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Nature and Value of Freely Dissolved EPS Ecosystem Services: Insight into Molecular Coupling Mechanisms for Regulating Metal Toxicity
journal contribution
posted on 2017-12-19, 00:00 authored by Weijun Shou, Fuxing Kang, Jiahao LuExtracellular polymeric substances
(EPSs) dispersed in natural
waters play a significant role in relieving impacts to microbial survival
associated with heavy metal release, yet little is known about the
association of freely dissolved EPS ecosystem services with metal
transformation in natural waters. Here, we demonstrate that dispersive
EPSs mitigate the metal toxicity to microbial cells through an associative
coordination reaction. Microtitrimetry coupled with fluorescence spectroscopy
ascribes the combination of freely dissolved EPSs from Escherichia
coli (E. coli) with Cu2+/Cd2+ to a coordination reaction associated with chemical static
quenching. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron
spectroscopy (XPS), and computational chemistry confirm that carboxyl
residues in protein-like substances of the EPSs are responsible for
the coordination. Frontier molecular orbitals (MOs) of a deprotonated
carboxyl integrate with the occupied d orbitals of
Cu2+ and/or d, s orbitals
of Cd2+ to form metal-EPS complexes. Microcosmic systems
show that because the metal-EPS complexes decrease cellular absorbability
of metals, E. coli survivals increase by 4.3 times
for Cu2+ and 1.6 times for Cd2+, respectively.
Based on bonding energies for six metals-EPS coordination, an associative
toxic effect further confirms that increased bonding energies facilitate
retardation of metals in the EPS matrix, protecting against E. coli apoptosis.
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metal transformationRegulating Metal Toxicity Extracellularcoordination reactionFreely Dissolved EPS Ecosystem Servicesmetal-EPS complexes decreasecoli survivals increaseXPSdispersive EPSsmetal releaseprotein-like substancescoli apoptosis4.3 timesassociative coordination reactionMOFTIREscherichia colifluorescence spectroscopyEPS matrix1.6 timesmetals-EPS coordinationdeprotonated carboxylCuform metal-EPS complexesorbitalMicrocosmic systems showEPS ecosystem servicescarboxyl residuesmetal toxicity
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