Bioremediation of Bacteria in Constructed Wetlands: Role of Endophytic and Rhizosphere Fungi

Constructed wetlands are increasingly recognised for their potential in wastewater treatment, particularly in the removal of pathogenic microorganisms. However, the mechanisms of removal are not fully understood. This study investigated the role of endophytic and rhizosphere fungi and associated secondary metabolites in the removal of pathogenic bacteria from wastewater. Endophytic and rhizosphere fungi were isolated from roots of wetland macrophytes (T. latifolia, C. papyrus and P. mauritianus) and screened for their antimicrobial effects on E. coli, Shigella spp., Salmonella spp. and Vibrio spp. Secondary metabolites were extracted from fungal isolates (broth cultures) and tested for their antibacterial activity as a possible mechanism of pathogen removal. Antimicrobial activity of the fungi and their metabolites, measured as zones of inhibition, was analysed using ANOVA at a 5% significance level. Active secondary metabolites were identified using GC-MS techniques. Four fungal isolates (three endophytic, one rhizospheric) from the genus Candida exhibited antimicrobial activity against E. coli, Salmonella spp., Shigella spp. and Vibrio spp. in vitro. There were significant differences in inhibition zones (p < 0.0001) between the different species of fungi. Fungus RTGRS did not show any antibacterial activity on Vibrio spp. and Shigella spp. but showed the highest zones of inhibition of 21.17 ± 0.75 against Salmonella spp. This study demonstrated that the selected wetland macrophytes harbour both endophytic and rhizosphere fungi that can produce bioactive compounds that have antimicrobial properties, inhibiting the growth of pathogenic bacteria E. coli, Salmonella spp., Shigella spp. and Vibrio spp., contributing to pathogen removal in CWs. The findings have implications for the design and operation of CWs, as it is important to select macrophytes that harbour fungi with antimicrobial properties. More research is needed on the use of these fungi in wastewater treatment in full-scale CWs.