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October, 2006
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Quorum Sensing: A phenomenon where microorganisms communicate and coordinate their behavior by the accumulation of signaling molecules. A reaction occurs when a substance accumulates to a sufficient concentration. This is most commonly seen in bacteria.

Bacterial Signaling

JoVE 10713

At times, a group of bacteria behaves like a community. To achieve this, they engage in quorum sensing, the perception of higher cell density that results in a shift in gene expression. Quorum sensing involves both extracellular and intracellular signaling. The signaling cascade starts with a molecule called an autoinducer (AI). Individual bacteria produce AIs that move out of the bacterial cell membrane into the extracellular space. AIs can move passively along a concentration gradient out of the cell, or be actively transported across the bacterial membrane. When cell density in the bacterial populations is low, the AIs diffuse away from the bacteria, keeping the environmental concentration of AIs low. As bacteria reproduce and continue to excrete AIs, the concentration of AIs increases, eventually reaching a threshold concentration. This threshold permits AIs to bind membrane receptors on the bacteria, triggering changes in gene expression across the whole bacterial community. Many bacteria are broadly classified as gram positive or gram negative. These terms refer to the color that the bacteria take on when treated with a series of staining solutions which were developed by Hans Christian Joachim Gram over a century ago. If bacteria pick up a purple color, they are gram-positive; if they look red, they are gram-negative. These stain colors are pic

 Core: Cell Signaling

Yeast Signaling

JoVE 10714

Yeasts are single-celled organisms, but unlike bacteria, they are eukaryotes—cells that have a nucleus. Cell signaling in yeast is similar to signaling in other eukaryotic cells. A ligand, such as a protein or a small molecule outside the yeast cell, attaches to a receptor on the cell surface. The binding stimulates second-messenger kinases (enzymes that phosphorylate specific substrates) to activate or inactivate transcription factors that regulate gene expression. Many of the yeast intracellular signaling cascades have similar counterparts in Homo sapiens, making yeast a convenient model for studying intracellular signaling in humans. Yeasts are members of the fungus kingdom. They use signaling for various functions, especially for reproduction. Yeasts can undergo “sexual” reproduction using mating pheromones, which are peptides—short chains of amino acids. Yeast colonies consist of both diploid and haploid cells. Both types of cells can undergo mitosis, but only diploid cells can undergo meiosis. When diploid cells undergo meiosis, the four resulting haploid cells, called spores, are not identical. In fact, the division of one diploid cell into four spores creates two “sexes” of yeast cells, each two cells of the type MAT-a and MAT-alpha. MAT-a cells secrete mating

 Core: Cell Signaling

What is Cell Signaling?

JoVE 10985

Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate to respond to the environment.

Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch information, while photoreceptors in the retina can detect light. Most cells, however, have evolved to respond to chemical signals, including hormones, neurotransmitters, and many other types of signaling molecules. Cells can even coordinate different responses elicited by the same signaling molecule. Typically, cell signaling involves three steps: (1) reception of the signal, (2) signal transduction, and (3) a response. In most signal reception, a membrane-impermeable molecule, or ligand, causes a change in a membrane receptor; however, some signaling molecules, such as hormones, can traverse the membrane to reach their internal receptors. The membrane receptor can then send this signal to intracellular messengers, which transduces the message into a cellular response. This intracellular response may include a change transcription, translation, protein activation, or many

 Core: Cell Signaling

Replication of the Ordered, Nonredundant Library of Pseudomonas aeruginosa strain PA14 Transposon Insertion Mutants

1Department of Pediatrics, Mucosal Immunology and Biology Research Center, Massachusetts General Hospital, 2Department of Molecular Biology, Massachusetts General Hospital, 3Department of Genetics, Harvard Medical School, 4Department of Pediatrics, Harvard Medical School

JoVE 57298

 Immunology and Infection

Live Cell Analysis of Shear Stress on Pseudomonas aeruginosa Using an Automated Higher-Throughput Microfluidic System

1Department of Chemistry, Doane University, 2Department of Biology, Doane University, 3Department of Pathology and Microbiology, University of Nebraska Medical Center, 4Department of Physics and Engineering, Doane University

JoVE 58926


Synthesis of Multi-walled Carbon Nanotubes Modified with Silver Nanoparticles and Evaluation of Their Antibacterial Activities and Cytotoxic Properties

1Center for Biomaterials, Biomedical Research Institute, Korea Institute of Science and Technology, 2School of Integrative Engineering, Chung-Ang University, 3Division of Synthetic Biology and Regenerative Medicine, Institute for Quantitative Health Science and Engineering, Michigan State University

JoVE 57384


Preparation, Imaging, and Quantification of Bacterial Surface Motility Assays

1Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 2Eck Institute for Global Health, University of Notre Dame, 3Department of Applied and Computational Mathematics and Statistics, University of Notre Dame, 4INRS-Institut Armand-Frappier, 5Department of Biology, Indiana University, 6Department of Biological Sciences, University of Notre Dame

JoVE 52338


Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

1Department of Microbiology and Immunology, University at Buffalo, State University of New York, 2Witebsky Center for Microbial Pathogenesis and Immunology, University at Buffalo, State University of New York, 3New York State Center of Excellence in Bioinformatics and Life Sciences, University at Buffalo, State University of New York

JoVE 51008

 Immunology and Infection

Generating Controlled, Dynamic Chemical Landscapes to Study Microbial Behavior

1Department of Civil, Environmental and Geomatic Engineering, Institute of Environmental Engineering, 2School of Mathematics and Statistics, University of Melbourne, 3Institute of Marine Sciences, University of California, Santa Cruz, 4Faculty of Life and Environmental Sciences, University of Tsukuba, 5Microbiology Research Center for Sustainability, University of Tsukuba, 6Department of Ecology and Evolutionary Biology, Princeton University

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JoVE 60589

 JoVE In-Press
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