General Microbiology - Schlegel, H. 1987

Prokaryotes: A Systematic Survey
Budding and Appendaged Bacteria (Group 4)

This group comprises Bacteria that differ significantly in shape from "conventional" bacteria; they feature protrusions, hypha-like outgrowths, or stalks made of mucous secretions (massive slime production is also possible) (Fig. 3.16, 3.17).

Budding bacteria and novel bacteria. The mode of Cell Division typical of Yeasts is called budding. Unlike binary fission (division in half), budding represents unequal cell division based on localized growth. The daughter cell (bud) is usually smaller than the mother cell and reaches normal size only after becoming independent. Budding bacteria include A number of aquatic and soil species. Hyphomicrobium vulgare is a denitrifying bacterium, and its enrichment culture can be obtained using a medium containing methanol and nitrate. This species is regularly found in standing waters, even in laboratory Water baths; it forms buds on long hyphae. Similar in appearance is the non-sulfur purple bacterium Rhodomicrobium vannielii. The Cell outgrowths and stalks of bacteria are called prosthecae (from the Greek prostheke meaning appendage), and the term "prosthecate bacteria" indicates that they possess such extensions. The best-known species belong to the genus Caulobacter (Caulobacter vibrioides, Asticcacaulis); they are also found in mold-like films on water baths, exhibit a characteristic Morphology, and undergo a complex developmental cycle.

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Fig. 3.16. Prosthecate and stalked bacteria.

Rod-shaped bacteria with polar flagella attach by the flagellated pole to solid surfaces, including other bacteria. A stalk then grows out from this pole; the cell undergoes normal (binary) fission, after which the daughter cell forms a flagellum again at the free pole.

Fig. 3.17. Caulobacter Cells attached to dead Bacillus megaterium cells. (Electron micrograph after metal shadowing; ~4,000×; A. L. Houwink)

Upon careful examination of Algae, crustacean shells, and neuston (surface-dwelling aquatic organisms), other strangely shaped bacteria were discovered, among which we can mention Prosthecomicrobium, Ancalomicrobium, and Pedomicrobium.

"Stalked" bacteria. Some widespread bacteria attach via stalks composed of mucus. Gallionella ferruginea is a bean-shaped cell. From its concave side, it secretes mucus in the form of fine fibrils which, as seen under a Microscope, form a helically twisted ribbon encrusted with iron hydroxide. Gallionella is the most well-known iron bacterium. It occurs in iron-containing waters (streams, drainage pipes, etc.) and grows massively, particularly in spring. Nevskia ramosa has been repeatedly isolated from surface films on ponds, marsh ditches, and water baths. Characteristic polar slime secretion apparently occurs only under nutrient limitation.