Atomic force microscopy was used to compare the dissolution morphology of iron (oxy)(hydr)oxide coated slides exposed to the dissimilatory iron reducing bacterium Shewanella oneidensis MR-1 and a Type II protein secretion mutant unable to reduce iron minerals without an exogenous electron shuttle. Dissolution morphologies of slides exposed to the wild-type organism were heterogeneous and consistent with the morphology of bacterial microcolonies observed by confocal microscopy. In contrast, dissolution morphologies of slides exposed to wild-type or mutant strains and the electron shuttling compound 9,10-anthraquinone-2,6-disulfonate were homogeneous. These results suggest that microcolony formation by the wild-type strain may limit dissolution whereas respiration using the shuttle compound relieves this limitation.
. Genetic complementation and nucleotide sequence analyses indicated that the CCMB1 respiratory mutant phenotype was due to mutation of a conserved histidine residue (H108Y) in a protein that displayed high homology to Escherichia coli CcmB, the permease subunit of an ABC transporter involved in cytochrome c maturation. Although CCMB1 retained the ability to grow on electron acceptors with high E 0 , the cytochrome content of CCMB1 was <10% of that of the wild-type strain. Periplasmic extracts of CCMB1 contained slightly greater concentrations of the thiol functional group (-SH) than did the wild-type strain, an indication that the E h of the CCMB1 periplasm was abnormally low. A ccmB deletion mutant was unable to respire anaerobically on any electron acceptor, yet retained aerobic respiratory capability. These results suggest that the mutation of a conserved histidine residue (H108) in CCMB1 alters the redox homeostasis of the periplasm during anaerobic growth on electron acceptors with low (but not high) E 0 . This is the first report of the effects of Ccm deficiencies on bacterial respiration of electron acceptors whose E 0 nearly span the entire redox continuum.
A thermophile, Thermus scotoductus SA-01, was cultured within a constant-temperature (65°C) microwave (MW) digester to determine if MW-specific effects influenced the growth and physiology of the organism. As a control, T. scotoductus cells were also cultured using convection heating at the same temperature as the MW studies. Cell growth was analyzed by optical density (OD) measurements, and cell morphologies were characterized using electron microscopy imaging (scanning electron microscopy [SEM] and transmission electron microscopy [TEM]), dynamic light scattering (DLS), and atomic force microscopy (AFM). Biophysical properties (i.e., turgor pressure) were also calculated with AFM, and biochemical compositions (i.e., proteins, nucleic acids, fatty acids) were analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the fatty acid methyl esters extracted from cell membranes. Here we report successful cultivation of a thermophile with only dielectric heating. Under the MW conditions for growth, cell walls remained intact and there were no indications of membrane damage or cell leakage. Results from these studies also demonstrated that T. scotoductus cells grown with MW heating exhibited accelerated growth rates in addition to altered cell morphologies and biochemical compositions compared with oven-grown cells. The term "extremophile" was first presented in 1974 by R. D. MacElroy to describe organisms that require extreme growth environments (or environments having conditions that humans cannot tolerate) (1). Since that time, thousands of extremophilic organisms have been identified in all three domains of the phylogenetic tree (Bacteria, Archaea, and Eukarya). These diverse organisms are further classified based on the environment in which they thrive. For example, thermophiles, like Thermus aquaticus, grow at high temperatures (Ͼ60°C) (2) while psychrophiles, e.g., Cryomyces antarcticus, prefer low temperatures (Ͻ15°C) (3). Members of the Acidobacteria phylum grow well in acidic environments (pH Ͻ 5) (4, 5) and are referred to as acidophiles. Barophiles or piezophiles such as Shewanella benthica require high pressures (Ͼ10 MPa) (6, 7), and halophiles like Halomonas spp. thrive in high-salt environments (up to 30%, wt/vol) (8). Some extremophiles thrive under multiple extreme conditions and are termed "polyextremophiles." For example, Natranaerobius thermophilus is an obligate anaerobic alkalithermophile that grows best at 55°C, 3.5 M Na ϩ , and pH 9.5 (9). The investigations of microbial communities that populate extreme environments such as hydrothermal vents and the Mariana trench have advanced our understanding of molecular and physiological responses underlying extremophile growth, survivability, and adaptation.Over the years, the effects of low-frequency (3-to 300-GHz) radiation, or microwave (MW) radiation, on living microorganisms have been studied (see Fig. S1 in the supplemental material). However, ther...
BackgroundWe investigated the surface characteristics of two strains of Shewanella sp., S. oneidensis MR-1 and S. putrefaciens 200, that were grown under aerobic conditions as well as under anaerobic conditions with trimethylamine oxide (TMAO) as the electron acceptor. The investigation focused on the experimental determination of electrophoretic mobility (EPM) under a range of pH and ionic strength, as well as by subsequent modeling in which Shewanella cells were considered to be soft particles with water- and ion-permeable outermost layers.ResultsThe soft layer of p200 is significantly more highly charged (i.e., more negative) than that of MR-1. The effect of electron acceptor on the soft particle characteristics of Shewanella sp. is complex. The fixed charge density, which is a measure of the deionized and deprotonated functional groups in the soft layer polymers, is slightly greater (i.e., more negative) for aerobically grown p200 than for p200 grown with TMAO. On the other hand, the fixed charge density of aerobically grown MR1 is slightly less than that of p200 grown with TMAO. The effect of pH on the soft particle characteristics is also complex, and does not exhibit a clear pH-dependent trend.ConclusionsThe Shewanella surface characteristics were attributed to the nature of the outermost soft layer, the extracellular polymeric substances (EPS) in case of p200 and lypopolysaccharides (LPS) in case of MR1 which generally lacks EPS. The growth conditions (i.e., aerobic vs. anaerobic TMAO) have an influence on the soft layer characteristics of Shewanella sp. cells. Meanwhile, the clear pH dependency of the mechanical and morphological characteristics of EPS and LPS layers, observed in previous studies through atomic force microscopy, adhesion tests and spectroscopies, cannot be corroborated by the electrohydrodynamics-based soft particle characteristics which does not exhibited a clear pH dependency in this study. While the electrohydrodynamics-based soft-particle model is a useful tool in understanding bacteria’s surface properties, it needs to be supplemented with other characterization methods and models (e.g., chemical and micromechanical) in order to comprehensively address all of the surface-related characteristics important in environmental and other aqueous processes.
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