Introduction

There are both aerobic and anaerobic microorganisms that are important to the advancement of biotechnology. Anaerobic microorganisms include obligate anaerobes that require oxidation-reduction potentials of β€”150 to β€”420 mV and facultative anaerobes that can grow at oxidation-reduction potentials between +300 and β€”420 mV (1). Oxygen must be excluded in working with obligate anaerobes.

Many important fermentation products are produced under anaerobic conditions (1-69). These include food products such as bread, yogurt, cheeses, wine, beer, sufu, and sauerkraut. Acetone, butanol, and ethanol are examples of industrial chemicals produced by anaerobes. Specialty chemicals produced by anaerobes include vitamins and pharmaceutical products. Major references describing the microbial products and the microorganisms that produce them include those by Erickson and Fung (2), Reed (3), Steinkraus (4), and Zeikus and Johnson (20).

Anaerobic digestion and biodegradation processes are applied widely to treat process waste products and in environmental restoration. Environmental microbiology is significant because of the beneficial impact of natural and nurtured processes and because of the isolation and identification of useful microorganisms that have evolved in natural environments. Anaerobic processes occur in production agriculture; cattle and sheep are still the greatest commercial success in harvesting and utilizing cellulosic plant products because of the anaerobic fermentations that occur in the rumen of these animals.

The taxonomy of anaerobes has evolved as new information has become available (64-66). Based on 16/18 S rRNA sequence comparisons, a universal phylogenetic tree has been described that includes bacteria, archaea, and eukarya (64,65). Anaerobes are found in all three branches of this tree.

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