Monthly Archives: June 2013

Microbial Ecology, Teaching and Research, Winogradsky

Watching Bacteria Grow: Winogradsky Panel Day 14

There are many interesting changes over the last few days. The black areas in the sulfur enriched mud are coalescing, and there are some light pinkish-red colonies developing at the surface. The olive-green band next to the orange is either disappearing or getting covered up as the orange stripe expands.

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The unenriched mud is developing more visible colonies too, as various browns and some very pale greens start to appear.  A few emerald greens are now visible, most of them very faint but there is one larger bright one with a big gas bubble.IMG_6014
It turns out that the bloodworms (midge larvae) are not dead.  In the past, when I have prepared columns (instead of a panel), they all die within the first few days.  Here, they seem to be doing quite well.  Notice the worm tracks in the top left (photos taken Day 11).  It will be interesting to see how the bacterial colonies develop in this area in the presence of this disturbance.

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Watching Bacteria Grow: Winogradsky Panel Day 7

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The panel is changing more slowly now, but the oranges and greens are getting richer and the sulfur-enriched mud is showing more and coalescing black spots.
IMG_5962The level of the mud dropped overnight.  This could be due to settling of the mud and/or release of gas bubbles.  There are some water-filled gaps, and the water level is lower.  There is now air above the entire length of the water surface, instead of just at the opening of the panel (top left).  Note that there is also a left to right gradient in the water, which was already present before settling.  Near the opening, there is brownish/red colonies growing on the walls, probably aerobes (requires oxygen) explaining why its not present further from the opening.  The water is murky from left to right, perhaps microbes that can tolerate low levels of oxygen, up to a point near the right side where the water layer is still clear.

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Watching Bacteria Grow: Winogradsky Panel Day 4

The Winogradsky panel is developing much more quickly than I had expected. Differences are noticeable from day to day.

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The panel at day 4.

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The colors at the interface are richer and thicker. The green sulfur bacteria below the orange layer are more obvious now.

IMG_5937The modified mud layer now has more black spots and there are now some bright green spots, probably green sulfur bacteria.  GSB are more tolerant of high H2S concentrations than the purple sulfur bacteria, so are growing well in the areas where the black spots tell us there is H2S.  Note the gas bubbles at the bottom center of the image.  The squiggly lines are actually paths left behind by the movement of small, red larvae of midge flies, called blood worms.  They made their way up to the top, and are now all apparently dead.  (And will be food for some bacteria).

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Watching Bacteria Grow: Winogradsky Panel

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One of the research projects in my lab is to investigate the microbial communities present in Winogradsky columns. You can read more about what a Winogradsky column is here.  Over the next little while, I will be carefully watching the development of the microbial communities over time.  This will help me set up a future experiment in which I will take samples over time and determine what bacteria are present and at what abundance to see how the community changes.  I will be posting regular updates as the Winogradsky panel develops.

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The set-up: the panel is 1′ x 2′ plexiglass with a 1/4″ gap filled with mud from a pond on Vassar campus, grow lamps, and time-lapse camera.

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The panel after 2 days. The panel was prepared by adding calcium carbonate, calcium sulfate, and dried leaves to mud from a pond on Vassar campus.  We sifted the mud to make a fine slurry.  We collected leaves from near the pond and baked them to dry them, then blended in a blender to make as fine a powder as possible.  The leaves serve as a source of cellulose.  This supplemented mud was poured to a depth of about 4 cm.  Then we poured unmodified mud (no additives) on top.  Instead of just layering on top though, the bottom layer was displaced, and most of it was pushed to the right side and up to the top.  You can see it clearly here: the mud with additives has the lighter grey color.

Note the orange and brownish-orange along the junction between the two muds. This is microbial growth, probably the phototrophic “purple bacteria.” Purple bacteria come in many colors, including red, orange, brown, and yes, purple.  They use light for energy but unlike plants they use H2S instead of water (H2O) as an electron source, and produce sulfur instead of oxygen.  You can also see it in the little circles where a spot of sulfur-enriched mud got surrounded by unmodified mud.

IMG_5886Close-up of the layers. There is a faint hint of green below the orange layer, these are green sulfur bacteria.

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Another close-up.

IMG_5884Close-up.  You can clearly see the layers of color starting to develop.  The whitish spots are actually gas bubbles, possibly CO2 or H2 produced from fermentation.  That CO2 will serve as a carbon source for autotrophs, and the H2 will serve as an energy source for hydrogenotrophs.  Some black specs are showing up in the modified mud.  Black is due to microbial production of hydrogen sulfide (H2S), which reacts with iron in the mud producing pyrite, which is black.

IMG_5903The back side of the panel. This side does not get direct light from the grow lamps. Some gets through on top and you can see the orange colored bacteria at the top. Note that the interface between the muds is less distinct here, showing that the colors on the illuminated side really are phototrophs.

 

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