Cyanomethylquinolones as a New Class of Potential Multitargeting Broad-Spectrum Antibacterial Agents.

This work identified a class of cyanomethylquinolones (CQs) and their carboxyl analogues as potential multitargeting antibacterial candidates. Most of the prepared compounds showed high antibacterial activities against most of the tested bacteria, exhibiting lower MIC values (0.125-2 µg/mL) than those of clinical norfloxacin, ciprofloxacin, and clinafloxacin. The low hemolysis, drug resistance, and cytotoxicity, as well as good predictive pharmacokinetics of active CQs and carboxyl analogues revealed their development potential. Furthermore, they could eradicate the established biofilm, facilitating bacterial exposure to these antibacterial candidates. These active compounds could induce bacterial death through multitargeting effects, including intercalating into DNA, up-regulating reactive oxygen species, damaging membranes directly, and impeding metabolism. Moreover, the highly active cyclopropyl CQ 15 exhibited more effective in vivo anti-MRSA potency than ciprofloxacin. These findings highlight the potential of CQs and their carboxyl analogues as multitargeting broad-spectrum antibacterial candidates for treating intractable bacterial infections.

Discovery of indolylacryloyl-derived oxacins as novel potential broad-spectrum antibacterial candidates.

The emergence of serious bacterial resistance towards clinical oxacins poses a considerable threat to global public health, necessitating the development of novel structural antibacterial agents. Seven types of novel indolylacryloyl-derived oxacins (IDOs) were designed and synthesized for the first time from commercial 3,4-difluoroaniline via an eight-step procedure. The synthesized compounds were characterized by modern spectroscopic techniques. All target molecules were evaluated for antimicrobial activities. Most of the prepared IDOs showed a broad antibacterial spectrum and strong activities against the tested strains, especially ethoxycarbonyl IDO 10d (0.25-0.5 µg/mL) and hydroxyethyl IDO 10e (0.25-1 µg/mL) exhibited much superior antibacterial efficacies to reference drug norfloxacin. These highly active IDOs also displayed low hemolysis, cytotoxicity and resistance, as well as rapid bactericidal capacity. Further investigations indicated that ethoxycarbonyl IDO 10d and hydroxyethyl IDO 10e could effectively reduce the exopolysaccharide content and eradicate the formed biofilm, which might delay the development of drug resistance. Preliminary exploration of the antibacterial mechanism revealed that active IDOs could not only destroy membrane integrity, resulting in changes in membrane permeability, but also promote the accumulation of reactive oxygen species, leading to the production of malondialdehyde and decreased bacterial metabolism. Moreover, they exhibited the capability to bind with DNA and DNA gyrase, forming supramolecular complexes through various noncovalent interactions, thereby inhibiting DNA replication and causing bacterial death. All the above results suggested that the newly developed indolylacryloyl-derived oxacins should hold great promise as potential multitargeting broad-spectrum antibacterial candidates to overcome drug resistance.

Variations of the nirS-, nirK-, and nosZ-denitrifying bacterial communities in a northern Chinese soil as affected by different long-term irrigation regimes.

Denitrification causes nitrogen loss from agricultural soils and emission of nitrous oxide (N2O). Water addition leads to an increase in soil moisture which greatly influenced soil denitrification. However, it is unclear how irrigation management affected the denitrifying bacterial communities in agricultural systems. In the present study, we investigated the abundance, diversity, and composition of the nirS-, nirK-, and nosZ-denitrifying bacterial communities in the soil under different long-term irrigation regimes by using real-time PCR (qPCR) and Illumina MiSeq sequencing approaches. Results showed that the abundance of nosZ gene was 3.94-6.01 and 35.09-60.21 times more than that of nirS and nirK genes, and the abundance of nirS gene was 5.84-15.30 times higher than that of nirK gene, respectively, in different irrigation treatments. However, the Alpha diversity indices of the nirK-denitrifying bacterial community were higher than those of the nirS- and nosZ-denitrifying bacterial communities. Proteobacteria was the predominant phylum for all the denitrifying bacterial communities, and significant differences were observed in relative abundance of Alphaproteobacteria and Betaproteobacteria in predominant class between different irrigation treatments for the nirS- and nosZ-denitrifying bacterial communities, respectively. Irrigation significantly affected the abundance, Shannon and Invsimpson indices, and structure of the nirS- and nosZ-denitrifying bacterial communities, whereas it only minor influenced the structure of the nirK-denitrifying bacterial community. Furthermore, the shifts in abundance, diversity, and structure of the nirS- and nosZ-denitrifying bacterial communities correlated significantly with the soil property variations; however, no soil property was significantly correlated with the abundance and Alpha diversity index of the nirK-denitrifying bacterial community. Our results demonstrate that different long-term irrigation regimes greatly altered the abundance, diversity, and structure of the nirS- and nosZ- rather than the nirK-denitrifying bacterial communities.

[Effects of legume-oat intercropping on abundance and community structure of soil N2-fixing bacteria]. / 豆科作物间作燕麦对土壤固氮微生物丰度和群落结构的影响.

In this study, real-time PCR and high-throughput sequencing approaches were employed to investigate the abundance and community structure of N2-fixing bacteria in a field experiment with three planting patterns (Oat monoculture, O; Soybean-oat intercropping, OSO; Mung bean-oat intercropping, OMO). The results showed that soil chemical properties varied significantly in different soil samples (P＜0.05). The abundance of nifH gene varied from 1.75×1010 to 7.37×1010 copies·g-1 dry soil in all soil samples. The copy numbers of nifH gene in OSO and OMO were 2.18, 2.64, and 1.92, 2.57 times as much as that in O at jointing and mature stages, with a significant decline from jointing to mature stage for all treatments (P＜0.05). Rarefaction curve and cove-rage results proved the nifH gene sequencing results were reliable, and the diversity index showed that the N2-fixing bacteria diversity of OSO was much higher than that of O. Azohydromonas, Azotobacter, Bradyrhizobium, Skermanella and other groups that could not be classified are the dominant genera, with significant differences in proportion of these dominant groups observed among all soil samples (P＜0.05). Venn and PCA analysis indicated that there were greater differences of nifH gene communities between jointing and mature stages; however, the OSO and OMO had similar communities in both stages. All these results confirmed that legume-oat intercropping significantly increased the abundance and changed the community composition of N2-fixing bacteria in oat soils.

[Selenium (Se)uptake and transformation mechanisms and physiological function in plant: A review]. / æ¤ç‰©ç¡’å¸æ”¶è½¬åŒ–æœºåˆ¶åŠç”Ÿç†ä½œç”¨ç ”ç©¶è¿›å±•.

Selenium (Se) is an essential nutrient for many organisms, including microbe, animal and human, but the Se uptake and transformation mechanisms and physiological roles in plant still are controversial until now. Se could improve the growth and tolerance of plant at an appropriate le-vel, but could be toxic at higher levels. Research concerning Se uptake and metabolism in plant were promoted by Se biofortification and Se phytoremediation induced by the issues of Se deficiency in food and Se pollution in special areas. Recently, the results of Se uptake and transformation in plant have indicated that there are significant differences of Se accumulation and physiological roles in various plants and significant influence of soil conditions on Se uptake of plant. In addition, the process of Se metabolism in Se hyperaccumulators and its regulation were revealed gradually with the studies on improvement of Se uptake in plant. According to the results of Se biofortification in crop and Se phytoremediation so far, we summarized the advances in the studies with the reference to Se distribution in environment, the detail process of Se uptake, key regulators of transformation and its physiological roles in plant. We hope this can provide a novel insight to further research upon Se in plant.

[Soil microbial diversity of artificial peashrub plantation on North Loess Plateau of China].

Peashrub (Caragana korshinskii Kom) is a kind of excellent shrub used for dune-fixation in Loess Plateau of China. In order to explore relationship between peashrub and soil microorganisms, microbial communities diversity associated with rhizoplane, rhizosphere and bulk soil of peashrub in Loess Plateau of China were characterized based on a culture-independent approach. Three 16S rDNA gene libraries were constructed, respectively, and each different profile was used to define an operational taxonomic unit (OTU). The numbers of microorganisms decreased as root proximity decreased and a few OTUs became dominant. Phylogenetic analyses indicated that Proteobacteria was the predominant group in rhizoplane, which included many alpha-Proteobacteria, partially consisted of rhizobia, and gamma-Proteobacteria beneficial to plant growth. In bulk soil, the most frequent OTUs were closely related to Archaea, while Acidobacteria was the dominant group in rhizosphere of peashrub. The diversity index (H') was higher in rhizosphere than in rhizoplane and bulk soil, whereas microbial populations in rhizoplane and bulk soil had the greater dominance indices (D). It was shown that there was a significant change in microbial species composition along the root gradient, shifting from complex plant-associated bacterial community in the root habitats to a simple bacterial community in the bulk soil. These results showed that plant roots and soil conditions created a selective environment for microbial populations.

[Identification of moderately halophilic strain DTY1 and study of its halotolerant mechanism].

A bacterial strain DTY1 was isolated from Caragana rhizosphere in Wuzhai, Shanxi. It was identified as Bacillus alcalophilus according to its morphological, physiological, biochemical characters and the sequence analysis of the 16S rDNA. The growth salinity of strain DTY1 was between 0 - 1.2mol/L NaCl. The optimum growth temperature and pH was 32 degrees C and 7 - 10, respectively. Strain DTY1 could accumulate 1.40mg/g ectoine in LB medium containing 0.17mol/L NaCl quantified by high-performance liquid chromatography. And the yield of ectoine improved as increasing of medium salinity. In this study, an ectB gene which potentially encoded a L-2, 4-diaminobutyric acid transaminase enzyme and involved in biosynthesis of ectoine was cloned by PCR-mediated screening from the genomic library of strain DTY1. Nucleotide sequencing indicated that the ectB gene contains 1284bp, and is predicated to encode a peptide of 427 amino acids, which shares 81% identity to that of the EctB of B. halodurans C-125. One potential sigma70 promoter and a 23bp palindromic sequence were found to locate at the upstream of ectB gene.