Interactions between Escherichia coli survival and manganese and iron oxides in water under freeze-thaw

Pathogenic survivals were dramatically affected by Fe3+ and Mn2+ under freeze-thaw (FT), and the dissolutions of manganese and iron oxides (MIOs) were also accelerated under FT. But the mutual influences of pathogenic bacterial survival and MIOs under FT have not been profoundly explored yet. In this work, aqueous systems containing Escherichia coli as well as synthetic ferrihydrite (Fh) and manganese dioxide (MnO2) were experimented under simulated FT cycles to study the mutual influences of metal oxides and bacteria survival while oxide dissolutions and appearances, bacterial morphology and activities (survival number, cell surface hydrophobicity (CSH) and superoxide dismutase (SOD)) were obtained. The results showed that broken E. coli cells by ice growth were observed, but both oxides promoted E. coli survival under FT stress and prolonged bacterial survival time by 1.2-2.9 times, which were mainly attributed to the release of Fe3+ and Mn2+ caused by FT. The dissolutions of Fh and MnO2 under FT, which took place at a low level in absence of E. coli cells, were markedly enhanced with bacterial interferences by 2-8 times and higher dissolved manganese concentrations were detected than iron. This was probably because that concentrated organic matters which were released from broken cells, rejected into unfrozen liquid layer and acted as electron donors and ligands to oxide dissolution. Compared with Fh system, more significant promotion of E. coli survival under FT in MnO2 systems were found because of more SOD generations associated with high dissolved manganese concentrations and the stronger cellular protection by MnO2 aggregations. The results suggested that FT significantly influenced the interactions between metal oxides and bacterial in water, resulting to changes in pathogen activity and metal element cycling. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the mutual influences between pathogenic bacteria and metal oxides under freeze-thaw conditions. The results showed that the dissolution of ferrihydrite and manganese dioxide under freeze-thaw conditions was enhanced by bacterial interferences, promoting the survival of Escherichia coli. The release of Fe3+ and Mn2+ caused by freeze-thaw and the concentrated organic matters from broken cells were identified as key factors affecting the interactions between metal oxides and bacteria.