How to get a really BIG culture of Physarum??

[Fred Bartlett]

I'm doing some experiments in a biology class (8th graders), but I'm having some trouble getting a decent-sized culture of P. polycephalum going. I'd love to do the classic maze experiment, but you need quite a bit of the smile mold for that - we don't have nearly enough for a single experiment. We are currently growing them on carageen gel (a lot like agar), or alternatively on moistened filter-paper. But no matter what we do, the plasmodium never gets very large, nor does it wander far from any oat flake (unless it is a very thin branch). We keep our cultures in the dark at 24°C. Does anyone have any tips?

Thanks in advance!

Fred

[ian]

Hi

Grow them on paper - it's less prone to contamination. Add fresh oats every time they cover the oats and add the oats in a ring around the existing patch sort of half overlapping with it. I add mine dry and trickle water onto them once they're added. After five or six days they should be taking a level tablespoonful  a day. I've got them to fill a 10cm square petri like this.

They won't wander until they've exhaused the food supply. If you want to force them out transfer the whole mass to a big piece of damp paper and loosely cover it in the dark - it'll start to migrate as the substrate dries out and you can cut out pieces or let it dry - leave it too long and it'll return to the part digest oats as it's the last place to dry.

[Fred Bartlett]

Thanks! I'll give it a try. But one problem is the oats. Before the slime mold can reach any considerable size, the older oat flakes start to mold. And transferring the slime mold to a new petri dish doesn't help, because then you aren't getting all of it, obviously, and then it is small again. But I certainly will give your suggestion a try! 

[Sarah Roberts]

Hi, here's my method, I found it more effective than using dry oats:

Try boiling the oats for a short time in a little water to make a thick porridge, let them cool and then give the plasmodium a small clump. Then you can tempt the organism from stale food onto some fresher food, and when it covers your new clump, lift the whole lot off gently and put onto some clean damp paper. Try to pick up the clump by the oats with tweezers, rather than cutting or piercing the plasmodium.  You can repeat this until it is all off the old food. At this point you can combine your cultures or start a new boxfull.  Have lots of large clean tupperwares ready!

With a healthy plasmodium this process happens in an hour or two, and after a week or so you can happily occupy most of your day looking after it. At this point you will be glad of your 8th graders.  

The plasmodium might appreciate a rinse with clean water every few days, and a rampage around an empty tupperware occaisionally.

If your plasmodium seems sad and despondent or just won't budge, try offering a little valerian root along with the porridge, either just dry or boiled up with the oats. 

[Fred Bartlett]

Thank you very much, Sarah - I'll try that too! I'll let you guys know what happened...

[ian]

I sanitise my oats in bulk by soaking in ethanol and boiling it off on a hot plate - it means I can prepare them in bulk and store them, and hand out small tubes of them as part of a kit during demos.