Application of heavy metal resistance related proteins for mercury bioremediation

• Main Authors: Kuo-Hsing Lin, 林國興
• Other Authors: Chieh-Chen Huang
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/25191695780063015284

博士 === 國立中興大學 === 生命科學系所 === 98 === Mercury and its derivates is known toxic to human beings as well as neurotoxicity to damage brain and led to neurondegeneration disease. In aquatic system, mercury is easily transferred to methylmercury by bacteria in the sediment. As some poisoned case in the past, such as Minamata in Japan in 1950s and Iraq in 1970, it is identified that methylmercury were taken in through food chain. Metallothioneins (MTs) are low-molecular-weight, cysteine-rich intracellular proteins with high affinity to toxic metal cations for detoxification, such as Cd2+, Hg2+ and MeHg+ and also possess the ability of scavenging reactive oxygen species. The tilapia, human and mouse MTs were expressed either in cytosol or fusion to outer membrane protein (OmpC) in the recombinant E. coli. Exposure to mercury or free radicals shows that outer-membrane-target ones had 10 to 20 % higher sequestering ability than cytosolically ones. In scavenging 2,2-azinobis(3-ethylbenzothiazoline-6 -sulfonic acid) diammonium salt free radicals, the outer membrane MTs had 10% higher scavenging ability than cytosolic MTs. Among three MTs, tilapia MT presents best activity of adsorbing mercury and scavenging radicals. Moreover, the caboxy-H2DCFDA was used to detect reactive oxygen species. It is observed that the oxidative stress decrease was dependent on cadmium binding ability as higher metal bonding ability led to lower oxidative stress induced by cadmium. Methylmercury is frequently found in aquatic system and could be amplified through food chain. On the other hand, the organomercurial lyase merB3 gene of Bacillus megaterium MB1 is known to have board spectrum organomercurials resistance enzymes. The purified MerB3 was characterized in vitro with the presence of phenylmercuric acetate (PMA) and methylmercury chloride (MMC) and present similar catalytic activity to MerB1 whereas, MerB2 did not possess the ability to degrade the two organomercurials. As introducing merB3 gene to zebrafish, the LC50 of wild type and transgenic zebrafish in MMC were 376nM and 404nM, respectively, while in PMA were 200nM and 237nM. The transgenesis show better resistance ability than wild type. However, the phenotype of teratogenic effects on tail was no obvious difference for both zebrafish.