GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

2. THE POSITION OF MICROORGANISMS IN NATURE

2.3. GENERAL PROPERTIES OF MICROORGANISMS

The primary characteristic of microorganisms, as reflected in their very name, is their microscopic size. This factor not only led to the Separation of these organisms from plants and animals, but is also intimately connected with their unique morphological features, metabolic activity and plasticity, widespread distribution in nature, and experimental convenience in the laboratory.

Cell size and the surface-to-volume ratio. The diameter of most Bacteria does not exceed one-thousandth of a millimeter. This unit is the micrometer, or micron (10³mm). Data on fine Cell Structure are typically given in nanometers: 1 nm = 10^-3 µm = 10^-6 mm. The size of small cyanobacteria, Yeasts, and Protozoa is about 10 µm. However, such extremely small organisms are characterized by a very large surface-to-volume ratio. If a cube with a side length of 1 cm (a volume of 1 cm³) is broken down into cubes with a side length of 1 µm, we obtain 10¹² cubes, each with a volume of 1 µm³. The total surface area of these cubes is 10,000 times greater than the surface area of the original cube. A volume of 1 µm³ is typical for an average bacterial cell.

A high surface-to-volume ratio drives intensive interaction with the environment. This results in an exceptionally rapid exchange of substances between the environment and the microbial cell. According to the rule formulated by German physiologist M. Rubner (1893), the resting METABOLISM/26.html">Energy Metabolism of an animal is proportional not to its mass, but to its body surface area. Extrapolating this rule to cellular levels, one would expect metabolic activity rates to differ by several orders of magnitude. Consequently, the growth rates of microorganisms are correspondingly high. For instance, in a 500 kg ox, approximately 0.5 kg of protein is synthesized per day, whereas 500 kg of Yeast can synthesize over 50,000 kg of protein in the same amount of time.

Metabolic plasticity. In Higher Plants and animals, changes in metabolism are relatively strictly constrained by a fixed set of Enzymes. Although the composition of enzymes changes during the individual development of an Organism, these variations are minor under differing environmental conditions. Microorganisms, by contrast, exhibit remarkable metabolic plasticity. A high capacity for adaptation is simply essential for bacteria, a necessity dictated by their small size. A bacterial cell can accommodate only a few hundred thousand protein molecules. Therefore, enzymes that are not currently needed cannot be kept in reserve. Certain enzymes required for Processing nutrients are synthesized only when the corresponding substrate appears in the immediate vicinity of The Cell. Such inducible enzymes can account for up to 10 % of the total protein content within the cell. Consequently, cellular regulatory mechanisms play a much more critical and pronounced role in microorganisms than in other living creatures.

DISTRIBUTION OF MICROORGANISMS. The small size of microorganisms is also of paramount importance for their ecology. While many plants and animals are restricted to specific continents, microorganisms are ubiquitous. Thanks to their minuscule size, they are easily dispersed by air currents. As a rule, a mere 1 gram of garden soil is sufficient to isolate a bacterial strain capable of growing on virtually any natural compound. By establishing specific selective conditions in a test tube, one can obtain enrichment cultures from a tiny sample of soil or sludge, and subsequently isolate pure cultures of most known microorganisms from them.

The small size of microorganisms makes it possible to cultivate and investigate populations consisting of 10⁸ - 10¹⁰ individual Cells within a single test tube or Petri dish, thereby facilitating the detection of rare phenomena such as Mutations or The transfer of acquired traits. Furthermore, this is achieved without The Need for complex equipment, vast spaces, or excessive time. The tremendous breakthroughs in biochemical and genetic research are largely owed to the sheer simplicity of WORKING WITH MICROORGANISMS.