A world of microorganisms lives in the soil and sediment. One way of observing their interactions and diversity is to create a window into some of the many soil processes through a culture gradient enrichment. Light is the primary enrichment factor with a focus on the sulfur-cycle microorganisms. The technique shown here is an adaptation of the Winogradsky column that further opens the window of observation from a column to a plate. Using time-lapse photography, processes that take weeks to develop are observed in about one and one-half minutes. The value of this video is that it should capture the attention and imagination of students and serve as a catalyst to discussion of the microbial ecology and microorganism dynamics in the world around us.
The Winogradsky column was developed by Sergi Winogradsky in the late 19th century to observe and isolate soil microorganisms. Generations of students have studied this miniature ecosystem that serves as a common visual learning tool. The objective of this study was to increase interest in the study of soil microorganisms involved in nutrient (i.e., sulfur) cycling and to use time-lapse photography as a tool to uncover subtle details of microbe growth that would otherwise be missed. The Winogradsky plate was constructed with two glass plates (21.6 x 27.9 cm) and foam spacers to create a frame to hold sediment from a pond. The sediment was enriched with 1 to 2% of calcium carbonate and magnesium sulfate. A cellulose source was homogenized with a small portion of the enriched sediment and placed at the bottom of the plate. The plate was filled with the enriched mud and water from the collection site. The plate was illuminated by a light source throughout the duration (~40 days) of the experiment. A camera was mounted in a single spot and a picture taken about every 24 hours. This approach made it possible to see the development of this model ecosystem in a detailed and progressive manner. We provide two learning resources: (i) a slide show with voice over to explain the set up and interpretation of the apparatus and results (long version) and (ii) a ~90-second animation (short version; also embedded in the slide show). The end result makes a valuable learning tool about the chemical process of the sulfur cycle and the biotic components that drive a biogeochemical cycle.
Figure 1: Mud Microbes in Motion (video of time-lapse photos).
Figure 2: Mud and Microbes: A Time-Lapse Photographic Exploration of a Sediment Bacterial Community (video and audio).
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