Bacteria are prokaryotes, so they lack a nucleus or organelles.
Sizes from 0.3 to 15 micrometers.
The world is full of bacteria. They are all over us,
inside us, they help us with metabolism, and they protect people from bad organisms.
More O2 is produced by bacteria
when by plants.
Some antibiotics can kill off
good bacteria that guard against yeast infections.
When you are on antibiotics, you should eat yogurt to replace
good bacteria.
Bacteria parts
"Salmonella"
Click to enlarge
Nucleoid = central circle of DNA (1 chromosome)
Inclusions = vacuoles, e.g. metachromatic inclusion which stores phosphorous
Plasmids = extrachromosomal DNA; these can provide resistance to antibiotics.
Cell membrane = phosphlipid bilayer with built-in ATP synthase and ETC (electron transport chain)
Cell wall = rigid layer of peptidoglycan
(polypeptides & sugar chains)
that keeps the shape of the bacterium even in
situations where there is too much or too little water
(hypotonic, hypertonic).
Ribosomes
Capsule (optional), also known as slime layer, which has the purpose sticking the bacteria
to some spot where food is hopefully plentiful e.g. teeth. It also hides the bacterium from
the immune system.
Made of glycocalyx.
Pili (singular pilus): protrusions that help the bacterium hang on to
other objects and which also allow bacteria to send genetic material to one another (F+ dominant
to F- recipient).
This gene transfer is like a simple early sexual system.
Lipopolysaccharide or LPS layer (optional):
this chemical is a neurotoxin for animals.
Cytoplasm.
Flagella (optional)
Shapes
There are three shapes:
Coccus = spherical, e.g. streptococcus
Bacillus = rod shaped, e.g. lactobacillus
Spirillium = spiral
Movement
Movement is via flagella. Bacteria have several flagella configuations.
Monotrichous = one flagellum
Lophotrichous = many flagella at one end
Amphitrichous = one flagellum at each end
Peritrichous = many flagella all over
Atrichous = no flagella
Swimming with flagella in pursuit of a chemical marker
is chemotaxis.
Energy / food consumption
There are four ways of getting energy:
phototrophic = it makes its own energy using light to
catalyze chemical reactions
chemotrophs = they consume chemical matter e.g. other organisms
aerobes = they consume oxygen
anaerobes = they are killed by O2
Perhaps also lithotrophs?
Antibiotics
Penicillin prevents bacteria from forming the peptidoglycan cell wall.
Resistance to penicillin is caused by a bacterium
developing an enzyme to break it down.
Tears have an enzyme lysozyme that breaks down peptidoglycan.
The bacteria that cause pink eye have an enzyme
that breaks down lysozyme.
Resistance to antibiotics is transferred between
bacteria due to plasmid transfer along a pilus.
Some antibiotics target bacterial ribosomes,
which are very different from non-bacterial ribosomes.
Examples: erythromycin, tetracycline.
Capsule / slime layer
The sticky layer lets bacteria stick to useful sites
e.g. to teeth, to rocks, to bronchioles (bronchitis).
Bacteria which lack the capsule are easily killed
by the immune system.
Reproduction
They reproduce by binary fission, which is like mitosis.
Endospores
In adverse environments, some bacteria form a
wall around the nucleoid that protects
them long-term, even for millions of years.
Anthrax has survived for millions of years in its
endospore form.
Endosymbiotic theory
This theory says that eukaryotes got their mitochondria
& chloroplasts by ingesting bacteria
but for some reason not eaten.
It is supported by at least the following evidence.
Mitochondria and chloroplasts are the same size as bacteria.
Mitochondria and chloroplasts produce energy in a very similar way to bacteria.
Mitochondria and chloroplasts have their own DNA, which are a single circular chromosome.
Mitochondria and chloroplasts DNA has been scanned and are very similar to the DNA
of bacteria.
Eukaryotes are known to ingest bacteria.
Nitrogen fixation
Some bacteria convert N2 to ammonia NH3.
This is useful to plants.
Toxicity
Only 1% of bacteria are harmful. The rest are helpful to various extents.
The Gram test (invented by Hans Gram) is supposed to test for toxicity
by detecting LPS.
Gram positive means nontoxic, Gram negative means toxic.
However there are many exceptions.
Symbiosis
There are 3 symbiotic modes:
Mutualism, in which both bacteria & host benefit.
Commensalism, in which bacteria benefit and host is neither harmed nor helped.
Parasitism, in which bacteria benefit but the host is harmed.
Well known bacteria
E. Coli
Clostridium botulidium
Streptococcus
Staphococcus
Congentoritis = causes pink eye
Borrelea burgdorferi = Lyme disease (left untreated it attacks the joints, then the brain)
Lactobacillus = used to make yogurt
Heliobacter pylori = causes ulcers
Trychonympha = bacteria that termites rely upon to break down wood.
