College of Natural Sciences

Faculty Focus features the work of individual faculty members in each of the departments in the College of Natural Sciences. In addition to a description of the projects and a brief listing of the person's related publications, the article includes his or her e-mail address so that you can ask questions or make comments. For a listing of past Faculty Focus articles, click here.

Understanding diatoms:
A class of microscopic organisms with a huge impact

Lynn Brant collecting samples--Photo courtesy of Andrew Thrall

Ever since he saw his first diatoms through a friend's microscope more than 30 years ago, Lynn Brant, associate professor of geology, has been fascinated by these tiny organisms. These single-celled algae are unique in having cell walls made of glassy silica. Because they photosynthesize (employ sunlight to generate their own food), diatoms help form the base of the food chain in aquatic environments. All ecosystems are dependent on this base, and diatoms are the most important producers in some habitats. There are some 12,000 named species of diatoms, but the true number may be in the hundreds of thousands. That means that one need not look far to find new species, as Brant has done on several occasions.

A single drop of water collected from a pond or lake or squeezed from a clump of aquatic plants may contain dozens of species of diatoms. Which species are found depends on the physical and chemical characteristics of the habitat and, quite often, the season. Because there are so many species and many of them have rather narrow tolerances for pH, conductivity (an indicator of total dissolved salts) and various combinations of nutrients, diatoms can be used to assess water quality and changes in aquatic environments over time. Many lakes preserve the silica of diatoms in their sediment, allowing the investigator to compare past diatom communities with those of today to determine how a lake has changed through time in response to climate change, human influences and events in Earth history. For example, Brant has studied changes in the diatom assemblage in a small pond in Montana caused by the melting glaciers and a volcanic eruption.

Decussata placenta--Photo courtesy of Steve Main, Wartburg College

There are many ways to study diatoms, and the techniques employed depend largely on the questions the scientist is trying to answer. Brant has concentrated on small, isolated bodies of water in mountainous regions of Montana and the Appalachians, and he has also done work on odd little habitats found in Iowa. The latter sites have not been well studied, some are endangered, and they sometimes contain strange and rare diatoms.

Donned in his rubber boots, Brant typically wades into some soggy place wearing a vest with pockets stuffed with collecting devices, small plastic bottles, a notebook and other tools. Sometimes he carries a pH meter or other instrument, and he determines his location with a GPS receiver. Squeezing a clump of saturated moss into a bottle produces a rivulet of water and, perhaps, diatoms. Other times, a turkey baster draws up a bit of sediment that might be full of diatoms. Another device Brant uses is one of his own design: a copper dredge on a rope can be thrown or lowered into deeper water to reach otherwise inaccessible spots. This device has been duplicated and used by others as far away as Mongolia. The problem of collecting microscopic organisms is that one never knows what is in those little bottles until work is done back in the laboratory.

Centric diatom--Photo courtesy of Kathy Walters, University of Iowa Microscopy Lab

For many purposes, it is the silica cell wall that is of interest to the diatomist. The sample must be cleaned of organic debris and even of the living contents of the diatoms themselves. Brant uses 30% hydrogen peroxide in a not-too-dangerous technique that produces a suspension of diatoms in water. A few drops of the suspension are dried on a glass coverslip, which is then glued--using a high-index mounting medium--to a standard microscope slide. A good slide will display some 30,000 to 50,000 clean, glistening diatoms through the microscope. Other techniques allow study of the colonies of diatoms (the physical groupings of individual cells in life) or a study of the ultrastructure (really tiny features) using an electron microscope.

When a new species is described in the literature, the author is allowed to name it. Brant was able to name one species after the friend who first introduced him to diatoms, the beginning of a life-long romance with these tiny creatures that provide the food in the ecosystem that ultimately enables fish to swim and eagles to soar.

Following is a selected list of Brant's publications related to the work discussed above as well as his e-mail address.

Brant, L.A. (2003). A new species of Meridion (Bacillariophyceae) from western North Carolina. Southeastern Naturalist, 2 (3), 409-418.

Brant, L.A., & Bahls, L. (1995). Paleoenvironmental impacts of volcanic eruptions upon a diatom community. In J.P.Kociolek & M.J.Sullivan (Eds.), A century of diatom research (pp. 151-161). Champaign, IL: Koeltz Scientific Books.

Edlund, M.B., & Brant, L.A. (1997). Frustulia bahlsii Sp. Nov., a freshwater diatom from the eastern U.S.A. Diatom Research, 12 (2) 207-216.

Edlund, M.B., Brant, L.A., Levkov, Z., & Nakov, T. (In press). An emended description of Decussata (Patrick) Lange-Bertalot & Metzeltin that includes protoplast organization and detailed valve and cingulum ultrastructure. Diatom Research, 21 (1).

lynn.brant@uni.edu