Difficult Genetics Problem

[mystic river 00]

Ok, after hours upon hours of trying to figure this darn thing out...I've given up and decided to rely on my fellow SDNers! Get ready, here it is..........

The Problem:

" You set up an experiment with two strains of genetically different basteria in a U-tube. The filter between the 2-sides is too small to allow physical contact between the bacteria. The solution has been purified of bacteria. After a time, you notice that some strain B cells have acquired some genetic characteristics of Strain A. Explain what is happening"

My thoughts:

I was thinking it was the same situation as Bernad Davis'.... "He constructed a U-tube in which the two arms were separated by a fine filter. The pores of the filter were too small to allow bacteria to pass through but large enough to allow easy passage of the fluid medium and any dissolved substances ( Figure 7-3). Strain A was put in one arm; strain B in the other. After the strains had been incubated for a while, Davis tested the content of each arm to see if cells had become able to grow on a minimal medium, and none were found. In other words, physical contact between the two strains was needed for wild-type cells to form."


so, I thought it was transformation but they need physical contact, and in this case, they don't. You obviously have to have exchange of DNA somehow, but I just don't know how?!!! ... how can it do that without viruses or physical contact??? In that case, the answer can't be conjugation, transformation, nor transduction, right?!!



AHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!


:::::::Runs away::::::::::





Ok, enough with this, I'm going to sleep...

---

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[AStudent]

Pilius

It's bacterial porn.

 

[Homer Doughnuts]

Think about it, it’s the transfer of genetic material between bacteria. What could move across the filter, how about a virus, specifically a bacteriophage. The first strain contained bacteria with viral DNA in the genome. The virus replicated and lysed the bacteria moving across the filter to infect the other strain transferring certain genetic characteristics. Viruses are routinely used to transfer genetic material between bacteria to select for different physical properties such as antibiotic resistance. At least that is what i think.

 

[AStudent]

Yeah what he said.....or magic.

Think about it, it’s the transfer of genetic material between bacteria. What could move across the filter, how about a virus, specifically a bacteriophage. The first strain contained bacteria with viral DNA in the genome. The virus replicated and lysed the bacteria moving across the filter to infect the other strain transferring certain genetic characteristics. Viruses are routinely used to transfer genetic material between bacteria to select for different physical properties such as antibiotic resistance. At least that is what i think.

 

[mystic river 00]

BUT "The solution has been purified of bacteria."

 

[Medikit]

so, I thought it was transformation but they need physical contact, and in this case, they don't. You obviously have to have exchange of DNA somehow, but I just don't know how?!!! ... how can it do that without viruses or physical contact??? In that case, the answer can't be conjugation, transformation, nor transduction, right?!!

How do you know it's not transduction? Why do you think that you need physical contact for transformation to occur? Some bacteria regularly uptake naked DNA.

 

[Homer Doughnuts]

BUT "The solution has been purified of bacteria."

That makes no sense in the tube are two different strains of bacteria separated by a filter ? If the solution is then purified how do you isolate a bacteria to determine that any genetic change has occurred in them? Are you sure that you didn't mean a purified solution was added to either side of the J tube, meaning no contamination was added to the B-Strain bacteria?

 

[jpro]

transformation. DNA floating around from dead bugs (lysis). Other bugs take up DNA through cell membrane receptors. There are no viruses in the medium. There is only bacteria. No pilus. That requires to close of a contact. Could not happen through a microscopic pore.

 

[LT2]

i posted in the mcat forum, but transformation is the correct answer. see my other post for details. transduction is possible, but only if the filter is large enough for phage to pass. these experiments most often demonstrate transformation or acquiring naked dna.

pm me if you still need help.

 

[Newquagmire]

transformation. DNA floating around from dead bugs (lysis). Other bugs take up DNA through cell membrane receptors. There are no viruses in the medium. There is only bacteria. No pilus. That requires to close of a contact. Could not happen through a microscopic pore.

the answer seems to be transformation, but i disagree with this explanation. lysis would not occur for no reason, and senescent and apoptotic cells would not have viable DNA to transmit.

 

[riceman04]

Ok, after hours upon hours of trying to figure this darn thing out...I've given up and decided to rely on my fellow SDNers! Get ready, here it is..........

The Problem:

" You set up an experiment with two strains of genetically different basteria in a U-tube. The filter between the 2-sides is too small to allow physical contact between the bacteria. The solution has been purified of bacteria. After a time, you notice that some strain B cells have acquired some genetic characteristics of Strain A. Explain what is happening"

My thoughts:

I was thinking it was the same situation as Bernad Davis'.... "He constructed a U-tube in which the two arms were separated by a fine filter. The pores of the filter were too small to allow bacteria to pass through but large enough to allow easy passage of the fluid medium and any dissolved substances ( Figure 7-3). Strain A was put in one arm; strain B in the other. After the strains had been incubated for a while, Davis tested the content of each arm to see if cells had become able to grow on a minimal medium, and none were found. In other words, physical contact between the two strains was needed for wild-type cells to form."


so, I thought it was transformation but they need physical contact, and in this case, they don't. You obviously have to have exchange of DNA somehow, but I just don't know how?!!! ... how can it do that without viruses or physical contact??? In that case, the answer can't be conjugation, transformation, nor transduction, right?!!



AHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!


:::::::Runs away::::::::::






Ok, enough with this, I'm going to sleep...

Sex pilli and conjugation (or is it binary fission)--> whichever one passes on Hrf factors (i think it is conjugation though)

 

[Buckeye(OH)]

It can't be pilli if the bacteria are prevented from contact.

 

[CoffeeCat]

the answer seems to be transformation, but i disagree with this explanation. lysis would not occur for no reason, and senescent and apoptotic cells would not have viable DNA to transmit.

Maybe lysis would occur if the bacteria were infected with a bacteriophage, which would not have been detected if it were still inside the bacteria. The bacteriophage would then be able to cross the barrier and infect the other bacteria.

 

[W222]

Some bacteria will lyse naturally and some will just let a small amount of DNA out. The plasmids present in Strain A will be transfered to B through the filter but the bacteria will remain seperate. Plasmid transfer doesn't need physical contact, a small portion of the bacteria will simply pick up the plasmid and start to express.

 

[FutureDocDO]

It's transformation. DNA tend to have TRANSPOSONS (transposable elements) that can excise out of host's DNA and move to infect other cells.

Ok, after hours upon hours of trying to figure this darn thing out...I've given up and decided to rely on my fellow SDNers! Get ready, here it is..........

The Problem:

" You set up an experiment with two strains of genetically different basteria in a U-tube. The filter between the 2-sides is too small to allow physical contact between the bacteria. The solution has been purified of bacteria. After a time, you notice that some strain B cells have acquired some genetic characteristics of Strain A. Explain what is happening"

My thoughts:

I was thinking it was the same situation as Bernad Davis'.... "He constructed a U-tube in which the two arms were separated by a fine filter. The pores of the filter were too small to allow bacteria to pass through but large enough to allow easy passage of the fluid medium and any dissolved substances ( Figure 7-3). Strain A was put in one arm; strain B in the other. After the strains had been incubated for a while, Davis tested the content of each arm to see if cells had become able to grow on a minimal medium, and none were found. In other words, physical contact between the two strains was needed for wild-type cells to form."


so, I thought it was transformation but they need physical contact, and in this case, they don't. You obviously have to have exchange of DNA somehow, but I just don't know how?!!! ... how can it do that without viruses or physical contact??? In that case, the answer can't be conjugation, transformation, nor transduction, right?!!



AHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!


:::::::Runs away::::::::::





Ok, enough with this, I'm going to sleep...

 

[LT2]

regarding conjugation (anything requiring the use of an F plasmid, pilus, hfr etc) you need cell to cell contact.

as for transduction, this is a possibility, however the filter must be large enough to let phage particles pass through.

the best option for this remains transformation. cells in a culture can lyse and spew their contents into the media for a number of reasons including starvation and deleterious environments. bacteria don't typically lyse via "apoptosis" and their DNA would be viable because the cell contents are released into the environment. this is typically seen, but is not limited to, species of Bacillus. all of the whole cells could be removed from the culture and the dna from the lysed cells would remain in the media.

as a ta for general micro (and a micro masters student), we do this experiment to demonstrate the capability of transformation vs conjugation (which requires cell to cell contact).

just my $0.02

good luck!

 

[W222]

Just some additional info, you can transform any bacteria by simply adding in a plasmid -- you dont need cell to cell contact or anything like that. If a plasmid is present in a solution then bacteria will naturally take it up and express it. If the filter in this case allows the passage of plasmid then bacteria on either side of the filter will naturally pick up plasmid and express it. Now, CaCl shock or E-shock will punch holes and increase bacterial uptake of the plasmid but this is not necessary.

The most likely explanation for the original problem is either a bacteriophage or plasmid transformation.

 

[jpro]

You don't even need a plasmid. Just naked DNA from dead bugs. It is just that simple.

 

[lagringa87xc]

not all bacteria are naturally competent...so this experiment would ony work with naturally competent bacteria such as my favorite, Bacillus subtilis.
but yes transformation seems to be the most logical answer.

 

[LabMonster]

regarding conjugation (anything requiring the use of an F plasmid, pilus, hfr etc) you need cell to cell contact.

as for transduction, this is a possibility, however the filter must be large enough to let phage particles pass through.

the best option for this remains transformation. cells in a culture can lyse and spew their contents into the media for a number of reasons including starvation and deleterious environments. bacteria don't typically lyse via "apoptosis" and their DNA would be viable because the cell contents are released into the environment. this is typically seen, but is not limited to, species of Bacillus. all of the whole cells could be removed from the culture and the dna from the lysed cells would remain in the media.

as a ta for general micro (and a micro masters student), we do this experiment to demonstrate the capability of transformation vs conjugation (which requires cell to cell contact).

LT's right, for the second time!

 

[drguy22]

i think its transformation, DNA can travel through the pore, but the cells have to be competent to pick it up.

 

[Newquagmire]

the best option for this remains transformation. cells in a culture can lyse and spew their contents into the media for a number of reasons including starvation and deleterious environments. bacteria don't typically lyse via "apoptosis" and their DNA would be viable because the cell contents are released into the environment. this is typically seen, but is not limited to, species of Bacillus. all of the whole cells could be removed from the culture and the dna from the lysed cells would remain in the media.

i assumed the environment was empirically optimized such that lysis would be a relatively rare occurence in this experiment when i answered. but i suppose even with 1 lysis event in 10^6 bugs, a tube filled with bacteria would have sufficient DNA release. if lysis occurs, it would release DNA capable of transforming neighboring cells. i think the rate of viable transformation events would be rather low though.

 

[iferg17]

I' ve got this paper to do and I can't figure it out so I think I'll let you guys do it for me........lazy and smart. We can recognize our own. Well done.

 

[Lvoen Bgilisis]

As transformation is the most likely mechanism for this phenomenon, you can never rule out the possible occurance of spontaneous mutations within one strain that results in some phenotypically similar characteristics of the other strain.

 

[Ambs]

There's a strong possibility that I'm a total nerd because this thread makes me very happy. I've been out of school since two years, and thinking of microbiology/genetics is fun.

 

[Amorphisgirl]

The Problem:

" You set up an experiment with two strains of genetically different basteria in a U-tube.

Basteria...sheez.... "OMFG the little basteria are coinhabiting!!" .....or something. Just kidding, mystic.

 

[UCDavisdude]

Omg, The Answer Is Obvious. A Bitter And Jelous Classmate Of Yours Came Along And Put It In The Tube. The Experiment Has Been Screwed Up Because Of Your Classmate.

 

[Newquagmire]

A Bitter And Jelous Classmate Of Yours Came Along And Put It In The Tube. The Experiment Has Been Screwed Up Because Of Your Classmate.

i stand corrected, this is obviously the answer

 

[Medikit]

i stand corrected, this is obviously the answer

I second this answer