In this study, we report the effect of the commercial nanoscale zerovalent iron (nZVI) on environmental bacteria, emphasizing the importance of nZVI-bacterial membrane interaction on nZVI toxicity as well as the adaptability of bacteria to nZVI. Exposure of Pseudomonas putida F1 to 0.1, 1.0, and 5.0 g/L of nZVI caused the reduction in colony forming units (CFUs) substantially for almost 3 orders of magnitude. However, a rebound in the cell number was observed after the prolonged exposure except for 5.0 g/L nZVI at which bacterial viability was completely inhibited. Upon exposure, nZVI accumulated on and penetrated into the bacterial cell membrane. Cell membrane composition analysis revealed the conversion of the cis to trans isomer of unsaturated fatty acid upon short-term nZVI exposure, resulting in a more rigid membrane counteracting the membrane-fluidizing effect of nZVI. Several cycles of repetitive exposure of cells to 0.1 g/L nZVI induced a persistent phenotype of P. putida F1 as indicated by smaller colony morphology, a more rigid membrane, and higher tolerance to nZVI. A low interaction between nZVI particles and the surface of the nZVI-persistent phenotypic cells reduced the nZVI-induced membrane damage. This study unveils the significance of nZVI-membrane interaction on toxicity of nZVI toward bacteria.

This work investigates polyvinylidene fluoride (PVDF) membrane modification to enhance its hydrophilicity and antibacterial properties. PVDF membranes were coated with nanoparticles of titanium dioxide (TiO2-NP) and silver (AgNP) at different concentrations and coating times and characterized for their porosity, morphology, chemical functional groups and composition changes. The results showed the successfully modified PVDF membranes containing TiO2-NP and AgNP on their surfaces. When the coating time was increased from 8 to 24 h, the compositions of Ti and Ag of the modified membranes were increased from 1.39 ± 0.13 to 4.29 ± 0.16 and from 1.03 ± 0.07 to 3.62 ± 0.08, respectively. The water contact angle of the membranes was decreased with increasing the coating time and TiO2-NP/AgNP ratio. The surface roughness and permeate fluxes of coated membranes were increased due to increased hydrophilicity. Antimicrobial and antifouling properties were investigated by the reduction of Escherichia coli cells and the inhibition of biofilm formation on the membrane surface, respectively. Compared with that of the original PVDF membrane, the modified membranes exhibited antibacterial efficiency up to 94% against E. coli cells and inhibition up to 65% of the biofilm mass reduction. The findings showed hydrophilic improvement and an antimicrobial property for possible wastewater treatment without facing the eminent problem of biofouling.

No abstract

The detection of vanillin during the metabolism of ferulic acid by several Bacillus strains has been reported; however, its occurrence is not yet understood. Herein, the potential enzymes involved in vanillin production during ferulic acid metabolism in the previously reported butanol-tolerant Bacillus subtilis strain GRSW1-B1 were explored. The recombinant E. coli cells that overexpressed phenolic acid decarboxylase (PadC) rapidly converted ferulic acid to 4-vinylguaiacol. The detection of vanillin was concurrent with a decrease in 4-vinylguaiacol. In addition, the reversible abiotic conversion of 4-vinylguaiacol and apocynol was observed. The overexpression of CypD, a Bacillus P450, resulted in notable production of vanillin. The two-step conversion of ferulic acid yielded 145 μM over 72 h at pH 9. Vanillin yields of approximately 258 μM and 212 μM were obtained from ferulic acid metabolism by recombinant E. coli coexpressing PadC and CypD after conversion for 72 h, at pH 9 and 10, respectively. Several possibilities that underlie the production of vanillin were discussed. This information is useful for understanding ferulic acid metabolism by Bacillus strains and for further improving this strain as a host for the production of valuable compounds from biomass.

While nanoscale zero valent iron (NZVI) is a promising alternative for in situ remediation, its potential environmental impact is a major concern. Herein, irreversible small colony variant (SCV) of Pseudomonas putida F1, obtained from the repetitive exposure to NZVI, was firstly reported. This SCV phenotype exhibited several altered characteristics including slower growth rate or longer lag phase, loss of swimming ability, and reduced biofilm formation. Regardless of reversibility, the persistence to gentamicin was used to distinguish the phenotypic variant from the normal phenotype and to further explore factors affecting this occurrence. By the third cycles of the repetitive exposure to 0.1 and 0.5 g/l of NZVI, the frequency of the phenotypic variant increased by 67-and 342-times, in comparison to those of non-exposed cells, respectively. While the repetitive exposure to 0.5 g/l of Fe(II) also resulted in the rising of the gentamicin-persistent phenotype by 65-fold by the third cycle of exposure, the repetitive exposure to either oxidized NZVI or Fe(III) did not induce the phenotypic variant. These results suggest that the emergence of this phenotype appears to associate with the NZVI-mediated oxidative stress. Together, this study suggests that the exposure to NZVI could trigger the emergence of phenotypic variants which could result in an environmental fitness trade-off.