{"id":1001,"date":"2013-01-03T10:45:33","date_gmt":"2013-01-03T14:45:33","guid":{"rendered":"http:\/\/www.ttgnet.com\/journal\/?p=1001"},"modified":"2013-01-03T10:45:33","modified_gmt":"2013-01-03T14:45:33","slug":"thursday-3-january-2012","status":"publish","type":"post","link":"https:\/\/www.ttgnet.com\/journal\/2013\/01\/03\/thursday-3-january-2012\/","title":{"rendered":"Thursday, 3 January 2012"},"content":{"rendered":"

09:45 –<\/span> I’ve been dithering about whether or not to include a mixed bacteria culture in the Life Science kits. Well, not literally a culture, because a culture is by definition reproducing. Such cultures are provided in a nutrient broth or on a nutrient agar slant, and require special handling, often including refrigeration. They’re normally shipped next-day air and must be opened and used within a couple days after they arrive. Even allowing the culture to sit undisturbed over a weekend can cause problems. The problem is that cultures continue reproducing until they run out of nutrients and become senescent. Mutations occur, and eventually the culture becomes useless.
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Other than freeze-drying a culture, there are two ways to avoid that. First, one can reculture every few days to every few weeks, transferring a small amount of the culture to fresh media, and then repeating the reculturing as necessary to maintain a robust culture. That’s obviously not practical for pre-packaged science kits. Option two is to put the bacteria into stasis (essentially, hibernation) by inoculating either a sterile saline solution or a sterile PBS (phosphate-buffered saline) solution with the bacteria. The saline\/PBS contains no nutrients, so the bacteria don’t reproduce. Stored in the dark at room temperature, such saline\/PBS specimens may remain viable for anything from a few years to many decades, depending on the particular bacterial species and other factors.
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The problem is that I don’t have years to decades to find out which species are suited to stasis, and there’s not a whole lot in the literature other than for pathogens. I’d like to provide a mixed group of non-pathogenic bacteria that encompass the three basic morphologies as well as examples of Gram-positive and Gram-negative species. It’d also be nice to have an example of a species that is a facultative anaerobe. On that basis, I’ve tentatively chosen Bacillus subtilis<\/em>, Micrococcus luteus<\/em>, and Rhodospirillum rubrum<\/em>.
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So, here’s what I think I’m going to do. Make up and autoclave a liter of saline or (probably) PBS. Using aseptic procedures, transfer about 5 mL of a robust mixed culture of those three species in nutrient broth to the 1 L of sterile saline, mix, and then fill 200 sterile 15 mL polypropylene centrifuge tubes to 5 mL each. Recap and tape each of the tubes, label them, and store them in the dark at room temperature.
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Worst case, at least a few individuals of each species should survive statis, so reculturing in nutrient broth or on a nutrient agar slant or plate should produce colonies of each of the three species. Of course, I may be expecting too much of 7th or 8th grade students, not many of whom are very skilled in aseptic procedures. I suspect many, even most, of the tubes will end up contaminated with environmental bacteria, but I’ll have done what I can do.
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\n","protected":false},"excerpt":{"rendered":"

09:45 – I’ve been dithering about whether or not to include a mixed bacteria culture in the Life Science kits. Well, not literally a culture, because a culture is by definition reproducing. Such cultures are provided in a nutrient broth or on a nutrient agar slant, and require special handling, often including refrigeration. They’re normally shipped next-day air and must be opened and used within a couple days after they arrive. Even allowing the culture to sit undisturbed over a weekend can cause problems.<\/p>\n

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