The Ecology of Vibrio cholerae in Bangladesh
Cholera is a deadly diarrheal disease caused by the bacterium Vibrio cholerae. Although cholera still occurs throughout the developing world, including an ongoing epidemic in Haiti that has killed some 10,000 people, only in Bangladesh does it occur in regular, bi-annual cycles. The milieu of factors that trigger these seasonal epidemics is unknown. To address this question, I am investigating the dependence of the environmental dynamics of V. cholerae on ecological factors such as the climate and the abundance of other microorganisms. This work is based at the International Center for Diarrheal Disease Research, Bangladesh (icddr,b).

The dependence of Vibrio cholerae dynamics on salinity
Vibrio cholerae is a halophilic bacterium, which means it moves and grows best in salty water. This makes the esturaine environment of the Ganges delta an ideal habitat for this organism. However, salinity within the delta varies significantly throughout the year due to the seasonal precipitation cycle. Therefore, it has been proposed that the spring cholera epidemic is facilitated by elevated levels of salinity at the end of the dry season, when the water pressure in the aquifer is low and seawater intrudes inland. To address this question, I am measuring the abundance of V. cholerae along the Ganges River, between the Bay of Bengal and Dhaka, over the course of many months. In addition to measuring bacterial abundance using conventional methods, I am also monitoring the entire microbial community structure within the river by using high-throughput sequencing methods.

Microbial friends and foes of Vibrio cholerae
Pathogenic Vibrio cholerae forms several ecological relationships that contribute to or antagonize its fitness in the environment. For example, while the exoskeletons of microscopic plankton provide V. cholerae with a surface for colonization, vibriophage kills the bacterium and limits cholera epidemics. Furthermore, V. cholerae possesses a quorum-sensing system with which it can initiate genetic programs in response to the presence of other bacteria. For example, dormant V. cholerae begins to grow when it senses a quorum of active V. cholerae cells the environment. Whether or not V. cholerae responds to other species of bacteria in the environment is unknown. I am using high-throughput sequencing to measure the microbial community structure in an urban waterway in Dhaka during a cholera epidemic. This analysis will reveal whether the abundance of other genera of bacteria co-fluctuates with or forecasts the abundance of V. cholerae during this time.

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