DNA sequencing, phylogenetic and mapping studies suggest that the class 1 integron found in pathogens arose when one member of the diverse family of environmental class 1 integrons became embedded into a Tn402 transposon. However, the timing of this event and the selective forces that first fixed the newly formed element in a bacterial lineage are still unknown. Biocides have a longer use in clinical practice than antibiotics, and a qac (quaternary ammonium compound) resistance gene, or remnant thereof, is a normal feature of class 1 integrons recovered from clinical isolates. Consequently, it is possible that the initial selective advantage was conferred by resistance to biocides, mediated by qac. Here, we show that diverse qac gene cassettes are a dominant feature of cassette arrays from environmental class 1 integrons, and that they occur in the absence of any antibiotic resistance gene cassettes. They are present in arrays that are dynamic, acquiring and rearranging gene cassettes within the arrays. The abundance of qac gene cassettes makes them a likely candidate for participation in the original insertion into Tn402, and as a source of a readily selectable phenotype. More broadly, the increasing use of qac and other biocides at the present time seems likely to promote the fixation of further novel genetic elements, with unpredictable and potentially adverse consequences for human health and agriculture.

Using a door-to-door approach to integrate inter-and intra-city travel times, this paper simulates the changes in regional territorial and population accessibility, spatial equity, as well as the winner and loser cities resulting from High-speed rail (HSR) network development in the Yangtze River Delta, China. HSR network development has a minimal effect on decreasing the disparity in overall territorial accessibility but leads to an obvious decrease in the disparity in population accessibility. Seven types of winner and loser cities are summarised according to their net winner population and stations locations. Poor access to the city centre from HSR stations is a common problem for many cities in the YRD, and more integrated development is needed for future HSR planning and construction.

No abstract

No abstract

PM2.5 is a main source of China’s frequent air pollution. Using real-time monitoring of PM2.5 data in 338 Chinese cities during 2014–2017, this study employed multi-temporal and multi-spatial scale statistical analysis to reveal the temporal and spatial characteristics of PM2.5 patterns and a spatial econometric model to quantify the socio-economic driving factors of PM2.5 concentration changes. The results are as follows: (1) The annual average value of PM2.5 concentration decreased year by year and the monthly average showed a U-shaped curve from January to December. The daily mean value of PM2.5 concentration had the characteristics of pulse-type fluctuation and the hourly variation presented a bimodal curve. (2) During 2014–2017, the overall PM2.5 pollution reduced significantly, but that of more than two-thirds of cities still exceeded the standard value (35 μg/m3) regulated by Chinese government. PM2.5 pollution patterns showed high values in central and eastern Chinese cities and low values in peripheral areas, with the distinction evident along the same line that delineates China’s uneven population distribution. (3) Population agglomeration, industrial development, foreign investment, transportation, and pollution emissions contributed to the increase of PM2.5 concentration. Urban population density contributed most significantly while economic development and technological progress reduced PM2.5 concentration. The results also suggest that China in general remains a “pollution shelter” for foreign-funded enterprises.

Phenanthrene-degrading bacterium strain ZX4 was isolated from an oil-contaminated soil, and identified as Sphingomonas paucimobilis based on 16S rDNA sequence, cellular fatty acid composition, mol% G + C and Biolog-GN tests. Besides phenanthrene, strain ZX4 could also utilize naphthalene, fluorene and other aromatic compounds. The growth on salicylic acid and catechol showed that the strain degraded phenanthrene via salicylate pathway, while the assay of catechol 2,3-dioxygenase revealed catechol could be metabolized through meta-cleavage pathway. Three genes, including two of meta-cleavage operon genes and one of GST encoding gene were obtained. The order of genes arrangement was similar to S-type metapathway operons. The phylogenetic trees based on 16S rDNA sequence and meta-pathway gene both revealed that strain ZX4 is clustered with strains from genus Sphingomonas.

No abstract

No abstract