Microbiology
- study of organisms too small to be studied by naked eye e.g. microbes
viruses: non-cellular
prokaryotes: bacteria, archaea
eukaryotes: protists, algae, fungi
- most microorganisms carry out life processes independent of other cells
- two main themes:
basic science of life
impact on humans directly or indirectly
Living Conditions microbial community
- can exist in microbial communities
- live in many conditions e.g. volcanoes, hot springs, ice
- bacteria interact with each other & other organisms in either competition or cooperation
- able to alter their environment
- make up most of earth’s biomass
total number of microbial cells is ~5x1030
Disease
- infectious diseases caused by pathogens
cause of death in many underdeveloped countries e.g. malaria, TB
in 20th century ~1680m people died of infectious diseases
- controlled by combination of vaccines, antibiotics & hygiene
- new diseases always emerging
Benefits of Microbes
- some food materials require microbiological activity e.g. yoghurt, cheese & beer
- required for agriculture:
nutrient cycling: microbes convert nutrients into forms that are accessible to plants
animal husbandry: microbes in stomach of cattle & sheep degrade cellulose in grass to make it
easier to digest
N2 fixation: bacteria use atmospheric N to synthesise NH3 reducing cost and pollution of fertiliser
- required for energy & environment:
methanogenic bacteria produce natural gas
convert waste products & surplus grain to biofuels e.g. ethanol
bioremediation: clean up degrading pollutants e.g. spilled oil
- required for industrial microbiology & biotechnology:
genetically modified microorganisms synthesise high commercial value products e.g. insulin
artemisinin (drug for malaria) can be cheaply produced using yeast
Problems with Microbes
- grow in food so preservation is required:
spoil food
cause food-borne disease
History of Microorganisms
- 1665: Robert Hooke developed first microscope and discovered fungus growing on leather
- 1676: Antoni van Leeuwenhoek first described bacteria
,- mid 1800s: germ vs miasma theory
people believed disease was caused by bad air so tried to eradicate it by getting rid of bad smells
Dr. William Farr believed cholera was transmitted by air and thought conc. of ‘miasmata’ was
worse near the Thames and lower in the surrounding hills
- mid to late 19th century: improvement of microscopes meant a good medieval PPE
development of microbiology was seen
spontaneous generation: theory that living creatures could arise from non-living matter and that
the process was normal
1822-1895: Marie & Louis Pasteur disproved spontaneous generation theory by conducting 2
experiments Experiment 1:
- put nutrient broth in flask
- sterilised flask and left swan neck attached
Experiment 2:
- put nutrient broth in flask
- sterilised flask and removed swan neck
- in exp. 1, no microbes grew as they couldn’t travel against
gravity in swan neck to the broth
- in exp. 2, microbes grew as they were able to enter the
broth
- if spontaneous generation was real, microbes would’ve
grown in exp. 1
- Pasteurs’ work led to methods to stop microbe growth e.g.:
sterilisation: killing all microorganisms including dormant forms
pasteurisation: destruction of bacteria able to reproduce by brief heating
- Pasteurs’ also developed vaccines against anthrax & rabies
- 1884: Hank Christian Gram developed gram staining method
gram staining method: method for distinguishing 2 major classes of bacteria based on cell wall
composition
- Robert Koch developed germ theory & simple methods for obtaining bacteria in pure samples
Fanny Hesse said to use agar instead of the potato & gelatine that Koch was using
Koch’s Postulates: criteria for proving that specific microorganisms cause diseases
1) causative microbe must be found in every case of disease and be absent from healthy host
2) microbe isolated & grown outside host
3) microbe introduced to healthy host & host must get disease
4) microbe is re-isolated from host
Koch’s Postulates led to discovery of causes for anthrax, TB & cholera
, Lecture 2: Introduction & Overview of Prokaryotes and their Cell Structure
Three Domains
1) Eurkarya
multicellular organisms, plants, fungi & animals
2) Archaea
single celled organisms living in extreme environments
3) Bacteria
- phylogeny relating to three domains of life is sorted based on sequence analysis of ribosomal RNA,
genes & other stuff
Properties of Cells
- compartmentalisation
cell is open system and substances move in & out
- growth
- evolution
- some:
are mobile
are differentiated
can communicate
Flagellum
Cytoplasmic Membrane Cell Wall
S-layer
layer of protein
function not fully
understood
Membrane Structure in Bacteria
Functions
- barrier: separated cell from environment
- selectively permeable barrier: controls movement of molecules in & out of cells
prevents leakage & acts as gateway
- protein anchor: site of many proteins participating in transport, bioenergetics & chemotaxis
chemotaxis: movement of organism in response to chemical stimulus
- site of respiration & photosynthesis
- energy conservation: site of generation & proton motive force
proton motive force: occurs when cell membrane is energised due to electron transport reaction
causing cell to produce energy that can be used straight away (e.g. to move flagella) or to be stored
as ATP
Active Transport
- movement of particle from low concentrations to high concentrations
allows dilute nutrients taken up efficiently
- uptake rate shows saturation at low external concentrations
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