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Gram-Positive Bacteria: Bacteria which retain the crystal violet stain when treated by Gram's method.
Source: Rhiannon M. LeVeque1, Natalia Martin1, Andrew J. Van Alst1, and Victor J. DiRita1
1 Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America
Bacteria are diverse microorganisms found nearly everywhere on Earth. Many properties help distinguish them from…
Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Author: Luisa Ikner
The spectrum of research in environmental microbiology is broad in scope and application potential. Whether the work is bench-scale with known bacterial isolates, or in the field collecting soil or water samples…
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…
Examining Microbial Colony Structures
To begin, collect your allocated culture plates and then remove the Parafilm and lid from one of them.
Place the uncovered plate under a dissecting microscope and then observe the individual communities within each quadrant of the plate.
As the colonies are identified, fill out the observed colony…
Bacteria and fungi are two highly diverse groups of organisms that can have significant beneficial or detrimental impacts on human health. For this reason, it is important to understand and distinguish between individual species of these groups. As you will recall, biological taxonomists group organisms based on their phylogenetic relatedness. The three domains of life, Bacteria, Archaea, and…
Nutrient Agar and Bacterial Culture Plate Preparation
Add 23 g of nutrient agar to a 2,000 mL beaker containing 1 L of distilled water 4 – 5 days before the activity.
Place the beaker on a hotplate and set the hotplate to high, stirring the mixture with a stirring rod.
When the agar has dissolved into the water, use a hot pad to…