An RNA-based Approach to Elucidate the Diversity of Bacterial Communities of Bengal Delta Plain Aquifers with a Focus on Arsenic Metabolizing Bacteria

Das, Simanti (2017) An RNA-based Approach to Elucidate the Diversity of Bacterial Communities of Bengal Delta Plain Aquifers with a Focus on Arsenic Metabolizing Bacteria. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Simanti Das (12MS042)) MSThesis_SimantiDas.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Arsenic (As) contamination in groundwater aquifers is a major problem in countries like Argentina, Bangladesh, Chile, China, parts of United States of America, India and Vietnam. In India, several districts of West Bengal including Nadia, Malda, Murshidabad, North and South 24 Parganas, and Bardhaman, which are part of the Bengal Delta Plains (BDP) have been reported to have groundwater As concentration >50μg/L which is much higher than the maximum permissible limit set by World Health Organization (WHO) at 10μg/L. Microbial detoxification appears to be a useful bioremediation technique to render As free drinking water. But this method requires in-depth knowledge of the bacterial communities that are involved in the biogeochemical cycling of As in aquifers. The diversity and distribution of bacterial communities of the two gray sand aquifer (GSA) boreholes 28 and 204 (used in the present study) in Karimpur, Nadia were recently studied using 16S rDNA and aioA gene phylogeny. But this study was done using environmental DNA clone library approach and may have been error-prone due to the presence of extracellular DNA. So this present study was conducted to improve the resolution of the bacterial community structure by using the cDNA clone library and 16S rDNA sequencing approaches. Special emphasis was put on studying the As-metabolizing bacteria and how their distribution changes over time with varying environmental parameters and elemental concentrations. Sampling was done in monsoon (Aug’16) and post-monsoon (Feb’17) from 28 and 204. Environmental parameters were measured in situ at the time of sampling and were found to vary significantly between two sampling seasons. As concentration increased significantly from 2010 to 2017. Based on taxonomic affiliation of 61 clones sequenced, Proteobacteria were found to be the most dominant phylum in both wells across time. But Well 28 clone libraries also had sequences from other bacterial phyla like Bacteroidetes, Ignavibacteriae, Actinobacteria, Firmicutes and Acidobacteria which were never encountered in 2010 and 2011. It is possible that because of the greater resolution of the cDNA libraries, the sequences of rarer bacterial phyla are being encountered. As-metabolizing bacterial communities also change over time with As(V) reducing bacteria only present in 2016 and 2017 libraries. The increasing concentrations of As along with varying environmental factors are thought to be driving this change. Phylogenetic diversity analyses showed 16S rDNA signatures of bacteria known to be involved in As cycling like Dechloromonas, Melioribacter, Geothrix and Aquabacterium. Sequences generated in this study clustered separately from those obtained from the previous study thereby reaffirming the heterogeneity in the bacterial community which has developed over time.

Actions (login required)

View Item