Biological self-protection inspired engineering of nanomaterials to construct a robust bio-nano system for environmental applications

Abstract

Nanomaterials can empower microbial-based chemical production or pollutant removal, e.g., nano zero-valent iron (nZVI) as an electron source to enhance microbial reducing pollutants. Constructing bio-nano interfaces is critical for bio-nano system operation, but low interfacial compatibility due to nanotoxicity challenges the system performance. Inspired by microorganisms' resistance to nanotoxicity by secreting extracellular polymeric substances (EPS), which can act as electron shuttling media, we design a highly compatible bio-nano interface by modifying nZVI with EPS, markedly improving the performance of a bio-nano system consisting of nZVI and bacteria. EPS modification reduced membrane damage and oxidative stress induced by nZVI. Moreover, EPS alleviated nZVI agglomeration and probably reduced bacterial rejection of nZVI by wrapping camouflage, contributing to the bio-nano interface formation, thereby facilitating nZVI to provide electrons for bacterial reducing pollutant via membrane-anchoring cytochrome c. This work provides a strategy for designing a highly biocompatible interface to construct robust and efficient bio-nano systems for environmental implication.

Fig. 1.. Schematic diagram of bio-inspired modification of nanomaterials using microbial EPS. (A) Mechanism of microbial mitigation of nanotoxicity by secreting EPS. (B) Scheme for the preparation of bio-inspired nZVI using EPS and construction of bio-nano system.

Fig. 2.. Characterization of nanomaterials and bio-nano systems.

(A) TEM images and water contact angle of nZVI_bio and nZVI. Variation of the (B) BET surface area, (C) Tafel scans, (D) OCP, and (E) hydrodynamic diameter of nZVI_bio with varying EPS/Fe mass ratios from 0 to 0.5. SEM images of the (F) bio-nZVI_bio system and (G) bio-nZVI system along with the corresponding schematic diagram.

Fig. 3.. NBS reduction by the bio-nano systems.

(A) Performance of NBS reduction by bacteria, nanomaterials, and bio-nano systems after a 48-hour treatment. (B) Sustainability of the bio-nano systems at a nanomaterial dose of 20 mg/liter.

Fig. 4.. Variation of bacterial activity in bio-nano systems.

(A) Growth recovery of S. oneidensis MR-1 after exposure to varying dosages of nZVI_bio and nZVI with an initial OD₆₀₀ of 0.01. (B) Flow cytometry analysis showing the viabilities of S. oneidensis MR-1 after a 2-hour exposure to different dosages of nZVI_bio and nZVI. The red color represents the live cells, and the blue color represents the injured or dead cells. a.u., arbitrary units. (C) Lactate consumption by S. oneidensis MR-1 after a 48-hour exposure to nZVI_bio and nZVI (20 mg/liter), with an initial sodium lactate concentration of 18 mM. (D) ATP generation rate of S. oneidensis MR-1 after a 2-hour exposure to nZVI_bio and nZVI (20 mg/liter). The ATP concentration was determined using the BacTiter-Glo Microbial Cell viability assay kit, and the ATP generation rate was calculated through linear fitting of the ATP concentration to incubation time. (E) NADH content of S. oneidensis MR-1 after a 2-hour exposure to nZVI_bio and nZVI (20 mg/liter). Asterisk represents the significance at P < 0.05.

Fig. 5.. Transcriptomic analysis of bacterial responses to nanomaterial exposure.

(A) Number of up-/down-regulated genes in bacteria after exposure to nZVI_bio or nZVI (20 mg/liter). (B) Fold change in the expression of various bacterial genes after exposure to nZVI_bio or nZVI (20 mg/liter). (C) Verification of intracellular ROS levels and membrane permeability in bacteria after a 2-hour exposure to nZVI_bio or nZVI (20 mg/liter). (D) Schematic diagram illustrating distinct stress responses of S. oneidensis MR-1 to nZVI_bio and nZVI in bio-nano systems. The red arrow represents the response of S. oneidensis MR-1 to nZVI_bio, the green arrow represents the response of S. oneidensis MR-1 to nZVI, and the arrow length correlates with the response level. Acetyl-CoA, acetyl coenzyme A; TCA, tricarboxylic acid.

Fig. 6.. Pathway of electron transfer from nanomaterials to bacteria.

(A) NBS reduction efficiency of various strains coupled with Fe(II), H₂, riboflavin, nZVI_bio, or nZVI in the absence of carbon source. WT, WT alone; WT + Fe(II), WT coupled with Fe(II); WT + H₂, WT coupled with H₂; WT + nZVI_bio, WT coupled with nZVI_bio; WT + nZVI_bio + RF, WT coupled with nZVI_bio and riboflavin; ΔhydAΔhyaB + nZVI_bio, hydrogenase knockout strain coupled with nZVI_bio; WT + nZVI, WT coupled with nZVI; WT + nZVI + RF, WT coupled with nZVI and riboflavin; ΔhydAΔhyaB + nZVI, hydrogenase knockout strain coupled with nZVI. (B) Schematic illustration of the two-chamber galvanic cell with nanomaterials loaded on carbon paper as the anode and S. oneidensis MR-1 loaded on carbon felt as the cathode. Titanium wire connected the electrodes, and a proton exchange membrane separated the two chambers_. (C) SEM and EDS mapping images of the carbon paper and carbon felt. (D) NBS reduction efficiency of the abiotic group, the open circuit group, and the closed circuit group in the two-chamber galvanic cell. (E) NBS or nitrate reduction efficiency of different strains coupled with nZVI_bio or nZVI in the absence of carbon source. ΔcymA, CymA knockout strain; ΔomcAΔmtrC, OmcA and MtrC knockout strain; ΔmtrF, MtrF knockout strain. (F) Schematic mechanisms of electron transfer from extracellular nanomaterials to intracellular sites for NADH synthesis and from intracellular sites to the periplasm or extracellular space for pollutant reduction. NAD⁺, nicotinamide adenine dinucleotide (oxidized form).

Fig. 7.. Mechanism diagram for high stability and high efficiency of the bio-nZVI_bio system.

ADP, adenosine 5′-diphosphate.