| Recently, the discovery of perchlorate, ClO4, in a large number of water, ground and foods, has been gaining increasing attention all over the world due to its interference with the function of the thyroid gland as well as its potential health impact at low-dose exposure. Therefore, to search for the effective method for removing these pollutants, became the main environmental problem world widely. Research showed that micro-biological degradation play an important role in the transport and transformation of these pollutants, finally disappearing from the environment. It also was the primary handiest and economy way of removing contaminants. Under the anaerobic surroundings, bacteria reduced the perchlorate to innocuous chloride iron with the degradation via the sequence:ClO4→ClO3→ClO2→Cl+O2. Transformation of perchlorate to chlorate, ClO3, was the rate-limiting step with complete conversion to chloride. Perchlorate reducing microorganisms (PRMs) were ubiquitous in the natural environment, and applied to perchlorate remedation through enrichment. After a series of separation and purification procedures, two strains were identified by molecular biological methods and biotechnology informatics, two important elements of the growth conditions, temperature and pH, were determined after a train of tests.The main contents and results of the research as following:Firstly, total DNA was extracted from the effluent of JD15 and JD22, which were from Jiangbin and Dagang wastewater treatment plant, respectively, and 16S rDNA fragments were amplified, cloned and sequenced, the sequencing results were blasted in the Genebank of NCBI, the corresponding bacterial species were compared with the micro-organisms in EBI and constructing the phylogenetic tree. The analysis results showed that the 16S rDNA of JD15 showed 100% homology to the Dechloromonas sp SIUL, and JD22 showed 97% homology to the Dechlorospirillum.Secondly, the research analyzed JD15 and JD22 further by molecular biological methods and biotechnology informatics, the results showed that JD15 was found up to 99% similarity to Dechloromonas agitate in a subunit of perchloric reductase, and JD22 was found up to 99% similarity to Dechlorospirillum sp in a subunit of perchloric reductase.Thirdly, changing their growth factors, bacterial growth curves were drew by measuring the OD value of Dechloromonas agitate and Dechlorospirillum every other day, while bacterial degradation curves were drew by using the ion chromatography. The results showed that Dechloromonas agitate and Dechlorospirillum grow faster and better under the conditions of 24℃and pH7. Biomass reached the maximum within 7-10 days, then turned down and began to decline. Bacteria consumed a large number of nutrients, the metabolites accumulated rapidly. Eventually, they died and autolyzed. The removal rate of perchlorate reached 86%±6.5% in 14 days, which was gradually weakened with the decline of the strains. Through the experiment discovered the most suitable temperature is 24～30℃, clearly, when the temperature was above 37℃or below 15℃, the efficiencies decreased. Degradation rate can be influenced by other factors such as pH, it will achieve maximum under the condition of pH=7. |
