Abstract
Water quality is an important aspect of human life. The urbanisation and agricultural developments in South Africa have prompted the need to investigate two major rivers. That is, the Vaal and Jukskei Rivers for quality. The objective of this study was to first determine physiochemical properties (Total Dissolved Solids, pH, and electrical conductivity). Heavy metal concentrations and microbial diversity of water samples were also determined. Molecular docking was performed on selected fish liver proteins, zebrafish (Danio rerio). This fish species was used for this study because of its similarity in genetic features to Homo sapiens.
Water samples were analysed for physiochemical properties on-site using a portable probe. Heavy metal and secondary metabolite concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS) and ultra-high performance liquid chromatography (UHPLC), respectively. Molecular docking was then performed on the identified heavy metals and secondary metabolites using Molegro virtual docker. To establish the impact of microbiological water pollution in the rivers, microbial community profiling was conducted through high throughput sequencing (V1 to V3 region) with the Illumina ®MiSeq-2000 DNA sequencing system. PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) was used to predict the functional potential of the microbial communities.
Electrical conductivity and pH levels in all river samples were within the prescribed WHO and South African water quality standards for domestic use, aquatic ecosystems, livestock watering and irrigation. However, EC levels of the Vaal River were higher than the prescribed WHO standard, with a mean average of 726 μS/cm, with the highest reading of 744 μS/cm found upstream of the river. The Jukskei River had an acceptable mean average of 479 μS/cm downstream. However, a high reading of 688 μS/cm was found downstream of the river. Eleven heavy metals were analysed, Aluminium (Al), Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Magnesium (Mg), Manganese (Mn), Nickel (Ni), Lead (Pb), Selenium (Se), and Zinc (Zn). The Jukskei River had higher concentrations of all metals studied than the Vaal River. Molecular docking results revealed that a weak affinity/interaction was observed with the heavy metals on the selected proteins. Of the docked phenols, 4-nitrophenol, 2,4-dimethylphenol ,and 2-chlorophenol had the chief molecular
docking scores on phosphofructokinase and cytochrome P450, inferring that these metabolites may have potential detrimental impacts on metabolic processes that are either inhibitory or physiologically modifying. 16S rDNA sequencing revealed that Firmicutes, Bacteroidetes, Proteobacteria, Campylobacter and Actinobacteria were the most abundant microbial groups. Functional metagenomics showed that the predicted functional pathways were significantly enriched upstream compared to downstream of the Jukskei River. The Jukskei River was more abundant in carbohydrate metabolism and protein synthesis pathways. However, no predicted functional pathways were significantly enriched in the Vaal River. The Vaal River was most abundant in super pathways of glycolysis and protein synthesis pathways. The results, in essence suggest that activities such as poor waste disposal reduce the water quality of both the Jukskei and Vaal Rivers, as well as potential metabolic function disturbances in fish liver proteins.
Keywords: water pollution, physiochemical parameters, heavy metal, microbial profiling, functional metagenomics, molecular docking, protein-ligand interactions.