Liquid Culture of Worms
|25 mL||75 mL||1M KHPO4, pH 6.0||(136.1g KH2PO4 per 1000mL; start with 800 mL and adjust to pH 6.0 with solid KOH (approx 15 g) before bringing up to volume. Make 100 mL aliquots.)|
|0.5mL||1.5mL||5mg/mL cholesterol in 95% EtOH||(warm to 37° C o/n to dissolve. Don't worry if it comes out of solution.)|
|Sterilely supplement each 500 mL with:|
|1.5 mL 1M MgSO4|
3 mL 0.5M CaCl2
5 mL 100X trace metals solution
|(trace metals= 0.346 g FeSO4.7H2O; 0.930 g Na2EDTA; 0.098 g MnCl2.4H2O; 0.144 g ZnSO4.7H2O; 0.012 g CuSO4.5H2O per 500 mL. Autoclave. Keep in dark (wrap in foil).)|
|5 mL KCitrate, pH 6.0||(21.02 g citric acid, monohydrate per 100mL; start with 80 mL and adjust to ph 6.0 with solid KOH (approx 17g) before bringing up to volume.)|
Can also add 5 mL 100X Nystatin (buy from Gibco, keep in freezer) but it's not always necessary. (antifungal agent)
Preparation of E. Coli in large amounts
We make our E.Coli for liquid culture worm food in large batches that then are frozen at -80° C and thawed when needed. Lately we have used the DH10B strain. The E. Coli growth is done in a 200L fermenter for several hours, spun down in large centrifuges and has yielded 2-3.5 kg pure bacteria (in paste form). This is then resuspended in a combination of M9 and glycerol until it is a "pipettable" liquid. The following ingredients are needed (based on 200L reaction):
Items 2-4 are placed in the fermenter with enough water to fill up tp 200L and then sterilized. The phosphate solution is then sterilely added as are the starter cultures. The bacteria is grown at 37° C for ~4.5 hours and then collected. For resuspending you will need to have autoclaved the following:
You will also want to mix in some glycerol once resuspended (~20%).
Growing the worms
Start by growing 5-10 medium (100 mm) plates of your worms containing a mixture of young and adult worms. When they have nearly starved the plates, wash the worms off with S-basal or M9 solution, pipetting the liquid onto each plate and swirling before pipetting off. Wash 2or 3 times to maximize the number of worms you get. You can wash them directly into 500 mL of S-basal in a baffled flask or if you want to quantitate the volume of worms, collect in a 50 mL conical first (or 15 mL conical) and spin down. Then pipette into your flask. Add 1-3mL E. Coli (amount depends on amount of worms and/or quality of batch of E.Coli but generally speaking start with no more than 1 mL). Shake @20° C on a platform shaker at ~240 rpm. Take approximately 100-200 uL aliquot every day and dump it on an unseeded worm plate to check that the worms are growing and whether they need more food. (It is perhaps easiest to judge food necessity by how clear/opaque the liquid appears after a few minutes of letting the worms settle to the bottom of the flask.) In general, we have found that feeding a culture 1-3 mL a day works well. After a few days you will notice the culture become cluttered with brown oval pellets, presumably worm debris/waste. After 4-5 days (longer for some mutants) your worms should be gravid adults and ready to harvest. If dauers are forming you have probably not added enough food and/or the culture is too dense. However, care must be taken to not add too much food at any one time as the worms can suffocate from lack of oxygen. If after 5 days you do not have enough gravid worms, it is possible to let the culture grow another generation but you will have to clean the culture by sucrose floating (see below) and then resuspend only 0.75-1.0 mL worms per flask.
Synchronization for staging worms
Once you have gravid adults, you will want to first separate the live worms from all the debris/dead worms in the culture. This can be done by sucrose floating as follows:
Note: for doing timecourses you will need to grow up 3-5 cultures of worms rather than 1.
Staging for timecourses
3-4 days before you know you will be bleaching your worms and collecting eggs, you will want to pour ~60 large plates (150mm) with the following media:
4.5 g NaCl
3.75 g Bactopeptone
30g Bactoagar (Difco)
7.5 g Bactotryptone
3.75 g Yeast extract
3.0 mL cholesterol (5 mg/mL in ethanol)
1.5 Liter distilled water
1.5 mL CaCl2 (1M)
1.5 mL MgSO4 (1M)
37.5 mL Potassium Phosphate (1M, pH 6) mix thoroughly
The day after you bleached your worms you will want to plate the eggs onto these plates. We have found it useful to sucrose float once more to separate the L1's from the carcasses from which they hatched. A manageable mount of worms per plate is approx. 100 uL spun-down worms pre-sucrose floating or a proportional amount of sucrose-floated worms (approximately 10-50 ul). Plates are then put at 20° C.
For L3 staging timecourse, you will want to begin monitoring your worms under the Nomarski scope 32-36 hrs after plating. We usually begin collecting 1/7th of the plates when the Pnp cells are indicative of early L3 stage, that is they are fairly big and look ready to divide for the first time. Time collection will vary depending on the specific experiment you want to do.
You will want to keep a large stock of M9 at 20° C in preparation for harvesting. Doing almost everything at 20° C, pipette M9 onto the plates you want to collect (several mLs per plate) and let shake or swirl by hand for a few seconds/minutes . Then pipette off the liquid with worms into 50 ml conicals. Repeat step again and wash into conicals. Spin worms down briefly in clinical centrifuge and wash with M9 2-3 times to get rid of as much bacteria as possible. In the past we have had trouble with bacteria washing off in flakes and then spinning down with the worms, thereby inflating the real volume yield of worms. For 7 plates we usually see ~1 mL worms. Transfer to 15 mL conical and add 4x volume of trizol reagent. Vortex briefly, flash freeze in liquid nitrogen, thaw at 37° C and repeat sequence once more. Freeze at -80° C until ready to make RNA.
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