• Research in Plant Disease
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• v.23 no.3
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• pp.212-227
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• 2017

Pseudomonas chlororaphis O6, isolated from the roots of dryland, field-grown commercial wheat in the USA, enhances plant health and therefore it is used in agriculture as a biofertilizer and biocontrol agent. The metabolites produced by this pseudomonad stimulate plant growth through direct antagonism of pathogens and by inducing systemic resistance in the plant. Studies upon P. chlororaphis O6 identify the pathways through which defined bacterial metabolites generate protection against pathogenic microbes, insects, and nematodes. P. chlororaphis O6 also triggers plant resistance to drought and salinity stresses. The beneficial determinants are produced from bacterial cells as they form biofilms during root colonization. Molecular control these processes in P. chlororaphis O6 involves the global regulatory Gac/Rsm signaling cascade with cross-talk between other global regulatory pathways. The Gac/Rsm regulon allows for coordinate phasing of expression of the genes that encode these beneficial traits among a community of cells. This review provides insights on the Gac/Rsm regulon in expression of beneficial traits of the P. chlororaphis O6 which can contribute to help yield enhancement and quality in agricultural production.

• Journal of Microbiology
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• v.40 no.4
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• pp.260-266
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• 2002

Bacterial strains were isolated from biofilms formed on glass slides submerged in seawater in Dae-Ho Dike. Eight strains showing fast attaching ability were selected and identified. Their exopolysaccharide (EPS)-producing ability and EPS properties were characterized. Based on Microlog System, 4 among the 8 strains were identified as Micrococcus luteus and the rest were Bacillus thuringiensis, Bacillus megaterium,, Staphylococcus saprophyticus and Agrobacterium vitis. A, vitis was reidentified as Sulfitobacter pontiacus based on 16S rDNA sequence data. The amount of water-soluble EPS produced by the 8 strains ranged from 0.114 to 1.329 g$.$l$\^$-1/ and the productivity was negatively correlated with the cell biomass. The molecular weight of the produced EPS ranged from 0.38 to 25.19$\times$10$\^$4/ Da. Glucose and galactose were ubiquitous sugar components. Mannose, ribose, and xylose were also major sugar components. The molecular weight and composition of the EPS showed strain-specific variation.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.6
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• pp.661-674
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• 2010

Bacterial biomass and its activity were measured in two kinds of granular activated carbon (GAC), the experimental and existing biofiltration system in a drinking water plant. The bacterial biomass was around 210 to 250 nmol P/g WW with phospholipid concentration at acclimation of ozonation treatment. The phospholipid biomass shows more or less a declining gradient along filter depth and no clear seasonality in its values. On the other hand, the microbial activity of [$^3H$]-thymidine and [$^{14}C$]-acetate incorporation within cells increased significantly along the filter depth, showing the difference of three fold between the upper and bottom layer. These factors support the different microbial composition or metabolic activity along the depth of GAC column. Turnover rates, the rate of bacterial biomass and production of biofilm, ranged from 0.26 /hr to 0.37 /hr, indicating a highly rapid recovery itself at amature state. In the non-ozonation treatment, the bacterial biomass was lower than in the ozonation and biological activity also declined towards the filter depth. The biomass levels during cessation of ozonation in the existing GAC filters were 68% of the actively ozonated state.

• Journal of Microbiology and Biotechnology
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• v.27 no.3
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• pp.542-551
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• 2017

Small phytochemicals have been successfully adopted as antibacterial chemotherapies and are being increasingly viewed as potential antibiofilm agents. Some of these molecules are known to repress biofilm and toxin production by certain bacterial and yeast pathogens, but information is lacking with regard to the genes allied with biofilm formation. The present study was performed to investigate the inhibitory effect of burdock root extract (BRE) and of chlorogenic acid (CGA; a component of BRE) on clinical isolates of Klebsiella pneumoniae. BRE and CGA exhibited significant antibiofilm activity against K. pneumoniae without inflicting any harm to its planktonic counterparts. In vitro assays supported the ${\beta}$-lactamase inhibitory effect of CGA and BRE while in silico docking showed that CGA bound strongly with the active sites of sulfhydryl-variable-1 ${\beta}$-lactamase. Furthermore, the mRNA transcript levels of two biofilm-associated genes (type 3 fimbriae mrkD and trehalose-6-phosphate hydrolase treC) were significantly downregulated in CGA- and BRE-treated samples. In addition, CGA inhibited biofilm formation by Escherichia coli and Candida albicans without affecting their planktonic cell growth. These findings show that BRE and its component CGA have potential use in antibiofilm strategies against persistent K. pneumoniae infections.

• Journal of Environmental Science International
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• v.21 no.12
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• pp.1449-1454
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• 2012

The ion selective microelectrodes (ISME) have been applied to observe the continuous profiles of NO3-N and NH4-N in bulk solutions or biofilms. In order to evaluate the performance and applicability of ion concentration measuring system, the characteristics, such as slope of calibration curve, detection limit and potentiometric selectivity coefficient were investigated. The slopes of calibration curve showed high degree of correspondence for each target ion concentrations. And the detection limits of nitrate and ammonia ion selective microelectrode were 10-4.7 M and 10-4.4 M, respectively. These ion selective microelectrodes were proved that their own performance could be maintained for 16 days after making. NO3-N and NH4-N selective microelectrodes were also adapted to detect the continuous ion profiles of cilia media packed MLE (Modified Ludzack-Ettinger) process. And the monitored nitrate and ammonia ion profiles with the ion selective microelectrode were stable and well corresponded to the results with conventional ion chromatograph. However, the electric potential was unstable until 8 hr because of the unknown noise. The tip shape and performance of the ion selective microelectrode was stably kept over 2 days continuous monitoring.

• KSBB Journal
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• v.29 no.4
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• pp.225-231
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• 2014

A microbial fuel cell (MFC) and bioelectrochemical systems are novel bioprocesses which employ exoelectrogenic biofilm on electrode as a biocatalyst for electricity generation and various useful chemical production. Previous reports show that electrogenic biofilms of MFCs are time varying systems and dynamically interactive with the electrically conductive media (carbon paper as terminal electron acceptor). It has been reported that maximum power point tracking (MPPT) method can automatically control load by algorithm so that increase power generation and columbic efficiency. In this study, we developed logic based control strategy for external load resistance by using $LabVIEW^{TM}$ which increases the power production with using flat-plate MFCs and MPPT circuit board. The flat-plate MFCs inoculated with anaerobic digester sludge were stabilized with fixed external resistance from $1000{\Omega}$ to $100{\Omega}$. Automatic load control with MPPT started load from $52{\Omega}$ during 120 hours of operation. MPPT control strategy increased approximately 2.7 times of power production and power density (1.95 mW and $13.02mW/m^3$) compared to the initial values before application of MPPT (0.72 mW and $4.79mW/m^3$).

• Economic and Environmental Geology
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• v.33 no.5
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• pp.353-365
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• 2000

After their first appearance on Earth, bacteria have exerted significant influence on geochemical behavior of elements. Numerous evidence of their control on geochemistry through geologic history has been observed in a variety of natural environments. They have mediated weathering rate, formation of secondary minerals, redox transformation of metals and metalloids, and thus global cycling of elements. Such ability of bacteria receives so considerable attention from microbiologists, mineralogists, geologists, soil scientists, limnologists, oceanographers, and atmospheric scientists as well as geochemists that a new and interdisciplinary field of research called 'geomicrobiology' is currently expanding. Some recent subjects of geomicrobiology which are studied extensively are as follows: 1) Functional groups distributed on bacterial cell walls adsorb dissolved cations onto cell surfaces by electrostatic surface complexation, which is followed by hydrous mineral formation. 2) Dissimilatory metal reducing bacteria conserve energy to support growth by oxidation of organic matter coupled to reduction of some oxidized metals and/or metalloids. They can be effectively used in remediating environments contaminated with U, As, Se, and Cr. 3) Bacteria increase the rate of mineral dissolution by excreting proton and ligands such as organic acids into aqueous system. 4) Thorough investigation on the effects of biofilm on geochemical processes is needed, because most bacteria are adsorbed on solid substrates and form biofilms in natural settings.

• The Plant Pathology Journal
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• v.29 no.1
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• pp.59-66
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• 2013

Colonization studies previously performed with a green-fluorescent-protein, GFP, labeled derivative of Bacillus amyloliquefaciens FZB42 revealed that the bacterium behaved different in colonizing surfaces of plant roots of different species (Fan et al., 2012). In order to extend these studies and to elucidate which genes are crucial for root colonization, we applied targeted mutant strains to Arabidopsis seedlings. The fates of root colonization in mutant strains impaired in synthesis of alternative sigma factors, non-ribosomal synthesis of lipopeptides and polyketides, biofilm formation, swarming motility, and plant growth promoting activity were analyzed by confocal laser scanning microscopy. Whilst the wild-type strain heavily colonized surfaces of root tips and lateral roots, the mutant strains were impaired in their ability to colonize root tips and most of them were unable to colonize lateral roots. Ability to colonize plant roots is not only dependent on the ability to form biofilms or swarming motility. Six mutants, deficient in abrB-, sigH-, sigD-, nrfA-, yusV and RBAM017410, but not affected in biofilm formation, displayed significantly reduced root colonization. The nrfA- and yusV-mutant strains colonized border cells and, partly, root surfaces but did not colonize root tips or lateral roots.

• Journal of Periodontal and Implant Science
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• v.32 no.4
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• pp.827-836
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• 2002

The present study was performed to evaluate how cellular and humoral immune responses were perturbed by immunization of mixed periodontal bacterial biofilms. Each group of mice was immunizared with 1) Poqhyromonas gingivalis (P. gingivaliis) grown as a planktonic culture, 2) Fusobacterium nucleatum (F. nucleatum), 3) P. gingivalis grown as a biofilm, or 4) mixed P. gingivalis plus F. nucleatum grown as a biofilm culture, respectively. Immune mouse sera were collected from each mouse. Spleens were harvested to isolate T cells and consequently stimulated with antigen presenting cells and P. gingivalis whole cell antigen to establish P. gingivalis-specific T cell lines. There were no significant differences in the mean anti- gingivalis IgG antibody titers among mouse groups. Immunization of mice with pure P. gingivalis biofilm or mixed P gingivalis plus F. nucleatum biofilm resulted in significant reduction o f antibody avidity and opsonophagocytois function. INF-$\gamma$production by P. gingivalis-specific T cell lines was also substantially recluced in mouse groups immunized with the biofilm. It was concluded that P. gingivalis biofilm perturbs the cellular and humoral immune responses in periodontal disease.

• Journal of Microbiology and Biotechnology
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• v.26 no.2
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• pp.373-384
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• 2016

The membrane-aerated biofilm reactor (MABR) is a promising municipal wastewater treatment process. In this study, two cross-flow MABRs were constructed to explore the carbon and nitrogen removal performance and bacterial succession, along with changes of influent loading shock comprising flow velocity, COD, and NH₄-N concentrations. Redundancy analysis revealed that the function of high flow velocity was mainly embodied in facilitating contaminants diffusion and biosorption rather than the success of overall bacterial populations (p > 0.05). In contrast, the influent NH₄-N concentration contributed most to the variance of reactor efficiency and community structure (p < 0.05). Pyrosequencing results showed that Anaerolineae, and Beta- and Alphaproteobacteria were the dominant groups in biofilms for COD and NH₄-N removal. Among the identified genera, Nitrosomonas and Nitrospira were the main nitrifiers, and Hyphomicrobium, Hydrogenophaga, and Rhodobacter were the key denitrifiers. Meanwhile, principal component analysis indicated that bacterial shift in MABR was probably the combination of stochastic and deterministic processes.