Monday, March 7, 2011

Meet Elsa!

For this week, I will guide you through the basics of the reproduction and storage of bacteria. Plus, I will show you an insight into the difficulties of working sterile on a bench. For scientists working with a certain species of microbe, it is crucial to keep their ‘pets’ in an always available condition. So in any case of new experiments they can reach back for a pool which is exactly the same, therefore representative in a forthcoming study. The three most common ways of doing this are lyophilization, storage in liquid nitrogen or passaging. During this week’s lab session we gained practice in the last one, so I just quickly summarize the first two.

Some fellows in the sun.
Lyophilization is also called freeze-drying. It starts with cooling down our sample to a very low temperature, 
than applying vacuum on it. Using this method, we can get rid of all the frozen water in the material, therefore it is easily preserved. In case of microbes, even after many years you could make your creatures come alive by simply dropping that lyophilized bacteria strain to a bottle of culturing medium. Moreover, lyophilization is not a secret tool used only by microbiologists. I’m sure you drink instant coffee sometimes. Well, those little crunchy powder-like particles you pour water on are indeed lyophilized.

I should confess that liquid nitrogen is real fun! Imagine a liquid with a temperature of −196 °C; −321 °F.  It was not at our seminar, but fortunately sometimes I had the chance to ‘play with’ this material. It looks like as the clearest water, but immediately creating a cloud of steam as you pour it to a container. Slowly that cloud reduces itself to a thing layer of mist swirling over the surface of the pool you created. As you drop some tubes of cells into it, that seemingly calm ocean starts on hissing and creating more and more mist, while your tube is happily cavorting around. Personally, I always think of it as some kind of futuristic material. If you don’t have the chance to meet this substance, search for some youtube videos, surely you will find some literally cool. Back to our topic, at this extremely low temperature bacteria can be stored safely, and brought alive much later just as in the case of lyophilization.

Making the 'indented agar tubes'. The culturing medium mixed with agar
is heated up, poured into the test-tubes, then it is left to cool down and
solidify on this indented rack.
This week, all of us were given an unknown (at least by us, students) species of microbe. One of our tasks during the semester is to characterize and eventually determine our new friend. For this purpose we should keep our fellow alive, so every week we can pursue new tests on her, better said on her descendants. (I named my microbe Elsa, so that is why I’m arbitrarily gonna refer to her as a she. Before anyone wants to condemn me sexist, I declare that my decision to call her a she was purely based on my very first impression. She is grayish but rather white, seems to be pretty fragile and ethereal. I think she is beautiful in a sense.) Unfortunately, I can’t show a picture of her now, but I’ll upload one with the next post, I promise. (Yes, the title of this post was kind of a bait, I'm sorry. However, here is you reward: I appreciate you didn't give up reading! :)

The descendant story, I stroke up before, should be explained. Otherwise, there might be too much unanswered questions left in you. Bacteria reproduce themselves usually by binary fission, this term simply means that one cell doubles its DNA and divides into two daughter cells. These daughters are absolutely identical to each other in their genome (all hereditary information of an organism), and also have no difference to their preexistent ‘mum’. Therefore, they are called clones. That is why I’m going to be able to nurse Elsa for this whole semester. However, it should be made clear that if I would keep Elsa at conditions which are the best for her to proliferate, then I would end up having a half room of Elsas. Not being my intention, I should turn to some other practice. Yes, I could grow a certain size of population, dry-freeze them in smaller portions or store them in liquid nitrogen. Than every week pick a little tube of Elsa, ‘melt it’ do my tests on her, next week a new tube, and on and on… However we are to approach this problem from another angle. We are continuously going to passage a little pinch of her every week to a new, empty agar surface. Storing this little group of clones on 28 °C will render us only a plate full of Elsa for next week, which can be used for experiments and for passaging a crumb of Elsa for next weeks observations.

If you enlarge this pic, you can see the sticks end smoldering.
This passaging process is relatively easy, however requires a little bit of practice. Sterile work is critical; otherwise, you might contaminate your plate with other species and cannot proceed with your experiment. We used a Bunsen burner as the primary sterilizing tool. In approximately the 15 centimeter radius of the flame the air can be announced bacteria free, because of the heat. Our chosen bacteria were kept on agar, but in a test tube. (The pictures tell more about the creation of such storing equipments.) During the whole passaging process we tried to keep everything close to the flame. As an initial step we heated up a little metal stick so it is completely sterile. For handling the tubes, the tube’s caps and the stick with two hands, we were taught a practical hold. I won’t spend many lines detailing this, rather I decided to shoot a short footage of that process next class, so you can get more close to the work done in lab. I’ll only give a basic explanation. We touched the mouth of the open test-tubes into the flame, so they are sterile, and just after this did we plug our stick into the tube to pick out a little amount of our creatures. After that we turned to a new microbe-free agar test-tube, spread the clump of microbes from our stick to the surface of it. This resulted in a new agar surface with much less cells on it, so we can let them thrive there for a week, without overgrowth.
I end this post with a picture I like a lot. Our seminar is on every Tuesday from 14.00 to 19.00,
so around the end the lights of the sunset pierce in through the window. All these equipment,
our teacher writing on the board, don't tell me it is not nice..


  1. The photos are quite stirring; a great addition to the writing. I keep wondering if the template takes my attention away from the postings or adds to them. I am still undecided on that part, but I am enjoying the posts themselves.