Multidrug-resistant (MDR) bacterial infections are a severe threat to public health owing to their high risk of fatality. Noticeably, the premature degradation and undeveloped imaging ability of antibiotics still remain challenging. Herein, a selenium nanosystem in response to a bacteria-infected microenvironment is proposed as an antibiotic substitute to detect and inhibit methicillin-resistant Staphylococcus aureus (MRSA) with a combined strategy. Using natural red blood cell membrane (RBCM) and bacteria-responsive gelatin nanoparticles (GNPs), the Ru–Se@GNP-RBCM nanosystem was constructed for effective delivery of Ru-complex-modified selenium nanoparticles (Ru–Se NPs). Taking advantage of natural RBCM, the immune system clearance was reduced and exotoxins were neutralized efficiently. GNPs could be degraded by gelatinase in pathogen-infected areas in situ; therefore, Ru–Se NPs were released to destroy the bacteria cells. Ru–Se NPs with intense fluorescence imaging capability could accurately monitor the infection treatment process. Moreover, excellent in vivo bacteria elimination and a facilitated wound healing process were confirmed by two kinds of MRSA-infected mice models. Overall, the above advantages proved that the prepared nanosystem is a promising antibiotic alternative to combat the ever-threatening multidrug-resistant bacteria.

The contamination and outflow of atmospheric polycyclic aromatic hydrocarbons (PAHs) in the Chinese Northern Plain, a region with a total area of 300 000 km2 and a high PAH emission density, were investigated. Polyurethane foam (PUF) and PM10 samples were collected at 46 sites located in urban, rural (towns or villages), and control (remote mountain) areas in the winter from November 2005 to February 2006. The observed concentrations of atmospheric PAHs were generally higher than those reported for developed countries and southern Chinese cities. It was found that there was no significant difference in air PAH concentrations between the urban and the rural areas (514 +/- 563 ng/m3 and 610 +/- 645 ng/ m3, respectively), while the PAH concentrations at the control sites (57.1 +/- 12.6 ng/m3) were 1 order of magnitude lower than those at the other sites. The primary reason for the similarity in PAH concentrations between urban and rural areas was the fact that the predominant sources of biomass and domestic coal combustion were widely spread over the study area. The partition constants (K(PM10)) of PAHs were significantly correlated to the corresponding values of subcooled liquid-vapor pressure (pL0). However, the regression slopes of log K(PM10) versus log pL0 were much steeper than -1, indicating adsorption dominated over absorption. Three distinct patterns of outflow from the study area were identified by forward trajectory and cluster analysis.

Robust and highly fluorescent N-doped carbon dots (CDs) are obtained from a hybrid source, alginic acid and ethanediamine. During a hydrothermal process, the raw materials are propelled to form nano-size particles; these resultant CDs possess desirable functional groups on the particle surface. We have further investigated their optical performance under various pH conditions as well as their capacity for sensing metal ions. The N-doped CDs especially exhibit remarkable acid-evoked fluorescence enhancement under acidic conditions. Finally, the as-prepared CDs are tested for their ability to detect of Fe 3+ in acidic pure water and urban river water media, the fluorescence-quenching mechanism and recovery properties of the CDs/Fe 3+ mixture are also investigated.

Graphene oxide (GO) has attracted great interest in many different areas, as a delivery vehicle for antibacterial agents and has shown high potential. Although silver nanoparticles (AgNPs) have strong antibacterial effect, the biological application of AgNPs is often hindered by their aggregation and low stability. In this study, we developed an approach of polyoxyethylene bis (amine) (PEG) directed AgNPs grown on GO, then we combined the two materials to prepare a series of functionalized GO bearing different size AgNPs, and studied the size effects of AgNPs on growth inhibition of Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus). We evaluated the antibacterial effect of GO@PEG@AgNPs on E.coli and 16 loaded on a greater number of GO, the higher will be the load efficiency, so that smaller-sized AgNPs show stronger antibacterial activity.The time-and concentration-dependent antibacterial effects of the four GO@PEG@AgNPs composites were evaluated by OD 600 . As shown in Fig 4B, before treatment with the four composites, the OD 600 value of E. coli was 0.77 and that of S. aureus 0.85. Furthermore, after treatment with 10 µg/mL GO@PEG@AgNPs composites for 4 h, the OD 600 of E. coli decreased to 0.2 (Fig 4Ba), indicating almost no E. coli survival, whereas the OD 600 of S. aureus was 0.4 (Fig 4Bb), indicating that the cytotoxicity of GO@PEG@Ag composites were greater to E. coli than to S. aureus. We also observed the same trend in concentration dependence (Fig 3S) of toxicity to E. coli and S. aureus treated with the four composites. As shown in Fig 4A, for each composite, the number of surviving E. coli was smaller than that of surviving S. aureus. Moreover, in the group treated with 10 nm GO@PEG@AgNPs, nearly no E. coli bacterial colony on the LB agar plate was formed, and only a few E. coli cells remained viable in the treated culture, markedly lower than the number of viable S. aureus cells. This result may be because of the greater thickness of gram-positive than gram-negative bacteria cell walls. Ca 2+ and Mg 2+ can decrease the antibacterial activity of GO@PEG@AgNPsTo investigate the effect of 10 nm GO@PEG@AgNPs on the bacterial surface, various metallic ions such as Zn 2+ , Cu 2+ , K + , Na + , Ca 2+ , and Mg 2+ on bacterial suspensions were investigated. The results revealed that the OD600 of E.coli clearly increased when Ca 2+ and Mg 2+ were added to the bacterial suspensions, indicating that the antimicrobial activity of the nanoparticles decreased (Fig 5). Antibacterial Fig 4. Viable bacteria remaining in the LB-agar plates of E. coli and S.aureus after being treated with four types GO@PEG@AgNPs respectively (A) (a and f are control groups, b and g are 80 nm, c and h are 50 nm, d and i are 30 nm, e and j are 10 nm), Effect of time antibacterial activity (B) of four types GO@PEG@AgNPs represented by OD600 for (a) E. coli and (b) S. aureus.

No abstract

Fe(III) oxyhydroxides play critical roles in arsenic immobilization due to their strong surface affinity for arsenic. However, the role of bacteria in Fe(II) oxidation and the subsequent immobilization of arsenic has not been thoroughly investigated to date, especially under the micro-oxic conditions present in soils and sediments where these microorganisms thrive. In the present study, we used gel-stabilized gradient systems to investigate arsenic immobilization during microaerophilic microbial Fe(II) oxidation and Fe(III) oxyhydroxide formation. The removal and immobilization of dissolved As(III) and As(V) proceeded via the formation of biogenic Fe(III) oxyhydroxides through microbial Fe(II) oxidation. After 30 days of incubation, the concentration of dissolved arsenic decreased from 600 to 4.8 μg L-1. When an Fe(III) oxyhydroxide formed in the presence of As(III), most of the arsenic ultimately was found as As(V), indicating that As(III) oxidation accompanied arsenic immobilization. The structure of the microbial community in As(III) incubations was highly differentiated with respect to the As(V)-bearing ending incubations. The As(III)containing incubations contained the arsenite oxidase gene, suggesting the potential for microbially mediated As(III) oxidation. The findings of the present study suggest that As(III) immobilization can occur in microoxic environments after microbial Fe(II) oxidation and biogenic Fe(III) oxyhydroxide formation via the direct microbial oxidation of As(III) to As(V). This study demonstrates that microbial Fe(II) and As(III) oxidation are important geochemical processes for arsenic immobilization in micro-oxic soils and sediments.

No abstract

Bio-production of optically pure L-lactic acid from food waste has attracted much interest as it can treat organic wastes with simultaneous recovery of valuable by-products. However, the yield of L-lactic acid was very low and no optically pure L-lactic acid was produced in the literature due to (1) the lower activity of enzymes involved in hydrolysis and L-lactic acid generation, and (2) the participation of other enzymes related to D-lactic acid and acetic and propionic acids production. In this paper, a new strategy was reported for effective production of optically pure L-lactic acid from food waste at ambient temperature, i.e. via regulating key enzyme activity by sewage sludge supplement and intermittent alkaline fermentation. It was found that not only optically pure L-lactic acid was produced, but the yield was enhanced by 2.89-fold. The mechanism study showed that the activities of enzymes relevant to food waste hydrolysis and lactic acid production were enhanced, and the key enzymes related to volatile fatty acids and D-lactic acid generations were severally decreased or inhibited. Also, the microbes responsible for L-lactic acid production were selectively proliferated. Finally, the pilot-scale continuous experiment was conducted to testify the feasibility of this new technique.