scholarly journals Extracellular Electron Transport-Mediated Fe(III) Reduction by a Community of Alkaliphilic Bacteria That Use Flavins as Electron Shuttles

2013 ◽  
Vol 80 (1) ◽  
pp. 128-137 ◽  
Author(s):  
Samuel J. Fuller ◽  
Duncan G. G. McMillan ◽  
Marc B. Renz ◽  
Martin Schmidt ◽  
Ian T. Burke ◽  
...  
Keyword(s):  
Bacterial Communities ◽  
High Performance ◽  
Iron Reduction ◽  
Molecular Mechanisms ◽  
Electrochemical Analysis ◽  
Content Type ◽  
Electron Shuttles ◽  
Final Electron ◽  
Extracellular Electron Transport ◽  
Final Electron Acceptor

ABSTRACTThe biochemical and molecular mechanisms used by alkaliphilic bacterial communities to reduce metals in the environment are currently unknown. We demonstrate that an alkaliphilic (pH > 9) consortium dominated byTissierella,Clostridium, andAlkaliphilusspp. is capable of using iron (Fe3+) as a final electron acceptor under anaerobic conditions. Iron reduction is associated with the production of a freely diffusible species that, upon rudimentary purification and subsequent spectroscopic, high-performance liquid chromatography, and electrochemical analysis, has been identified as a flavin species displaying properties indistinguishable from those of riboflavin. Due to the link between iron reduction and the onset of flavin production, it is likely that riboflavin has an import role in extracellular metal reduction by this alkaliphilic community.

scholarly journals Molecular Dissection of Bacterial Nanowires

mBio ◽  
2013 ◽  
Vol 4 (3) ◽  
Author(s):  
Thomas Boesen ◽  
Lars Peter Nielsen
Keyword(s):  
Conclusive Evidence ◽  
Geobacter Sulfurreducens ◽  
Electron Conduction ◽  
Content Type ◽  
Type Iv ◽  
Pilin Subunit ◽  
Type Iv Pilin ◽  
Final Electron ◽  
Conductive Properties ◽  
Final Electron Acceptor

ABSTRACTThe discovery of bacterial conductive structures, termed nanowires, has intrigued scientists for almost a decade. Nanowires enable bacteria to transfer electrons over micrometer distances to extracellular electron acceptors such as insoluble metal oxides or electrodes. Nanowires are pilus based and inGeobacter sulfurreducensare composed of the type IV pilin subunit PilA. Multihemec-type cytochromes have been shown to attach to nanowire pili. Two hypotheses have been proposed for electron conduction in nanowires. The first (termed the metal-like conductivity or MLC hypothesis) claims that the pilus itself has the electron-conductive properties and the attached cytochromes mediate transfer to the final electron acceptor, whereas the second hypothesis (termed the superexchange conductivity or SEC hypothesis) suggests that electrons are “hopping” between heme groups in cytochromes closely aligned with the pilus as a scaffold. In their recent article inmBio, Vargas et al. [M. Vargas, N. S. Malvankar, P.-L. Tremblay, C. Leang, J. A. Smith, P. Patel, O. Snoeyenbos-West, K. P. Nevin, and D. R. Lovley, mBio 4(2):e00210-13, 2013] address this ambiguity through an analysis of strain Aro-5, aG. sulfurreducensPilA mutant lacking aromatic residues in the nonconserved portion of PilA. These residues were suspected of involvement in electron transport according to the MLC hypothesis. TheG. sulfurreducensmutant had reduced conductive properties, lending important support to the MLC hypothesis. The data also highlight the need for further and more conclusive evidence for one or the other hypothesis.

scholarly journals Anaerobic α-Amylase Production and Secretion with Fumarate as the Final Electron Acceptor in Saccharomyces cerevisiae

2013 ◽  
Vol 79 (9) ◽  
pp. 2962-2967 ◽  
Author(s):  
Zihe Liu ◽  
Tobias Österlund ◽  
Jin Hou ◽  
Dina Petranovic ◽  
Jens Nielsen
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Folding ◽  
Protein Secretion ◽  
Electron Acceptor ◽  
Anaerobic Growth ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Content Type ◽  
Final Electron ◽  
Final Electron Acceptor

ABSTRACTIn this study, we focus on production of heterologous α-amylase in the yeastSaccharomyces cerevisiaeunder anaerobic conditions. We compare the metabolic fluxes and transcriptional regulation under aerobic and anaerobic conditions, with the objective of identifying the final electron acceptor for protein folding under anaerobic conditions. We find that yeast produces more amylase under anaerobic conditions than under aerobic conditions, and we propose a model for electron transfer under anaerobic conditions. According to our model, during protein folding the electrons from the endoplasmic reticulum are transferred to fumarate as the final electron acceptor. This model is supported by findings that the addition of fumarate under anaerobic (but not aerobic) conditions improves cell growth, specifically in the α-amylase-producing strain, in which it is not used as a carbon source. Our results provide a model for the molecular mechanism of anaerobic protein secretion using fumarate as the final electron acceptor, which may allow for further engineering of yeast for improved protein secretion under anaerobic growth conditions.

scholarly journals Sulfur Species as Redox Partners and Electron Shuttles for Ferrihydrite Reduction by Sulfurospirillum deleyianum

2014 ◽  
Vol 80 (10) ◽  
pp. 3141-3149 ◽  
Author(s):  
Regina Lohmayer ◽  
Andreas Kappler ◽  
Tina Lösekann-Behrens ◽  
Britta Planer-Friedrich
Keyword(s):  
Iron Reduction ◽  
Elemental Sulfur ◽  
Reduction Process ◽  
Sulfur Source ◽  
Sulfur Species ◽  
Content Type ◽  
Electron Transfer Pathway ◽  
Electron Shuttles ◽  
Enzymatic Reduction ◽  
Abiotic Oxidation

ABSTRACTIron(III) (oxyhydr)oxides can represent the dominant microbial electron acceptors under anoxic conditions in many aquatic environments, which makes understanding the mechanisms and processes regulating their dissolution and transformation particularly important. In a previous laboratory-based study, it has been shown that 0.05 mM thiosulfate can reduce 6 mM ferrihydrite indirectly via enzymatic reduction of thiosulfate to sulfide by the sulfur-reducing bacteriumSulfurospirillum deleyianum, followed by abiotic reduction of ferrihydrite coupled to reoxidation of sulfide. Thiosulfate, elemental sulfur, and polysulfides were proposed as reoxidized sulfur species functioning as electron shuttles. However, the exact electron transfer pathway remained unknown. Here, we present a detailed analysis of the sulfur species involved. Apart from thiosulfate, substoichiometric amounts of sulfite, tetrathionate, sulfide, or polysulfides also initiated ferrihydrite reduction. The portion of thiosulfate produced during abiotic ferrihydrite-dependent reoxidation of sulfide was about 10% of the total sulfur at maximum. The main abiotic oxidation product was elemental sulfur attached to the iron mineral surface, which indicates that direct contact between microorganisms and ferrihydrite is necessary to maintain the iron reduction process. Polysulfides were not detected in the liquid phase. Minor amounts were found associated either with microorganisms or the mineral phase. The abiotic oxidation of sulfide in the reaction with ferrihydrite was identified as rate determining. Cysteine, added as a sulfur source and a reducing agent, also led to abiotic ferrihydrite reduction and therefore should be eliminated when sulfur redox reactions are investigated. Overall, we could demonstrate the large impact of intermediate sulfur species on biogeochemical iron transformations.

scholarly journals Combination of Voriconazole and Anidulafungin for Treatment of Triazole-Resistant Aspergillus fumigatus in anIn VitroModel of Invasive Pulmonary Aspergillosis

2012 ◽  
Vol 56 (10) ◽  
pp. 5180-5185 ◽  
Author(s):  
Adam R. Jeans ◽  
Susan J. Howard ◽  
Zaid Al-Nakeeb ◽  
Joanne Goodwin ◽  
Lea Gregson ◽  
...  
Keyword(s):  
High Performance ◽  
Molecular Mechanisms ◽  
Invasive Pulmonary Aspergillosis ◽  
Fungal Growth ◽  
Pulmonary Aspergillosis ◽  
Antifungal Effect ◽  
Content Type ◽  
Exposure Response ◽  
Relationship Of

ABSTRACTVoriconazole is a first-line agent for the treatment of invasive pulmonary aspergillosis. Isolates with elevated voriconazole MICs are increasingly being seen, and the optimal treatment regimen is not defined. We investigated whether the combination of voriconazole with anidulafungin may be beneficial for the treatment ofA. fumigatusstrains with elevated voriconazole MICs. We used anin vitromodel of the human alveolus to define the exposure-response relationships for a wild-type strain (voriconazole MIC, 0.5 mg/liter) and strains with defined molecular mechanisms of triazole resistance (MICs, 4 to 16 mg/liter). All strains had anidulafungin minimum effective concentrations (MECs) of 0.0078 mg/liter. Exposure-response relationships were estimated using galactomannan as a biomarker. Concentrations of voriconazole and anidulafungin were measured using high-performance liquid chromatography (HPLC). The interaction of voriconazole and anidulafungin was described using the Greco model. Fungal growth was progressively inhibited with higher drug exposures of voriconazole. Strains with elevated voriconazole MICs required proportionally greater voriconazole exposures to achieve a comparable antifungal effect. Galactomannan concentrations were only marginally reduced by anidulafungin monotherapy. An additive effect between voriconazole and anidulafungin was apparent. In conclusion, the addition of anidulafungin does not markedly alter the exposure-response relationship of voriconazole. A rise in serum galactomannan during combination therapy with voriconazole and anidulafungin should be interpreted as treatment failure and not attributed to a paradoxical reaction related to echinocandin treatment.

scholarly journals The Physiological Roles of Vitamin E and Hypovitaminosis E in the Transition Period of High-Yielding Dairy Cows

Animals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1088
Author(s):  
Satoshi Haga ◽  
Hiroshi Ishizaki ◽  
Sanggun Roh
Keyword(s):  
Dairy Cows ◽  
High Performance ◽  
Molecular Mechanisms ◽  
Transition Period ◽  
Disease Risk ◽  
Serum Vitamin ◽  
Physiological Role ◽  
Density Lipoprotein ◽  
Alpha Tocopherol ◽  
Transition Dairy Cows

Levels of alpha-tocopherol (α-Toc) decline gradually in blood throughout prepartum, reaching lowest levels (hypovitaminosis E) around calving. Despite numerous reports about the disease risk in hypovitaminosis E and the effect of α-Toc supplementation on the health of transition dairy cows, its risk and supplemental effects are controversial. Here, we present some novel data about the disease risk of hypovitaminosis E and the effects of α-Toc supplementation in transition dairy cows. These data strongly demonstrate that hypovitaminosis E is a risk factor for the occurrence of peripartum disease. Furthermore, a study on the effectiveness of using serum vitamin levels as biomarkers to predict disease in dairy cows was reported, and a rapid field test for measuring vitamin levels was developed. By contrast, evidence for how hypovitaminosis E occurred during the transition period was scarce until the 2010s. Pioneering studies conducted with humans and rodents have identified and characterised some α-Toc-related proteins, molecular players involved in α-Toc regulation followed by a study in ruminants from the 2010s. Based on recent literature, the six physiological factors: (1) the decline in α-Toc intake from the close-up period; (2) changes in the digestive and absorptive functions of α-Toc; (3) the decline in plasma high-density lipoprotein as an α-Toc carrier; (4) increasing oxidative stress and consumption of α-Toc; (5) decreasing hepatic α-Toc transfer to circulation; and (6) increasing mammary α-Toc transfer from blood to colostrum, may be involved in α-Toc deficiency during the transition period. However, the mechanisms and pathways are poorly understood, and further studies are needed to understand the physiological role of α-Toc-related molecules in cattle. Understanding the molecular mechanisms underlying hypovitaminosis E will contribute to the prevention of peripartum disease and high performance in dairy cows.

scholarly journals Phylogenetic and metabolic diversity have contrasting effects on the ecological functioning of bacterial communities

2021 ◽  
Vol 97 (3) ◽  
Author(s):  
Constantinos Xenophontos ◽  
Martin Taubert ◽  
W Stanley Harpole ◽  
Kirsten Küsel
Keyword(s):  
Bacterial Communities ◽  
Species Interactions ◽  
Phylogenetic Diversity ◽  
Molecular Mechanisms ◽  
Linear Models ◽  
Theory Development ◽  
Metabolic Diversity ◽  
Community Functioning ◽  
Metabolic Functions ◽  
Independent Effects

ABSTRACT Quantifying the relative contributions of microbial species to ecosystem functioning is challenging, because of the distinct mechanisms associated with microbial phylogenetic and metabolic diversity. We constructed bacterial communities with different diversity traits and employed exoenzyme activities (EEAs) and carbon acquisition potential (CAP) from substrates as proxies of bacterial functioning to test the independent effects of these two aspects of biodiversity. We expected that metabolic diversity, but not phylogenetic diversity would be associated with greater ecological function. Phylogenetically relatedness should intensify species interactions and coexistence, therefore amplifying the influence of metabolic diversity. We examined the effects of each diversity treatment using linear models, while controlling for the other, and found that phylogenetic diversity strongly influenced community functioning, positively and negatively. Metabolic diversity, however, exhibited negative or non-significant relationships with community functioning. When controlling for different substrates, EEAs increased along with phylogenetic diversity but decreased with metabolic diversity. The strength of diversity effects was related to substrate chemistry and the molecular mechanisms associated with each substrate's degradation. EEAs of phylogenetically similar groups were strongly affected by within-genus interactions. These results highlight the unique flexibility of microbial metabolic functions that must be considered in further ecological theory development.

scholarly journals Rough diamonds in emerging markets: legacy, competitiveness, and sustained high performance

2019 ◽  
Vol 26 (3) ◽  
pp. 363-386
Author(s):  
Seung Ho Park ◽  
Gerardo R. Ungson
Keyword(s):  
Human Capital ◽  
Emerging Markets ◽  
High Performance ◽  
Core Competencies ◽  
Market Potential ◽  
Government Support ◽  
Screening Tests ◽  
Institutional Voids ◽  
Content Type ◽  
Over Time

Purpose The purpose of this paper is to uncover the underlying drivers of sustained high performing companies based on a field study of 127 companies in Brazilian, Russian, Indian and Chinese (BRIC) and Association of Southeast Asian Nations (ASEAN) emerging markets. Understanding these companies provides a complementary way of appraising the growth, development and transformation of emerging markets. The authors synthesize the findings in an overarching framework that covers six strategies for building and sustaining legacy that leads to the succession of intergenerational wealth over time: overcoming institutional voids, inclusive markets, deepening localization, nurturing government support, building core competencies and harnessing human capital. The authors relate these strategies to different levels of development using Prahalad and Hart’s BOP framework. Design/methodology/approach This study examines the underlying drivers of sustained high-performance companies based on field studies from an initial set of 105,260 BRIC companies and close to 500 companies in ASEAN. The methods employed four screening tests to arrive at a selection of the highest-performing firms: 70 firms in the BRIC nations and 58 firms from ASEAN. Following the selection, the authors constructed cases using primary interviews and secondary data, with the assistance of Ernst & Young and with academic colleagues in Manila. These studies were originally conducted in two separate time periods and reported accordingly. This paper synthesizes the findings of these two studies to arrive at an extended integrative framework. Findings From the cases, the authors examine six strategies for building and sustaining legacy that lead to high performance over time: overcoming institutional voids, creating inclusive markets, deepening localization, nurturing government support, building core competencies and harnessing human capital. To address the evolving state of institutional voids in these countries, the authors employ similar methods to hypothesize the placement of these strategies in the context of the world economic pyramid, initially formulated as the “bottom of the pyramid” framework. Originality/value This paper synthesizes and extends the authors’ previous works by proposing the concept of legacy to describe the emergence and succession of local exemplary firms in emerging markets. This study aims to complement extant measures of nation-growth based primarily on GDP. The paper also extends the literature on institutional voids in shifting the focus from the mix of voids to their evolving state. Altogether, the paper provides a complementary narrative on assessing the market potential of emerging markets by adopting several categories of performance.

scholarly journals Oral Bacterial Communities in Individuals with Type 2 Diabetes Who Live in Southern Thailand

2013 ◽  
Vol 80 (2) ◽  
pp. 662-671 ◽  
Author(s):  
Kanokporn Kampoo ◽  
Rawee Teanpaisan ◽  
Ruth G. Ledder ◽  
Andrew J. McBain
Keyword(s):  
Type 2 Diabetes ◽  
Dental Caries ◽  
Bacterial Communities ◽  
Glycosylated Hemoglobin ◽  
Content Type ◽  
Supragingival Plaque ◽  
Southern Thailand ◽  
Acid Tolerant ◽  
Dna Profiles

ABSTRACTType 2 diabetes mellitus is increasingly common in Thailand and elsewhere. In the present investigation, the bacteriological composition of saliva and supragingival plaque in Thai diabetics with and without active dental caries and in nondiabetics was determined by differential culture and eubacterial DNA profiling. Potential associations between fasting blood sugar and glycosylated hemoglobin (biomarkers of current and historical glucose control, respectively) with decayed, missing, and filled teeth and with salivaryStreptococcusandLactobacilluscounts were also investigated. The incidence of active dental caries was greater in the Thai diabetics than in nondiabetics, and the numbers of total streptococci and lactobacilli were significantly higher in supragingival plaque from diabetics than in nondiabetics.Lactobacilluscounts in the saliva and supragingival plaque of diabetics with active caries were significantly higher than those in diabetics without active caries. Oral eubacterial DNA profiles of diabetic versus nondiabetic individuals and of diabetics with active caries versus those without active caries could not be readily differentiated through cluster analysis or multidimensional scaling. The elevated caries incidence in the Thai diabetics was positively associated with numbers of bacteria of the acidogenic/acid-tolerant generaStreptococcusandLactobacillus. Lactobacillusbacterial numbers were further elevated in diabetics with active caries, although salivary eubacterial DNA profiles were not significantly altered.

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