Dynamics of Prokaryotic Growth

rri m he greatest contributor to methods of culturing bacte-t ria was Robert Koch (1843-1910), a German physician who combined a medical practice with a productive research career for which he received a Nobel Prize in 1905. Koch was primarily interested in identifying disease-causing bacteria. To do this, however, he soon realized it was necessary to have simple methods to isolate and grow these particular species. He recognized that a single bacterial cell could multiply on a solid medium in a limited area and form a distinct visible mass of descendants.

Koch initially experimented with growing bacteria on the cut surfaces of potatoes, but he found that a lack of nutrients in the potatoes prevented growth of some bacteria. To overcome this difficulty, Koch realized it would be advantageous to be able to solidify any liquid nutrient medium. Gelatin was used initially, but there were two major drawbacks—it melts at the temperature preferred by many medically important organisms and some bacteria can digest it. In 1882, Koch and others experimented with using agar. This solidifying agent was used to harden jelly at the time and proved to be the perfect answer.

Today, we take pure culture techniques for granted because of their relative ease and simplicity. Their development in the late 1800s, however, had a major impact on microbiology. Within 20 years, the agents causing most of the major bacterial diseases of humans were isolated and characterized. The concept that bacteria divide to form cells of similar shape and size to the original was established once and for all. The recognition that shapes, sizes, and metabolic properties characterize different bacterial species had a tremendous impact on the growth of the young science of bacteriology.

—A Glimpse of History

Bacteria growing on an agar plate

can grow at temperatures above the boiling point of water but not at room temperature. Many species can only grow within an animal host, and then only in specific areas of that host.

Because of the medical significance of some bacteria, as well as the nutritional and industrial use of microbial by-products, microbiologists must be able to identify, isolate, and cultivate many species. To do this, one needs to understand the basic principles involved in prokaryotic growth while recognizing that a vast sea of information is yet to be discovered.

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