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My cells had grown well in 40 mM arsenate in glass tubes, using two different frozen stocks and fresh and stored medium. But they didn't grow at all in the disposable polypropylene tubes (pp tubes). So I did a quick test of how the pp tubes inhibit growth. Here's the experimental plan I drew on the whiteboard outside my office:
I took cells from the glass-tube cultures and put them into (1, group on the left) glass tubes with arsenate medium from the pp tube cultures, (2, group in the middle) glass tubes with fresh arsenate medium, and (3, pp tubes with fresh arsenate medium).
And here's the results:
Thick growth in the glass tubes, even in the medium containing the corpses of cells that died when this medium was in plastic tubes. No growth in pp tubes.
So the pp tubes don't cause some stable toxic change to the medium.
is this supposed to be data? clarify your figures, please.
ReplyDeleteDear anonymous,
ReplyDeleteThe whiteboard photos are clear, they are a "chalk'n'talk" equivalent of a couple of PowerPoint slides.
R
do you screw the caps on tightly for both types of tube? might there be differences in the oxygenation of the growth medium or is this controlled for/something you've already looked at?
ReplyDeleteNice experiment! Just curious- have you tested if fresh media, mock-incubated in glass tubes, can support bacterial growth when transferred to polypropylene? I know the issue of absorption of the arsenite by the glass has been discussed, but I'm curious if the glass either leeches out a protective chemical, or absorbs enough arsenic to allow better bacterial growth.
ReplyDelete"So the pp tubes don't cause some stable toxic change to the medium."
ReplyDeleteThat would appear to suggest one of two things at work: (1) something leeching out of the pp tubes that doesn't have a long half-life in the medium (volatile or unstable) or (2) there is something about glass tubes that reduces the toxicity of the arsenate.
Pre-incubae As medium in glass, transfer to glass and pp tubes, inoculate with cells. If you get growth only in glass, it supports (1). If you get growth in both, it supports (2).
Of course, there is the obvious question that should be asked: is the result you've presented here repeatable?