Poly-β-(1,6)-N-acetylglucosamine (PNAG), the chief mediator of intercellular adhesion in many bacteria, plays an important role in biofilm formation. The pgaABCD locus was recognized from the whole genome sequence of...Poly-β-(1,6)-N-acetylglucosamine (PNAG), the chief mediator of intercellular adhesion in many bacteria, plays an important role in biofilm formation. The pgaABCD locus was recognized from the whole genome sequence of A. junii SH205. The enzyme glycosyltransferase, PgaC, catalyzes the production of PNAG with N-acetyl-D-glucosamine monomer. In this study, the possibility of PNAG biosynthesis in A. junii SH205 with its own PgaC was explored with the aid of bioinformatics. Multiple alignments of PgaC sequences of different bacteria were used to identify conserved amino acid residues that might be critical for the functioning of the protein. Three-dimensional model of A. junii SH205 PgaC was generated for spatial visualization of amino acid residues. The analyses have shown that the protein PgaC has five conserved amino acids, Asp<sup>140</sup>, Asp<sup>233</sup>, Gln<sup>269</sup>, Arg<sup>272</sup> and Trp<sup>273</sup>, critical for the activity of enzyme. Interaction of UDP-N-acetylglucosamine within the conserved pocket of glycosyltransferase was explored from molecular docking studies.展开更多
For the 2008 Olympic Games, drastic control measures were implemented on industrial and urban emissions of sulfur dioxide （SO2）, nitrogen oxides （NOx） and other pollutants to address the issues of poor air quality...For the 2008 Olympic Games, drastic control measures were implemented on industrial and urban emissions of sulfur dioxide （SO2）, nitrogen oxides （NOx） and other pollutants to address the issues of poor air quality in Beijing. To investigate the effects of SO2 and NOx reductions on the particulate sulfate and nitrate concentrations as well as their size distributions, size-segregated aerosol samples were collected using micro-orifice uniform deposit impactors （MOUDIs） at urban and downwind rural sites in Beijing before and after full-scale controls. During the sampling period, the mass concentrations of fine particles （PMI.s） at the urban and rural sites were 94.0 and 85.9 p.g m-3, respectively. More than 90% of the sulfates and 60% of nitrates formed as fine particles. Benefiting from the advantageous meteorological conditions and the source controls, sulfates were observed in rather low concentrations and primarily in condensation mode during the Olympics. The effects of the control measures were separately analyzed for the northerly and the southerly air-mass-dominated days to account for any bias. After the control measures were implemented, PM, sulfates, and nitrates were significantly reduced when the northerly air masses prevailed, with a higher percentage of reduction in larger particles. The droplet mode particles, which dominated the sulfates and nitrates before the controls were implemented, were remarkably reduced in mass concentration after the control measures were implemented. Nevertheless, when the polluted southerly air masses prevailed, the local source control measures in Beijing did not effectively reduce the ambient sulfate concentration due to the enormous regional contribution from the North China Plain.展开更多
Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical ...Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer （CPMA） combined with a differential mobility analyzer （DMA） was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm3 for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm3 for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation （NPF） event decreased considerably, indicating the significant contribution of organics to new particle growth.展开更多
文摘Poly-β-(1,6)-N-acetylglucosamine (PNAG), the chief mediator of intercellular adhesion in many bacteria, plays an important role in biofilm formation. The pgaABCD locus was recognized from the whole genome sequence of A. junii SH205. The enzyme glycosyltransferase, PgaC, catalyzes the production of PNAG with N-acetyl-D-glucosamine monomer. In this study, the possibility of PNAG biosynthesis in A. junii SH205 with its own PgaC was explored with the aid of bioinformatics. Multiple alignments of PgaC sequences of different bacteria were used to identify conserved amino acid residues that might be critical for the functioning of the protein. Three-dimensional model of A. junii SH205 PgaC was generated for spatial visualization of amino acid residues. The analyses have shown that the protein PgaC has five conserved amino acids, Asp<sup>140</sup>, Asp<sup>233</sup>, Gln<sup>269</sup>, Arg<sup>272</sup> and Trp<sup>273</sup>, critical for the activity of enzyme. Interaction of UDP-N-acetylglucosamine within the conserved pocket of glycosyltransferase was explored from molecular docking studies.
基金the National Key Basic Research Program of China (973program)，a key project of the Shandong Provincial Environmental Protection Department，the Niche Area Development Scheme of the Hong Kong Polytechnic University，the Hong Kong Research Grants Council，the central level,scientific research institutes for basic R & D special fund business
文摘For the 2008 Olympic Games, drastic control measures were implemented on industrial and urban emissions of sulfur dioxide （SO2）, nitrogen oxides （NOx） and other pollutants to address the issues of poor air quality in Beijing. To investigate the effects of SO2 and NOx reductions on the particulate sulfate and nitrate concentrations as well as their size distributions, size-segregated aerosol samples were collected using micro-orifice uniform deposit impactors （MOUDIs） at urban and downwind rural sites in Beijing before and after full-scale controls. During the sampling period, the mass concentrations of fine particles （PMI.s） at the urban and rural sites were 94.0 and 85.9 p.g m-3, respectively. More than 90% of the sulfates and 60% of nitrates formed as fine particles. Benefiting from the advantageous meteorological conditions and the source controls, sulfates were observed in rather low concentrations and primarily in condensation mode during the Olympics. The effects of the control measures were separately analyzed for the northerly and the southerly air-mass-dominated days to account for any bias. After the control measures were implemented, PM, sulfates, and nitrates were significantly reduced when the northerly air masses prevailed, with a higher percentage of reduction in larger particles. The droplet mode particles, which dominated the sulfates and nitrates before the controls were implemented, were remarkably reduced in mass concentration after the control measures were implemented. Nevertheless, when the polluted southerly air masses prevailed, the local source control measures in Beijing did not effectively reduce the ambient sulfate concentration due to the enormous regional contribution from the North China Plain.
基金supported by the following projects:the National Key R&D(Research and Development)Program of China(No.2016YFC0202800:Task 1)the National Natural Science Foundation of China(Nos.41475127,41571130021)the framework research program on ‘Photochemical smog in China’ financed by the Swedish Research Council(No.639-2013-6917)
文摘Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer （CPMA） combined with a differential mobility analyzer （DMA） was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm3 for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm3 for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation （NPF） event decreased considerably, indicating the significant contribution of organics to new particle growth.
