Species profile: Cupriavidus metallidurans

Cupriavidus metallidurans (C. metallidurans) is the second prominent actor in the Aurelia project: a rod-shaped, motile, mesophilic/ extremophilic species typically found in metal-contaminated soils. I’ve been getting to know this particular species more intimately over the past couple of weeks, though I’ve been working with it for over a month. I ordered a freeze-dried, purified culture from ATCC (43123) and began culturing it last month, beginning in the Speculative Life BioLab at the Milieux Institute, and shipping it off on agar plates to the microbiology lab at Saint Mary’s University.

My first experiments with it were to test if I could grow it on food-grade beef broth that I found at a local grocery store, substituting for lab-grade beef extract (because I didn’t have any). I internet-sourced a kitchen-sciencey, more DIY protocol, published in 1920 by the Journal of Bacteriology, and decided to give it a try. It worked very well, even though I fudged the exact amounts (in the true spirit of cooking) because there is no way to accurately measure chemical ratios when buying deliciously-prepared beef broth in a Tetra Pak. The microbes didn’t seem to mind the additional garlic, onions and spices. The culture thrived fairly well out of its freeze-dried sleep and off it went via Priority Post.

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My most recent culture, showing grouping and motility patterns that create lace-like structures.

This peculiar little “bug” is best known for transforming gold chloride, a neurotoxic form of aqueous gold, into 24k gold micro-nuggets in a short period of time, like within a week! Gold chloride is sometimes produced by dissolving gold from ore using Aqua Regia, a volatile acid. Although Aqua Regia was apparently never used in the Nova Scotia gold mining industry, very small amounts of gold chloride may be present in the gold mine tailings we have visited/ collected here in Nova Scotia. C. metallidurans is a non-pathogenic soil microbe that some believe has been doing the work of producing gold in the earth naturally, all along. See “Research Resources” for a few scientific papers on this particular characteristic of C. metallidurans.

I observed my most recent culture through a standard compound microscope, taking the time to slowly note its cultural behavior. I’d retrieved an agar plate from where it was being stored in the fridge (at 4˚C) for the past few days, and streaked it on a glass slide with some distilled water. I did not think it motile at first because none of the bacteria moved at all. After it began to warm up to room temperature, however, movement occurred, with individual bacteria wiggling around to cluster and form lace-like structures as holes and channels were created by the motility patterns. After a few more minutes, all movement stopped again. Room temperature isn’t warm enough to keep these buddies active for long – they need warmth. It will be interesting to observe another culture straight out of the toasty warm 30˚C incubator to see if the behavior and patterning is the same.

I have several liquid cultures of inoculum prepared, in order to test C. metallidurans on contaminated soil samples. This testing will follow my current tests to culture plates of the soil samples alone, to see if any other extremophilic microbes might be present in the toxic waste which would compete with my new colonies.

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A healthy plate of C. metallidurans
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Plates made from liquid C. metallidurans cultures in lab-grade beef extract. On the right, the cultures were harmed by exposure to UV (daylight) before the incubator-shaker was shielded with foil. The culture on the left was at the far back of the shaker and better protected from UV exposure. The right flask had to be discarded.

This little bug, if proven through my experiments to behave the way it might in a native environment (say, next to a volcano), within the contaminated gold mine tailings, could provide an excellent microbial remediation method (in addition to other methods). My interest is exclusively in giving micro-amounts of gold back to the earth, as a poetic gesture of good will and decolonization. But, in the hands of an industry player, perhaps it might be found lucrative for other purposes. How do I feel about that? Part of publishing my original research in an open format like a public blog is to protect it. My success in this research-creation project and its open-source publication may serve to prevent industrial profiteering from my sci-artistic endeavour: I am purposely sabotaging any attempts that could be made at patenting an industrial solution that stems from my research. Come to me first with your queries, gold mining companies, so that we can have a discussion about ethics and ecology.

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