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Basic Microbiology
Published in Philip A. Geis, Cosmetic Microbiology, 2020
Summarizing the observed types of bacterial shapes and sizes is difficult due to the far-ranging diversity of the bacteria. However, in general eubacterial species range from very small (nanobacteria, 0.05 mm–0.2 mm in diameter) to very large (Epulopiscium fisheloni, 600 mm × 80 mm). An “average-sized” bacterium such as Escherichia coli is 1.5 mm × 2.6 μm. The most basic morphologies observed in bacteria are the coccus (pl. cocci) and the bacillus or “rod” (pl. bacilli) (Figure 1.2). In addition, the cocci and bacilli can associate in characteristic arrangements such as in pairs of two or four, chains, or filaments and clusters. Many bacteria can be identified by these characteristic arrangements such as Staphylococcus (grape-like clusters of cocci) and Streptococcus (chains of cocci) species. Several bacteria are characterized by a spiral or corkscrew morphology such as the Vibrio, the Spirilla, and the Spirochetes. An additional “morphology” observed in bacteria is amorphic or pleomorphic where consistent regular morphologies are not observed usually due to the lack of a rigid cell wall as observed in the genus Mycoplasma.
Isolation and cultivation of candidate phyla radiation Saccharibacteria (TM7) bacteria in coculture with bacterial hosts
Published in Journal of Oral Microbiology, 2020
Pallavi P. Murugkar, Andrew J. Collins, Tsute Chen, Floyd E. Dewhirst
The preferred term for the smallest viable bacteria is ultramicrobacteria (UMB) [64]. There is a substantial literature on the theoretical minimum size of a bacterium, which grew out of an effort to refute claims of bacterial cells orders of magnitude smaller than 0.2 µm in diameter. The disputed papers were the purported bacterial fossils in Martian meteorite ALH84001 [65] and nanobacteria in pathogenic calcifications and stone formations [66]. Examples of cultivation of UMB cells with equivalent diameters of 0.2 to 0.4 µm and volumes of 0.004 to 0.034 µm3 include members of the well-known genera Chlamydia and Mycoplasma, isolates from urban soil [67], Sphingopyxix alaskensis [68], Dialister invisis from the human oral cavity [69], and Nanoarchaeum equitans [70]. The lower boundary of the UMB minimum size is reliably based on cultivated organisms. As CPR organisms are cultured, the minimum viable cell size will likely drop somewhat, but is thought that a volume of 0.002 µm3 (diameter 0.156 µm) is about the limit [41,71].