13c. Bacteria and other microorganisms - The photosynthetic bacteria

The Photosynthetic bacteria, like the nitrifying bacteria are a very diverse group of bacteria. There are the purple sulfur, purple non-sulfur and the green photosynthetic bacteria. They occupy different environmental niches and show great structural differences.
At left is a light microscope image of photosynthetic bacteria. Each cell in this micrograph (some cells are dividing) are about 1-2 microns in length








Another light micrograph shows Chromatium sp., a purple sulfur bacterium. The blue granules you see in the cells are sulfur granules that accumulate.







This is an electron micrograph (ultrathin section) of Chromatium buderii. The cell is in the process of dividing. It is full of chromatophores (small spherical structures) which house the enzymes involved in photosynthesis. Unlike green plants, these bacteria split hydrogen sulfide (H2S) instead of water (H2O) to generate their reducing power (H+) needed to carry out photosynthesis.












This ultrathin section of Chromatium buderii shows more detail of the chromatophores which are produced bu invagination of the cytoplasmic membrane. The large "white" round structures are empty sulfur granules. Empty because the process used to produce the ultrathin section dissolves away all of the sulfur in the granule.












This is another photosynthetic bacterium, Thiocystis sp. These cells forms aggregates of 8 or more cells as illustrated in this freeze-etching. They also are encased in a fibrous, slimy material that can be seen in the background.














Another freeze-etching of Thiocystis sp. showing some of the internal features of the cell. Sulfur granules can be seen as well as many smaller chromatophores packed tightly in the cytoplasm. An occasional PHB (po;y-bety hydroxy butyate) granule can also be seen. The freeze-etching strtches the polymer.










This is an ultrathin section of Ectothiorhodospira mobilis, a photosynthetic spirillum with large thylakoids (bundles) of photosynthetic membranes or lamellar stacks.

















This ultrathin section shows the tubular membranes of Thiopedia pfennigii. Again, an occasional sulfur granule (empty hole) can be seen. Like the nitrifying bacteria, the extensions of the cell membrane are differentiated into sites for photosynthetic enzymes and increased membrane surface area.









This ultrathin section is of Prosthecobacterium sp., and is another type of photosynthetic bacterium. In this case, the photosynthetic apparatus is in the oval vesicles located adjacent to the cytoplasmic membranes

There are many other types of photosynthetic bacteria, some with different variations on the theme of membranes involved, and in the habitats that they occupy. What has always puzzled me are the numerous forms of bacteria that carry out the same function, yet differ dramatically in structure. Why is that?