Deposition and Survival of <i>Escherichia coli</i> O157:H7 on Clay Minerals in a Parallel Plate Flow System

Understanding bacterial pathogens deposition and survival processes in the soil–groundwater system is crucial to protect public health from soilborne and waterborne diseases. However, mechanisms of bacterial pathogen–clay interactions are not well studied, particularly in dynamic systems. Also, little is known about the viability of bacterial pathogens when attached to clays. In this study, a parallel plate flow system was used to determine the deposition kinetics and survival of <i>Escherichia coli</i> O157:H7 on montmorillonite, kaolinite, and goethite over a wide range of ionic strengths (IS) (0.1–100 mM KCl). <i>E. coli</i> O157:H7 deposition on the positively charged goethite is greater than that on the negatively charged kaolinite and montmorillonite. Although the zeta potential of kaolinite was more negative than that of montmorillonite, kaolinite showed a greater deposition for <i>E. coli</i> O157:H7 than montmorillonite, which is attributed to the chemical heterogeneity of clay minerals. Overall, increasing IS resulted in an increase of <i>E. coli</i> O157:H7 deposition on montmorillonite and kaolinite, and a decrease on goethite. Interaction energy calculations suggest that <i>E. coli</i> O157:H7 deposition on clays was largely governed by DLVO (Derjaguin–Landau–Verwey–Overbeek) forces. The loss of bacterial membrane integrity was investigated as a function of time using the Live/Dead BacLight viability assay. During the examined period of 6 h, <i>E. coli</i> O157:H7 retained its viability in suspension and when attached to montmorillonite and kaolinite; however, interaction with the goethite was detrimental. The information obtained in this study is of fundamental significance for the understanding of the fate of bacterial pathogens in soil environments

Sorption of Pb(II) by Nanosized Ferrihydrite Organo-Mineral Composites Formed by Adsorption versus Coprecipitation

Nanosized iron hydroxides and organic matter (OM) are important scavengers of nutrient elements and dissolved trace-metals in geologic systems. Despite this, little is known about the sorption characteristics of metals to the iron–OM nanocomposites formed by adsorption (adsorption of OM on presynthesis ferrihydrite) versus coprecipitation (formation of ferrihydrite in the presence of OM). This study investigates lead (Pb) sorption behaviors on ferrihydrite–humic acid (Fh–HA) composites through batch sorption coupled with Pb-L_III EXAFS. We report that composites formed by coprecipitation have a higher carbon content, smaller specific surface area, and faster Pb sorption rate compared to the equivalent composites formed by adsorption of HA to preformed Fh. Pb sorption on the composites is enhanced at pH < 5 than that on pure Fh, and coprecipitated and adsorbed composites sorb almost equivalent amount of Pb. We identify a bidentate edge-sharing Pb complex on the ferrihydrite surface with a PbFe bond length of 3.33 Å and a bidentate inner-sphere Pb complex on the HA fraction of the composite. More Pb ions are associated with the HA fraction of the composites with the increases of pH from 4 to 6.5. More Pb ions are sequestrated by the organic fraction in the adsorbed than in the coprecipitated composites. This research therefore has important implications for predicting the mobility and fate of Pb in iron and organic rich soils and sediments

<i>M</i>. <i>tuberculosis</i> targets human phagocytosis pathways.

<p>(A) Local PPI network between <i>M</i>. <i>tuberculosis</i> proteins (red nodes) and human proteins (blue nodes) involved in phagocytosis. (B) Schematic showing phagocytosis pathways. The RHO family GTPases RAC1 and CDC42 play roles in phagosome formation. Phagosomes undergo sequential fusion with early endosomes, late endosomes and lysosomes. The small GTPase RAB5A is involved in the fusion of phagosomes with early endosomes. The small GTPase RAB7A is known to mediate trafficking between phagosomes and late endosomes or lysosomes. The GTPase RAB11A mediates recycling of endosomes to the plasma membrane. PI3K (PIK3R1, PIK3R2 and PIK3CA) regulates metabolism of phosphoinositides, which play essential roles during phagocytosis. CHMP3 is a component of the ESCRT complex. RAC1 is also involved in stimulation of NADPH oxidase activity in macrophages.</p

Pathogen–host PPI network of <i>M</i>. <i>tuberculosis</i>.

<p>(A) Flow chart showing the construction of pathogen–host PPI network of <i>M</i>. <i>tuberculosis</i> using PSS-PPI. (B) Graphical representation of predicted pathogen–host PPI network of <i>M</i>. <i>tuberculosis</i>. Nodes represent proteins of <i>M</i>. <i>tuberculosis</i> (red) and human (blue). Edges represent predicted interactions. (C) Overlap between <i>M</i>. <i>tuberculosis</i> proteins in predicted PPI network and “survivasome” of <i>M</i>. <i>tuberculosis</i>. (D) Overlap between human proteins in the predicted PPI network and human proteins involved in <i>M</i>. <i>tuberculosis</i> infection identified by RNAi screening.</p

PSS-PPI and SSI template library.

<p>(A) An example of PSS. 1CD9 is the complex structure of GCSF (chain A) and GCSF-receptor (chain B). 1I1R is the complex structure of human herpesvirus 8 protein vIL-6 (chain B) and human interleukin-6 receptor beta subunit IL6ST (chain A). 1I1R and 1CD9 are structurally similar but have very low sequence similarity. GCSF means granulocyte colony-stimulating factor. (B) Schematic of PSS-PPI. (C) Flow chart showing the approach used for constructing the SSI template library.</p

<i>M</i>. <i>tuberculosis</i> targets human proteins involved in HIV infection.

<p>(A) <i>M</i>. <i>tuberculosis</i> was predicted to target human proteins that are also targeted by HIV-1. (B) The <i>M</i>. <i>tuberculosis</i>-HIV-human PPI network. Nodes represent proteins of <i>M</i>. <i>tuberculosis</i> (red), HIV-1 (yellow), and human (blue). (C) <i>M</i>. <i>tuberculosis</i> was predicted to target human proteins that regulate HIV replication.</p

Predicted PPIs between <i>M</i>. <i>tuberculosis</i> and human immune response pathways.

<p>(A) Local PPIs network between <i>M</i>. <i>tuberculosis</i> proteins (red nodes) and human proteins (blue nodes) involved in the NF-κB signaling pathway. (B) Schematic of the NF-κB signaling pathway. Proteins found to be targeted by <i>M</i>. <i>tuberculosis</i> are indicated by black stars.</p

Performance of PSS-PPI.

<p>(A) Flow chart showing construction of the pathogen–human PPI network of HIV-1 using PSS-PPI. (B) Predicted PPI number and overlapped positive PPI number vs. PSS score. (C) Venn diagram of overlap between HIV-human PPIs from PSS-PPI (PSS-score cutoff = 0.5), HIV-human protein-interaction database and high-throughput screening.</p

Data_Sheet_1_Nitrite-Oxidizing Bacteria Community Composition and Diversity Are Influenced by Fertilizer Regimes, but Are Independent of the Soil Aggregate in Acidic Subtropical Red Soil.PDF

<p>Nitrification is the two-step aerobic oxidation of ammonia to nitrate via nitrite in the nitrogen-cycle on earth. However, very limited information is available on how fertilizer regimes affect the distribution of nitrite oxidizers, which are involved in the second step of nitrification, across aggregate size classes in soil. In this study, the community compositions of nitrite oxidizers (Nitrobacter and Nitrospira) were characterized from a red soil amended with four types of fertilizer regimes over a 26-year fertilization experiment, including control without fertilizer (CK), swine manure (M), chemical fertilization (NPK), and chemical/organic combined fertilization (MNPK). Our results showed that the addition of M and NPK significantly decreased Nitrobacter Shannon and Chao1 index, while M and MNPK remarkably increased Nitrospira Shannon and Chao1 index, and NPK considerably decreased Nitrospira Shannon and Chao1 index, with the greatest diversity achieved in soils amended with MNPK. However, the soil aggregate fractions had no impact on that alpha-diversity of Nitrobacter and Nitrospira under the fertilizer treatment. Soil carbon, nitrogen and phosphorus in the soil had a significant correlation with Nitrospira Shannon and Chao1 diversity index, while total potassium only had a significant correlation with Nitrospira Shannon diversity index. However, all of them had no significant correlation with Nitrobacter Shannon and Chao1 diversity index. The resistance indices for alpha-diversity indexes (Shannon and Chao1) of Nitrobacter were higher than those of Nitrospira in response to the fertilization regimes. Manure fertilizer is important in enhancing the Nitrospira Shannon and Chao1 index resistance. Principal co-ordinate analysis revealed that Nitrobacter- and Nitrospira-like NOB communities under four fertilizer regimes were differentiated from each other, but soil aggregate fractions had less effect on the nitrite oxidizers community. Redundancy analysis and Mantel test indicated that soil nitrogen, carbon, phosphorus, and available potassium content were important environmental attributes that control the Nitrobacter- and Nitrospira-like NOB community structure across different fertilization treatments under aggregate levels in the red soil. In general, nitrite-oxidizing bacteria community composition and alpha-diversity are depending on fertilizer regimes, but independent of the soil aggregate.</p

Image_1_Effects of Interfaces of Goethite and Humic Acid-Goethite Complex on Microbial Degradation of Methyl Parathion.PDF

<p>Microbial degradation plays an essential role in the removal of hydrophobic organic compounds (HOCs) dispersed in soil and sediment, and its performance is greatly affected by mineral particles which regulate HOCs bioavailability by interfacial adsorption. Likewise, bacteria cells attach to the surfaces of mineral particles as well but how bacterial attachment affects biodegradation is largely unknown. Here we report inhibitory effects of goethite and humic acid (HA)-goethite complex addition on microbial degradation of methyl parathion (MP). Using attenuated total reflectance-Fourier transform infrared spectroscopy, we observed that the adhesion of bacterial cells responsible for MP degradation on goethite occurred and the adhesive strength increased over time. We then replaced goethite with phosphate-adsorbed goethite to weaken the goethite-bacteria association and the inhibition of MP biodegradation was alleviated. These results suggested the formation of goethite-bacteria association hinder MP biodegradation. Meanwhile, our results showed that HA coating prevented bacterial attachment on goethite particles along with a drastically increased MP adsorption by goethite. The combined effect would lead to decreased mass fluxes of MP to bacterial cells and could represent another mechanism responsible for the decreased degradation rate observed in the current study.</p