It has been far too long since I have written for my blog. What follows is a post that I had initially started in October 2016, but never got around to finishing. This was partly because I was busy and partly because what was expected to take about six to eight weeks, actually took far longer than that. There has always been a hands on element to my Marine Biology classes, but this past school year (2016-2017) I tried to make a bigger shift. I feel that there will always be an element of information presenting, but I have been trying to cut back on the volume of information that students need to "know." I don't want students doing independent research all the time and I'm not sure that I want to launch completely into project based learning (PBL). So now I'm somewhere in the middle. Looking for meaningful activities that can supplement and reinforce the general topics we are covering. It would be great to develop these types of things outside of the school year, but that never works out the way that I would like it to and, whenever I try activities out on my own, they always work differently when I try to do them with students in class. A new activity that I jumped into without really knowing how well it would to turn out or what I would end up having the students do with the results, is constructing Winogradsky columns. Sound crazy? Maybe a little, but what better way to expose students to scientific experimentation with unknown results than to just do it. The purpose of this activity is to create simple ecosystems to grow microorganisms. Initially developed by Sergius Winogradsky, these cultures are unique compared to the traditional, single organism growth gels that scientists often use because multiple species are growing in their normal medium. Starting with mud collected along a shoreline, shredded newspaper and egg yolk are mixed in to supply carbon and sulfur based nutrients into the system that different microorganisms would require. The information I found about setting up these systems all referred to mud being collected from along the shore of a pond or the edge of a stream; freshwater habitats. But, being a Marine Biology course, we started with some estuarine mud collected near some mangroves; a salt water habitat. (Problem?) While the estuarine mud contained quite a bit of organic material, in contrast to the mud that is often found around freshwater, the particles were particularly small making the mud more dense. (Problem?) The aroma of anaerobic (without oxygen) decomposition that had been taking place in the mud was potent. The sulfides give a smell of rotten eggs, which was hard to handle by some students. After collecting a sample and stirring in the shredded newspaper and egg yolk, the mud was poured into a 20 oz soda bottle that had the top removed. A bit of the water from where the mud was collected was added to the top of the mud and, finally, plastic wrap was used to cover the bottle to reduce water loss by evaporation. So the cultures were set aside in a well lit area at the back of class and the natural processes began. Initially, the microorganisms are carrying out aerobic (with oxygen) respiration since there is an abundance of oxygen present from the mixing and pouring preparation of the system. As time passes, the oxygen levels drop. Near the top of the column, oxygen can still enter from the outside, but it gets used up just as quickly. The result is that lower in the column, microorganisms have to rely on anaerobic processes. By way of their own natural processes, the microorganisms change the conditions in different levels of the Winogradsky column meaning that only certain types can be found in certain layers. Eight weeks later, we were approaching the end of the semester and the end of the half-year course. It was crunch time and the results were less than inspiring. One of the columns was green throughout giving the impression that aerobic algae had proliferated in all the layers. It is possible that the sediment in this system was too well mixed or it did not have the opportunity to settle enough to allow for layers to form. The other two had a couple of very small areas of pink or purple where bacteria had started to grow. (See above right) While this was basically the point, the colored areas were very small and they did not start forming until the very end of the experiment period. Any of the literature that I had read about Winogradsky columns, indicated that students should make observations of physical changes each week. With very little happening until the very end, there wasn't much of anything for the students to observe. Why this happened could be the result of the type of sediment (very small, dense particles) and that it was a saline environment opposed to freshwater as described in any of the descriptions I had seen. Not to be dissuaded by poor results, I let the systems continue to develop despite the course having concluded. Not much had happened, but at least something had started. Would this actually go somewhere meaningful? Could this activity be salvaged for the next group of students to take the class? With everything else from the school year going on, I had basically forgotten about the Winogradsky columns until nearly the end of the school year. The bottle that had been green remained so. It may have gotten a bit darker and the color may have spread to more of the bottle. My general conclusion that the green color was the result of extensive algae growth, but, if there were excessive amounts of sulfur based nutrients present, it is possible that green sulfur bacteria were able to multiply. The other two bottles had larger areas of pink or purple, but these were still pretty isolated, only being found on one side of the system and not really in a layer. (See above left) It was good to know that the microorganisms were able to continue developing, but disappointing given ideal results that I had seen produced elsewhere. (See above right) One aspect that I have since considered that may have been a limiting factor is the original nutrient content of the mud. The mud that I had collected came from the water side of a stand of mangroves. Instructions generally call for "black mud," which would be very high in organic material. This would likely be better found among or to the shore side of the mangroves. So it didn't work out as expected. In these conditions, making weekly observations does not seem to be a viable option, but something still could be done. With the time provided by the conclusion of the school year, I decided to actually look at what had developed. Using a plastic dropper I gently scraped the side of one of the bottles with pink growth and sucked up a little bit of water. I added the sample to a microscope slide and observed what I had collected at 400x magnification. While this system was not distinctly green, there were several different species of algae visible. (See above) Some of these appeared to be species of diatoms. Not much seemed to be happening in most of these cells, but one had chloroplasts clearly moving throughout and a couple appeared to be in the midst of dividing. I finally found some of the pink that had been collected from the bottle. At the highest magnification available, the bacteria appeared simply as tiny pink dots. (See above right) It would likely be difficult for students to be able to identify the exact species that they find, but perhaps this would be a good opportunity to use microscopes and make detailed drawings of their observations.
With some modification, this could be a more beneficial activity and definitely something that I will try again with students. And while it may not have worked out the way I had hoped, the students were able to see some trial and error and I have been able to share the final results with them on Twitter. http://archive.bio.ed.ac.uk/jdeacon/microbes/winograd.htm http://www.hhmi.org/biointeractive/winogradsky-columns-microbial-ecology-classroom http://www.hhmi.org/biointeractive/poster-winogradsky-column-microbial-evolution-bottle
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