Growth on Geological Time Scales in the Antarctic Cryptoendolithic Microbial Community

In the process of biogenous weathering of Beacon sandstone in the McMurdo Dry Valleys (Ross Desert), Antarctica, periods of microbial growth, on the time scale of 103-104 years, alternate with sudden exfoliation events. The present study addressed the question of whether microbial growth is continuous between exfoliation events or whether each exfoliation is followed by a period of comparatively rapid growth and then an extended period of steady state. The color intensity (Munsell lightness value) of the rock surface is an indicator of relative age of the crust within the exfoliation cycle, permitting measurement of changes in microbial biomass on a geological time scale. Results indicate that microbial growth is continuous and that exfoliation occurs when the microbial biomass reaches the carrying capacity of the cryptoendolithic habitat.     

Struvite Precipitation Induced by a Novel Sulfate-Reducing Bacterium Acinetobacter calcoaceticus SRB4 Isolated from River Sediment

This article presents a study of struvite formation in liquid medium induced by the sulfate-reducing bacterium Acinetobacter calcoaceticus SRB4, a strain isolated from river sediment. We identified the bacterial strain A. calcoaceticus SRB4 and analyzed its micromorphology. The minerals formed were studied with an electroprobe microanalyzer, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray diffraction, thermogravimetry, differential thermogravimetry, and differential scanning calorimetry. Acinetobacter calcoaceticus SRB4 was found to induce struvite precipitation, whereas sterile control cultures did not. Many transparent stick-shaped struvite precipitates were distributed at the bottom of the conical flasks in the experimental group. Most bacteria were spherical and a large quantity of spherical struvite particles (less than 200 nm in diameter) adhered to the bacterial surface. An electron probe microanalysis showed that the precipitates contained C, O, P, Mg, and other elements. Fourier transformation infrared spectra showed that the precipitates contained crystalline water, NH₄⁺, and PO₄^3? groups. X-ray diffraction spectra showed that the precipitates were struvite crystals, with preferential orientation and lattice distortion. Thermogravimetry showed that the weight loss was caused by the evaporation of crystalline water at temperatures lower than 136°C and the release of ammonia from struvite at temperatures of 136–228.5°C. In this article, we discuss the possible mechanism of struvite formation and the possible role played by A. calcoaceticus SRB4. Our study extends our understanding of the phosphate biomineralization mechanism and should prove useful in recycling phosphorus in wastewater.     

Iodine Excess Induces Hepatic Steatosis Through Disturbance of Thyroid Hormone Metabolism Involving Oxidative Stress in BaLB/c Mice

Iodine excess is emerging as a new focus. A better understanding of its hazardous effects on the liver will be of great benefit to health. The aim of this study is to illustrate the effects of iodine excess on hepatic lipid homeostasis and explore its possible mechanisms. One hundred twenty BaLB/c mice were given iodine at different levels (0, 0.3, 0.6, 1.2, 2.4, and 4.8 mg I/L) in drinking water for 1 or 3 months. Lipid parameters and serum thyroid hormones were measured. Hepatic type 1 deiodinase activity and oxidative stress parameters were evaluated. The mRNA expression of sterol regulatory element-binding protein-1c (SREBP-1c) and fatty acid synthase (FAS) was detected by real-time polymerase chain reaction. Dose-dependent increase of hepatic triglyceride content was detected (r?=?0.680, P?<?0.01) in iodine-loaded groups. Evident hepatic steatosis was observed in 2.4 and 4.8 mg I/L iodine-loaded groups. The activities of antioxidant enzymes (glutathione peroxidase and superoxide dismutase) were decreased, and the malondialdehyde level was increased by excessive iodine in both serum and liver in a dose-dependent manner, accompanying the decrease of hepatic D1 activity. That resulted in the increase of serum total thyroxine and the decrease of serum total triiodothyronine in iodine-loaded groups. The mRNA expression of SREBP-1c and FAS was increased in iodine-loaded groups in response to the change of serum triiodothyronine. Present findings demonstrated that iodine excess could dose dependently induce hepatic steatosis. Furthermore, our data suggested that the disturbance of thyroid hormone metabolism involving oxidative stress may play a critical role in iodine excess-induced hepatic steatosis.     

Role of Pigment Epithelium-Derived Factor (PEDF) in Arsenic-Induced Cell Apoptosis of Liver and Brain in a Rat Model

Although studies have shown that arsenic exposure can induce apoptosis in a variety of cells, the exact molecular mechanism of chronic arsenicosis remains unclear. Based on our previous study on human serum, the present study was to determine whether pigment epithelium-derived factor (PEDF) plays a role in the damage induced by chronic arsenic exposure in a rat model and to explore the possible signaling pathway involved. Thirty male Wistar rats were randomly divided into three groups and the arsenite doses administered were 0, 10, and 50 mg/L, respectively. The experiment lasted for 6 months. Our results showed that level of arsenic increased significantly in serum, liver, brain, and kidney in arsenic-exposed groups. It was indicated that PEDF protein was widely distributed in the cytoplasm of various types of cells in liver, brain, and kidney. PEDF protein level was only changed when the arsenite dose reached 50 mg/L in liver and brain, whereas it was not changed in the kidney. In order to investigate the possible mechanism of PEDF-exerted damages upon arsenite exposure, apoptosis in liver and brain was assessed. The proportion of apoptotic cells gradually increased with increasing arsenic administration. The ratio of Bax/Bcl-2 in the high arsenic group (50 mg/L) was significantly higher than that in the control group. Therefore, we thought PEDF played a role in cell apoptosis of liver and brain which induced by sodium arsenite exposure, and the results also demonstrated that Bax and Bcl-2 might be two key targets in the action of PEDF.     

Influence of Arsenate on Lipid Peroxidation Levels and Antioxidant Enzyme Activities in Bacillus cereus Strain XZM002 Isolated from High Arsenic Aquifer Sediments

Bacillus cereus strain XZM002 isolated from high arsenic aquifer sediments of Datong Basin was applied to examine the effects of arsenate stress on antioxidant enzyme activities, lipid peroxidation levels and cell growth inhibition rate. After 2 d exposure, the cell growth inhibition rate enhanced with an increase of As(V) concentrations (0, 800, 1600 μg/l). Reactive oxygen species and glutathione contents, lipid peroxidation levels, and antioxidant enzymes (glutathione peroxidase, and other three) activities of the treated cells were significantly higher than those of the controls during 3 d exposure (p < 0.05). Besides, the levels of nine parameters reached maximum after 2 d exposure and increased significantly with increasing arsenate stress (p < 0.05). However, they returned to levels similar to those of the control on the fourth day of exposure. The results suggested that the antioxidant defense system in B. cereus strain XZM002 could protect the cells from oxidative damage induced by arsenate.     

Zinc Transporter 7 Induced by High Glucose Attenuates Epithelial-to-Mesenchymal Transition of Peritoneal Mesothelial Cells

Zinc (Zn) is an essential micronutrient and cytoprotectant involved in preventing many types of epithelial-to-mesenchymal transition (EMT)-driven fibrosis in vivo. The zinc-transporter family SLC30A (ZnT) is a pivotal factor in the regulation of Zn homeostasis. However, its function in EMT in peritoneal mesothelial cells (PMCs) remains unknown. This study explored the regulation of zinc transporters and the role they play in cell EMT, particularly in rat peritoneal mesothelial cells (RPMCs), surrounding glucose concentrations and the molecular mechanism involved. The effects of high glucose (HG) on zinc transporter gene expression were measured in RPMCs by real-time PCR. We explored ZnT7 (Slc30A7): the effect of ZnT7 over-expression and siRNA-mediated knock-down on HG-induced EMT was investigated as well as the underlying molecular mechanisms. Over-expression of ZnT7 resulted in significantly inhibited HG-induced EMT in RPMCs, while inhibition of ZnT7 expression using a considerable siRNA-mediated knock-down of RPMCs increased the levels of EMT. Furthermore, over-expression of ZnT7 is accompanied by down-regulation of TGF-β/Smad pathway, phospho-Smad3,4 expression levels. The finding suggests that the zinc-transporting system in RPMCs is influenced by the exposure to HG. The ZnT7 may account for the inhibition of HG-induced EMT in RPMCs, likely through targeting TGF-β/Smad signaling.     

IL‐1β and TNF‐α induce neurotoxicity through glutamate production: a potential role for neuronal glutaminase

Glutaminase 1 is the main enzyme responsible for glutamate production in mammalian cells. The roles of macrophage and microglia glutaminases in brain injury, infection, and inflammation are well documented. However, little is known about the regulation of neuronal glutaminase, despite neurons being a predominant cell type of glutaminase expression. Using primary rat and human neuronal cultures, we confirmed that interleukin‐1β (IL‐1β) and tumor necrosis factor‐α (TNF‐α), two pro‐inflammatory cytokines that are typically elevated in neurodegenerative disease states, induced neuronal death and apoptosis in vitro. Furthermore, both intracellular and extracellular glutamate levels were significantly elevated following IL‐1β and/or TNF‐α treatment. Pre‐treatment with N‐Methyl‐d ‐aspartate (NMDA) receptor antagonist MK‐801 blocked cytokine‐induced glutamate production and alleviated the neurotoxicity, indicating that IL‐1β and/or TNF‐α induce neurotoxicity through glutamate. To determine the potential source of excess glutamate production in the culture during inflammation, we investigated the neuronal glutaminase and found that treatment with IL‐1β or TNF‐α significantly upregulated the kidney‐type glutaminase (KGA), a glutaminase 1 isoform, in primary human neurons. The up‐regulation of neuronal glutaminase was also demonstrated in situ in a murine model of HIV‐1 encephalitis. In addition, IL‐1β or TNF‐α treatment increased the levels of KGA in cytosol and TNF‐α specifically increased KGA levels in the extracellular fluid, away from its main residence in mitochondria. Together, these findings support neuronal glutaminase as a potential component of neurotoxicity during inflammation and that modulation of glutaminase may provide therapeutic avenues for neurodegenerative diseases.     

Differential and Isomer-Specific Modulation of Vitamin A Transport and the Catalytic Activities of the RBP Receptor by Retinoids

Retinoids are vitamin A derivatives with diverse biological functions. Both natural and artificial retinoids have been used as therapeutic reagents to treat human diseases, but not all retinoid actions are understood mechanistically. Plasma retinol binding protein (RBP) is the principal and specific carrier of vitamin A in the blood. STRA6 is the membrane receptor for RBP that mediates cellular vitamin A uptake. The effects of retinoids or related compounds on the receptor’s vitamin A uptake activity and its catalytic activities are not well understood. In this study, we dissected the membrane receptor-mediated vitamin A uptake mechanism using various retinoids. We show that a subset of retinoids strongly stimulates STRA6-mediated vitamin A release from holo-RBP. STRA6 also catalyzes the exchange of retinol in RBP with certain retinoids. The effect of retinoids on STRA6 is highly isomer-specific. This study provides unique insights into the RBP receptor’s mechanism and reveals that the vitamin A transport machinery can be a target of retinoid-based drugs.