The reduction of ferric iron (Fe­(III)) to ferrous iron (Fe­(II)) by dissimilatory iron-reducing bacteria is widespread in anaerobic environments. The oxidation of Fe­(II) in aerobic environments has been found to produce hydroxyl radicals (•OH); however, the role of iron-reducing bacteria in the process has not been well understood. Here, Shewanella oneidensis MR-1-mediated redox transformation of four typical iron (oxyhydr)­oxides and the production of reactive oxygen species were investigated. The results showed that the production of •OH was mainly determined by the insoluble Fe­(II) formed during microbially mediated reduction and also mediated by the mineralogical phase. Moreover, this study for the first time observed the exogenetic iron-independent production of •OH by S. oneidensis MR-1, and the integrated pathway of •OH generation during the iron redox process was revealed. Superoxide (O2 •–) was indicated as a key intermediate species that was produced by both abiotic and biotic pathways, and •OH was generated by both the exogenetic iron-dependent Fenton-like reaction and exogenetic iron-independent pathways. S. oneidensis MR-1 played a pivotal role in both the reduction of Fe­(III) and the production of O2 •–. These findings contribute substantially to our understanding of the generation mechanism of reactive oxygen species at oxidation–reduction boundaries in the environment.

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The soils around the world's largest antimony mine have been contaminated by high concentrations of Sb and As, which might influence microbial diversity in the surrounding soils. The ecological effects of bioavailable Sb and As on the composition and diversity of microbial community in soils remain unknown. In this study, the relative abundance, taxonomic diversity and composition of bacterial community in soils from a typical Sb mine area, and the relationship between the bacterial community and bioavailable concentrations as well as environmental factors have been investigated comprehensively using high-throughput sequencing (HTS) and diffusive gradients in thin films (DGT). The results indicated that Proteobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Actinobacteria, Gemmatimonadetes, and Cyanobacteria were the dominant bacterial populations at phylum level in all soil samples, accounting for more than 80% of the bacteria sequenced. The abundance and diversity of bacterial community vary along a metal contamination gradient. Redundancy discriminate analysis (RDA) revealed that 74.74% of bacterial community variation in the contaminated soils was explained by six environmental factors (pH, Sb, As, potential ecological risk index (RI), TC, TN), among which pH, Sb, and As were dominant factors influencing the composition and diversity of bacteria. This study contributes to our understanding of microbial diversity in a local ecosystem and introduces the option of studying bioavailable Sb and As using DGT.

The selective sorption of dissolved organic matter (DOM) on minerals is a widespread geochemical process in the natural environment. Recent studies have explored the influence of this process on the molecular fractionation of DOM at water–mineral interfaces. However, it remains unclear how molecular fractionation affects the photochemistry of DOM. Here, we demonstrate that the adsorptive fractionation of DOM on ferrihydrite greatly reduces its photoproduction of reactive oxygen species (ROS) including 1O2, O2 •–, and •OH normalized to organic carbon (ROSOC). The ROSOC for 1O2, O2 •–, and •OH were positively correlated with the abundances of polyphenols and oxygenated polycyclic aromatics, which were also observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis to be preferentially sequestered by ferrihydrite. The molecules that preferentially remained in the solution after adsorption displayed low levels of ROSOC. The molecular fractionation of DOM induced by adsorption on ferrihydrite therefore influenced the molecular components and also significantly reduced the photoreactive fractions of DOM in waters. These results are very important in promoting our understanding of the effects of molecular fractionation on the biogeochemical features, behaviors, and implications of DOM in the environment.

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This article proposes a new random event-triggering scheme to design filter of positive semi-Markovian jump systems with intermittent sensor faults. To obtain a balance of saving network resources and improving system performance, a random event-triggering mechanism consisting of time-and event-triggering modes is constructed. A Bernoulli distribution-based stochastic variable is introduced to orchestrate the switching of two triggering modes. A concept of hybrid gain performance is presented to guarantee that the filter can attenuate the affect from the disturbance and sensor faults. Then, a random event-triggered filter is designed for positive semi-Markovian jump systems subject to intermittent sensor faults. Under the designed filter, hybrid gain performance is achieved. Furthermore, the proposed approach is extended to the systems with stochastically incorrect sensor measurement. A linear programming method is employed for describing and computing the presented conditions. Finally, the validity of the results is verified via two examples.