Characterization of the microbial diversity of groundwater in water wells in the Arava valley Israel

Groundwater extracted from water wells is the only source of water available for human consumption in the Arava Valley in the Negev desert in Israel. It has been observed that water wells in this region have a tendency to clog more rapidly than water wells worldwide. Clogging causes a decrease in extraction effectiveness and even in a shortage of water supply. When clogging occurs, the rehabilitation of the water well is highly expensive and, in many cases, ineffective. Early works indicate that a major part of the clogging develops due to accumulation of microbial communities in structures known as biofilms. Characterizing the microbial communities found in groundwater and understanding their role in biofilm formation will enable monitoring and aid in the development of tools for the prevention of well clogging. In this study, groundwater samples extracted from six water wells were collected for phylogenetic analysis of their microbial community. For this microbial community analysis, we used the 16S rRNA gene amplicon sequencing together with shotgun metagenomics sequencing. Our study reveals differences in the microbial community composition in each well. The microbial communities in wells that extract water from unconfined aquifers, are dominated by the Protobacteria phylum (up to 50%). In contrast, in well that extract water from confined aquifer the dominant phylum is Bacteroidetes (up to 25%). Furthermore, in all the samples, high proportions of the micro- organisms remained unassigned at the phylum and class levels which hold the potential for discovery of novel microorganisms. Despite the differences in the overall communities, there are bacteria associated with biofilm formation that appeared in all the samples, perhaps providing us with indicators of well clogging.