Enhanced mutualistic symbiosis between soil phages and bacteria with elevated chromium-induced environmental stress

Background Microbe–virus interactions have broad implications on the composition, function, and evolution of microbiomes. Elucidating the effects of environmental stresses on these interactions is critical to identify the ecological function of viral communities and understand microbiome environmental adaptation. Heavy metal-contaminated soils represent a relevant ecosystem to study the interplay between microbes, viruses, and environmental stressors. Results Metagenomic analysis revealed that Cr pollution adversely altered the abundance, diversity, and composition of viral and bacterial communities. Host–phage linkage based on CRISPR indicated that, in soils with high Cr contamination, the abundance of phages associated with heavy metal-tolerant hosts increased, as did the relative abundance of phages with broad host ranges (identified as host–phage linkages across genera), which would facilitate transfection and broader distribution of heavy metal resistance genes in the bacterial community. Examining variations along the pollutant gradient, enhanced mutualistic phage–bacterium interactions were observed in the face of greater environmental stresses. Specifically, the fractions of lysogens in bacterial communities (identified by integrase genes within bacterial genomes and prophage induction assay by mitomycin-C) were positively correlated with Cr contamination levels. Furthermore, viral genomic analysis demonstrated that lysogenic phages under higher Cr-induced stresses carried more auxiliary metabolic genes regulating microbial heavy metal detoxification. Conclusion With the intensification of Cr-induced environmental stresses, the composition, replication strategy, and ecological function of the phage community all evolve alongside the bacterial community to adapt to extreme habitats. These result in a transformation of the phage–bacterium interaction from parasitism to mutualism in extreme environments and underscore the influential role of phages in bacterial adaptation to pollution-related stress and in related biogeochemical processes.

Chromium Stress in Plants: Toxicity, Tolerance and Phytoremediation

Extensive industrial activities resulted in an increase in chromium (Cr) contamination in the environment. The toxicity of Cr severely affects plant growth and development. Cr is also recognized as a human carcinogen that enters the human body via inhalation or by consuming Cr-contaminated food products. Taking consideration of Cr enrichment in the environment and its toxic effects, US Environmental Protection Agency and Agency for Toxic Substances and Disease Registry listed Cr as a priority pollutant. In nature, Cr exists in various valence states, including Cr(III) and Cr(VI). Cr(VI) is the most toxic and persistent form in soil. Plants uptake Cr through various transporters such as phosphate and sulfate transporters. Cr exerts its effect by generating reactive oxygen species (ROS) and hampering various metabolic and physiological pathways. Studies on genetic and transcriptional regulation of plants have shown the various detoxification genes get up-regulated and confer tolerance in plants under Cr stress. In recent years, the ability of the plant to withstand Cr toxicity by accumulating Cr inside the plant has been recognized as one of the promising bioremediation methods for the Cr contaminated region. This review summarized the Cr occurrence and toxicity in plants, role of detoxification genes in Cr stress response, and various plants utilized for phytoremediation in Cr-contaminated regions.

Enhanced Mutualistic Symbiosis Between Soil Phages and Bacteria With Elevated Chromium-induced Environmental Stress

Background: Microbe-virus interactions have broad implications on the composition, function, and evolution of microbiomes. Elucidating effects of environmental stresses on these interactions is critical to identify the ecological function of viral communities and understand microbiome environmental adaptation. Heavy metal-contaminated soils represent a relevant ecosystem to study the interplay between microbes, viruses and environmental stressors.Results: Metagenomic analysis revealed that Cr pollution adversely altered the abundance, diversity and composition of viral and bacterial communities. Host-phage linkage based on CRISPR indicated that, in soils with high Cr contamination, the abundance of phages associated with heavy metal tolerant hosts increased, as did the relative abundance of phages with broad host ranges (identified as host-phage linkages across genera), which would facilitate transfection and broader distribution of resistance genes in the bacterial community. Examining variations along the pollutant gradient, phage-bacteria interactions shifted to a more protective mutualistic relationship in the face of greater environmental stresses. Specifically, the fractions of lysogens in bacterial communities (identified by integrase genes within bacterial genomes and prophage induction assay by mitomycin-C) were positively correlated with Cr contamination levels. Furthermore, viral genomic analysis demonstrated that lysogenic phages under higher Cr-induced stresses carried more auxiliary metabolic genes regulating microbial heavy metal detoxification.Conclusion: With the intensification of Cr-induced environmental stresses, the composition, replication strategy, and ecological function of the phage community all evolve alongside the bacterial community to adapt to extreme habitats. This results in a transformation of the phage-bacteria interaction from parasitism to protective mutualism in extreme environments, and underscores the influential role of phages in bacterial adaptation to pollution-related stress and in related biogeochemical processes.

Se Changed the Component of Organic Chemicals and Cr bioavailability in Pak Choi Rhizosphere Soil Contaminated with Cr

Rhizosphere organic chemicals response and its role on Cr/Se adsorption is of great importance to understand Cr/Se bioavailability in Cr contaminated soil with the application of Se. In the current work, the processes were carried out using rhizobox experiment (Brassica campestris L. ssp. Chinensis Makino). The results showed that in soil contaminated by 200 mg kg-1 Cr(III), Se(Ⅳ) complexed with Cr(Ⅲ) and carboxylic acid (cis-9,10-Epoxystearic acid, hexadecanedioic acid) reduced Cr(Ⅵ) to Cr(Ⅲ), thus increasing of Cr adsorption, furtherly, decreasing Cr bioavailability. While, in soil contaminated by 120 mg kg-1 Cr(Ⅵ), Se(Ⅵ) competed for adsorption sites with Cr(Ⅵ) and salicylic acid activated insoluble Cr(III), thus decreasing Cr adsorption, finally, increasing Cr bioavailability. Moreover, with Cr contamination, Se bioavailability in soil was enhanced by the secretion of carboxylic acid, which can reduce Se to lower valent state, compete the adsorption sites and complex with Se oxyanion. These results yielded a better understanding of rhizosphere dynamics regulating by Se application in Cr contaminated soil. Moreover, the current study supplemented the theoretical basis for beneficial elements application as an environment-friendly resource to facilitate cleaner production in heavy metal contaminated soil.

The Long-Term Effects of Dredging on Chromium Pollution in the Sediment of Meiliang Bay, Lake Taihu, China

Sediment dredging is a common remediation tool for polluted water bodies. However, the long-term effects of dredging on chromium (Cr) contamination remain unclear. This study was conducted to evaluate the long-term effects of sediment dredging on Cr contamination in Lake Taihu, six years after dredging was performed. In this study, high-resolution equilibrium dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) sampling techniques were used for sampling total dissolved Cr and DGT-labile Cr(VI) at the sediment water interface. The results show that the vertical averaged concentrations of total dissolved Cr in summer (112.6 ± 28.8 μg/L) and winter (115.3 ± 29.9 μg/L) in the non-dredged site were above the fisheries water quality standard (AEPC, 2002). They were 38% lower in overlying water and 20% lower in sediment pore water in the dredged site in winter, while in summer the reduction was not evident. The concentration of total dissolved Cr in the dredged site was significantly higher in spring and autumn than those in the non-dredged site, which was probably caused by the large rainfall and river discharge during the two seasons. The vertically averaged concentrations of DGT-labile Cr(VI) in both the non-dredged and dredged sites did not exceed the drinking water quality standard requirements (WHO, 1993). Modeling of DGT-induced fluxes from sediment into overlying water showed a higher response time (Tc) and lower adsorption rate (k1) and desorption rate (k−1) in the dredged site except in summer, indicating that sediment dredging decreased Cr mobility in sediments. Overall, these results confirm that sediment dredging decreased the risk of Cr contamination in winter in Lake Taihu.

Chromium Reduction via a Semi-Conducting Hematite Electrode: Implications for Microbial Cycling of Metals in Natural Soils

Semi-conducting Fe oxide minerals, such as hematite, are well known to influence the fate of contaminants and nutrients in many environmental settings and influence microbial growth under suboxic to anoxic conditions through a myriad of different processes. Recent studies of Fe oxide reduction by Fe(II) have demonstrated that reduction of Fe at one surface can result in the release of Fe(II) different one. Termed Fe(II) catalyzed recrystallization, this phenomena is attributed to conduction of additional electrons through the mineral structure from the point of contact to another which occurs because of the minerals’ semi-conductivity. While it is well understood that Fe(II) plays a central role in redox cycling of elements, the environmental implications of Fe(II) catalyzed recrystallization need to be further explored. Here, we provide evidence that the Fe mineral conductivity underpinning Fe(II) catalyzed recrystallization can couple the reduction of Cr, a priority metal contaminant, with an electron source that is cannot directly affect Cr. This is shown for both an abiotic electron source, a potentiostat, as well as the metal reducing bacteria Shewanella Putrefaciens. The implications of this work show that semiconductive minerals may be links in subsurface electrical networks that physically distribute redox chemistry and suggests novel methods for remediating Cr contamination in groundwater.

Chromium Reduction via a Semi-Conducting Hematite Electrode: Implications for Microbial Cycling of Metals in Natural Soils

Semi-conducting Fe oxide minerals, such as hematite, are well known to influence the fate of contaminants and nutrients in many environmental settings and influence microbial growth under suboxic to anoxic conditions through a myriad of different processes. Recent studies of Fe oxide reduction by Fe(II) have demonstrated that reduction of Fe at one surface can result in the release of Fe(II) different one. Termed Fe(II) catalyzed recrystallization, this phenomena is attributed to conduction of additional electrons through the mineral structure from the point of contact to another which occurs because of the minerals’ semi-conductivity. While it is well understood that Fe(II) plays a central role in redox cycling of elements, the environmental implications of Fe(II) catalyzed recrystallization need to be further explored. Here, we provide evidence that the Fe mineral conductivity underpinning Fe(II) catalyzed recrystallization can couple the reduction of Cr, a priority metal contaminant, with an electron source that is cannot directly affect Cr. This is shown for both an abiotic electron source, a potentiostat, as well as the metal reducing bacteria Shewanella Putrefaciens. The implications of this work show that semiconductive minerals may be links in subsurface electrical networks that physically distribute redox chemistry and suggests novel methods for remediating Cr contamination in groundwater.

Assessment of heavy metal concentrations and its potential eco-toxic effects in soils and sediments in Dong Cao catchment, Northern Vietnam

The environmental risks associated with the concentration of metals in soils and sediments due to their toxicological properties on living organisms are not yet sufficiently studied in North Vietnam. Soil samples and sediments collected from three weirs (W1, W2 and W4) of the Dong Cao catchment (49.7 ha) and from the downstream Cua Khau reservoir (CK) were analyzed for heavy metal concentrations and geochemical parameters. Bioassays were then applied to assess the toxicity of these soils and sediments based on a test of phytotoxicity with garden cress (Lepidium savitum) and the BioTox test for toxicity to bacteria, using Allivibrio fischeri. Metal concentrations in sediments (Cr and Cu) were significantly higher in the Dong Cao catchment (W1 and W4) in comparison with the reservoir area. The toxicity of soils and sediments of W1 and W4 was detected at a low level by the two bioassay tests. Inhibition of light emission by Allivibrio fischeri was slightly reduced for soils and sediments of W1 and W4 after 15-min of the contact. Similarly, this slight impact has been reflected in the growth and seed germination of Lepidium savitum in the sediment samples collected from the weirs of Dong Cao catchment. The major pollutant metals were Cr, Cu and Zn. Cr contamination is undoubtedly derived from rocks whereas Cu and Zn are most likely associated with human activities (local agricultural inputs and atmospheric fallout).

Foreground contribution to the inferred cosmological parameters from Planck

Previous analyses of cosmic microwave background (CMB) measurements [T. Wibig and A. W. Wolfendale, Mon. Not. R. Astron. Soc. 360 (2005) 236, arXiv:astro-ph/0409397; Mon. Not. R. Astron. Soc. 448 (2015) 1030, arXiv:1507.0677.] have revealed contamination by areas of high cosmic ray activity in the Milky Way. Here, we update studies, looking at the most recent Planck release of residual maps. We search for possible effects of foreground contamination in the reconstruction of the [Formula: see text]CDM cosmological parameters. We focus on the Hubble parameter [Formula: see text] and the optical depth to reionization [Formula: see text], both of which exhibit discrepancies between CMB-inferred values and low-redshift measurements (“the delta [Formula: see text] problem”). Using the publicly available “component separated” Planck temperature maps, we single out three distinct regions: the “loops”, “chimneys” and “low CR” regions, which disproportionately contributed to CR contamination of WMAP data. We find that two of the four maps are strongly affected by removal of anomalously high or low CR activity regions. However, the Commander method, used to produce the angular power spectrum at low ([Formula: see text]) multipoles in cosmological analyses, appears robust under these changes. Finally, we use the inferred Hubble parameter [Formula: see text] as a proxy to look for general directional dependence of the CMB power spectrum, finding a small but robust dependence on the Galactic longitude. Although there is some evidence for a continuing CR contamination, it is insufficient to provide an answer to the delta [Formula: see text] problem, or to the optical depth problem, though dependence of the derived [Formula: see text] on direction seems significant. The geometrical pattern — striations along constant longitudes — suggests CR contamination as distinct from a truly cosmological effect.