Bacterial community structure and composition of tropical river and drinking water – insights from deep sequencing and correlation to environmental drivers

Abstract

The aim of the thesis is to study the bacterial communities of tropical river water and its derived and treated drinking water in correlation with environmental factors to yield a comprehensive understanding of the respective ecosystems and their driving forces. We determined physico-chemical, microbiological and trophic level variables in tropical river water with a watershed dominated by pristine forest, urban, and agricultural land use types during low and high hydrological regimes. Principal component analysis showed that land use was the most influential factor driving the tropical riverine system. This finding was supported by the fact that significant correlations among physico-chemical and microbiological variables were only possible with pooled data of all land use types rather than individual land use data. Of all variables tested only biological oxygen demand, nutrients, Clostridium perfringens and chlorophyll-a significantly discriminated sampling sites according to land use types indicating their high sensitivity towards diverse influences. Characterisation of water samples using Illumina MiSeq sequencing of the 16S rRNA gene showed that riverine microbial communities were greatly driven by watershed land-use rather than environmental or climate characteristics. Land-use promoted allochtonous bacterial sequences, eutrophication-linked bacterial sequences, and extinction and stress to indigenous taxa. Despite the considerable variation across watershed land-use types, the overall microbial richness was contributed by among-site richness rather than within-site richness. Microbial communities showed a remarkable stability over time irrespective of climatic perturbations emphasizing the possibility of being temporally predictable. Comprehensive investigation of a tropical drinking water treatment plant fed by water from the pristine location of the investigated tropical riverine system showed coherent dynamics of taxa, and microbial community shifts along the treatment barriers of the drinking water treatment plant. By sequencing 16S rRNA gene amplicons at adequate depth, a high degree of microbial diversity and overrepresentation of typical freshwater genera including Undibacterium, Novosphingobium and Cylindrospermopsis were observed. Undibacterium had a considerable contribution to the abundance of the phylum Proteobacteria and demostrated a remarkable ability to predict microbial diversity. Shifts in community structure were due to substantial elimination of bacterial taxa by sand filtration, and significant enrichment of rare abundant taxa following chlorination. Taxa coherent dynamics across treatment barriers revealed the presence of a series of discrete microbial secondary succession punctuated by treatment barriers. Based on microbial community succession data, the fate of noxious bacteria in drinking water treatment plant is potentially predictable. The outcome of this study provided critical insights into the potential factors shaping the riverine system and drinking water treatment plant in tropical environment. The fact that this is the first comprehensive study covering the critical aspects of source and drinking water in tropical environment, the results can be of great importance in designing appropriate riverine and treatment plant management approaches, and identifying suitable monitoring tools in order to boost source water quality and performance of drinking water treatment plants in tropical environment.