Department of Microbiology, Columbia University, New York, USA
Received 17 September, 2006
Revised 21 April, 2007
Accepted 24 May, 2007
Correspondence to Donghui Zhu, Department of Microbiology, Columbia University, 701 W 168 Street, HHSC#610, New York 10032, USA Tel: +1 212 342 1399; fax: +1 212 342 1677; e-mail: [email protected]