The Relationship Between Blue‐green Algae and Bacteria

Abstract

Summary Recent studies of bacteria and blue‐green algae in the electron microscope have shown striking similarities in the basic cellular architecture of the two groups. This evidence has been presented in detail above and may be summarized as follows: (I) The cell envelope of blue‐green algae bears a superficial resemblance to the cell wall of bacteria, particularly to the Gram‐positive organisms. Like bacteria, blue‐green algae also possess a mucopeptide component as an important part of the cell wall. However, the composition of this mucopeptide component resembles more closely that of Gram‐negative bacteria, though more species of blue‐green algae need examination before the relationship can be established with any certainty. (2) The older distinction between the chromatophores of photosynthetic bacteria and the lamellae of blue‐green algae has been shown to be superficial. In both forms the essential feature of the photosynthetic apparatus is a pair of membranes enclosing a space; this may be large in bacterial chromatophores or small in ‘true’ lamellae. This basic structure is seen in higher plants where the lamellar systems are enclosed in a membrane‐bounded structure, the chloroplast. No such membrane isolates the photosynthetic machinery of bacteria and blue‐green algae. (3) No membrane isolates the nuclear material of blue‐green algae or bacteria. The nucleoplasm of these two groups is structurally similar and show the same morphological changes with variations of fixative treatment. (4) Both bacteria and blue‐green algae lack mitochondria, true vacuoles and an endoplasmic reticulum. Membranous structures (mesosomes) are widespread in bacteria and recently similar structures have been seen in blue‐green algae. (5) The nucleoplasm presumably divides by an amitotic process, as no stages of mitosis or meiosis have been observed in either group. The cell division in blue‐green algae shows a superficial resemblance to that of Gram‐positive bacteria. Recent observations on the cytoplasmic inclusions of the two groups have been presented above, but no pattern has yet emerged. The spores of the two groups have also been discussed and the little detailed observation available supports earlier suggestions of some important differences between the two groups. Bacteria and blue‐green algae also resemble each other and differ from other organisms in their method of ornithine biosynthesis, their apparent absence of sterols and their sensitivity to certain antibiotics. The evidence here summarized supports the suggestion that bacteria and blue‐green algae should be isolated in a group distinct from all other organisms. Two speculative aspects of the problem have been discussed: their evolutionary relationship with other organisms and with each other. With regard to the latter, it seems probable that bacteria and blue‐green algae arose from a common ancestor, since it is unlikely that so many features common to the cells of both groups arose independently more than once.

The Lipids of Agaricus bisporus

“…Merdinger (1969) was unable to identify any choline or inositol in lipid extracts of the yeast-like fungus, Pullularia pullulans; phosphatidylethanolamine and phosphatidylserine were the principal phospholipids. In agreement with previous reports (Nichols, Harris & James, 1965 ;Echlin & Morris, 1965), Nichols (1968) was unable to find any phosphatidylcholine, phosphatidylinositol or phosphatidylethanolamine in extracts of blue-green algae.…”

Phylogenetic Relationships of the Procaryota and the Origin of the Eucaryotic Cell

“…There is now an extensive literature dealing with the fine structural and other characteristics of the Procaryota. Only the principal conclusions can be outlined here, but the earlier work has already been lucidly summarized by Stanier and van Niel (1962) and Stanier (1964) while Echlin and Morris (1965) have provided a fairly detailed review of the literature prior to 1965. Later contributions, some of which are considered below, have added to, but not materially altered, the broad interpretations of procaryotic and eucaryotic structure.…”

“…Membranous bodies, known as mesosomes, have heen described for various bacteria (Literature in Echlin andMorris, 1965 andin Ryter, 1968). Azotobacter agilis has a more elaborate system of vesicles and tubules (Pangborn, Marr and Robrish, 1962) evidently similar to those of Rhodospirillum rubrum, while structures, which seem to he morphologically indistinguishable from the thylakoid groups of some photosynthetic procaryotes, are encountered in the autotrophic nitrifying bacteria Nitrosocystis (Plate i.…”

Role of signal peptides in targeting of proteins in cyanobacteria

“…In addition to thylakoids (26), cyanobacteria contain another membrane pathway shared by all eubacterial species: a cell envelope consisting of a cytoplasmic membrane, periplasm, and outer membrane (12). The signal peptides of proteins destined for the cell envelope also contain the conserved features stated previously.…”