Exam 1 Flashcards
what is a microbe?
a microbe is a living organism that requires a microscope to be seen (most diverse group of science)
- viruses are grouped with microbes because they infect all forms of life
examples of microbes
bacteria, archea, and eukaryotes (fungi algae, protozoa)
Where are microbes found?
everywhere! hydrothermal vents, salines, arctic marine sediment
why is the human microbiome useful?
digestion, to see good from bad
why study microbes?
they have shaped human culture since our earliest civilizations
positively: microbes produce 50% of the world’s oxygen and all its fermented foods (bread, beer, cheese)
negatively: disease that causes death and suffering
how do we know about microbes?
most knowledge was accumulated after 1900, driven by advances in microscopy and molecular techniques
application of microbes in environmental health
knowledge: microbes are key players in most elemental cycles
manage: use of microbes in biodegradation of pollutants, wastewater treatment plants
application of microbes in health
knowledge: microbes supply essential nutrients to hosts, but can also cause disease
manage: fighting infectious disease managing microbiome for better health
application of microbes in industry
knowledge: microbial metabolism can enrich and spoil foods
manage: use/control microbes in food, medicine and biofuel production
louis pasteur (pasteurization)
broth was boiled to kill all microbes, after a year, none appeared.
the flask was tipped to allow the broth to reach the microbes, microbes quickly multiplied
(showed microbes were not appearing out of nowhere, disproved spontaneous generation)
culture independent approach: sequencing
data led to identify domains:
bacteria
archaea (first life on earth)
eukarya
bacteria + archaea = similar membrane composition
archaea + bacteria = no nucleas, gene expression machinery
germ theory of disease
many diseases are caused by microbes
central dogma: Koch’s postulates
ability to isolate and culture bacteria is essential
koch’s postulates
ordered set of criteria for establishing a causative link between an infectious agent and a disease
1. suspected microbe is always present in disease hosts and absent in healthy hosts
2. suspected microbe is grown in pure culture outside hosts - no other microbes present in culture
3. cultured microbe is introduced into healthy hosts- individuals become sick with same disease as original hosts
4. same microbial suspect is re-isolated from sick individuals
Edward jenner
typically credited with developing first vaccination approach: deliberately infected patients with material he collected from cowpox lesions
lady Mary Mantagu
introduced the practice of smallpox inoculation to Europe in 1717, learned from people in Turkey and Africa
Lynn Margulis
proposed that eukaryotic organelles, such as mitochondria and chloroplasts, evolved by endosymbiosis from prokaryotic cells engulfed by preeukaryotes (mitochondria)
why was the endosymbiosis theory highly controversial?
implied more complex ancestry of living species through lateral exchange of genetic material, instead of vertical decent with modification
microscopy has revealed:
- Earth is a microbial world. There are no unexpected places…
- We are just as microbial as we are human
- Bacteria are beautiful!
why bother observing microbial cells?
to understand why these organisms cause these phenomena, a closer look can help
to understand how microorganisms interact with each other
size at which objects can be distinguished depends on…
density of photoreceptors of observer’s eye
resolution
the smallest distance by which two objects can be separated and still distinguishes
human eye
about 100-200 µm resolution
detection
ability to determine the presence of an object
magnification
an increase in the apparent size of an image to resolve smaller separations between objects. we can detect microbes in a culture or environment, but only resolve single cells by magnification (see separated from one another)
microbial characteristics
- the shape of the bacteria gives you information about the type of bacteria it could be
- how they are aggregated gives you more information on what it may be
colony characteristics (describing colony morphology has become primary step in microbial identification)
size, color, texture, elevation, form, margin (edge of colony)
microscopy at different size scales
different microscopes are required to resolve various cells and sub cellular structures
why are we unable to look directly through an electron microscope to see the objects it can resolve?
our bare eyes cannot see electrons
size of object impacts…
what wavelength or EMR is needed
goal to resolve vs. detect impacts…
if the microscopy method uses stains, fluorescence or ligh scattering
alive vs. dead cells to visualize impacts…
does the microscopy method require fixation and/or staining/hybridization?
eukaryotic microbes
protozoa, algae, fungi (10-100µm) can be seen under a light microscope
prokaryotic microbes
bacteria, archaea (0.4-10µm) sub cellular structures are typically too small to resolve by light microscopy
phages and viruses
mostly in 5-200nm range, cannot be resolved by light microscopy
electromagnetic radiation conditions to resolve an object
contrast - cytoplasm absorbs light similarly to water (often undetectable with standard bright field microscopy)
wavelength - can be maximum 2x size of the object (visible light 0.4-0.75 µm, so smallest object = 0.2 µm)
magnification - light rays must spread far enough to match our eyes resolution (about 200µm) for visible light up to 1,000X magnification possible while maintaining resolution
interaction of light with matter
absorption is important in visualizing objects by microscopy
magnification relies on refraction (bend)
scattering of light is key to dark field microscopy
magnification requires the bending of light rays
refraction
wavefronts of light shift direction as they enter a substance of higher refractive index
what happens when light rays enter glass with parabolic curvature (a lens)
parallel rays bend such that all rays meet at a certain point, called the focal point (more curvature = more magnified)
bright field microscopy
generates a dark image over a light background
to increase resolution on bright field microscopy….
- use shorter-wavelength light
-increase contrast
to increase lens quality…
-use multiple lenses in compound microscopes
capture more light waves by…
-using a wider lens closer to specimen (wider angle of light captured)
-higher refraction by medium between specimen and objective: use immersion oil
fixation and staining
+ cells remain in a fixed position (stuck to slide), increase contrast, ability to do differential staining, staining specific parts of cell
- cells are typically killed
wet mount preparation
+ observation of cells in natural state
- little contrast; sample dries out quickly
simple stain
adds dark color specifically to cells, but not to the external medium or surrounding tissue (methylene blue)
