The contents of free sesquioxides are relatively high in acidic
soils (Table 2). The isoelectric point (pI) of Fe/Al (hydro) oxides is
much higher (8.5) than that ofE. coliO157:H7 (4.2)[30]. Hence,
in acidic soils, the Fe/Al (hydro) oxides carry net positive charges,
while the inoculatedE. coliO157:H7 were negatively charged. The
amount of positive charge on Fe/Al (hydro) oxides increased as
the pH decreased. Thus, the increase in the electrostatic attraction between the Fe/Al (hydro) oxides andE. colia celerated thebacterial adhesion[31]. Previous studies reported that the high
E. coliO157:H7 adsorption on soil minerals can result in a rapid
decline in its viability[32]. A series of chemical and physical processes contributed to this phenomenon. Although bacteria need
iron element to form ferritins, the excess iron released from soil
minerals can overwhelm outer membrane regulatory proteins and
form toxic precipitates, such as lethal hydroxyl radicals [33].In
contrast, electrostatic attraction forces between bacteria and soil
minerals induced more bacterial retention and lower viability[32].
Asadishad et al.[34]found that antimicrobial effects only existed in
the positively charged biomaterial surface. Furthermore, some aluminum may be possibly transported into cells via the citrate–iron
uptake system[35]. The higher contents of Al oxides in soils with
lower pH contributed to the higher bioavailability of toxic Al, which
interferes with mineral nutrition of cells, particularly phosphate
metabolism. Therefore, the adsorption ofE. coliO157:H7 on soil
minerals and Fe-/Al- (hydro) oxides in acidic soils would cause a
rapid decline inE. coliO157:H7 quantities
The contents of free sesquioxides are relatively high in acidicsoils (Table 2). The isoelectric point (pI) of Fe/Al (hydro) oxides ismuch higher (8.5) than that ofE. coliO157:H7 (4.2)[30]. Hence,in acidic soils, the Fe/Al (hydro) oxides carry net positive charges,while the inoculatedE. coliO157:H7 were negatively charged. Theamount of positive charge on Fe/Al (hydro) oxides increased asthe pH decreased. Thus, the increase in the electrostatic attraction between the Fe/Al (hydro) oxides andE. colia celerated thebacterial adhesion[31]. Previous studies reported that the highE. coliO157:H7 adsorption on soil minerals can result in a rapiddecline in its viability[32]. A series of chemical and physical processes contributed to this phenomenon. Although bacteria neediron element to form ferritins, the excess iron released from soilminerals can overwhelm outer membrane regulatory proteins andform toxic precipitates, such as lethal hydroxyl radicals [33].Incontrast, electrostatic attraction forces between bacteria and soilminerals induced more bacterial retention and lower viability[32].Asadishad et al.[34]found that antimicrobial effects only existed inthe positively charged biomaterial surface. Furthermore, some aluminum may be possibly transported into cells via the citrate–ironuptake system[35]. The higher contents of Al oxides in soils withlower pH contributed to the higher bioavailability of toxic Al, whichinterferes with mineral nutrition of cells, particularly phosphatemetabolism. Therefore, the adsorption ofE. coliO157:H7 on soilminerals and Fe-/Al- (hydro) oxides in acidic soils would cause arapid decline inE. coliO157:H7 quantities
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