Size of Bacteria

Bacteria vary greatly in size according to the species. Some are 

Measurements show some variation depending upon the staining solution used and the method of application. In dried and fixed smears, the cell wall and slime layer do not stain with weakly staining dyes such as methylene blue but do stain with the intensely staining pararosaniline, new fuchsin, crystal violet, and methyl violet. The great majority of bacteria have been measured in fixed and stained preparations. In some instances dried, negatively stained smears have been used. Therefore, the method employed should be specified when measurements of bacteria are reported otherwise the results will be of doubtful v alue. 

Some bacteria measure as large as 80 p in length others as small as 0.2 ix. However, the majority of the commonly encountered bacteria, including the disease producers, measure about 0.5 n in diameter for the spherical cells and 0.5 by 2 to 3 p for the rod forms. Bacteria producing spores are generally larger than the nonspore-producing species. The sizes of some common species in dried and stained smears are as follows Escherichia coli, 0.5 by 1 to 3 

The most commonly employed method for measuring bacteria is by means of an ocular micrometer. Measurements may also be made by using a camera-lucida attachment and drawing oculars, or by projecting the real image on a screen and measuring the bacteria. 

The same factors that cause variations in the shape of bacteria also affect their size. With few exceptions, young cells are much larger than old or mature forms. Cells of B. subtilis from a 4-hr. culture measure five to seven times longer than cells from a 24-hr. culture. Variations in width are less pronounced. The organism Corynebacterium diphtheriae is a notable exception to the rule of decreasing cell size with age. 

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Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

Microfiltration. Microfiltration is a pressure-driven membrane filtration process and has already been discussed in Chapter 8 for the separation of heterogeneous mixtures. Microfiltration retains particles down to a size of around 0.05 xm. Salts and large molecules pass through the membrane but particles of the size of bacteria and fat globules are rejected. A pressure difference of 0.5 to 4 bar is used across the membrane. Typical applications include ... 

Mitochondria are about the size of bacteria. They have a diameter of 0.2 to 0.5 gm and are 0.5 to 7 p.m long. They are bounded by two lipid bilayers, the inner one being highly folded. These folds are called cristae. The innermost space of the mitochondrion is called the matrix. They have their own DNA in the form of at least one copy of a circular double helix (Chap. 7), about 5 p.m in overall diameter it differs from nuclear DNA in its density and denaturation temperature by virtue of being richer in guanosine and cytosine (Chap. 7). The different density from nuclear DNA allows its separation by isopycnic centrifugation. Mitochondria also have their own type of ribosomes that differ from those in the cytoplasm but are similar to those of bacteria. 

Experiments were run in a clean room equipped with filters that would eliminate particles the size of bacteria (which are several microns in size), but could not eliminate seeds that can be hundreds of times smaller (See Section 3.2). 

Not only are mitochondria roughly the size of bacteria, they have several other features that have led researchers to suspect that they may once have been free-living bacteria that were "captured" by eukaryotic cells. They have their own genetic information (DNA). They also make their own ribosomes that are very similar to those of bacteria. These ribosomes allow the mitochondria to synthesize some of their own proteins. Finally, mitochondria are actually self-replicating they grow in size and divide to produce new mitochondria. All of these characteristics suggest that the mitochondria that produce the majority of the ATP for our cells evolved from bacteria "captured" perhaps as long as 1.5 X 10 years ago. 

Koch and Schaechter (K3) have pointed out a number of unsatisfactory features in use of cell age as an index or measure of cell structure. In particular they note that the model based on this predicts no correlation between the life spans of sister cells, whereas in fact these life spans are found to be correlated. Again, they note that the mass of cells at division (bacterial cells, at any rate) shows less spread about a mean value than does the age of cells at division. They also report that they have found that the mean size of bacteria, at division, changes in a regular fashion when cells are transferred to a medium in which growth rate and bacterial size are different. 

The EPR effect can be observed with macromolecules having apparent molecular size larger than 40-800 kDa [14-22, 29-31], or more to the size of bacteria [32]. Namely, biocompatible polymeric drugs having size larger than the renal clearance threshold (more than 40 kDa) exhibit the EPR effect [14-22]. 

Fig. 5.4 Relative size of bacteria and host s organelles. Mouse spleen infected with B. anthracis. Bacteria seen as dark, oval objects. Host nuclei marked HN host mitochondria marked M. (Roth, Lewis and Williams, 1960.)...

Other medical robots include robotic nurses that can monitor patients vital signs and alert physicians to crises and smart wheelchairs that can automatically maneuver around obstacles. Scientists are also working on developing nanorobots the size of bacteria that can be swallowed and sent to perform various tasks within human bodies, such as removing plaque from the insides of clogged arteries. 

Escherichia coli.B and electrical sizing of bacterias, Blophys.J., 13 1005-1013 (1973). 

Kubitschek HE. Electronic counting and sizing of bacteria. Nature 1958 182 234-235. 

The population size of bacteria and unicellular algae as a function of time in a growth culture is illustrated by Figure 11.12, which shows a population curve for a bacterial culture. Such a culture is started by inoculating a rich nutrient medium with a small number of bacterial cells. Bacteria multiply exponentially in the log phase. 

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