GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

5. STRUCTURE OF THE MICROBIAL CELL

5.2. MICROBIAL CELL MEMBRANES

5.2.2. Membrane Structures in Prokaryotes

In some Bacteria, the membrane envelops the Cytoplasm without any folds or invaginations. However, when the growth rate of the cytoplasmic membrane exceeds that of The Cell wall, membrane invagination occurs, leading to The formation of intracellular membrane structures of varying complexity.

Gram-negative bacteria. In Gram-negative bacteria, membrane structures are poorly developed and appear as peripheral membrane folds, such as in Escherichia coli and Proteus vulgaris (Fig. 5.7). Exceptions include certain groups of Gram-negative bacteria (nitrogen fixers, nitrifiers, methane-oxidizing, and phototrophic bacteria) in which membrane structures have a more complex Organization.

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Fig. 5.7. Membrane structures of Gram-negative (a, c) and Gram-positive (b) bacteria.

For example, in nitrifying bacteria (Nitrobacter, Nitrosomonas, Nitrosococcus), membrane structures are lamellar (plate-like) and located in clusters at The Cell periphery, in the center, or near one of the cell poles.

Based on the organization of their intracytoplasmic membranes, methane-oxidizing bacteria are divided into two types. In Cells of the first type, membrane structures take the form of flattened vesicles closely arranged in parallel to one another. This is characteristic of the rod-coccus group of bacteria (Methylomonas, Methylococcus). Vibroid methane-oxidizing microorganisms (Methylosinus, Methylocystis) feature a system of paired membranes running along the cell periphery parallel to the cytoplasmic membrane, which constitutes the second type of cells. It is hypothesized that in methanotrophic bacteria, these membrane structures are functionally responsible for methane oxidation, as indirect experiments indicate they play a role in cellular respiratory activity. However, direct evidence for this is lacking. It is quite likely that the large surface area of these membrane structures provides the necessary level of Respiration and phosphorylation processes within the cells.

Thylakoids and chromatophores are the analogs of plant METABOLISM/14.html">Chloroplasts and are characteristic of phototrophic bacteria. These photosynthetic membranes are similar in Structure and Chemical composition to the cytoplasmic membrane, but they contain light-absorbing pigments (bacteriochlorophylls, carotenoids) as well as Components of the photosynthetic Electron Transport Chain and the phosphorylation system.

Gram-positive bacteria. In Gram-positive bacteria, membrane structures are well-developed, more complexly organized, and form intracellular membrane structures known as mesosomes. Mesosomes were first described in Bacillus cereus. Based on their morphological features, lamellar, vesicular (bubble-shaped), and tubular mesosomes are distinguished. Mixed-type mesosomes are frequently observed in bacterial cells. Mesosomes are considered to be sites for The entry of transforming DNA into the cell, the attachment of Plasmids, and the synthesis of exoenzymes, as well as inert structures arising from an excess of membrane material. It has also been suggested that mesosomes are involved in Cell Division.