Saturday, April 23, 2011

More and more microbiology

As it is spring break now at the university, I decided to share some links with you.

My first close encounter with microbes was at a site called Small Things Considered. You might ask how a website can make a close encounter to someone, but if you start reading that blog you'll see how capturing and informative it is! I had my first microbiology lecture only last semester, but reading this blog served as an aperitif before beginning my studies!
About a year ago, I was surfing on the internet and stumbled into one of their posts which occurred to be quite mind-boggling. It is about a phenomenon that as autumn arrives there are some leaves which do not turn entirely yellow, rather have some patterns of green remaining in them. It seems that there is not simply a bacteria operating behind this incident. The microbe responsible for keeping patches of the leaves green and alive lives in the gut of a moth's larvea! This larvae utilizes the microbe for stimulating plant tissue to keep on photosynthetizing, therefore supplying the moth's larvae with nutrients..  Read the whole article here!
If you'd hear news on microbiology from true professionals, than this blog is a must for you!!

Here is a website I came across quite recently. I'm still in the process of discovering it, but by now I can ensure you that it is definitely worth checking! It approaches microbes from a very easily digestible and understandable way. Have fun!

Now, here is a book I adore. Though we study microbiology in Hungarian, our teachers advised to check this book out. I was fortunate enough that a dear friend of mine owns a copy and he was willing to lend it to me. It is a very detailed overall book on microbiology, containing all the recent discoveries! It is designed for rather those who study/intend to study microbiology at university level.
Brock Biology of Microorganisms by Michael MadiganJohn Martinko 

Sunday, April 17, 2011

I like to move it, move it!

Bacteria with typical lophotrichous flagella.
'lopho' means tuft and 'trichous' means hair.

Last class along with the various staining procedures we had a look at how bacterial cells get from points A to B. Not all bacteria are motile; however, those that are have various ways to do so. They bear flagella or cilia, and some of them use neither of these, but rather glide.

The experiment we did in class was pretty simple. We had Pseudomonas sp. and Proteus sp. on indented agar in test tubes. We cleaned some microscope slides and placed a drop of water onto them, then used our sterile stick to pick some of the 'boys' from the agar to mix them in the water on the slide. As this suspension turned relatively homogenous we placed a very thin glass cover onto the microbe solution drop. This was important, so we could use the 100x objective which requires immersion oil.

Swarming of the Proteus miriablis Source.
The Proteus sp. turned out to be exceptionally motile. It has ‘peritrichous’ flagella, meaning there are flagella all around its ‘body’. However, these kinds of whips are capable of forming a bundle. This bunch of flagella moves coordinately and propels the cell in a particular direction. This rapid motility exhibits an amazing phenomenon on a Petri dish. If you place a colony of Proteus onto agar, it will show concentric circles. The reason for this is that the cells on the edge of the colony tend to move faster than those in the middle. These outer guys move rapidly away in all directions from the original colony. After a while they settle down and start dividing. Therefore, their daughter cells become the outer ones, rushing away to form new settlements. This kind of motion is called ‘swarming’.

Typical flagella arrangement types. Source.

Unfortunately, we had no device for recording these motions at the university. Though, I found some intriguing pieces of footage on YouTube which I recommend you watch!

This third one is just to show you what we experienced when we dipped a piece of glass into the immersion oil we use for microscopy. The oil's refractive index is the same as glass' so you are unable to distinguish the two.

Sunday, April 10, 2011

Bacteria worth munching on

Here, I present a mostly unknown aspect of the sauerkraut making process. I’ll guide you to the backstage where you can meet the microbes responsible for creating this tasty side dish. (Well, it isn’t only a side, there are gorgeous meals made from it. Here is one for those who’d take a plunge in the Hungarian kitchen, presented by one of my blogger classmates.)

Leuconostoc mesenteroides. Source.
What the heck is the sauerkraut? The image of a bunch of fermented, spicy shredded cabbage leaves might not seem appealing, though it is delicious. Moreover is it healthy. I did a little research on the history of this food and discovered some intriguing data. It is thought to be the Chinese who ‘invented’ it while building the Great Wall. Later, it conquered Europe, benefiting sailors the most. During longlasting sea journeys the lack of vitamin C occurred quite regularly, resulting in a nasty disease, scurvy. The sauerkraut can be stored without much extra care for months. Therefore, it was perfect for seafarers to have it with them as a depot of vitamins. Well made sauerkraut has a long lasting expiration date due to its low pH and high salt concentration which not many microbes can withstand. The exceptional few who can are the ones who create the conditions, in which the fermentation results in cabbage becoming sauerkraut. Let’s have a closer look at them.

The human factor in making sauerkraut starts and actually ends with: slicing up the cabbage, mixing some salt and spices with it, and placing this mess into a container. Not to be forgotten, it is crucial to place some weight onto it, so it is compressed and relatively air free, providing anaerobic conditions. If you are still hesitant about how to do it, there are plenty of videos on this topic, so you cannot blow it.

Traditional barrel for making sauerkraut. Source.
Along the approximately five weeks of the fermentative process a nice timeline can be set about the alternation of different bacteria who contribute to the finest sauerkraut. Four main characters are to be introduced. All of them require water for living, but where does this come from, as we don’t put any into our sour cabbage making bucket? It is the salting step which ‘sucks’ out the water from the cabbage. Imagine a tin of salt that you have left open for weeks! Usually the tiny fine grains of salt aggregate into much bigger sized particles. This is due to the so called ‘hygroscopic’ nature of salt (NaCl). In that case it ‘binds’ the water from the air, forming lager salt chunks. This analogy works with the cabbage; its cells contain heaps of water which is driven out by the salt. In that form, water is more accessible for bacteria, which results in the growth of members of the Enterobacteriaceae family. As mentioned before, high salt concentration serves as a barrier for many microbes to stay alive in our cabbage mixture. Only the Gram-positive ones endure the 2.5% NaCl concentration. The Enterobacteriaceae boys utilize the solute oxygen creating favorable conditions for the Leuconostoc mesenteroides the initiator of the fermenting process.

Lactobacillus plantarum. Source.
The Leuconostoc synthesizes carbon-dioxide, lactic-acid, and alcohol. The acid lowers the pH of the whole solution, making it even more selective. As the lactic-acid concentration increases the two members of the Lactobacillus genus, the L. brevis and the L. plantarum start exercising their beneficial effects. These guys produce even more lactic-acid, creating an even lower pH. And giving the taste (among all the spices you used) to the cabbage. The L, plantarum is quite popular in other food making processes, too. For example, pickles, some cheese, kefir (called by one of my best friends as ‘rotten milk’) and stockfish require this microbe to be present during their creation.

"Side-effects of staining bacteria."
A picture we took at class and I forgot to include in my post last time. 
What we did at class, was that after applying the 50 gramm salt and some spices to the 2 kilos of shredded cabbage we placed a plastic bag of pebbles onto it, then closed it into a bucket. Over 5 weeks we kept measuring the pH, it was unexpected that it dropped to 3.8 right after one week, and remained the same until the end… 3.8 is right, but we thought it would be a slower process. After the five weeks we put some of the juice onto microscope slides and stained them with Gram, make a guess whether it was positive or not! J