Pauline Lee

Many of us know of bacteria as germs. Germs make us sick. Since the existence of bacteria was first discovered in 1676, much of the scientific literature has been focused on pathogens and that has also framed our view of bacteria. Yet, the majority of bacteria we come in contact with on a daily basis are not pathogenic. Actually, the tremendous contributions from bacteria in maintaining our world are often unrecognized or unappreciated. The photosynthetic bacteria Cyanobacteria, commonly known as blue-green algae in the oceans and bodies of fresh water, presently provides 50 percent of the oxygen found in our atmosphere. Cyanobacteria fossils date back more than 3 1/2 billion years. Scientists think that they helped change the young planet’s anaerobic environment to one with sufficient atmospheric oxygen that has enabled other, more complex life forms to develop.

Bacteria are indispensable for plant growth. One teaspoonful of fertile soil contains 100 million to 1 billion bacteria. They are microscopic but rich in chemical diversity. Bacteria can decompose complex organic matter to simple forms so that plants can use them as nutrients. They can break down pesticides and pollutants in soil; they can produce compounds that inhibit growth of pathogens. Bacteria can alter the soil environment to favor certain plant communities over others. They affect water availability to plants by their interaction with soil particles. They can form symbiotic partnerships with plants to produce compounds that make elements usable by plants that would otherwise be unusable. An example of this conversion is nitrogen fixation by Cyanobacteria in the roots of plants that transforms nitrogen from air to other forms of nitrogen. This reduces the need for farmers to add nitrogen fertilizer to their plants. In fact, the chloroplast in plant cells originated from a symbiotic Cyanobacterium, taken up by a green algal ancestor of the plants sometime in the Precambrian Era (4500-5000 million years ago). Recognizing the untapped power of soil and plant bacteria in enhancing agricultural productivity, companies such as Monsanto are investing millions of dollars in research and development in this area.

Bacteria can be found everywhere and can live in extreme conditions, including temperatures above boiling or in the cold under 800 meters of ice in the Antarctic. One species can even survive blasts of radiation 1,000 times greater than would kill a human being. There may be thousands of species of bacteria, the majority still unknown to man. Thanks to developments such as low-cost high-throughput sequencing of DNA, researchers can sequence the individual bacterial genome, which will help them to understand what unique sequences of nucleic acids provide the bacteria with their special capabilities. As scientists are realizing the full importance of the microbial world, it is becoming clear that microbes provide ecosystem services that are crucial to local and global sustainability. To illustrate how bacteria interact beneficially with human beings, a discussion of how bacteria help to maintain our health will be presented next month.