The phylum
Spirochaetes
comprises of Gram-negative, chemoheterotrophic bacteria characterized by their specific structure
and mechanism of motility.
Salient Features :
The various vital and important salient features of the spirochaetes are as
enumerated below :
(1) They are slender long bacteria having diameter 0.1 to 3.0
μm, and length 5 to 250 μm ; and
predominantly with a
flexible and helical shape that may sometimes also occur in the form
of chains.
(2) Multiplication of the
spirochaetes invariably takes place by transverse fission.
(3) The
bacterial cells consist of protoplasmic cylinder interwined with either one or more
axial fibrils,
that originate in nearly equal number from the subterminal attachment disc
strategically located at either ends of the aforesaid
proto-plasmic cylinder. Importantly,
both the
protoplasmic cylinder as well as the axial fibrils are duly enclosed in the outer
envelope meticulously. However, the unattached ends of the axial fibrils may invariably get
extended beyond the terminals of the protoplasmic cylinder that finally be observed as
‘polar
flagella’.
(4) The
motility existing in the spirochaetes are usually found to be of three types, namely :
(
i) Obtained by the rapid rotation about the long axis of the helix
(
ii) Derived by the flexion of the bacterial cells, and
(
iii) Brought about by the locomotion invariably observed along a helical or a serpentine
path
(5) It has been observed that many species of
spirochaetes are so slim that they may exclusively
and vividly visible in a
light-microscope either by the help of a phase-contrast microscope
or a
dark-field optics.
(6) The spectacular and distinctive features of the
spirochaete morphology are quite evident by
means of an
‘electron micrograph’ which explicitely reveals the following characteristicfeatures, such as :
• Central protoplasmic cylinder contains
cytoplasm and nucleoid, which is subsequently
bounded by a
plasma membrane together with a Gram-negative type cell wall.
• Central protoplasmic cylinder actually corresponds to the body of other accessible Gramnegative
bacteria.
• Evidently two or more than a hundred prokaryotic flagella, known as
axial fibrils,
periplasmic flagella
(or endoflagella), extend from either ends of the cylinder and
invariably overlap one another in the centre segment of the cell as depicted in Fig. 3.11(
a),(b) and (c).
(7) Interestingly, the
spirochaetes may be anaerobic, facultatively anaerobic or even-aerobic in
nature.
(8) Carbohydrates, amino acids, long-chain fatty acids (
e.g., palmitic acid, stearic acid, oleic
acid etc.), and long-chain fatty alcohols may cater for carbon as well as energy sources.
(9) Certain spirochaetes may have inclusions but no evidence of any
‘endospore formation’ has
been reported.
(10) Important genera essentially include:
Borrelia, Cristispira, Leptospira, Spirochaeta, and
Treponema.
The characteristic features of the
‘Spirochaete Genera’ viz., dimensions (μm) and flagella,G + C content (mol %), oxygen relationship, carbon + energy source, and habitats