Spirochaetes

Spirochaetes

The phylum Spirochaetes [Greek: spira = a coil ; and chaete = hair] essentially and distinguish-ably 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 ‘po-lar 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 characteristic features, 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 Gram-negative 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 are summarized in Table 3.10.

Importantly, the 2nd edition of Bergey’s Manual divides the phylum spirochaetes into one class, one order (Spirochaetales), and three families, namely : Spirochaetaceae, Serpulinaceae, and Leptospiraceae.