Spiroplasma
Authors: Gasparich Gail E. , Kuo Chih‐Horng , Foissac Xavier 
Published: September 2020

Spi.ro.plas'ma. Gr. fem. n.
speira
(L. transliteration
spira
) a coil, spiral; Gr. neut. n.
plasma
something formed or molded, a form; N.L. neut. n.
Spiroplasma
spiral form.

Tenericutes / Mollicutes / Entomoplasmatales / Spiroplasmataceae / Spiroplasma

Cells are pleomorphic, varying in size and shape from
helical
and branched nonhelical filaments to spherical or ovoid. The helical forms, usually 100–200 nm in diameter and 3–5 μm in length, generally occur during the exponential phase of growth and in some species persist during stationary phase. The cells of some species are short (1–2 μm). In certain cases, helical cells may be very tightly coiled, or the coils may show continuous variation in amplitude. Spherical cells ∼300 nm in diameter and nonhelical filaments are frequently seen in the stationary phase, where they may not be viable, and in all growth phases in suboptimal growth media, where they may or may not be viable. In some species during certain phases, spherical forms may be the replicating form.
Helical filaments are motile, with flexional and twitching movements, and often show an apparent rotatory motility. Fibrils are associated with the membrane, but flagella, periplasmic fibrils, or other organelles of locomotion are absent
. Fimbriae‐like and pili‐like structures observed on the cell surface of insect‐ and plant‐pathogenic spiroplasmas are believed to be involved in host‐cell attachment and conjugation (Ammar et al., 2004; Özbek et al., 2003), but not in locomotion. Cells divide by binary fission, with doubling times of 0.7–37 h. Facultatively anaerobic. The temperature growth range varies among species, from 5 to 41°C.
Colonies on solid media are frequently diffuse
, with irregular shapes and borders, a condition that reflects the motility of the cells during active growth. Colony type is strongly dependent on the agar concentration. Colony sizes vary from 0.1 to 4.0 mm in diameter. Colonies formed by nonmotile variants or mutants, or by cultures growing on inadequate media are typically umbonate with diameters of 200 μm or less. Some species, such as
Spiroplasma platyhelix
, have barely visible helicity along most of their length and display little rotatory or flexing motility. Colonies of motile, fast‐growing spiroplasmas are diffuse, often with satellite colonies developing from foci adjacent to the initial site of colony development. Light turbidity may be produced in liquid cultures. Chemo‐organotrophic. Acid is produced from glucose. Hydrolysis of arginine is variable. Urea, arbutin, and esculin are not hydrolyzed. Sterol requirements are variable. An optimum osmolality, usually in the range of 300–800 mOsm, has been demonstrated for some spiroplasmas. Media containing mycoplasma broth base, serum, and other supplements are required for primary growth, but after adaptation, growth often occurs in less complex media. Defined or semi‐defined media are available for some species. Resistant to 10,000 U/ml penicillin. Insensitive to rifampicin, sensitive to erythromycin and tetracycline.
Isolated from the surfaces of flowers and other plant parts, from the guts and hemolymph of various insects and crustaceans, and from tick triturates. Also isolated from vascular plant fluids
(
phloem sap
)
and insects that feed on the fluids
. Specific host associations are common. The type species,
Spiroplasma citri
, is pathogenic for citrus (e.g., orange and grapefruit), producing “stubborn” disease. Experimental or natural infections also occur in horseradish, periwinkle, radish, broad bean, carrot, and other plant species.
Spiroplasma kunkelii
is a maize pathogen. Some species are pathogenic for insects. Certain species are pathogenic, under experimental conditions, for a variety of suckling rodents (rats, mice, hamsters, and rabbits) and/or chicken embryos. Genome sizes vary from 780 to 2,220 kb (PFGE).

DNA G
+
C content
(
mol
%): 24–31 (
T
m
, Bd).

Type species
:
Spiroplasma citri
Saglio et al. 1973
AL
.