Appraisal of the composition, structure, diversity, and functioning of bacterial and fungal communities in drinking water systems: A case study in the developing world

Bacterial and fungal communities' successions were examined in a typical drinking water system in South Africa (Global South) using metagenomic sequencing. Bacterial taxa abundance was similar in water matrices but not in biofilm samples with Bacteroidota being higher in tap water and Actinobacteriota, Firmicutes, and Chloroflexi in biofilms. Fungal taxa abundance varied less, with Rozellomycota and Basidiomycota being interchangeably abundant. Both bacterial and fungal taxa and richness decreased during chlorination, but bacterial increased and fungal decreased in the distribution system. Fungal and particularly bacterial communities' diversity in raw water was closely clustered together with biofilm samples, which could suggest that biofilms act as a sink and reservoir for microbes found in raw water, however microbes' resuspension or dispersion from biofilms was less likely. Functional profile prediction revealed the presence of mainly common metabolic pathways for pathogenesis, antibiotic or chlorine resistance, with the denitrification pathway being significantly enriched within the distribution network. Finally, changes in residual chlorine had a larger influence on the composition and structure of bacterial fractions than the fungal communities. Given that drinking water systems in the developing world are ridden with many challenges, assessing both planktonic and biofilm communities is much-needed, particularly at their distal ends where chlorine decay is more pronounced and microbial regrowth can be an issue of prime concern. Finally, metagenomics analyses can shed light on bacterial and fungal succession and dynamics across the water supply chain and identify microbial risks. This can inform evidence-based interventions to underpin improved water quality and protect public health in South Africa and further afield.