Characterization of sediment bacteria involved in selenium reduction

Bacterial reduction of selenium (Se) oxyanions (Se[VI] and Se[IV]) to elemental Se (Se[0]) is one of the major biogeochemical processes removing Se from agricultural drainage water and depositing Se in the sediment. This study was conducted to characterize Se-reducing bacterial populations in Lost Hills evaporation pond sediment and to observe their response to Se(VI) and organic C amendments. Se(VI) was removed from the dissolved phase in the sediment slurries amended with organic C with a decrease in redox potential (Eh). Se(VI) concentrations decreased from 2137 to 79 microg L-1 after 9 days of incubation in a 5% soil slurry. Upon our screening process, 9 Se(VI)- and 14 Se(IV)-reducing bacteria were isolated from sediment slurries and identified by amplification and sequencing of 16S rDNA. Bacillus strains appeared to be dominant in the bacterial assemblages active in Se(VI) and Se(IV) reduction in the sediment. Halomonas pacifica and Staphylococcus warneri were also identified as Se(IV)-reducers. Indigenous bacteria have a significant role in the biogeochemical cycling of Se and may be stimulated by addition of a suitable organic source for Se reduction. The bacterial strains isolated from salt-affected and Se-contaminated Lost Hills evaporation pond sediment may have potential application in removing Se from high salt drainage water.     

Effects of Stimulation of Copper Bioleaching on Microbial Community in Vineyard Soil and Copper Mining Waste

Long-term copper application in vineyards and copper mining activities cause heavy metal pollution sites. Such sites need remediation to protect soil and water quality. Bioremediation of contaminated areas through bioleaching can help to remove copper ions from the contaminated soils. Thus, the aim of this work was to evaluate the effects of different treatments for copper bioleaching in two diverse copper-contaminated soils (a 40-year-old vineyard and a copper mining waste) and to evaluate the effect on microbial community by applying denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA amplicons and DNA sequence analysis. Several treatments with HCl, H₂SO₄, and FeSO₄ were evaluated by stimulation of bioleaching of copper in the soils. Treatments and extractions using FeSO₄ and H₂SO₄ mixture at 30°C displayed more copper leaching than extractions with deionized water at room temperature. Treatment with H₂SO₄ supported bioleaching of as much as 120 mg kg⁻¹ of copper from vineyard soil after 115 days of incubation. DGGE analysis of the treatments revealed that some treatments caused greater diversity of microorganisms in the vineyard soil compared to the copper mining waste. Nucleotide Blast of PCR-amplified fragments of 16S rRNA gene bands from DGGE indicated the presence of Rhodobacter sp., Silicibacter sp., Bacillus sp., Paracoccus sp., Pediococcus sp., a Myxococcales, Clostridium sp., Thiomonas sp., a firmicute, Caulobacter vibrioides, Serratia sp., and an actinomycetales in vineyard soil. Contrarily, Sphingomonas was the predominant genus in copper mining waste in most treatments. Paracoccus sp. and Enterobacter sp. were also identified from DGGE bands of the copper mining waste. Paracoccus species is involved in the copper bioleaching by sulfur oxidation system, liberating the copper bounded in the soils and hence promoting copper bioremediation. Results indicate that stimulation of bioleaching with a combination of FeSO₄ and H₂SO₄ promoted bioleaching in the soils and can be employed ex situ to remediate copper-impacted soils.     

Improved Enrichment and Isolation of Polycyclic Aromatic Hydrocarbons (PAH)-Degrading Microorganisms in Soil Using Anthracene as a Model PAH

Lack of attention to soil and microbial characteristics that influence PAHs degradation has been a leading cause of failures in isolation of efficient PAH degraders and bioaugumentation processes with microbial consortia. This study compared the classic method of isolation of PAHs-degraders with a modified method employing a pre-enrichment respirometric analysis. The modified enrichment of PAH degrading microorganisms using in vitro microcosm resulted to reduced enrichment period and more efficient PAH-degrading microbial consortia. Results indicate that natural soils with strong heterotrophic microbial activity determined through pre-enrichment analysis, are better suited for the isolation of efficient PAH degrading microorganisms with significant reduction of the enrichment period.     

Bacterial reduction of selenate to elemental selenium utilizing molasses as a carbon source

Selecting an inexpensive and effective organic carbon source is the key to reducing the cost in selenium (Se) remediation. Five bacteria were screened based on their ability in using molasses as an organic carbon source to reduce selenate [Se(VI)] in drainage water. Efficiency of Se removal differed in the molasses-added drainage water containing different bacteria, with an order of Enterobacter taylorae>Pantoea sp. SSS2>Klebsiella sp. WRS2>Citerobacter freundii>Shigella sp. DW2. By using E. taylorae, 97% of the added Se(VI) (1000 microg/L) was reduced to elemental Se [Se(0)] in an artificial drainage water during an 11-day experiment, and 93% of Se(VI) in a natural agricultural drainage water was reduced to Se(0) and organic Se during a 7-day experiment. E. taylorae also rapidly removed Se(VI) in agar-coated sand columns. During 45 days of the experiment, more than 92% of influent Se was removed from the drainage water with a molasses range of 0.01-0.1%. This study reveals that molasses may be a cost-effective organic carbon source used by Se(VI)-reducing bacteria to remove Se from agricultural drainage water in field.     

Hexavalent Chromium Reduction by Immobilized Cells and the Cell-Free Extract of Bacillus sp. ES 29

Bacillus sp. ES 29 (ATCC: BAA-696) is an efficient chromate reducing bacterium. We evaluated hexavalent chromium (Cr[VI]) reduction by immobilized intact cells and the cell-free enzyme extracts of Bacillus sp. ES 29 in a bioreactor system. Influences of different flow rates (3 to 14 mL h?1), Cr(VI) concentration (2 to 8 mg L?1), and immobilization support materials (Celite, amberlite, and Ca-alginate) on Cr(VI) reduction were examined. Both immobilized intact cells and the cell-free extract of Bacillus sp. ES 29 displayed substantial Cr(VI) reduction. Increasing flow rates from 3 to 6 mL h?1 did not affect the rate of Cr(VI) reduction, but above 6 mL h?1, the Cr(VI) reducing capacity of the immobilized intact cells and cell-free extract of Bacillus sp. ES 29 decreased. With both intact cells and the cell-free extracts, the rate of Cr(VI) reduction was inversely related to the concentration. Intact cells immobilized to Celite displayed the highest rate (k = 0.443 at 3 mL h?1) of Cr(VI) reduction. For the immobilized cell-free extract, maximal reduction (k = 0.689 at 3 mL h?1) was observed with Ca-alginate. Using initial Cr(VI) concentrations of 2 to 8 mg L?1 at flow rates of 3 to 6 mL h?1 both immobilized intact cells and the cell-free extracts reduced 84 to 98% of the influent Cr(VI). Results indicate that immobilized cells and the cell-free extracts of Bacillus sp. ES 29 could be used for large-scale removal of Cr(VI) from contaminated water and waste streams in containment systems.     

In vitro sensitivity of environmental isolates of pathogenic dematiaceous fungi to azole compounds and a phenylpropyl-morpholine derivative

The in vitro sensitivity (minimum inhibitory concentrations; MICs) of 42 environmental isolates of pathogenic dematiaceous fungi to 7 azole compounds, viz. thiabendazole, ketoconazole, miconazole, econazole bifonazole, Bay n 7133, Bay 1 9139 and phenylpropyl-morpholine derivative, R_o14-4767/002 was studied by an agar dilution method using Emmon's Sabouraud dextrose agar (ESDA) as the culture medium.The isolates of Fonsecaea pedrosoi, Cladosporium carrionii, Exophiala jeanselmei and Ramichloridium subulatum were most sensitive to bifonazole with mean MICs of 0.06 g/ml or less; Phialophora verrucosa had an MIC of 0.05 g/ml to ketoconazola and R_o14-4767/002, respectively. Ochroconis sp had an MIC of 0.025 g/ml to R_o14-4767/002 and Cladosporium tennuisimum 0.39 g/ml to ketoconazole. Econazole and thiabendazole also showed good antifungal activity. The fungi were relatively resistant to the more recently developed azoles, viz. Bay n 7133 and Bay 1 9139, the later failing to inhibit C. tennuisimum at a concentration of 100 g/ml. The minimum fungicidal concentrations (MFC) of the drugs wree mostly within 2 to 8 fold of the MICs.     

Development of a perchlorate reductase-based biosensor for real time analysis of perchlorate in water

Perchlorate (ClO4-) contamination of ground water is a widespread problem in the U.S., which can adversely affect human health and wildlife. Current methods for detecting and quantifying ClO4- in water are time consuming, expensive and sometimes subject to complex procedures. This study reports the construction of a ClO4- reductase-based biosensor for rapid determination of ClO4- in water. Using a 3 mm GCE (glass carbon electrode), a ClO4- sensing bio-electrode was constructed by coating an aliquot of a Dechlorosoma sp. ClO4- reductase on nafion (ion-exchange matrix) layer pre-coated on the polished surface of the GCE. The response time to ClO4- was approximately 111+/-28 s. Kinetic evaluation of the sensor response to ClO4- revealed linear increases (r2>99%) in 10 min with k values of 10.3, 24.2, 33.9 and 48.2 at 25, 50, 75 and 100 microg/L, respectively. A strong linear correlation was established between biosensor response (nA) and ion-chromatography conductivity readings (microS). Biosensor response to ClO4- was maximal at applied potential range of -0.6 to -1.0 V. ClO4- reduction was maximal in the range of 7.6 to 8.0. The ClO4- biosensor was significantly stable after repeated use (24 analyses conducted on day 1 over a 10-h period at room temperature). This study indicates great potential for the development of a portable biosensor for real time analysis of ClO4- in water.     

Isolation of Exophiala jeanselmei from bat guano

Exophiala jeanselmei was isolated from two out of 75 samples of bat guano. The isolates hydrolysed urea and tyrosine, assimilated sodium nitrate and produced a zone of haemolysis on blood agar, They were pathogenic for laboratory mice when injected subcutaneously, intraperitoneally or intravenously.     

The commonly-used DNA probe for diffusely-adherent Escherichia coli cross-reacts with a subset of enteroaggregative E. coli

Background  

The roles of diffusely-adherent Escherichia coli (DAEC) and enteroaggregative E. coli (EAEC) in disease are not well understood, in part because of the limitations of diagnostic tests for each of these categories of diarrhoea-causing E. coli. A HEp-2 adherence assay is the Gold Standard for detecting both EAEC and DAEC but DNA probes with limited sensitivity are also employed.