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Assistant Professor Dr. Skorn Mongkolsuk
Thailand Outstanding Scientist Award Year 1998

The Achievements of Dr. Skorn Mongkolsuk

During the past decade, research in Dr. Skorn's laboratory can be divided into two main phases. The first phase commenced after joining the Department of Microbiology, Faculty of Science, Mahidol University. Professor Dr. Stitaya Sirisinha kindly pointed out the problem of liver fluke infection in the northeastern region of Thailand and the shortcomings of parasite (Opisthorchis viverrini) detection by conventional methods. With these ideas in mind, a research project on the isolation and characterization of repeated DNA sequence and ribosomal RNA genes for use as DNA probes to spectifically detect the parasite was initiated in collaboration with Professor Dr. Stitaya. The highly repeated DNA sequences from O. civerrini, and the ribosomal RNA genes, were successfully cloned and sequenced. Characterization of the cloned repeated DNA showed that it could be used as a highly specific, but moderately sensitive DNA probe to detect the parasite. The probe sensitivity could be increased be making oligonucleotide primers corresponding to the sequence for PCR detection. Analysis of the ribosomal RNA gene sequence revealed variable regions interspersed among conserved regions. The sequence of variable regions are ideal for making parasite specific primers for PCR reactions which allow highly specific and sensitive detection of the parasite. Additional research on finer tuning of these DNA probes could lead to useful tools to aid in parasite detection, rapid disease diagnosis, and epidemiological study.

 

The second phase of research work began when Dr. Skorn moved to the Department of Biotechnology, Faculty of Science, Mahidol University and received a joint appointment as head of the Laboratory of Biotechnology, Chulabhorn Research Institute. Thailand is a major producer of agricultural products. Billions of baht are lost through crop disease and yield reduction. It is thus a logical choice to diversify and direct our research into this field. Consequently, we embarked a research program on Xanthomonas, a family of plant pathogen and soil bacteria. Xanthomona is known to infect every economically important crop. One active plant defense response against bacterial infection is to increase th synthesis of reactive oxygen species (ROS) including H2O2, organic peroxide, and superoxide. ROS functions in the siganal transduction of plant defense response in addition to directly killing bacteria and inhibiting proliferation. In order to grow inside the plant, bacteria need to protect themselves from harmful ROS. We have discovered important physiological parameters in Xanthomona that lead to protection from ROS. Exposure of Xanthomona to low levels of peroxide and superoxide not only induce synthesis of oxidative stress protective enzymes, such as catalase and alkyl hydroperoxide reductase but also confer protection against subsequent exposure to killing concentrations of oxidants. This inducible response is an important component of bacterial stress survival. To understand the molecular mechanism of the ROS inducible response, we adopted a multigene analysis approach. The rational of this approach is based on an assumption that analysis of one structural or regulatory gene might not give a clear understanding of a bacterial global stress response. Thus, the structural genes responsible for peroxide metabolism, i.e. catalase, alkyl hydroperoxide reductase, glutathione reductase, and a peroxide sensor transcription regulator oxyR, were isolated from Xanthomona. All of these genes were characterized at the molecular levels, and results show that many aspects of their regulation, chromosomal organization and biochemical properties, differ from other bacteria. Mutant analysis of these genes also revealed unique physiological properties. These results suggest that Xanthomona oxidative stress response differs from other previously studied bacteria. In our search for genes involved in peroxide metabolism, we have isolated a novel gene designated ohr for organic hydroperoxide resistance. Analysis of the amino acid sequence revealed that homologues of ohr are present in the genomes of many diverse families of bacteria, but their functions are still unknown. It is our hope that current work on biochemical characterization of Ohr will lead to clearer understanding of its physiological role and lead to the discovery of a new pathway of peroxide metabolism.

 

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