Acknowledgements
We are grateful to KURDI of Kasetsart University, NRCT, Thailand and the JSPS-NRCT Core-University Program on ‘Microbial Resources’ and ‘Biotechnology’ for financial and technical support. Special thanks are due to Professor Dr Y. Yamada, Professor Dr T. Seki and Assistant Professor Dr H. Kawasaki for their valuable suggestions and kind encouragement. Many thanks go to the students, technicians and others who helped with some experiments.