Water 2015, xx, 1-x; doi:10.3390/—— OPEN ACCESS water ISSN 2073-4441 www.mdpi.com/journal/water Article Local interactions of Vibrio cholerae with environmental drivers and phytoplankton: insight from a long-term field campaign in Matlab, Bangladesh L. RIGHETTO 1, *, R. U. ZAMAN 2 , L. MARI 1 , Z. H. MAHMUD 2 , E. BERTUZZO 3 , M. CIDDIO 1 , R. CASAGRANDI 1 , S. ISLAM 2 , A. RINALDO 3,4 , M. GATTO 1 1 Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy 2 Environmental Microbiology Lab, International Center for Diarrhoeal Diseases Research, Dhaka, Bangladesh 3 Laboratory of Ecohydrology ECHO/IIE/ENAC, Ecole Polytechnique Fédérale Lausanne, Lausanne, Switzerland 4 Dipartimento ICEA, Università di Padova, Padova, Italy * Author to whom correspondence should be addressed; E-mail: lorenzo.righetto@polimi.it Received: xx / Accepted: xx / Published: xx Abstract: The study of the ecology of Vibrio cholerae is still a debated issue, but certainly is relevant to discerning the key elements that allow the pathogen to be (or become) endemic in a region. In general, the processes leading to the survival and thriving of V. cholerae in aquatic environments involve several and entwined drivers, which encompass both abiotic and biotic factors. In this work we report on a long-term field campaign, conducted in one of the ponds which lie by the local villages of the area of Matlab, Bangladesh, a well-known cholera endemic region. There, during a period of 20 months, we monitored both abiotic drivers and the densities of V. cholerae O1 and phytoplankton, which is one of the possible actors involved in symbiotic interactions with bacteria. We make use of statistical analyses to test for associations of V. cholerae with the other measured variables, aiming in particular at identifying the most significant factors via stepwise-regression methods and relative risk analysis. Phytoplankton turns out to be associated with V. cholerae density in almost all our tests, even though a few statistics related to our meteorological data are sufficient to reproduce the observed V. cholerae density patterns. Our analysis can be useful to single out the processes governing V. cholerae ecology, in order to build process-based models that can inform epidemiological tools on the actual drivers of cholera seasonality in endemic regions.