Potential dissemination mechanism of the tetC gene in Aeromonas media from the aerobic biofilm reactor under oxytetracycline stresses

The tetC gene has been found to be one of the most widely distributed tetracycline resistance (tet) genes in various environmental niches, but the detailed dissemination mechanisms are still largely unknown. In the present study, 11 tetC-containing Aeromonas media strains were isolated from an aerobic biofilm reactor under oxytetracycline stresses, and the genome of one strain was sequenced using the PacBio RSII sequencing approach to reveal the genetic environment of tetC. The tetC gene was carried by an IS26 composite transposon, named Tn6434. The tetC-carrying Tn6434 structure was detected in all of the A. media strains either in a novel plasmid pAeme2 (n=9) or other DNA molecules (n=2) by PCR screening. The NCBI database searching result shows that this structure was also present in the plasmids or chromosomes of other 13 genera, indicating the transferability of Tn6434. Inverse PCR and sequencing confirmed that Tn6434 can form a circular intermediate and is able to incorporate into a preexisting IS26 element, suggesting that Tn6434 might be responsible for the dissemination of tetC between different DNA molecules. This study will be helpful in uncovering the spread mechanism of tet genes in water environments.     

拉氏中值定理的发现与证明

给出了拉氏中值定理的发现过程和一个新的证明方法．     

络合萃取法处理高浓度H酸废水

研究了用络合萃取法回收H酸废母液中染料中间体的多种影响因素，得出了最佳工艺参数。实验结果表明，通过萃取工艺，H酸废母液中染料中间体回收率可达90％以上，萃余液中CODcr d (1000-3000)mg/L之间，此工艺可使废母液中的回收物浓缩5－10倍，萃取剂可以再生回用。