Bacteriology 102:
Growth of Iron Bacteria

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Iron Bacteria
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Especially relevant to a demonstration in the UW-Madison Bacteriology 102 Course
and not intended to be authoritative for applied or research purposes.

This page is still in the initial stage of construction and will sooner or later include a discussion of the habitats and physiology of iron-oxidizing bacteria and associated organisms which accumulate insoluble ferric iron compounds of biological and non-biological origin. These organisms can seep into the water table and shallow wells, causing major taste and odor problems in drinking water. Determining the "epidemiology" of this problem – following a stream back to a habitat of iron-oxidizing bacteria by using classical and DNA-based bacterial identification methods – can be a valuable exercise in environmental microbiology. Information (with further links and other references) can be found on the U.S. Geological Survey's "What's the Red?" site. More information (including video clips) is found on the Boresaver site. I am not an expert on iron-related bacteria (not yet, anyway!), but a few words about the organisms follow the photos.

Below are a few photos of a stream in Hayward, Wisconsin where these organisms are found in abundance. Looking downstream in the first photo, large orange-colored masses are seen on the left. These masses are composed mainly of the iron oxide-accumulating bacterium Leptothrix, and their appearance is associated with a spring which feeds into the stream at that point. The presence of these bacteria is then obvious along the course of the stream for several blocks to the outlet in Lake Hayward.

Below on the left we see a closer view of the spongy, orange masses which form a frothy sediment in the sample bottle on the right.

Farther downstream, mats of these bacteria cover the bottom of the stream. At right is a typical microscopic view of this condition, showing mainly the sheath-forming bacterium Leptothrix. Many of the sheaths appear "hollow" – i.e., devoid of the cells which originally formed the sheaths around themselves.

Regarding its source of energy and carbon, Leptothrix is classified as a chemoheterotroph. Also, the term chemoorganotroph is usually associated with this type of organism. Remember the definitions associated with this terminology:

In this near-neutral pH environment, ferric oxides which are produced spontaneously – or by true iron-oxidizing bacteria – adhere to and impregnate the sheaths of Leptothrix and are thus concentrated in the large masses of this organism.

True iron-oxidizers include Gallionella and Thiobacillus ferrooxidans – both of which are classified as chemoautotrophs and (as is usually the case for chemoautotrophs) chemolithotrophs. From our definitions:

Gallionella is found in near-neutral environments and produces stalks composed of colloidal ferric hydroxide. It does not appear to be present in the particular microscopic image above, but it is quite recognizable and often seen when a sample is thoroughly scanned with a phase-contrast microscope. T. ferrooxidans favors a very low pH where spontaneous production of ferric oxides does not occur.

Selected Groups of Bacteria
Bacteriology 102 Website
Page last modified on 1/14/04 at 10:00 AM, CST.
John Lindquist, Department of Bacteriology,
University of Wisconsin – Madison