adversely affect all organisms. Therefore, it is important to find an eco-friendly way to reduce heavy metal accumulation in crops. Based on their heavy metal resistance and growth-promoting characteristics, functional bacterial strains were screened and their effects on growth and heavy metal accumulation in wheat were verified via shaking flask adsorption and sand culture tests. Eighteen functional strains were isolated from the rhizospheric soil of Salvia setaria. Among them, Bacillus megaterium N3 and Serratia liquefaciens H12 were most effective at resisting high Cd (650 mg·L-1) and Pb (2700 mg·L-1) concentrations, and at producing indole-3-acetic acid (IAA) (56.6 mg·L-1and 69.1 mg·L-1, respectively), siderophores, and 1-Amino-1-cyclopropanecarboxylic acid (ACC) deaminase. Static incubation experiments showed that strains N3 and H12 significantly increased the NH4+ concentration and pH, and decreased the Cd (63.1%-73.8%) and Pb (69.1%-81.8%) concentration in solution. In sand cultures, strains N3 and H12 not only increased the dry weight of wheat roots (47.2%-97.4%) and shoots (65.3%-153%) significantly, but also significantly reduced the Cd (49.2%-68.3%) and Pb (27.4%-84.5%) content in wheat roots and shoots. Thus, the results provide strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safer production of crops.

[Community Structure and Predictive Functional Analysis of Surface Water Bacterioplankton in the Danjiangkou Reservoir].

Bacterioplankton are important components of aquatic ecosystems, and play a crucial role in the global biogeochemical cycle of nitrogen. In this study, surface-water samples were collected from Kuxin (the center of Danjiangkou Reservoir) and Qushou (the Middle Route of the South-to-North Water Diversion Project's canal head) in the Danjiangkou Reservoir in May 2016. Total DNA was isolated, and high-throughput sequencing was performed to analyze the community structure and diversity of bacteria. Phylogenetic analyses of 16S rDNA sequences showed that bacterial communities included species from 12 major phylogenetic groups. The predominant phylogenetic groups included Proteobacteria, Bacteroidetes, Firmicutes, Cyanobacteria, and Verrucomicrobia. The microbial biodiversity of Danjiangkou Reservoir bacterioplankton was greater in water samples from Qushou than in those from Kuxin. PICRUSt (phylogenetic investigation of communities by reconstruction of unobserved states) was used to determine the metabolic and functional abilities of the observed bacterial communities. Our results revealed a wide genetic diversity of organisms involved in various essential processes, such as Amino acid transport and metabolism, Transcription, Energy production and conversion, and Carbohydrate transport and metabolism. Thirty-five metabolic pathways involving nitrogen were detected. Key genes impacting the nitrogen cycle were detected in both the Kuxin and Qushou samples, and these encoded enzymes involved in nitrogen fixation (nifH), nitrification (hao), denitrification (narG、nirK、norB、nosZ), and assimilatory and dissimilatory nitrogen reduction to ammonia (nasA、narB、napA、nirA、nirB、nrfA). Copy numbers of 16S rRNA genes of each detected phylotype of Danjiangkou Reservoir bacterioplankton were uniformly higher in water samples from Kuxin than in water samples from Qushou. Our analyses of differences in nitrogen abatement potential between water samples, based on bacterial community composition and function, provide a foundation for setting water environmental protection policies in the Danjiangkou Reservoir.

One-Pot Synthesis of Phenylglyoxylic Acid from Racemic Mandelic Acids via Cascade Biocatalysis.

Phenylglyoxylic acid (PGA) are key building blocks and widely used to synthesize pharmaceutical intermediates or food additives. However, the existing synthetic methods for PGA generally involve toxic cyanide and complex processes. To explore an alternative method for PGA biosynthesis, we envisaged cascade biocatalysis for the one-pot synthesis of PGA from racemic mandelic acid. A novel mandelate racemase named ArMR showing higher expression level (216.9 U·mL-1 fermentation liquor) was cloned from Agrobacterium radiobacter and identified, and six recombinant Escherichia coli strains were engineered to coexpress three enzymes of mandelate racemase, d-mandelate dehydrogenase and l-lactate dehydrogenase, and transform racemic mandelic acid to PGA. Among them, the recombinant E. coli TCD 04, engineered to coexpress three enzymes of ArMR, LhDMDH, and LhLDH, can transform racemic mandelic acid (100 mM) to PGA with 98% conversion. Taken together, we provide a green approach for one-pot biosynthesis of PGA from racemic mandelic acid.

[Composition and Predictive Functional Analysis of Rhizosphere Bacterial Communities in Riparian Buffer Strips in the Danjiangkou Reservoir, China].

Microbial communities play crucial roles in the global biogeochemical nitrogen cycle. To our knowledge, the compositions and functions of rhizosphere communities in riparian buffer strips have not been reported. In this study, rhizosphere soil samples were collected from herbs (Vetiveria zizanioides and Phragmites australis), trees (Pyrus betulifolia), and shrubs (Discocleidion rufescens) in the Danjiangkou Reservoir in June 2017. High-throughput sequencing was performed to analyze the community structure and diversity of bacteria. Phylogenetic analysis based on 16S rDNA sequences shows that the bacterial communities can be divided into 31 major phylogenetic groups. The dominant phylogenetic groups include Proteobacteria, Bacteroidetes, Actinobacteria, Gemmatimonadetes, and Acidobacteria. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was used to determine the metabolic and functional abilities of the observed bacterial communities. Our results reveal a wide genetic diversity of organisms involved in various essential processes such as biosynthesis of other secondary metabolites, transcription, Glycan biosynthesis and metabolism, cell growth and death, and carbohydrate metabolism. Based on the 16S rRNA gene copy number of the detected phylotype, the bacterial rhizospheres of plants in riparian buffer strips can be ranked as follows:Discocleidion rufescens > Phragmites australis > Vetiveria zizanioides > Pyrus betulifolia. We analyzed the differences of different plants from the perspective of bacterial community composition and function and provide a foundation for vegetation construction and water environmental protection in riparian buffer strips of the Danjiangkou Reservoir.

Pichia nanzhaoensis sp. nov. and Pichia paraexigua f.a., sp. nov., two yeast species isolated from rotting wood.

Four yeast strains were isolated from rotting wood samples collected in the Baotianman Nature Reserve in Henan Province, Central China. On the basis of sequence analysis of the D1/D2 domains of the large subunit rRNA gene and the internal transcribed spacer regions, they were suggested to be two novel species of the genus Pichia. Pichia nanzhaoensis sp. nov. produces one to four spherical ascospores per ascus, and is most closely related to Candida pseudolambica. Pichia paraexigua f.a., sp. nov. is a sister taxa to Pichia exigua, but the formation of ascospores was not observed on various sporulation media. P. nanzhaoensis sp. nov. can weakly assimilate inulin, whereas P. paraexigua sp. nov. can weakly assimilate d-glucosamine. The type strain of Pichia nanzhaoensis is NYNU 178136T (=CICC 33279T=CBS 15346T) and the type strain of Pichia paraexigua is NYNU 178135T (=CICC 33278T=CBS 15237T).