Screening And Resistance Mechanism Study On A Cadmium Resistant Strain

The prevalence of heavy metal pollution is one of the world's environmental problems.Bioremediation is an efficient way for the disposal of heavy metals. One of the key basic objectives is to screen the tolerant and high enriching bacteria from the environment,and further optimize the bacteria to repair and govern the heavy metals.The rapid development of the modern microbiology and molecular biology technically provides a high-performance and convenient way for the investigation.At present,the most important thing is how to obtain the tolerant and high enriching bacteria,and try to make a breakthrough and utilization from their mechanism.The purpose of the study was divided into two parts:first of all,the use of bioinformatics techniques is to analyze the important micro-organisms Cd-associated proteins- Cadmium Resistance Transporter for homology comparison and phylogenetic analysis.Cd transporter of the amino acid sequence is obvious species-specific.Cd transporter of Staphylococcus Aureus is differcent in genus,but Bacillus,as well as a Mycobacterium of the protein sequence has a good conservative;they are more than 4 times of all the inter-membrane protein.The function of transmembrane reflects the protein structure and function of the uniform.Cd transporter protein sequence to the secondary structure mainly isα-helix,β-folded and random coil.The exception of B.cereus.R309803,the sequence up to the secondary structure isα-helix. Projections from three-dimensional structure,most of Cd transporter protein folding sequence is multidrug efflux transporter AcrB transmembrane domain, which is very stable and efficient.Screening and resistance mechanism study on a sadmium resistant strain were as follows.In the analysis of biological information,based on tolerance or Cd-rich micro-organisms were screened,optimization and identification,and Cd adsorption mechanism and the role of the preliminary study and discussion. Collected from the suburban of Chengdu,chemical plant outfall sludge,dilute the concentration,the use of Cd²⁺ concentration gradient separation increased screening.A strain is isolated from 200mg/L Cd²⁺ medium.1,Strains morphological analysis,the physiological and biochemical experiments,16SrDNA identified as Enterobacter cloacae.2,The strain which is fast growing in hard natural environment,can grow in M9 medium.The adsorption capacity of Cd to increase 9%,adsorption capacity of 54mg/g.3,Strains can live in the 1500mg/L Cd²⁺ liquid medium,400mg/L Cd²⁺ solid growth medium.The best growing conditions:pH6.4 beef extract medium,34℃culture,the culture liquid to appropriate 22-34h.4,The resistant strains to Cd may be encoded by the genome.Through transmission electron microscopy(TEM) both inside and outside of the cell changes showed that the adsorption of Cd²⁺ the cell surface rough,irregular shape.Resistance mechanism is mainly extracellular precipitation.Finally,conclusions are made as follow by refering and analyzing: bioinformatic analysis was an important guide and assist to experiment; Cadmium Resistance Transporterare obvious species-specific and similar to those of third level structure;screened Enterobacter cloacea with a high tolerance to high Cd accumulation characteristics,genetic engineering can be used as host bacteria,bioabsorbent material;resistance mechanism is mainly extracellular precipitation.