BISC209: Lab6
ID Cultured Bacteria by 16srDNA Sequencing and Analysis
Besides working on getting your soil sample DNA isolated, amplified by pcr, inserted in a cloning vector, transformed into E. coli, and the 16s rDNA insert sequenced in an automatic sequencer so you can identify a more represenative scope of the bacterial flora in your soil sample, you have been working simultaneously, through traditional microbiological culturing techniques, to isolate and identify some of the culturable bacteria by morphology and metabolism differentiation. Look how much you have accomplished in these few short weeks!!
By this point you have isolated pure colonies of some soil bacteria on general and enrichment media and you have gotten some preliminary information about the morphologic and metabolic characteristic of the bacteria you have chosen to identify. You will continue learning about how these bacteria are different from one another and how they contribute to their community. At the same time we want to identify these bacteria by their 16s rDNA unique sequences in a similar way as we did for our unknown general soil sample bacteria. This time we will use a Taq polymerase that will not be as accurate as our proof reading polymerase we used previously, but should be good enough to get our identifications.
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Prepare DNA from 4 Bacterial Colonies
1. Each person will choose 4 unique colonies (try to pick colonies that are clearly different from each other from a variety of the enrichment media)
2. Touch a colony with a P10 tip and resuspend the non-visible material in 20 microliters of sterile water with 0.05% Non-idet P40 (NP40). NP40 is a detergent that keeps hydrophobic domains dispersed and, thus, helps to solubilize membranes.
Resist the urge to pick up too much cell material!! The tinest invisible bit will do and is better than too much, which can inhibit the pcr reaction!
3. Repeat for your other 3 colonies.
4. Boil the samples in the 0,05% NP40 for 5 min. You can do this in the thermal cycler if you set a program to boil. This will lyse the cells and to inactivate bacterial enzymes.
PCR AMPLIFICATION of 16s rDNA from lysates
Note: All reagents for the pcr should be kept on ice and the master mix should be thawed on ice. Since Taq can function at room temp, we don't want the reaction to start until all the tubes are in the thermal cycler.
The components below have been aliquoted and prepared for you and are in pcr tubes of your team color. Label 5 pcr tubes carefully with a Sharpie on the top and side of the tube with a unique identifier for each bacterial colony (your initials and a number: Carl Woese CW-1). The other tube is for a neg control.
For the negative control use 2 microliters of water in place of the template DNA (boiled lysate). When you have mixed your DNA into the master mixture by tapping VERY LIGHTLY or flicking to be sure that all reagents are mixed and not adhering to the tube wall, take your tubes to the thermal cycler when your instructor says it's ready. Keep them on ice until then but wipe off the bottom of the tubes before putting them into the machine. Make a template key in your lab notebook as to where in the thermal cycler you put your tubes
Master Mix recipe for each reaction: TOTAL VOL 23 microliters
WEAR GLOVES AT ALL TIMES AND DON'T TOUCH THE INSIDE OF THE TUBE CAPS OR YOUR PIPET TIPS--Always use a new tip when going into anything in a pcr reaction. Contamination is a real problem in pcr
REAGENT and VOLUME
Promega Master Mix 2x 12.5 microliters
16S_ 8F(15 pmol) primer 2.0 microliter
16S_149R (15 pmol) 2.0 microliter
nuclease free water 6.5 microliter
Add 2 microliters of our boiled lysate with the template DNA
The thermal cycler program is generally the same for all pcr reactions but the annealing temperature (melting) is dependent on the primer pair. When you design primers , the primer melting temp. can be calculated based on the GC content and other factors. Think about which would be harder to denature: GC pairs or AT pairs and why? For 8F and 1492R, a range of 45-55C is ok, although higher temp. may lead to increased specificity that excludes some organisms' DNA from being amplified.
The length of the fragment you are amplifying determines the extension time. A general rule of thumb is to use an extension time of 1kb per minute. Here, we amplify with primers designed for the 8th and 1492th positions in the 16s rDNA gene region. Therefore our fragment is expected to be about 1.5kb long, so we will use an extension time of 1.5 minutes per cycle.
The pcr will run for 2.5 hours or so. We can leave it overnight with the last cycle at HOLD AT 4C and your instructor will freeze away your pcr products so be sure they are labeled clearly.
Culturable Bacteria Identification continued
Read, record last weeks tests.
Compare the OF-glucose tubes to an uninoculated OF-glucose tube.
Follow the procedure to read the Starch plates and record your results.
This is a great week to check your organism for motility. You will inoculate a SIM tube for each organism and a broth tube to perform the hanging drop technique for motility next week.
Perform any other morphological stains (if useful)
Examine the role of your bacterium in the soil ecosystem Enterotube?
Do these data support or confuse the identification? Spend some time listing future tests that might be most useful in the identification of your organisms based on The Prokayotes or reference articles you are collecting.
