Protists regulate microbially mediated organic carbon turnover in soil aggregates.

Soil protists, the major predator of bacteria and fungi, shape the taxonomic and functional structure of soil microbiome via trophic regulation. However, how trophic interactions between protists and their prey influence microbially mediated soil organic carbon turnover remains largely unknown. Here, we investigated the protistan communities and microbial trophic interactions across different aggregates-size fractions in agricultural soil with long-term fertilization regimes. Our results showed that aggregate sizes significantly influenced the protistan community and microbial hierarchical interactions. Bacterivores were the predominant protistan functional group and were more abundant in macroaggregates and silt + clay than in microaggregates, while omnivores showed an opposite distribution pattern. Furthermore, partial least square path modeling revealed positive impacts of omnivores on the C-decomposition genes and soil organic matter (SOM) contents, while bacterivores displayed negative impacts. Microbial trophic interactions were intensive in macroaggregates and silt + clay but were restricted in microaggregates, as indicated by the intensity of protistan-bacterial associations and network complexity and connectivity. Cercozoan taxa were consistently identified as the keystone species in SOM degradation-related ecological clusters in macroaggregates and silt + clay, indicating the critical roles of protists in SOM degradation by regulating bacterial and fungal taxa. Chemical fertilization had a positive effect on soil C sequestration through suppressing SOM degradation-related ecological clusters in macroaggregate and silt + clay. Conversely, the associations between the trophic interactions and SOM contents were decoupled in microaggregates, suggesting limited microbial contributions to SOM turnovers. Our study demonstrates the importance of protists-driven trophic interactions on soil C cycling in agricultural ecosystems.

Microbial autotrophy explains large-scale soil CO2 fixation.

Microbial communities play critical roles in fixing carbon from the atmosphere and fixing it in the soils. However, the large-scale variations and drivers of these microbial communities remain poorly understood. Here, we conducted a large-scale survey across China and found that soil autotrophic organisms are critical for explaining CO2 fluxes from the atmosphere to soils. In particular, we showed that large-scale variations in CO2 fixation rates are highly correlated to those in autotrophic bacteria and phototrophic protists. Paddy soils, supporting a larger proportion of obligate bacterial and protist autotrophs, display four-fold of CO2 fixation rates over upland and forest soils. Precipitation and pH, together with key ecological clusters of autotrophic microbes, also played important roles in controlling CO2 fixation. Our work provides a novel quantification on the contribution of terrestrial autotrophic microbes to soil CO2 fixation processes at a large scale, with implications for global carbon regulation under climate change.

Neuroprotective Effect of Hydrogen Sulfide Subchronic Treatment Against TBI-Induced Ferroptosis and Cognitive Deficits Mediated Through Wnt Signaling Pathway.

Emerging evidence shows that targeting ferroptosis may be a potential therapeutic strategy for treating traumatic brain injury (TBI). Hydrogen sulfide (H2S) has been proven to play a neuroprotective role in TBI, but little is known about the effects of H2S on TBI-induced ferroptosis. In addition, it is reported that the Wnt signaling pathway can also actively regulate ferroptosis. However, whether H2S inhibits ferroptosis via the Wnt signaling pathway after TBI remains unclear. In this study, we first found that in addition to alleviating neuronal damage and cognitive impairments, H2S remarkably attenuated abnormal iron accumulation, decreased lipid peroxidation, and improved the expression of glutathione peroxidase 4, demonstrating the potent anti-ferroptosis action of H2S after TBI. Moreover, Wnt3a or liproxstatin-1 treatment obtained similar results, suggesting that activation of the Wnt signaling pathway can render the cells less susceptible to ferroptosis post-TBI. More importantly, XAV939, an inhibitor of the Wnt signaling pathway, almost inversed ferroptosis inactivation and reduction of neuronal loss caused by H2S treatment, substantiating the involvement of the Wnt signaling pathway in anti-ferroptosis effects of H2S. In conclusion, the Wnt signaling pathway might be the critical mechanism in realizing the anti-ferroptosis effects of H2S against TBI. TBI induces ferroptosis-related changes characterized by iron overload, impaired antioxidant system, and lipid peroxidation at the chronic phase after TBI. However, NaHS subchronic treatment reduces the susceptibility to TBI-induced ferroptosis, at least partly by activating the Wnt signaling pathway.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems.

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Core Species Derived from Multispecies Interactions Facilitate the Immobilization of Cadmium.

Microbial consortia have opened new avenues for heavy-metal remediation. However, the limited understanding of the overall effect of interspecific interactions on remediation efficacy hinders its application. Here, the effects of multispecies growth and biofilm formation on Cd immobilization were explored from direct and multiple interactions through random combinations of two or three rhizosphere bacteria. In monocultures, Cd stress resulted in an average decrease in planktonic biomass of 26%, but through cooperation, the decrease was attenuated in dual (21%) and triple cultures (13%), possibly involving an increase in surface polysaccharides. More than 65% of the co-cultures exhibited induction of biofilm formation under Cd stress, which further enhanced the role of biofilms in Cd immobilization. Notably, excellent biofilm-forming ability or extensive social induction makes Pseudomonas putida and Brevundimonas diminuta stand out in multispecies biofilm formation and Cd immobilization. These two core species significantly increase the colonization of soil microorganisms on rice roots compared to the control, resulting in a 40% decrease in Cd uptake by rice. Our study enhances the understanding of bacterial interactions under Cd stress and provides a novel strategy for adjusting beneficial soil consortia for heavy-metal remediation.

Phagotrophic Protists Modulate Copper Resistance of the Bacterial Community in Soil.

Protist predation is a crucial biotic driver modulating bacterial populations and functional traits. Previous studies using pure cultures have demonstrated that bacteria with copper (Cu) resistance exhibited fitness advantages over Cu-sensitive bacteria under the pressure of protist predation. However, the impact of diverse natural communities of protist grazers on bacterial Cu resistance in natural environments remains unknown. Here, we characterized the communities of phagotrophic protists in long-term Cu-contaminated soils and deciphered their potential ecological impacts on bacterial Cu resistance. Long-term field Cu pollution increased the relative abundances of most of the phagotrophic lineages in Cercozoa and Amoebozoa but reduced the relative abundance of Ciliophora. After accounting for soil properties and Cu pollution, phagotrophs were consistently identified as the most important predictor of the Cu-resistant (CuR) bacterial community. Phagotrophs positively contributed to the abundance of a Cu resistance gene (copA) through influencing the cumulative relative abundance of Cu-resistant and -sensitive ecological clusters. Microcosm experiments further confirmed the promotion effect of protist predation on bacterial Cu resistance. Our results indicate that the selection by protist predation can have a strong impact on the CuR bacterial community, which broadens our understanding of the ecological function of soil phagotrophic protists.

Rice-crayfish co-culture increases microbial necromass' contribution to the soil nitrogen pool.

The rice-crayfish co-culture (RC) is a putative sustainable agricultural system. However, studies on the ecological effects of long-term RC systems were still lacking. Here, we compare enzymatic stoichiometry, microbial necromass, and microbial community between the RC and rice monoculture systems (RM). Soil enzymatic stoichiometry analysis showed that after transformation from RM to RC for about three years, ammonium nitrogen (NH4+-N) availability increased to depress relative N-acquiring enzyme production, especially for leucine aminopeptidase. The contents of microbial necromass increased approximately onefold in the RC system, making microbial necromass' contribution to the soil nitrogen (N) reach up to 46.72%. Elevation in NH4+ decreased N-acquiring enzyme, and a relatively more effective C acquisition likely benefited microbial necromass retention and production in the RC system. This study highlights that the rice-crayfish co-culture could modify the N pool of the surface paddy soil.

Screening of Genes Co-Associated with Sudden Infant Death Syndrome and Infectious Sudden Death in Infancy and Bioinformatics Analysis of Their Regulatory Networks.

OBJECTIVES: The common differentially expressed mRNAs in brain, heart and liver tissues of deceased sudden infant death syndrome (SIDS) and infectious sudden death in infancy (ISDI) confirmed by autopsy was screened by bioinformatics to explore the common molecular markers and pathogenesis of SIDS and ISDI. METHODS: The datasets of GSE70422 and GSE136992 were downloaded, the limma of R software was used to screen differentially expressed mRNA in different tissue samples of SIDS and ISDI decedents for overlapping analysis. The clusterProfiler of R software was used to conduct gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The protein-protein interaction (PPI) network was constructed by STRING database, while the hub gene was screened by cytoHubba plug-in. RESULTS: Compared with the control group, there were 19 significant differentially expressed genes in the tissue samples of SIDS and ISDI decedents, among which 16 in the heart tissue and 3 in the liver tissue, and the astrotactin 1 (ASTN1) gene expression difference in the heart tissue was most significant. The PPI network identified Ras homolog family member A (RHOA), integrin subunit alpha 1 (ITGA1), and H2B clustered histone 5 (H2BC5) were hub genes. The analysis of GO and KEGG showed that differentially expressed genes were enriched in the molecular pathways of actin cytoskeleton regulation, focal adhesion and response to mycophenolic acid. CONCLUSIONS: ASTN1, RHOA and ITGA1 may participate in the development of SIDS and ISDI. The enrichment of differentially expressed genes in immune and inflammatory pathways suggests a common molecular regulatory mechanism between SIDS and ISDI. These findings are expected to provide new biomarkers for molecular anatomy and forensic identification of SIDS and ISDI.

MRG Chip: A High-Throughput qPCR-Based Tool for Assessment of the Heavy Metal(loid) Resistome.

Bacterial metal detoxification mechanisms have been well studied for centuries in pure culture systems. However, profiling metal resistance determinants at the community level is still a challenge due to the lack of comprehensive and reliable quantification tools. Here, a novel high-throughput quantitative polymerase chain reaction (HT-qPCR) chip, termed the metal resistance gene (MRG) chip, has been developed for the quantification of genes involved in the homeostasis of 9 metals. The MRG chip contains 77 newly designed degenerate primer sets and 9 published primer sets covering 56 metal resistance genes. Computational evaluation of the taxonomic coverage indicated that the MRG chip had a broad coverage matching 2 kingdoms, 29 phyla, 64 classes, 130 orders, 226 families, and 382 genera. Temperature gradient PCR and HT-qPCR verified that 57 °C was the optimal annealing temperature, with amplification efficiencies of over 94% primer sets achieving 80-110%, with R2 > 0.993. Both computational evaluation and the melting curve analysis of HT-qPCR validated a high specificity. The MRG chip has been successfully applied to characterize the distribution of diverse metal resistance determinants in natural and human-related environments, confirming its wide scope of application. Collectively, the MRG chip is a powerful and efficient high-throughput quantification tool for exploring the microbial metal resistome.

Microscale heterogeneity of the soil nitrogen cycling microbial functional structure and potential metabolism.

Soil aggregates, with complex spatial and nutritional heterogeneity, are clearly important for regulating microbial community ecology and biogeochemistry in soils. However, how the taxonomic composition and functional attributes of N-cycling-microbes within different soil particle-size fractions under a long-term fertilization treatment remains largely unknown. Here, we examined the composition and metabolic potential for urease activity, nitrification, N2 O production and reduction of the microbial communities attached to different sized soil particles (2000-250, 250-53 and <53 µm) using a functional gene microarray (GeoChip) and functional assays. We found that urease activity and nitrification were higher in <53 µm fractions, whereas N2 O production and reduction rates were greater in 2000-250 and 250-53 µm across different fertilizer regimes. The abundance of key N-cycling genes involved in anammox, ammonification, assimilatory and dissimilatory N reduction, denitrification, nitrification and N2 -fixation detected by GeoChip increased as soil aggregate size decreased; and the particular key genes abundance (e.g., ureC, amoA, narG, nirS/K) and their corresponding activity were uncoupled. Aggregate fraction exerted significant impacts on N-cycling microbial taxonomic composition, which was significantly shaped by soil nutrition. Taken together, these findings indicate the important roles of soil aggregates in differentiating N-cycling metabolic potential and taxonomic composition, and provide empirical evidence that nitrogen metabolism potential and community are uncoupled due to aggregate heterogeneity.

Influence of Legacy Mercury on Antibiotic Resistomes: Evidence from Agricultural Soils with Different Cropping Systems.

Agricultural soils are important reservoirs for antibiotic resistance genes (ARGs), which have close linkage to human health via crop production. Metal stress in environments may function as a selection pressure for antibiotic resistomes. However, there is still a lack of field studies focusing on the effect of historical mercury (Hg) contamination on antibiotic resistomes in agricultural soils. Here, we explored the ARG profile in soils with different cropping systems (paddy and upland) and linked them to legacy Hg exposure. We found that ARG profiles were significantly different between paddy and upland soils. However, both paddy and upland soils with long-term field Hg contamination harbored higher diversity and abundance of ARGs than non-polluted soils. The co-occurrence network reveals significant associations among Hg, Hg resistance genes, mobile genetic elements (MGEs), and ARGs. Together with path analysis showing legacy Hg possibly affecting soil resistomes through the shifts of soil microbiota, Hg resistance genes, and MGEs, we suggest that legacy Hg-induced potential co-selection might elevate the ARG level. Redundancy analysis further supports that legacy Hg pollution had a significant association with ARG variations in the paddy and upland soils (P < 0.01). Collectively, our results highlight the underappreciated role of legacy Hg as a potential persistent selecting agent in contributing to soil ARGs in agroecosystems.

Different Effects of Soil Fertilization on Bacterial Community Composition in the Penicillium canescens Hyphosphere and in Bulk Soil.

This study investigated the effects of long-term soil fertilization on the composition and potential for phosphorus (P) and nitrogen (N) cycling of bacterial communities associated with hyphae of the P-solubilizing fungus Penicillium canescens Using a baiting approach, hyphosphere bacterial communities were recovered from three soils that had received long-term amendment in the field with mineral or mineral plus organic fertilizers. P. canescens hyphae recruited bacterial communities with a decreased diversity and an increased abundance of Proteobacteria relative to what was observed in soil communities. As core bacterial taxa, Delftia and Pseudomonas spp. were present in all hyphosphere samples irrespective of soil fertilization. However, the type of fertilization showed significant impacts on the diversity, composition, and distinctive taxa/operational taxonomic units (OTUs) of hyphosphere communities. The soil factors P (Olsen method), exchangeable Mg, exchangeable K, and pH were important for shaping soil and hyphosphere bacterial community compositions. An increased relative abundance of organic P metabolism genes was found in hyphosphere communities from soil that had not received P fertilizers, which could indicate P limitation near the fungal hyphae. Additionally, P. canescens hyphae recruited bacterial communities with a higher abundance of N fixation genes than found in soil communities, which might imply a role of hyphosphere communities for fungal N nutrition. Furthermore, the relative abundances of denitrification genes were greater in several hyphosphere communities, indicating an at least partly anoxic microenvironment with a high carbon-to-N ratio around the hyphae. In conclusion, soil fertilization legacy shapes P. canescens hyphosphere microbiomes and their functional potential related to P and N cycling.IMPORTANCE P-solubilizing Penicillium strains are introduced as biofertilizers to agricultural soils to improve plant P nutrition. Currently, little is known about the ecology of these biofertilizers, including their interactions with other soil microorganisms. This study shows that communities dominated by Betaproteobacteria and Gammaproteobacteria colonize P. canescens hyphae in soil and that the compositions of these communities depend on the soil conditions. The potential of these communities for N and organic P cycling is generally higher than that of soil communities. The high potential for organic P metabolism might complement the ability of the fungus to solubilize inorganic P, and it points to the hyphosphere as a hot spot for P metabolism. Furthermore, the high potential for N fixation could indicate that P. canescens recruits bacteria that are able to improve its N nutrition. Hence, this community study identifies functional groups relevant for the future optimization of next-generation biofertilizer consortia for applications in soil.

Polyoxometalate-Based Metal-Organic Frameworks for Selective Oxidation of Aryl Alkenes to Aldehydes.

Polyoxometalates (POMs) show considerable catalytic performance toward the selective oxidation of alkenes to aldehydes, which is commercially valuable for the production of pharmaceuticals, dyes, perfumes, and fine chemicals. However, the low specific surface area of POMs as heterogeneous catalysts and poor recyclability as homogeneous catalysts have hindered their wide application. Dispersing POMs into metal-organic frameworks (MOFs) for the construction of POM-based MOFs (POMOFs) suggests a promising strategy to realize the homogeneity of heterogeneous catalysis. Herein, we report two new POMOFs with chemical formulas of [Co(BBTZ)2][H3BW12O40]·10H2O (1) and [Co3(H2O)6(BBTZ)4][BW12O40]·NO3·4H2O (2) (BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene) for the selective oxidation of alkenes to aldehydes. Compound 1 possesses a non-interpenetrated three-dimensional (3D) cds-type open framework with a 3D channel system. Compound 2 displays a 3D polyrotaxane framework with one-dimensional channels along the [100] direction. In the selective oxidation of styrene into benzaldehyde, compound 1 can achieve a 100% conversion in 4 h with 96% selectivity toward benzaldehyde, which is superior to that of compound 2. A series of control experiments reveal that the co-role of [BW12O40]5- and Co2+ active center as well as a more open framework feature co-promote the catalytic property of the POMOFs in this case. This work may suggest a new option for the development of POMOF catalysts in the selective oxidation of alkenes.

A role for copper in protozoan grazing - two billion years selecting for bacterial copper resistance.

The Great Oxidation Event resulted in integration of soft metals in a wide range of biochemical processes including, in our opinion, killing of bacteria by protozoa. Compared to pressure from anthropologic copper contamination, little is known on impacts of protozoan predation on maintenance of copper resistance determinants in bacteria. To evaluate the role of copper and other soft metals in predatory mechanisms of protozoa, we examined survival of bacteria mutated in different transition metal efflux or uptake systems in the social amoeba Dictyostelium discoideum. Our data demonstrated a strong correlation between the presence of copper/zinc efflux as well as iron/manganese uptake, and bacterial survival in amoebae. The growth of protozoa, in turn, was dependent on bacterial copper sensitivity. The phagocytosis of bacteria induced upregulation of Dictyostelium genes encoding the copper uptake transporter p80 and a triad of Cu(I)-translocating PIB -type ATPases. Accumulated Cu(I) in Dictyostelium was monitored using a copper biosensor bacterial strain. Altogether, our data demonstrate that Cu(I) is ultimately involved in protozoan predation of bacteria, supporting our hypothesis that protozoan grazing selected for the presence of copper resistance determinants for about two billion years.

Transcriptome Response to Heavy Metals in Sinorhizobium meliloti CCNWSX0020 Reveals New Metal Resistance Determinants That Also Promote Bioremediation by Medicago lupulina in Metal-Contaminated Soil.

The symbiosis of the highly metal-resistant Sinorhizobium meliloti CCNWSX0020 and Medicago lupulina has been considered an efficient tool for bioremediation of heavy metal-polluted soils. However, the metal resistance mechanisms of S. meliloti CCNWSX00200 have not been elucidated in detail. Here we employed a comparative transcriptome approach to analyze the defense mechanisms of S. meliloti CCNWSX00200 against Cu or Zn exposure. Six highly upregulated transcripts involved in Cu and Zn resistance were identified through deletion mutagenesis, including genes encoding a multicopper oxidase (CueO), an outer membrane protein (Omp), sulfite oxidoreductases (YedYZ), and three hypothetical proteins (a CusA-like protein, a FixH-like protein, and an unknown protein), and the corresponding mutant strains showed various degrees of sensitivity to multiple metals. The Cu-sensitive mutant (ΔcueO) and three mutants that were both Cu and Zn sensitive (ΔyedYZ, ΔcusA-like, and ΔfixH-like) were selected for further study of the effects of these metal resistance determinants on bioremediation. The results showed that inoculation with the ΔcueO mutant severely inhibited infection establishment and nodulation of M. lupulina under Cu stress, while inoculation with the ΔyedYZ and ΔfixH-like mutants decreased just the early infection frequency and nodulation under Cu and Zn stresses. In contrast, inoculation with the ΔcusA-like mutant almost led to loss of the symbiotic capacity of M. lupulina to even grow in uncontaminated soil. Moreover, the antioxidant enzyme activity and metal accumulation in roots of M. lupulina inoculated with all mutants were lower than those with the wild-type strain. These results suggest that heavy metal resistance determinants may promote bioremediation by directly or indirectly influencing formation of the rhizobium-legume symbiosis.IMPORTANCE Rhizobium-legume symbiosis has been promoted as an appropriate tool for bioremediation of heavy metal-contaminated soils. Considering the plant-growth-promoting traits and survival advantage of metal-resistant rhizobia in contaminated environments, more heavy metal-resistant rhizobia and genetically manipulated strains were investigated. In view of the genetic diversity of metal resistance determinants in rhizobia, their effects on phytoremediation by the rhizobium-legume symbiosis must be different and depend on their specific assigned functions. Our work provides a better understanding of the mechanism of heavy metal resistance determinants involved in the rhizobium-legume symbiosis, and in further studies, genetically modified rhizobia harboring effective heavy metal resistance determinants may be engineered for the practical application of rhizobium-legume symbiosis for bioremediation in metal-contaminated soils.

Massilia phosphatilytica sp. nov., a phosphate solubilizing bacteria isolated from a long-term fertilized soil.

A Gram-stain-negative and rod-shaped bacterial strain, 12-OD1T, with rock phosphate solubilizing ability was isolated from agricultural soil in Hailun, Heilongjiang, PR China. The isolate was affiliated to the genus Massilia, based on 16S rRNA gene sequence alignments, having the highest similarities with Massilia putida6 NM-7T (98.67 %), Massilia kyonggiensis TSA1T (98.28 %), and Massilia norwichensis NS9T (98.07 %), respectively. The DNA G+C content was 67.72 mol% and DNA-DNA hybridization showed low relatedness values (less than 47 %) between strain 12-OD1T and other phylogenetically related species of the genus Massilia. The predominant isoprenoid quinone was Q-8 and the polar lipid profile comprised diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The major fatty acids were C17 : 0 cyclo (25.4 %), C16 : 0 (23.4 %) and summed feature 3 (C16 : 1ω7c and/or C16 : 1 ω6c) (22.5 %), which differentiates it from close relatives within the genus Massilia. Combined genetic, physiological and biochemical properties indicate that strain 12-OD1T is a novel species of the genus Massilia, for which the name Massilia phosphatilytica sp. nov., is proposed, with the type strain 12-OD1T (=CCTCC AB 2016251T=LMG 29956T=KCTC 52513T).

Bacterial resistance to arsenic protects against protist killing.

Protists kill their bacterial prey using toxic metals such as copper. Here we hypothesize that the metalloid arsenic has a similar role. To test this hypothesis, we examined intracellular survival of Escherichia coli (E. coli) in the amoeba Dictyostelium discoideum (D. discoideum). Deletion of the E. coli ars operon led to significantly lower intracellular survival compared to wild type E. coli. This suggests that protists use arsenic to poison bacterial cells in the phagosome, similar to their use of copper. In response to copper and arsenic poisoning by protists, there is selection for acquisition of arsenic and copper resistance genes in the bacterial prey to avoid killing. In agreement with this hypothesis, both copper and arsenic resistance determinants are widespread in many bacterial taxa and environments, and they are often found together on plasmids. A role for heavy metals and arsenic in the ancient predator-prey relationship between protists and bacteria could explain the widespread presence of metal resistance determinants in pristine environments.

A polyoxometalate-encapsulating cationic metal-organic framework as a heterogeneous catalyst for desulfurization.

A new cationic triazole-based metal-organic framework encapsulating Keggin-type polyoxometalates, with the molecular formula [Co(BBPTZ)3][HPMo12O40]⋅24 H2O [compound 1; BBPTZ = 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl] is hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The structure of compound 1 contains a non-interpenetrated 3D CdSO4 (cds)-type framework with two types of channels that are interconnected with each other; straight channels that are occupied by the Keggin-type POM anions, and wavelike channels that contain lattice water molecules. The catalytic activity of compound 1 in the oxidative desulfurization reaction indicates that it is not only an effective and size-selective heterogeneous catalyst, but it also exhibits distinct structural stability in the catalytic reaction system.

Copper tolerance mechanisms of Mesorhizobium amorphae and its role in aiding phytostabilization by Robinia pseudoacacia in copper contaminated soil.

The legume-rhizobium symbiosis has been proposed as an important system for phytoremediation of heavy metal contaminated soils due to its beneficial activity of symbiotic nitrogen fixation. However, little is known about metal resistant mechanism of rhizobia and the role of metal resistance determinants in phytoremediation. In this study, copper resistance mechanisms were investigated for a multiple metal resistant plant growth promoting rhizobium, Mesorhizobium amorphae 186. Three categories of determinants involved in copper resistance were identified through transposon mutagenesis, including genes encoding a P-type ATPase (CopA), hypothetical proteins, and other proteins (a GTP-binding protein and a ribosomal protein). Among these determinants, copA played the dominant role in copper homeostasis of M. amorphae 186. Mutagenesis of a hypothetical gene lipA in mutant MlipA exhibited pleiotropic phenotypes including sensitivity to copper, blocked symbiotic capacity and inhibited growth. In addition, the expression of cusB encoding part of an RND-type efflux system was induced by copper. To explore the possible role of copper resistance mechanism in phytoremediation of copper contaminated soil, the symbiotic nodulation and nitrogen fixation abilities were compared using a wild-type strain, a copA-defective mutant, and a lipA-defective mutant. Results showed that a copA deletion did not affect the symbiotic capacity of rhizobia under uncontaminated condition, but the protective role of copA in symbiotic processes at high copper concentration is likely concentration-dependent. In contrast, inoculation of a lipA-defective strain led to significant decreases in the functional nodule numbers, total N content, plant biomass and leghemoglobin expression level of Robinia pseudoacacia even under conditions of uncontaminated soil. Moreover, plants inoculated with lipA-defective strain accumulated much less copper than both the wild-type strain and the copA-defective strain, suggesting an important role of a healthy symbiotic relationship between legume and rhizobia in phytostabilization.

Survival in amoeba--a major selection pressure on the presence of bacterial copper and zinc resistance determinants? Identification of a "copper pathogenicity island".

The presence of metal resistance determinants in bacteria usually is attributed to geological or anthropogenic metal contamination in different environments or associated with the use of antimicrobial metals in human healthcare or in agriculture. While this is certainly true, we hypothesize that protozoan predation and macrophage killing are also responsible for selection of copper/zinc resistance genes in bacteria. In this review, we outline evidence supporting this hypothesis, as well as highlight the correlation between metal resistance and pathogenicity in bacteria. In addition, we introduce and characterize the "copper pathogenicity island" identified in Escherichia coli and Salmonella strains isolated from copper- and zinc-fed Danish pigs.