Microbial-mediated oxidative dissolution of orpiment and realgar in circumneutral aquatic environments

Arsenic (As) is a toxic metalloid that causes severe environmental contamination worldwide. Upon exposure to aqueous phases, the As-bearing minerals, such as orpiment (As2S3) and realgar (As4S4), undergo oxidative dissolution, in which biotic and abiotic activities both contributed significant roles. Consequently, the dissolved As and S are rapidly discharged through water transportation to broader regions and contaminate surrounding areas, especially in aquatic environments. Despite both orpiment and realgar are frequently encountered in carbonate-hosted neutral environments, the microbial-mediated oxidative dissolution of these minerals, however, have been primarily investigated under acidic conditions. Therefore, the current study aimed to elucidate microbial-mediated oxidative dissolution under neutral aquatic conditions. The current study demonstrated that the dissolution of orpiment and realgar is synergistically regulated by abiotic (i.e., specific surface area (SSA) of the mineral) and biotic (i.e., microbial oxidation) factors. The initial dissolution of As(III) and S2- from minerals is abiotically impacted by SSA, while the microbial oxidation of As(III) and S2- accelerated the overall dissolution rates of orpiment and realgar. In As-contaminated environments, members of Thiobacillus and Rhizobium were identified as the major populations that mediated oxidative dissolution of orpiment and realgar by DNA-stable isotope probing. This study provides novel insights regarding the microbial-mediated oxidative dissolution process of orpiment and realgar under neutral conditions.

Inorganic particle accumulation promotes nutrient removal of vertical flow constructed wetlands: Mechanisms and implications

Vertical flow constructed wetlands (VF CWs) are widely applied for treating eutrophic water due to prominent advantages in economy and ecology. Natural inorganic particles are ubiquitous in contaminated water and the accumulation of inorganic particles takes place spontaneously in VF CWs. To reveal how the accumulation of inorganic particles affects the transport and transformation of phosphorus (P) and nitrogen (N) in VF CWs, column experiments with and without inorganic particle loading were conducted for over 180 days. The morphology and mass balance of P and N, microbial community structure and hydraulic characteristics of VF CWs were investigated. The average total phosphorus (TP) and total nitrogen (TN) removal efficiencies in VF CWs with inorganic particle loading were steady at 90.4 ± 1.9% and 87.8 ± 2.3%, respectively. Inorganic particle accumulation improved TP removal mainly via adsorption and plant uptake, while enhanced TN removal was mainly attributed to higher plant uptake and microbial degradation. Of particular interest was that plant biomass production was doubled by the concentrated nutrients (e.g., bioavailable P and N) in the rhizosphere, accompanied by the accumulation of inorganic particles up to 9.5 g L^-1. Accumulated particles increased the bacterial abundance by 7.7-fold, and the diversity of the bacterial community associated with P and N transformations was significantly enhanced (p < 0.05). ³¹P NMR and P fractionation revealed that the elevated P proportion in the substrate was mainly in the form of iron-bound inorganic P. Moreover, inorganic particle accumulation decreased the substrate hydraulic conductivity, while it showed limited effect on the reduction of the hydraulic retention time.

VV Reduction by Polaromonas spp. in Vanadium Mine Tailings

Vanadium (V) is an important metal with critical industrial and medical applications. Elevated V contamination, however, can be a threat to the environment and human health. Microorganisms can reduce the more toxic and mobile V^V to the less toxic and immobile V^IV, which could be a detoxification and energy metabolism strategy adopted by V-reducing bacteria (VRB). The limited understanding of microbial responses to V contamination and the mechanisms for V^V reduction, however, hamper our capability to attenuate V contamination. This study focused on determining the microbial responses to elevated V concentration and the mechanisms of V^V reduction in V tailings. The bacterial communities were characterized and compared between the V tailings and the less contaminated adjacent mineral soils. Further, V^V-reducing enrichments indicated that bacteria associated with Polaromonas, a genus belonging to the family Burkholderiaceae, were potentially responsible for V^V reduction. Retrieved metagenome-assembled genomes (MAGs) suggested that the Polaromonas spp. encoded genes (cymA, omcA, and narG) were responsible for V^V reduction. Additionally, Polaromonas spp. was metabolically versatile and could use both organic and inorganic electron donors. The metabolic versatility of Polaromonas spp. may be important for its ability to flourish in the V tailings.

Snow microbiome functional analyses reveal novel aspects of microbial metabolism of complex organic compounds

Microbes active in extreme cold are not as well explored as those of other extreme environments. Studies have revealed a substantial microbial diversity and identified cold-specific microbiome molecular functions. We analyzed the metagenomes and metatranscriptomes of 20 snow samples collected in early and late spring in Svalbard, Norway using mi-faser, our read-based computational microbiome function annotation tool. Our results reveal a more diverse microbiome functional capacity and activity in the early- vs. late-spring samples. We also find that functional dissimilarity between the same-sample metagenomes and metatranscriptomes is significantly higher in early than late spring samples. These findings suggest that early spring samples may contain a larger fraction of DNA of dormant (or dead) organisms, while late spring samples reflect a new, metabolically active community. We further show that the abundance of sequencing reads mapping to the fatty acid synthesis-related microbial pathways in late spring metagenomes and metatranscriptomes is significantly correlated with the organic acid levels measured in these samples. Similarly, the organic acid levels correlate with the pathway read abundances of geraniol degradation and inversely correlate with those of styrene degradation, suggesting a possible nutrient change. Our study thus highlights the activity of microbial degradation pathways of complex organic compounds previously unreported at low temperatures.

Microbial transformation of widely used pharmaceutical and personal care product compounds

Pharmaceutical and personal care products (PPCPs) are commonly used chemicals that are increasingly detected in urban-impacted environments, particularly those receiving treated wastewater. PPCPs may have toxicological effects on the macrofauna that are exposed through contaminated water; thus, there is interest in microbially mediated transformations that may degrade PPCPs. This review discusses specific examples of PPCP transformations that may occur in anoxic environments, including O-methylation and O-demethylation.

Bacterial Survival Strategies in an Alkaline Tailing Site and the Physiological Mechanisms of Dominant Phylotypes As Revealed by Metagenomic Analyses

Microorganisms inhabiting mine tailings require specific metabolic strategies to survive, which may hold potential for pollution clean up. Effective in situ bioremediation will rely on an in-depth understanding of the function of the bacterial communities, especially the abundant and metabolically active phylotypes. In this study, the bacterial communities collected from an alkaline tailing site were profiled by 16S rRNA gene amplicon sequencing as well as shotgun metagenomic analysis. Our results indicated that potentials for carbon and nitrogen fixation as well as metal resistance and transformation were widespread among the bacterial community members, especially in highly enriched phylotypes, such as members of Thiobacillus and Meiothermus. Important functional microbial guilds including carbon and nitrogen fixers may contribute to phytoremediation by providing nutrients for hyperaccumulator plants. In addition, metal-metabolizing bacteria may influence metal speciation and solubility. This discovery provides an understanding for microbial survival strategies in the tailings and lays the foundation for future potential manipulation of the tailing microbiome for in situ bioremediation.

Response of Soil Microbial Communities to Elevated Antimony and Arsenic Contamination Indicates the Relationship between the Innate Microbiota and Contaminant Fractions

Mining of sulfide ore deposits containing metalloids, such as antimony and arsenic, has introduced serious soil contamination around the world, posing severe threats to food safety and human health. Hence, it is important to understand the behavior and composition of the microbial communities that control the mobilization or sequestration of these metal(loid)s. Here, we selected two sites in Southwest China with different levels of Sb and As contamination to study interactions among various Sb and As fractions and the soil microbiota, with a focus on the microbial response to metalloid contamination. Comprehensive geochemical analyses and 16S rRNA gene amplicon sequencing demonstrated distinct soil taxonomic inventories depending on Sb and As contamination levels. Stochastic gradient boosting indicated that citric acid extractable Sb(V) and As(V) contributed 5% and 15%, respectively, to influencing the community diversity. Random forest predicted that low concentrations of Sb(V) and As(V) could enhance the community diversity but generally, the Sb and As contamination impairs microbial diversity. Co-occurrence network analysis indicated a strong correlation between the indigenous microbial communities and various Sb and As fractions. A number of taxa were identified as core genera due to their elevated abundances and positive correlation with contaminant fractions (total Sb and As concentrations, bioavailable Sb and As extractable fractions, and Sb and As redox species). Shotgun metagenomics indicated that Sb and As biogeochemical redox reactions may exist in contaminated soils. All these observations suggest the potential for bioremediation of Sb- and As-contaminated soils.

Reshaping Darwin's Tree: Impact of the Symbiome

Much of the undescribed biodiversity on Earth is microbial, often in mutualistic or pathogenic associations. Physically associated and coevolving life forms comprise a symbiome. We propose that systematics research can accelerate progress in science by introducing a new framework for phylogenetic analysis of symbiomes, here termed SYMPHY (symbiome phylogenetics).

Complete genome sequence of Desulfurispirillum indicum strain S5(T)

Desulfurispirillum indicum strain S5(T) is a strictly anaerobic bacterium isolated from river sediment in Chennai, India. D. indicum belongs to the deep branching phylum of Chrysiogenetes, which currently only includes three other cultured species. Strain S5(T) is the type strain of the species and it is capable of growth using selenate, selenite, arsenate, nitrate or nitrite as terminal electron acceptors. The 2,928,377 bp genome encodes 2,619 proteins and 49 RNA genes, and the information gained from its sequence will be relevant to the elucidation of microbially-mediated transformations of arsenic and selenium, in addition to deepening our knowledge of the underrepresented phylum of Chrysiogenetes.

Membrane lipids of symbiotic algae are diagnostic of sensitivity to thermal bleaching in corals

Over the past three decades, massive bleaching events of zooxanthellate corals have been documented across the range of global distribution. Although the phenomenon is correlated with relatively small increases in sea-surface temperature and enhanced light intensity, the underlying physiological mechanism remains unknown. In this article we demonstrate that thylakoid membrane lipid composition is a key determinate of thermal-stress sensitivity in symbiotic algae of cnidarians. Analyses of thylakoid membranes reveal that the critical threshold temperature separating thermally tolerant from sensitive species of zooxanthellae is determined by the saturation of the lipids. The lipid composition is potentially diagnostic of the differential nature of thermally induced bleaching found in scleractinian corals. Measurements of variable chlorophyll fluorescence kinetic transients indicate that thermally damaged membranes are energetically uncoupled but remain capable of splitting water. Consequently, a fraction of the photosynthetically produced oxygen is reduced by photosystem I through the Mehler reaction to form reactive oxygen species, which rapidly accumulate at high irradiance levels and trigger death and expulsion of the endosymbiotic algae. Differential sensitivity to thermal stress among the various species of Symbiodinium seems to be distributed across all clades. A clocked molecular phylogenetic analysis suggests that the evolutionary history of symbiotic algae in cnidarians selected for a reduced tolerance to elevated temperatures in the latter portion of the Cenozoic.

Metabolic effects of metformin in patients with impaired glucose tolerance

AIMS

To assess the effect of metformin on insulin sensitivity, glucose tolerance and components of the metabolic syndrome in patients with impaired glucose tolerance (IGT).

METHODS

Forty first-degree relatives of patients with Type 2 diabetes fulfilling WHO criteria for IGT and participating in the Botnia study in Finland were randomized to treatment with either metformin 500 mg b.i.d. or placebo for 6 months. An oral glucose tolerance test (OGTT) and a euglycaemic hyperinsulinaemic clamp in combination with indirect calorimetry was performed at 0 and 6 months. The patients were followed after stopping treatment for another 6 months in an open trial and a repeat OGTT was performed at 12 months.

RESULTS

Metformin treatment resulted in a 20% improvement in insulin-stimulated glucose metabolism (from 28.7 +/- 13 to 34.4 +/- 10.7 micromol/kg fat-free mass (FFM)/min) compared with placebo (P = 0.01), which was primarily due to an increase in glucose oxidation (from 16.6 +/- 3.6 to 19.1 +/- 4.4 micromol/kg FFM; P = 0.03) These changes were associated with a minimal improvement in glucose tolerance, which was maintained after 12 months.

CONCLUSIONS

Metformin improves insulin sensitivity in subjects with IGT primarily by reversal of the glucose fatty acid cycle. Obviously large multicentre studies are needed to establish whether these effects are sufficient to prevent progression to manifest Type 2 diabetes and associated cardiovascular morbidity and mortality. Diabet. Med. 18, 578-583 (2001)

Influence of microbes on the mobilization, toxicity and biomethylation of arsenic in soil

To understand the effects of microbial activity on the mobilization and speciation of arsenic in soil, the cycling of arsenic was studied in microcosm experiments under laboratory conditions. Particular attention was paid to the biomethylation of arsenic and to the toxicity of inorganic and organic arsenic species for microbes. Microbes enhanced mobilization of arsenic from soil by 19-24% compared to formaldehyde inhibited controls. Formation of dissolved methylated arsenic species by microbes was low (< 0.1%) during the 5-day incubation. Even though methylation may function as a detoxification method, it was of minor importance in the soil tested.

Chronic diabetic complications in patients with MODY3 diabetes

MODY3 diabetes, which is caused by a mutation in the hepatocyte nuclear factor-1alpha gene (HNF-1alpha) on chromosome 12, represents a relatively common monogenic form of diabetes in Finland. Age at onset of the disease can vary from 10 to 60 years, but little is known about the natural course of the disease, particularly the development of diabetes-related chronic complications. The availability of genetic markers now allows description of the clinical course of the disease. In order to examine the prevalence of chronic diabetic complications in MODY3, we examined 57 carriers with HNF-1alpha mutations for the presence of micro- and macrovascular complications. Thirty-four percent of the MODY patients had mild and 13% had severe non-proliferative or proliferative retinopathy; this figure did not differ from the figures in insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) patients matched for duration and glycaemic control but not for age. Neither did the prevalence of microalbuminuria differ between MODY3 and IDDM or NIDDM patients (19 vs 24 and 23%). Neuropathy was observed with the same frequency as previously reported in IDDM. Hypertension was less frequent in MODY3 and IDDM than in NIDDM (24.5 and 19 vs 53.7%; p < 0.001). Coronary heart disease was more common in MODY3 than in IDDM (16 vs 4.5%; p < 0.02) but less common than in the older NIDDM patients (33.3%; p < 0.02). In a multiple logistic regression analysis, poor glycaemic control was an independent risk factor for retinopathy (p = 0.03), microalbuminuria (p < 0.04) and neuropathy (p = 0.03). In conclusion, microangiopathic complications are observed with the same frequency in patients with MODY3 diabetes as in IDDM and NIDDM and are strongly related to poor glycaemic control.

Clinical and metabolic characteristics of type 1 and type 2 diabetes: an epidemiological study from the Närpes community in western Finland

Clinical and metabolic characteristics of all known Type 1 and Type 2 diabetic patients in a well-defined area in Western Finland are described. Retrospective data from the time of diagnosis and follow-up data were examined. Overall prevalence of diabetes was 25.4 cases per 1000 population. Patients were defined as having Type 1 or Type 2 diabetes based upon early insulin requirement and C-peptide levels. Applying these criteria 84% of the patients had Type 2 diabetes. Onset before the age of 40 years was observed in only 3% of Type 2 diabetic patients. This age limit therefore had a sensitivity of 97% and a specificity of 90% in correctly predicting Type 2 diabetes. At diagnosis, hypertension was observed in 2% of Type 1 and in 75% of Type 2 diabetic patients; the corresponding numbers at follow-up were 6 and 63%. At investigation, 27% of Type 1 and 22% of Type 2 diabetic patients had microalbuminuria. Retinopathy was observed in only 12% of Type 2 compared with 54% of Type 1 diabetic patients. The presence of retinopathy was associated with longer diabetes duration both among Type 1 and Type 2 diabetic patients. A significant decrease in C-peptide concentration was observed in Type 2 diabetic patients with increasing diabetes duration. The data therefore suggest that Type 2 diabetes is associated with a deterioration of beta-cell function with time.

Mechanisms of bacterial degradation and transformation of chlorinated monoaromatic compounds

Chloroaromatics are xenobiotic compounds of environmental concern. They can be removed from the environment by (bio)degradation or by (bio)transformation. Recognition of the mechanisms and requirements of their biodegradation is of cardinal importance for understanding the fate of these chemicals in the environment, and for developing methods for biological treatment of wastes containing compounds of this type. Cleavage of the carbon-halogen bond is the critical step in degradation of chloroaromatics. As exemplified with chlorophenols, chlorobenzoates and chlorobenzenes in this review, two distinct strategies are employed by bacteria for degradation of chlorinated aromatic compounds: the particular chlorine substituents are removed either directly from the aromatic ring (as an initial step in degradation) or after oxygenative ring cleavage (from chlorinated aliphatic intermediates). Direct elimination of chlorine substituents from the aromatic ring occurs by displacement with either hydroxyl groups (hydrolytically or oxygenolytically) or hydrogen atoms (reductive dechlorination). Dechlorinations of the latter type require reducing power and are significant in anaerobic environments, but have also been observed with strictly aerobic bacteria. Various biotransformation reactions, with only minor alteration of the parent compound, are an alternative to biogradation. Two environmentally significant transformation reactions discussed here are O-methylation and O-demethylation. The capability to O-methylate chlorinated hydroxybenzenes seems to be widespread in bacteria. O-Methylation is an environmentally important transformation reaction, since methylation increases the lipophilicity of the compound and thus the potential for bioaccumulation. Bacterial O-demethylation of chlorinated methoxylated compounds has been observed under both aerobic and anaerobic conditions.