Exploring The Sulfur Nutrient Cycle Using The Winogradsky Column

H O W- T O - D O - I T

Exploring the Sulfur Nutrient Cycle Using the Winogradsky Column
BRIAN ROGAN MICHAEL LEMKE M I C H A E L L E VA N D O W S K Y THOMAS GORRELL

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o fully understand the workings of the biological world, it is important that students have a fundamental sense of the natural cycles that provide the nutrients and energy that power life, as well as a sense of how thesesystems evolved. Many teachers cover carbon cycles and emphasize microbial processes when reviewing the complexities of nitrogen cycling, but often the sulfur cycle, if covered, is done so briefly. There may be many reasons for this: time limitations, the element is less prevalent than others as a biological constituent, or the topic is thought to be too complex. However, teaching the sulfur cyclein conjunction with the classic Winogradsky column exercise presents the opportunity to cover several important topics simultaneously. The exercise links microbial processes, concepts of biodiversity, inorganic chemistry, biogeochemical cycling, evolution, microbiology, and microbial ecol-

ogy to help meet the many demands and standards that are part of today’s science classes. The Winogradskycolumn is a glass or clear plastic column, filled with enriched soil or sediment. When developed, it has an anaerobic lower zone and aerobic upper zone that allow growth of microorganisms under conditions similar to those found in sediments and water rich in nutrients (Sylvia et al., 1998). Often teachers simply convey the message that different microorganisms exist in different strata of thecolumn and that some live in the aerobic and some in anaerobic zones. However, this is really where the discovery begins rather than ends! Explaining the complexity that lies within the depths of the ecosystem allows deeper insights into the microbial world. In the laboratory, the Winogradsky column demonstrates how the metabolic diversity of prokaryotes transforms sulfur, an essential constituent ofliving matter and an abundant element in the Earth’s crust (Stanier et al., 1976), to different forms with varying redox states, thus supplying nutrients and/or energy to the organism. The microbial assemblage that develops in the column spatially separates organisms into distinct layers several

BRIAN ROGAN teaches at The New Jewish High School, Waltham, MA 02453. MICHAEL LEMKE is in the BiologyDepartment, University of Illinois at Springfield, Springfield, IL 62703-5407. MICHAEL LEVANDOWSKY and THOMAS GORRELL work at Haskins Laboratory, Pace University, New York, NY 10038-1598.

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centimeters thick even though in the environment establishment of similar layers of different organisms would typically exist in a fewmillimeters of sediment. The Winogradsky column creates conditions that expand the volume of natural processes, allowing a clear view of naturally-occurring phenomena. Soil samples are collected from wetland habitats, amended with simple inorganic and organic materials, then exposed to light as an external energy source. The results are a multicolored column of soil and water, each color linked to achemical or biological process. The defined zones of microbes develop form according to concentration gradients of oxygen, sulfur, nutrients, and light. Each functional microorganism group is dependent on other functional microbial groups for development. The Winogradsky column was developed and named after Sergei Winogradsky (1856-1953), a Russian microbiologist. He studied the complexinteractions between environmental conditions and microbial activities using soil enrichment to isolate pure bacterial cultures (Madigan et. al, 2000). Louis Pasteur, Robert Koch, and other scientists isolated cultures for study, but Winogradsky’s work was one of the first to study microorganisms in mixed enrichment cultures. The fact that the exercise works under a wide range of circumstances is a...