Membranous Structures of Bacteria

Abstract

Most bacteria are extremely minute organisms. Their average size is about 5 μ (Ierusalimskii, 1963; Zarnea, 1963; Morowitz and Tourtellotte, 1964), and the smallest, the coccoid bacteria for instance, have a diameter of only 0.5-1 μ. Thus, cocci are a thousand times smaller than the average animal cell and are smaller even than such cell organelles as mitochondria, which can attain a length of 10, μ with a diameter of 0.5 μ. (Marr, 1960). A very significant index for illustration of the size of bacteria is the number of free hydrogen ions (H+) at pH 7 in a volume of liquid equal to the volume of the cell. In this case the cell of a coccus contains 5-50 hydrogen ions (Chen and Cleverdon, 1962). This does not mean that there are always 5-50 H+ ions in a cell in which the pH of the cytoplasm is 7. Different metabolic processes can alter the H+ concentration very considerably for certain short intervals of time, but the over-all effect due to these variations corresponds to the H+ concentration at pH 7. The small size of the bacterial cell is of very great significance for the biochemical processes occurring in it. The size of the cell is particularly important when it is reduced to a few tenths of a micron, only slightly exceeding the theoretically permissible minimum (0.05 μ), as in the case of some forms of mycoplasma (diameter 0.1 μ) (Pirie, 1964; Morowitz et al., 1962; Morowitz and Tourtellotte, 1964).