Bacterial Lab Notes
Conjugation: When one bacterium transfers genetic material to another through a pilus, spreading traits like antibiotic resistance. - Transformation: When a bacterium picks up free DNA from its surroundings (e.g., from dead bacteria), which can integrate and provide new abilities like antibiotic survival. - Transduction: When a bacteriophage (virus) accidentally carries DNA from one bacterium to another, causing genetic changes upon infection. - Mutation: A random change in an organism
Conjugation: When one bacterium transfers genetic material to another through a pilus, which can help spread traits like antibiotic resistance.
Transformation: When a bacterium picks up free DNA from its surroundings (usually from dead bacteria), which can mix with its own genes and sometimes give it new abilities, like surviving antibiotics.
Transduction: When a bacteriophage (virus) accidentally carries DNA from one bacterium to another, dropping off that DNA and causing genetic changes when it infects a new bacterium.
Mutation: A random change in an organism’s DNA, happening naturally or due to environmental factors, which can be helpful, harmful, or have no effect.
Destruction/Inactivation: When bacteria use special enzymes to break down or disable antibiotics, making the bacteria resistant.
Efflux: When bacteria use tiny pumps in their cell walls to push antibiotics out before they can do damage, resisting the antibiotics.
Gene: A small piece of DNA that contains instructions for making a protein, which dictates how an organism looks, grows, and functions.
Plasmid: A small, circular piece of DNA in bacteria, separate from their main chromosome, often carrying extra genes like those for antibiotic resistance, and capable of moving between bacteria.
Naked DNA: DNA that is not inside a cell or protected, floating freely in the environment, which bacteria can take in via transformation.
Pilus: A thin, hair-like structure on the surface of some bacteria, used for attachment to surfaces or other cells, and forming a bridge to share DNA during conjugation.
Bacteriophage: A virus that infects bacteria, injecting its DNA and potentially using the cell to make more viruses or transfer bacterial DNA between cells.
Type of Plate | Strain I (Strʳ on chromosome) | Strain II (Ampʳ on plasmid) | Reasoning |
|---|---|---|---|
LB | (+) | (+) | Both strains grow because there’s no antibiotic to stop them. |
LB+str | (+) | (-) | Strain I grows because it’s resistant to streptomycin; Strain II dies because it isn’t. |
LB+amp | (-) | (+) | Strain I dies because it doesn’t have ampicillin resistance; Strain II grows because it does. |
LB+str+amp | (-) | (-) | Neither strain grows because Strain I lacks Ampʳ and Strain II lacks Strʳ. |
Ampicillin (Amp): An antibiotic that kills bacteria by stopping them from making strong cell walls. Only bacteria with the ampicillin resistance gene (Amp ) can live, as this gene produces beta-lactamase to break down ampicillin.
Streptomycin (Str): An antibiotic that attaches to bacteria
s ribosomes, blocking protein production and killing the bacteria. Bacteria with the streptomycin resistance gene (Str ) have a mutation or enzyme protecting their ribosome.LB (Luria Broth or Lysogeny Broth): A nutrient-rich food source for bacteria, containing yeast extract, tryptone, and salt. When mixed with agar, it forms a solid LB plate for bacterial growth.
Plasmid Types
1. Fertility (F) Plasmids: Carry genes enabling bacteria to form a sex pilus for DNA transfer during conjugation, controlling the ability to share genetic material.
2. Resistance (R) Plasmids: Contain genes that make bacteria resistant to antibiotics or other harmful substances, allowing for rapid spread of antibiotic resistance.
3. Col Plasmids: Possess genes that produce bacteriocins, proteins that kill or inhibit the growth of other bacteria, thus providing a competitive advantage.
4. Degradative Plasmids: Contain genes that help bacteria break down unusual substances like oil or pesticides for food or energy.
Virulence Plasmids: (Also mentioned by some scientists) Help bacteria cause disease.
Pilus Types
1. Fimbriae (Attachment Pili): Short, hair-like pili that help bacteria stick to surfaces (e.g., cells, medical equipment) but do not transfer DNA.
2. Sex Pili (Conjugation Pili): Longer pili used during conjugation to connect two bacteria and form a bridge for DNA (usually plasmid) transfer.
3. Type IV Pili: Motile pili that aid bacteria in crawling along surfaces via twitching motility, attachment, and sometimes infection.
4. Curli Pili: Help bacteria form biofilms (slimy layers) that facilitate sticking together and provide protection against antibiotics or the immune system.