Biodegradation of dioxin compounds by Pseudomonas mendocina A6 strain

• Main Authors: LEE, SSU-YI, 李思毅
• Other Authors: WANG,HUI-LIANG
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/6n35t2

碩士 === 國立高雄師範大學 === 生物科技系 === 105 === Mud was obtained from the National Kaohsiung Normal University (NKNU) Yen-Chao campus and subjected to bacterial screening. The 16SrRNA gene and 16S-23S Internal Transcribed Space (ITS) region were used to identify a culture that was given the name P. mendocina A6. It was discovered that this culture may possess the genes which cause the destruction of dioxin benzine ring structures and the substitution of halogen compounds in dioxin that leads to dehalogenation. Previous studies have shown that P. mendocina A6 has seven genes that can degrade dioxin, of which two are ring-destroying genes and five are dechlorination genes. National Sun Yat-sen University (NSYSU) provided the seven dioxin-degrading primers used to carry out a comparison of the A6 gene identification and sequencing, and it was revealed that the A6 dioxin-degrading gene shares a 90% or higher level of similarity with the Pseudomonas mendocina NSYSU (already published), and that its ring-destroying and dechlorination genes are partially similar to those of the Pseudomonas mendocina ymp (published in the US) found on the National Center for Biotechnology Information (NCBI) website. Thus, the primers of the ymp's two ring-destroying genes and five dechlorination genes were independently designed in order to carry out a comparison of the A6's gene identification and sequencing, and it was revealed that the A6 and ymp's seven-stage degradation genes shared a similarity of about 95%. The two bacteria genes nucleotide sequences were then converted into protein to compare their amino acid composition, and it was found that the continuity and similarity levels of the two genes was 95% or higher, indicating that P. mendocina A6 also possesses a dioxin-degrading gene. P. mendocina A6's dioxin-degrading property was utilized to carry out a dioxin degradation test, in which the A6 reaction was added to sewage-contaminated soil and regular tube samplings were obtained over the span of two months and delivered to Cheng Shiu University Super Micro Mass Research & Technology Center to test their dioxin-degrading abilities. The tests showed that low concentrations of dioxin can be effectively reduced by about 60%. As for the standard tests for high concentrations of dioxin, weekly concentration readings were taken three weeks after the P. mendocina A6 reaction was added, and it was found that the A6 reduced dioxin levels by about 20%. Even though this figure was comparatively lower, the fact that it took only three weeks to degrade such a high concentration of dioxin compounds (which are exceptionally difficult to destroy) to this extent showed that the A6 was indeed effective. This also proved that P. mendocina A6 possessed the ability and genes to degrade dioxin compounds. Tests showed that the A6 culture was able to effectively reduce the chemical oxygen demand (COD) of organic matter in industrial waste by utilizing the strong oxidizing agent potassium dichromate to oxidize the organic material in wastewater. The amount of potassium dichromate consumed was expressed in terms of chemical oxygen demand (COD). A comparison of the changes in COD values in wastewater (between the group in which A6 was not added and the groups in which various concentrations of A6 were added) was carried out and expressed in analysis charts. It was found which that the COD values in the groups in which A6 was added declined form 600 mg/L to 160~240 mg/L, proving that the A6 bacteria was able to effectively reduce organic COD in wastewater.