Why does Physarum like chocolate?

[Amy Jane Huntley]

Hi There, I was wondering if anyone could offer an explanation as to why a strong positive chemotactic response towards chocolate may be observed. I recently did an experiment to test various food sources and chocolate was favoured quite highly by my Physarum but I'm struggling to find any evidence as to why this might be for the discussion in my uni report? Any help or suggestions would be most appreciated. A friend suggested it could be potassium present in the chocolate. I don't know the chemical compound of the chocolate used either. Thanks Amy x

[Amy Jane Huntley]

OK, I think it's the glucose present in the chocolate! I've found some good published journals where this has been tested and all have resulted in positive chemotaxis towards glucose so I'm going with that for my report! wish me luck :-) Amy x

[ian]

You can test for that - try feeding it neat cocoa powder,  cocoa plus sugar and cocoa plus milk powder.  It's attracted to some odd things -  I've found sweet paprika a strong attractant yet hot peppers repel - I'm going try blagging pure capsaicin from the lab and see if it's as simple as that. 

[Maria]

I do not have a journal entry to prove this, but I thought everything with polysaccharide s is a good food source for physarum. 

https://en.wikipedia.org/wiki/Polysaccharide 

Cellulose and chitin are examples of structural polysaccharides.

oats have a lot of them, so does sugar .... it is the one common ingredient in all of the preferred food sources of physarum ( oats, cornmeal, lactose, sugar, etc.)  - and right now I will definitely make agar with tonic water :D ( I would love to have physarum which glows under UV light :D ) 

Best  <  M 

[ian]

I don't know what access you'd have to them but physarum happily picks up quite a lot of the laboratory fluoresence dyes if they're soaked onto oats - I often feed them a red fluorescent dye for microscopy and they'll pick up calcofluor - the optical brightener in washing powders. 

One thing I've never persuaded them to swallow is luminescent pigment which is a pity because a true glow in the dark slime would be fun. 

[Maria]

Really? we tried a lot of different food colorings so far and easter egg color BUT after a day physarum got rid of the color. 

Did you use the optical brightener from the washing powder or did you use a special one from lab equipment? 

[ian]

It will ditch the colour fast so you have to keep feeding it - sole food source basically. I found it doesn't like blue food colouring very much either. I had to use pure lab grade dye - I don't think the detergent would do it any favours. 

[Maria]

Well, we are working on a long term solution ( we are art-students, so color is important) - but I might take this to a new question/ thread cause it has nothing to do with the original question.