Nitrite- and N2O-reducing bacteria respond differently to ecological factors in saline lakes.

The distribution of nitrite- and N2O-reducing bacteria is key to potential N2O emission from lakes. However, such information in highland saline lakes remains unknown. Here, we investigated the abundance and community composition of nitrite- and N2O-reducing bacteria in the sediments of six saline lakes on the Qing-Tibetan Plateau. The studied lakes covered a wide range of salinity (1.0-340.0 g/L). Results showed that in the studied saline lake sediments, nitrite-reducing bacteria were significantly more abundant than N2O-reducing bacteria, and their abundances ranged 7.14 × 103-8.26 × 108 and 1.18 × 106-6.51 × 107 copies per gram sediment (dry weight), respectively. Nitrite-reducing bacteria were mainly affiliated with α-, ß- and γ-Proteobacteria, with ß- and α-Proteobacteria being dominant in low- and high-salinity lakes, respectively; N2O-reducing bacterial communities mainly consisted of Proteobacteria (α-, ß-, γ- and δ-subgroups), Bacteroidetes, Verrucomicrobia, Actinobacteria, Chloroflexi, Gemmatimonadetes and Balneolaeota, with Proteobacteria and Bacteroidetes/Verrucomicrobia dominating in low- and high-salinity lakes, respectively. The nitrite- and N2O-reducing bacterial communities showed distinct responses to ecological factors, and they were mainly regulated by mineralogical and physicochemical factors, respectively. In response to salinity change, the community composition of nitrite-reducing bacteria was more stable than that of N2O-reducing bacteria. These findings suggest that nitrite- and N2O-reducing bacteria may prefer niches with different salinity.

Anti-Inflammatory Effects of an Extract from Pseudomonas aeruginosa and Its Purified Product 1-Hydroxyphenazine on RAW264.7 Cells.

The purpose of this study was to discuss the effects of an extract from the culture medium of Pseudomonas aeruginosa (P. aeruginosa) 2016NX1 (chloroform extract of P. aeruginosa, CEPA) and its purified product 1-hydroxyphenazine on RAW264.7 cell inflammation. Cell viability was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method. TNF-α production was determined by an ELISA method. The effects of CEPA and its purified product 1-hydroxyphenazine on cell morphology were investigated using an inverted microscope. Quantitative real-time PCR was performed to determine mRNA expression levels. CEPA and 1-hydroxyphenazine had no obvious toxicity to cells when their concentrations were no more than 20 µg ml-1 and 5 µg ml-1, respectively. Both CEPA and 1-hydroxyphenazine suppressed the secretion of TNF-α and significantly reduced the mRNA expression levels of TNF-α, IL-1ß, and IL-6. Both CEPA and 1-hydroxyphenazine inhibited M1 cell polarization after lipopolysaccharide (LPS) stimulation. The results in this article lay a good foundation for the biopharmaceutical applications of CEPA and 1-hydroxyphenazine in the future. CEPA and 1-hydroxyphenazine had certain anti-inflammatory activity, and inhibited LPS-induced RAW264.7 cell inflammation. Our findings suggest that CEPA and 1-hydroxyphenazine are potential chemicals with anti-inflammatory activity.

Isolation and Characterization of Pseudomonas sp. Cr13 and Its Application in Removal of Heavy Metal Chromium.

The purpose of this study was to elaborate the characteristics of Pseudomonas sp. Cr13, including physiological and biochemical characteristics, optimization of growth conditions, minimum inhibitory concentration of Cr6+ and resistance to other heavy metals, removal efficiency of Cr6+, and antibiotics sensitivity. A strain Pseudomonas sp. Cr13 was screened from mine-contaminated soils, which could tolerate high concentration of Cr6+ (up to 250 mg l-1) and Cd2+ (50 mg l-1). The optimum pH, NaCl concentration, and temperature for growth were 6, 10% NaCl, and 30 °C, respectively. The removal efficiency of Cr6+ by strain Pseudomonas sp. Cr13 was studied. The removal efficiency of Cr6+ decreased with the increased concentration of Cr6+. Under the optimal conditions, the maximum of the removal rate can reach up to 94.26% in contaminated soils. In addition, antibiotics sensitivity of this strain was investigated. It was found that this strain was sensitive to nine types of antibiotics, which would lay a good foundation for the choice of selective marker in genetic engineering modification of this strain. The results in this article would lay a good foundation for the bioremediation of heavy metals pollution in the future. Pseudomonas sp. Cr13 can tolerate high concentration of Cr6+ and partially remove Cr6+, which make Cr13 an attractive option for the bioremediation of heavy metal chromium (Cr). Our findings suggest that Pseudomonas sp. Cr13 is a potential bacterium with the ability of bioremediation of heavy metal Cr.

Analysis of Fungal Composition in Mine-Contaminated Soils in Hechi City.

Fungi play an important role in bioremediation of contaminated soil. However, the diversity of fungal populations in four mine-contaminated soils located in Hechi City has remained unexplored. In this study, high-throughput sequencing of ITS was performed to investigate the diversity and abundance of fungal communities in four mine-contaminated soils in Hechi city. Phylogenetic taxonomy showed that the fungal communities included five phyla. Ascomycota and Basidiomycota were the most abundant phyla in four samples. The most abundant fungi included Agaricomycetes, Nectriaceae, Eurotiomycetes, Mortierellaceae, Incertae sedis, Trichocomaceae, Sordariomycetes, and Fusarium. Various fungi with the potential of bioremediation and industrial application were discussed. The results of fungal composition will provide a clue for isolation of new fungi with the potential of bioremediation and industrial application. Furthermore, this study will lay a good foundation for modifying the indigenous fungi by genetic engineering in the future.

Preparing 3D-printable silk fibroin hydrogels with robustness by a two-step crosslinking method.

Regenerated silk fibroin (RSF) features excellent biocompatibility and high-strength mechanical properties. However, traditional RSF-based materials can hardly be applied in 3D printing, which has shown great potential in producing artificial implants. In this work, we report a 3D printable RSF hydrogel formed by a weak, chemically crosslinked network. After the 3D printing process, the mechanical properties of the above hydrogel can be remarkably improved by a ripening process. The maximum compressive modulus of this RSF hydrogel is 2.5 MPa, reaching the same order of magnitude as natural elastomers such as cartilage. The mechanical properties of this hydrogel are superior to most RSF-based 3D printed hydrogels. The investigation of gelation mechanism reveals that the chemically crosslinked network can constrain the growth of ß-sheet structures of RSF to form a dense and uniform physical network. Such a physically crosslinked network endows the high strength and good resilience of RSF hydrogels. With both good biocompatibility and mechanical properties, this double-network hydrogel has potential in producing 3D printed scaffolds for tissue engineering.

Chirality transfer based on reversible C-C bond formation/breaking in nickel(II) complexes.

The reaction of (1R)-(-)-myrtenal-derived benzothiazoline with nickel(II) acetate in ethanol exclusively gave a Schiff base-type nickel(II) complex having M helical configurational myrtenyl arms, which is reversibly converted to a non-innocent-type complex having additional S,S configurational asymmetric carbon centres.