Prokaryotes (Bacteria and Archea) collectively encompass a taxonomic and a metabolic diversity that far exceeds that of plants and animals (the so-called ‘higher animals’). This week we will set up a model microbial ecosystem (a microcosm) called a Winogradsky column that will simply and elegantly demonstrate a cross section of that diversity.
Sergei Winogradsky (1856-1953) who, along with Martinus Willem Beijerinck developed the technique, was a pioneering Russian microbiologist who worked in the late 1800’s and early 1900’s, when microbiology was still a fledgling science. At a time when microbiological methods barely existed and most microbiologists focused on the ‘germ-theory’ of disease, the isolation of individual microbes and the characterization of ‘domesticated’ laboratory strains, Winogradsky focused on environmental microbiology and developed techniques for cultivating and studying complex microbial communities (such as the Winogradsky column). In so doing, he made great advances in our understanding of environmental microbiology, microbial diversity, microbial physiology, microbial autotrophy (the ability to obtain energy from non-organic substances) and environmental nutrient cycling (particularly sulfur and nitrogen cycling). He is considered one of the founding fathers of microbial ecology.
The Winogradsky column is a miniature, self-contained ecosystem that in many ways models ecological conditions found in a typical Michigan lake in late summer. Spring thaw results in a mixing of lake water so that the water is more or less uniform at different depths. As summer progresses gradients begin to form in the water column (light gradient, temperature gradient, nutrient, O2 and H2S concentration gradients). These gradients result in a complex interaction of microbes with their environment and with one another resulting in a series of community successions and, ultimately, stratification of microbial populations in the water column.
Similarly, the Winogradsky column begins as a uniform slurry of soil, mud or lake sediment and water (preferably from some outdoor source) supplemented with nutrients (carbon and sulfur). The ingredients are mixed into a uniform slurry, poured into a tall, transparant vessicle such as a test tube, graduated cylinder or soda bottle and exposed to sunlight to provide energy for the system and to enrich for both aerobic and anoxic photosynthetic bacteria. The sediment, soil and water serve as inocula of diverse microbial populations with diverse metabolic processes.
A series of gradients (e.g. oxygen, H2S) soon develop in the column as a result of bacterial metabolic processes. For example, aerobic photosynthetic organisms and exposure to the air will produce O2 near the top of the column which can then be used by other microbes for aereobic respiration. Similarly, sulfate reducers in the anoxic region near the bottom of the column will produce H2S, which can be used by H2S utilizers and anoxic phototrophs. Different organisms soon gain a competitive advantage in different regions of the column causing a stratification and continual regional succession of organisms. Because this culture system more closely resembles a natural environment than do traditional culture methods, a wider variety of physiological types can be observed than by the more standard culture methods. Also, different microbes will be concentrated (enriched) in specific regions of the column where local conditions are optimal for their particular growth (e.g areobes at the top in the oxic zone and anaerobes at the bottom, anoxic zone). Winogradsky columns demonstrate the interdependence of diverse microorganisms in complex communities for survival and growth. As such, variations in Winogradsky column ingredients and manipulations are as infinite as your imagination will allow. Virtually any microbial process could be studied with the correct design and initial inocula.
Materials and Methodology
Field Collected Sediment
Paper Towels (Carbon Source)
Chemical Sources: FeSO4, CaCO3, Nitrogen rich Fertilizer
Test Tubes, Salt Water
Procedure * Bolded steps have already been completed
Your lab table will make 4 different Winogradsky Columns which vary in type of additional materials to add in. 1) Control; 2) FeSO4; 3) CaCO3; and 4) Nitrogen Fertilizer
Maintaining the columns
Once constructed, the Winogradsky columns can be kept for months to years. The microbial communities can slowly change over time and making them interesting to continually observe. To maintain the columns and prevent them from drying out, periodically add water so there is a layer of water on top of the sediment mixture. During weekly observations and Thursday lectures ensure that a layer of water remains on your colums.
Soil samples used to build Winogradsky columns should generally only contain non-pathogenic microbes. However, it is always best to practice safe science. As such, students and teachers should be careful to not directly touch, consume, or inhale contents of the Winogradsky columns. When handling the Winogradsky columns, make sure lids are tightened and secure. However (and this is of equal importance), make certain not to store the columns with lids tightened. Columns must be stored with the lids loose. Gases produced by microorganisms can build up quickly and must be allowed to escape to avoid a build-up of pressure that may lead to column explosion.
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