1. Hanoi University of Science, Biology Faculty and CETASD, 334 Nguyen Trai, Hanoi, Vietnam, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Ueberlandstrasse 133, CH-8600 Dübendorf, Switzerland, and University of Lausanne, Department of Fundamental Microbiology, Bâtiment de Biologie, CH-1015 Lausanne, Switzerland