Role of system biogeochemistry on the distribution and abundance of Vibrio organisms in Karnaphuli River estuary, Bangladesh
Microbial Ecology and Applied Microbiology
Final Report Abstract
In first studies we investigated the role of system biogeochemistry and catastrophic events (cyclones and landslides) on the distribution and abundance of Vibrio organisms in Karnaphuli River estuary, Bangladesh. Vibrio distribution patterns in the Karnaphuli estuary are mainly influenced by salinity and suspended particle load. Human waste in point pollution sources can also enrich Vibrio population, but this input was significant only in a limited area and did not greatly influence the general trend governed by the changes in salinity, turbidity and climatic events. Cyclones can not only cause damages by inundating vast coastal areas but also increase estuarine Vibrio population by sediment resuspension, likely triggering outbreaks of Vibrio-related diseases including devastating cholera. Vibrios and their proportion of total aerobic bacteria were highest after the cyclone, and also increased after the landslide. A cyclone did not significantly change pre-cyclone fecal coliform abundance, while this increased about 10-times after a severe landslide. Sediment resuspension (e.g., by landslide or cyclone events) could represent an additional source of organic-rich substrate for increased bacterial growth or involve a direct input of particle-attached Vibrio. Hence, the characterization and quantification of the benthic and suspended particle-attached microbial community deserves increased attention. The combination of both, extended salt intrusion and higher turbidities caused by stronger and more frequent storms and deforestation-derived erosion could increase the amount of vibrios in the coastal zone of the Bay of Bengal, further endangering aquatic resources and human health. In the Sunderban mangroves and adjoining estuarine waters different ecosystem compartments were screened for V. cholerae abundance. The content of chitin and cultivable vibrios was determined in different size fractions of suspended particulate matter. The main finding was that maximum values for V. cholerae O1 and chitin were both present in the same small size fraction <20 µm and not, as usually assumed and studied, in the larger size fractions which mostly harbor zooplankton, larger exuviae or a wide variety of phytoplankton. Since covariation does not imply causality, and SPM also peaks in this fraction, it is not possible to assert which of the particulate parameters had a major influence on Vibrio abundance: the amount of chitin or the simply the amount of suspended particles. This consideration is relevant for two main reasons: mangroves are environments naturally rich in chitinaceous organisms (e.g. plankton, detritus, shrimps, and crabs), and chitin abundance can favor Vibrio mutations. Further, the high density of shrimps and vibrios in aquaculture ponds and the nutrient input from megacities that induces coastal plankton blooms could favor the emergence of new and highly pathogenic Vibrio types in and near South Asian mangroves. Regarding the role of particle load on Vibrio dynamics, higher turbidities in tropical estuaries caused by stronger and more frequent cyclones and erosion associated with changing patterns of land use, together with more extensive salt intrusion could favor growth and habitat expansion of vibrios, with increasing risks for aquatic resources and human health in the coastal zone. To date there are no field studies linking V. cholerae diversity to chitin abundance along with other dissolved and particulate components such as mucin in wetland ecosystems, especially in the nanoplankton fraction. Knowledge of the seasonal variations of these parameters could help further clarify current cholera dynamics and future trends. Future Vibrio research in mangroves should include the determination of nitrate-reducing halophilic species in order to better characterize the structure of Vibrio cholerae habitats and uncover hitherto unknown links to the nitrogen cycle in wetlands.
Publications
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2008. Management of endangered mangrove coasts and human health: a proposed comparison of the Sundarban and Amazonian regions. In: Abstracts of EMECS 8 (Environmental Management of Enclosed Coastal Seas). Session 2: “Integrated Coastal Management- Issues on Ecological and Social Risk. Policy modification.” October 26th-30th, 2008, East China Normal University, Shanghai, China. pp. 70-71
Lara, R.J., Neogi, S.B, Islam, S., Yamasaki, S., Nair, G.B.
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Estuarine dynamics, management and human health: The case of Cholera. In: Abstracts of the 5th Meeting of the UNESCO-BRESCE European Working Group for Estuaries and Coastal Ecohydrology, 15th- 17th September 2008, Kavala, Greece
Lara, R.J.
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2009. Influence of estuarine dynamics and catastrophic climatic events on Vibrio distribution in the Karnaphuli Estuary, Bangladesh. EcoHealth 6: 279–286
Lara, R.J., Neogi, S.B, Islam, S., Mahmud, Z. H., Yamasaki, S., Nair, G.B.
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2010. A highly sensitive and specific multiplex PCR assay for simultaneous detection of Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus. Lett Appl Microbiol 51(3): 293-300
Neogi, S. B., Chowdhury, N., Asakura, M., Hinenoya, A., Haldar, S., Saidi, S. M., Kogure, K., Lara, R.J., Yamasaki, S.
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2010. Aquatic ecosystems, human health and ecohydrology. In: Vol. 10 “Ecohydrology and restoration”, L. Chícharo, M. Zalewski (vol. eds.). Treatise on Estuarine and Coastal Science, E. Wolanski, D. McLusky (eds). Elsevier, Amsterdam
Lara, R.J., Islam, M.S., Yamasaki, S., Neogi, S.B., Nair, G.B.
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2010. Mangroves in the Change: The Need of New Synthesis of Climate, Ecohydrology and Biomedical Research. In: J.M. Metras (Ed.). Mangroves: Ecology, Biology and Taxonomy. Botanical Research and Practices Series, Environmental Science, Engineering and Technology. Nova Science Publishers, Inc. New York. ISBN: 978-1-61728-991-0
Lara, R.J.
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2011. Vibrio cholerae in waters of the Sunderban mangrove: relationship with biogeochemical parameters and chitin in seston size fractions. Wetlands, Ecology and Management 19:109–119
Lara, R.J., Neogi, S.B, Islam, S.M., Mahmud, Z. H., Islam S., Paul D., Demoz B.B. Yamasaki, S., Nair. G. B., Kattner, G.
