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Based on 15N tracer technique, absorption of different concentrations of ammonium nitrogen (N-NH4+), nitrate nitrogen (N-NO3-) and glycine (N-Gly) by root of six species of alpine forage (Puccinellia tenuiflora, Poa crymophila, Festuca sinensis, Elymus nutans, Elymus sibiricus and Bromus inermis) was studied in a hydroponic culture. The uptake kinetic parameter was analyzed according to Michaelis-Menten equation. The Michaelis-Menten equation represents the velocity equation for the relationship between the initial rate of an enzymatic reaction and the substrate concentration. The result showed that the absorption range of ammonium nitrogen, nitrate nitrogen and glycine by root of six species of alpine plant were 1.1–20.9 μmol·g–1·h–1, 0.4–3.4 μmol·g–1·h–1 and 0.1–3.7 μmol·g–1·h–1, which accounts for 68.8%-74.7%, 12.0%-27.0% and 4.3%-13.4% of total absorptivity, respectively. The six kinds of P. tenuiflora, P. crymophila, F. sinensis, E. nutans, E. sibiricus and B. inermis showed significant difference in nitrogen absorption. At the same concentration, the absorption of nitrogen in different forms of the same herbage is different. The absorptive amount of ammonium nitrogen was the highest among them, then the glycine, the nitrate nitrogen was least absorbed. The results could provide a theoretical basis for nitrogen utilization in alpine forages. For example, P. tenuiflora showed a much higher ability of absorbing nitrogen nutrition in a high salt environment and could be a more suitable herbage to be planted in saline-alkali soil in the Qinghai-Tibet Plateau as compared with E. nutans.

Tunicosaponins are natural products extracted from Psammosilene tunicoides, which is an important ingredient of Yunnan Baiyao Powder, an ancient and famous Asian herbal medicine. The representative aglycones of tunicosaponins are the oleanane-type triterpenoids of gypsogenin and quillaic acid, which were found to manipulate a broad range of virus-host fusion via wrapping the heptad repeat-2 (HR2) domain prevalent in viral envelopes. However, the unknown biosynthetic pathway and difficulty in chemical synthesis hinder the therapeutic use of tunicosaponins. Here, two novel cytochrome P450-dependent monooxygenases that take part in the biosynthesis of tunicosaponins, CYP716A262 (CYP091) and CYP72A567 (CYP099), were identified from P. tunicoides. In addition, the whole biosynthesis pathway of the tunicosaponin aglycones was reconstituted in yeast by transforming the platform strain BY-bAS with the CYP716A262 and CYP716A567 genes, the resulting strain could produce 146.84 and 314.01 mg/L of gypsogenin and quillaic acid, respectively. This synthetic biology platform for complicated metabolic pathways elucidation and microbial cell factories construction can provide alternative sources of important natural products, helping conserve natural plant resources.

The spread of antibiotic resistance genes (ARGs) in the environment has aroused growing concern for human health and ecological safety. Recent studies have confirmed that engineered nanomaterials can increase the environmental risk of ARG dissemination mediated by conjugation and transformation. However, whether nanomaterials can mediate the transductive transfer of ARGs by phage infection has not been reported. In this work, the effect of nano-TiO2 on the horizontal transfer of ARGs to E. coli TG1 through transduction by constructed phage gM13 was investigated. Our results showed that nano-TiO2 concentration, particle size, mating time and the ratio of gM13/TG1 could influence the transductive transfer of ARGs. Further studies revealed that nano-TiO2 could promote bacteriophage attachment on cell surfaces, which contributed to gM13 infection. Meanwhile, increasing membrane permeability induced by nano-TiO2 could alleviate transmembrane resistance, which facilitated the infectious entry of phage gM13 into periplasmic space. The expressions of pilus-related genes were improved when E. coli TG1 was exposed to nano-TiO2. Thus, this work is beneficial for gaining a better understanding about the multiple environmental effects of increasingly released nanomaterials and is useful for the control of ARG dissemination in the environment.

Photocatalytic catalysis is widely used for pollutant degradation. Since some pollutants with oxidative nature are readily reduced rather than oxidized and reductive reaction caused by photogenerated electrons is limited in the presence of oxygen, photocatalytic reduction process is more applicable for the degradation of pollutants with oxidative nature than oxidation. In this work, a novel bio-photoelectric reductive degradation system (BPRDS), composed of an electrochemically active bacterium Shewanella oneidensis MR-1 and a visible-light photocatalyst Ag3PO4, was established under anaerobic conditions and its photodegradation performance was evaluated through degrading rhodamine B (RhB), a typical organic pollutant. The as-synthesized Ag3PO4 nanoparticles exhibited absorption in the entire visible spectral range of 400–800 nm. RhB could be degraded in BPRDS with visible light irradiation under anaerobic conditions, but not be decomposed in the absence of Shewanella cells. Block of Mtr respiratory pathway, a transmembrane electron transport chain, resulted in a reduction in degradation rate of RHB in BPRDS. Dose of riboflavin also substantially decreased the RhB degradation. These results suggest that the electrons released by Shewanella were involved in the RhB photodegradation, which was achieved via a stepwise N-deethylation process. In BPRDS, RhB was degraded by photoreduction, rather than photooxidation. This work is useful to develop integrated physico-chemical-microbial systems for pollutant degradation, facilitate better understanding about the biophotoelectric reductive degradation mechanisms and beneficial to their applications for environmental remediation. Keywords: Shewanella oneidensis MR-1, Anaerobic degradation, Microbial electron transfer, Nanomaterial, Photoreduction

Recently, paradoxical combinations of colistin with anti-Gram-positive bacterial agents were introduced as a treatment alternative for multidrug-resistant Acinetobacter baumannii (MDRAB) infection. We assessed the therapeutic efficacy of the colistin–linezolid combination regimen in vitro and in a murine model of Acinetobacter baumannii pneumonia. A multidrug-resistant clinical strain (MDRAB31) and an extensively drug-resistant clinical strain (XDRAB78) were used in this study. The survival rates of mice and bacterial counts in lung tissue were used to assess the effects of colistin–linezolid combination. The survival rates of colistin–linezolid combination groups significantly increased compared with colistin groups for MDRAB31 (72% versus 32%, P = 0.03) and for XDRAB78 (92% versus 68%, P = 0.031). The colistin–linezolid combination groups significantly reduced the bacterial counts in lung tissue compared with colistin groups for MDRAB31 and for XDRAB78 (P

Coronary artery disease (CAD) is a leading cause of death, and microRNAs (miRNAs) are widely involved in physiological and pathological processes of CAD. We chose the targetscore method calculated via the variational Bayesian Gaussian mixture model (VB-GMM) as the prediction method of target genes. By observing the density overlap, we selected the thresholds of miRNA-1 and miRNA-155. In total, 18 target genes of miRNA-1, and 19 target genes of miRNA-155 were identified. The threshold of miRNA-146a was selected using the |logFC| value, and 16 target genes were screened out. In this study, our major contribution was to predict the target messenger RNAs (mRNAs) of the chosen miRNAs with the gene expression profiles, which can effectively reduce the workload of screening. Although the validated genes constituted only a small part in the final prediction results, it is a good sign for research in the future. It means that we could provide new research aims for future studies focusing on miRNA regulatory mechanisms.

C-2α hydroxylated triterpenoids are a large class of plant secondary metabolites. These compounds, such as maslinic, corosolic and alphitolic acid, have important biological activities against HIV, cancer and diabetes. However, the biosynthesis pathways of these compounds have not been completely elucidated. Specifically, the cytochrome P450 (CYP) enzyme responsible for C-2α hydroxylation was unknown. In this study, a novel CYP enzyme that catalyzes C-2α hydroxylation was identified in Crataegus pinnatifida (Hawthorn) using a metabolic engineering platform. It is a multifunctional enzyme with C-2α oxidase activity on oleanane-, ursane- and lupane-type pentacyclic triterpenoids. In addition, the complete biosynthesis pathways of these three triterpenoids were reconstituted in yeast, resulting in the production of 384, 141 and 23 mg/L of maslinic, corosolic and alphitolic acid, respectively. This metabolic engineering platform for functional gene identification and strain engineering can serve as the basis for creating alternative pathways for the microbial production of important natural products.

Electrochemically active bacteria (EAB) are effective for the bioreduction of nitroaromatic compounds (NACs), but the exact reduction mechanisms are unclear yet. Therefore, 3-nitrobenzenesulfonate (NBS) was used to explore the biodegradation mechanism of NACs by EAB. Results show that NBS could be anaerobically degraded by Shewanella oneidensis MR-1. The generation of aminoaromatic compounds was accompanied with the NBS reduction, indicating that NBS was biodegraded via reductive approach by S. oneidensis MR-1. The impacts of NBS concentration and cell density on the NBS reduction were evaluated. The removal of NBS depends mainly on the transmembrane electron transfer of S. oneidensis MR-1. Impairment of Mtr respiratory pathway was found to mitigate the reduction of NBS, suggesting that the anaerobic biodegradation of NBS occurred extracellularly. Knocking out cymA severely impaired the extracellular reduction ability of S. oneidensis MR-1. However, the phenotype of ΔcymA mutant could be compensated by the exogenous electron mediators, implying the trans-outer membrane diffusion of mediators into the periplasmic space. This work provides a new insight into the anaerobic reduction of aromatic contaminants by EAB.

Electrochemically active bacteria (EAB) have attracted great attention in the pollutant biodegradation due to its unique extracellular reduction capacity. But the reduction ability of biogenic electron is insufficient to achieve degradation of many pollutants. Thus, in the present study, Shewanella oneidensis MR-1 was firstly employed to biofabricate visible light-responsive CdS nanocrystals. A bio-photoelectric reductive degradation system (BPRDS) which established by combining S. oneidensis MR-1 and self-synthesized CdS achieved efficient degradation of trypan blue under photoexcitation. Chemical analyses revealed that the cleavage of azo bonds resulted in the decolorization. Blocking of transmembrane electron transfer significantly decreased the decolorization efficiency of BPRDS. After incubating for 5 h, the removal of trypan blue in BPRDS inoculated with ΔmtrA, ΔmtrB, ΔmtrC/omcA, or ΔcymA mutants reduced by 16.46 %, 27.88 %, 25.03 %, and 57.9 %, respectively, compared with wild-type strain inoculated, which indicated that biogenic electron produced by anaerobic respiratory of S. oneidensis MR-1 acted as a hole scavenger and maintained the anaerobic photoexcitation of CdS in BPRDS. Photoexcitation was essential for the BPRDS. This work may provide a new strategy for anaerobic remediation of organic contaminants and be beneficial for the better understanding about anaerobic photodegradation mechanism.