| dc.description.abstract | Despite urban rivers/streams draining into Lake Victoria suffering from urbanization-
linked anthropogenic pollution, little is known about their microbiome diversity and structure, or
how they respond to intensive anthropogenic inputs. This study conducted a comprehensive
analysis of the spatial bacterial community distribution in the sediments of Kisat and Auji streams,
that flows through Kisumu City into Lake Victoria's Winam Gulf. Specifically, the study: i) used
16S rRNA gene-based Illumina MiSeq sequencing to determine the diversity and abundance of
sediment bacterial communities along the stream catchment impacted by varying levels of
urbanisation; ii) determined the presence of potential pathogens and the predicted functional
profiles of the sediment bacterial communities in the river to establish their role in the ecosystem,
and (iii) identified the key environmental factors (nutritional factors and heavy metals) influencing
compositional variations in these communities. The study adopted a stratified purposive sampling,
where 22 sediment samples were randomly collected from Lower, Mid and Upper catchment of
Auji and Kisat streams, stratified as highly, moderate and non-urbanized zones, respectively, based
on land use patterns. Results showed that polluted mid and lower catchment zones stream
sediments were highly enriched (p < 0.05) with Actinobacteria and Proteobacteria, and potential
pathogen groups such Corynebacterium, Staphylococcus, Cutibacterium, Turicella, Acinetobacter
and Micrococcus, including enterics such as Faecalibacterium, Escherichia, Klebsiella,
Enterococcus, Prevotella, Legionella, Vibrio and Salmonella. Further, Phylogenetic Investigation
of Communities by Reconstruction of Unobserved States (PICRUSt) analysis revealed enrichment
of genes associated with carbon and nitrogen metabolism and disease pathogenesis and
virulence in the lower and mid catchment zones stream sediment. Physicochemical analyses also
showed that the highly urbanized mid and lower stream catchment zones had significantly higher
(p < 0.05) total organic carbon (TOC), total nitrogen (TN), and total phosphorous (TP) content,
including severely pollution with toxic heavy metals such as lead (Pb), cadmium (Cd), and copper
(Cu) than the less urbanized upper catchment zone. Multivariate analysis suggested that TOC, Pb,
Cd, TN, pH and Cr were the significant drivers (p < 0.01) of spatial variation in community
structure, with Pb, TOC and Cd content being most influential sediment properties (p < 0.01).
Overall, these results suggest urban pollution significantly affects the stream sediment microbiome
and that the current waste management in Kisumu City is insufficient for the protection of public
health and aquatic ecosystems. Therefore, proactive and sustainable urban waste management
strategies are needed as the city undergoes rapid urbanization. | en_US |
