Perspectives on the origin of microfilaments, microtubules, the relevant chaperonin system and cytoskeletal motors--a commentary on the spirochaete origin of flagella

The origin of cytoskeleton and the origin of relevant intracellular transportation system are big problems for understanding the emergence of eukaryotic cells. The present article summarized relevant information of evidences and molecular traces on the origin of actin, tubulin, the chaperonin system for folding them, myosins, kinesins, axonemal dyneins and cytoplasmic dyneins. On this basis the authors proposed a series of works, which should be done in the future, and indicated the ways for reaching the targets. These targets are mainly: 1) the reconstruction of evolutionary path from MreB protein of archaeal ancestor of eukaryotic cells to typical actin; 2) the finding of the MreB or MreB-related proteins in crenarchaea and using them to examine J. A. Lake's hypothesis on the origin of eukaryote from "eocytes" (crenarchaea); 3) the examinations of the existence and distribution of cytoskeleton made of MreB-related protein within coccoid archaea, especially in amoeboid archaeon Thermoplasm acidophilum; 4) using Thermoplasma as a model of archaeal ancestor of eukaryotic cells; 5) the searching for the homolog of ancestral dynein in present-day living archaea. During the writing of this article, Margulis' famous spirochaete hypothesis on the origin of flagella and cilia was unexpectedly involved and analyzed from aspects of tubulins, dyneins and spirochaetes. Actually, spirochaete cannot be reasonably assumed as the ectosymbiotic ancestor of eukaryotic flagella and cilia, since their swing depends upon large amount of bacterial flagella beneath the flexible outer wall, but not depends upon their intracellular tubules and the assumed dyneins. In this case, if they had "evolved" into cilia and lost their bacterial flagella, they would immediately become immobile! In fact, tubulin and dynein-like proteins have not been found in any spirochaete.

MORPHOLOGY OF TREPONEMA MICRODENTIUM AS REVEALED BY ELECTRON MICROSCOPY OF ULTRATHIN SECTIONS

Listgarten, M. A. (Harvard School of Dental Medicine and Forsyth Dental Infirmary, Boston, Mass.), W. J. Loesche, and S. S. Socransky. Morphology of Treponema microdentium as revealed by electron microscopy of ultrathin sections. J. Bacteriol. 85:932-939. 1963.-Broth cultures of a strain of Treponema microdentium were harvested on Millipore filters, fixed in osmic acid, and sectioned for electron microscopy. The sections revealed that the spirochetes had an axial filament, made up of two fibrils approximately 150 A in diameter, which was situated between an external envelope approximately 140 A in thickness and a protoplasmic cylinder. The protoplasmic cylinder had a cross-sectional diameter of 100 to 200 mmu, and was surrounded by a double "membrane" consisting of two 40-A electron-dense structures separated by a 45-A space. Cross-sections of spirochetal "granules" revealed that the limiting membrane was continuous with the outer envelope of the spirochetes, and surrounded the protoplasmic cylinder and axial filament.

COLONIAL GROWTH OF ANAEROBIC SPIROCHETES ON SOLID MEDIA

Hardy, Paul H., Jr. (The Johns Hopkins University School of Medicine, Baltimore, Md.), Young C. Lee, and E. Ellen Nell. Colonial growth of anaerobic spirochetes on solid media. J. Bacteriol. 86:616-626. 1963.-A total of 14 strains of treponemes and one of Borrelia vincentii were cultivated as colonies on agar plates inoculated under ordinary atmospheric conditions, but incubated anaerobically. Every spirochete strain produced diffuse colonies with growth located primarily in the agar; in addition, eight treponeme strains also produced discrete colonies with surface growth. These represented stable colonial variants in several strains, and in one the spirochetes in the surface colonies showed permanently altered cellular morphology. Sufficient variation in colonial morphology was noted between strains to suggest that this may have some value in further classification of this group of microorganisms. Several conditions contributed to the successful growth of all strains as colonies, the most important of which was the use of a firm jelling agar preparation, Ionagar No. 2, that permitted preparation of plates with a final agar concentration of 0.7%. Agar concentrations of 0.9%, or above, in media inhibited treponeme growth.

USE OF A BACTERIAL CULTURE FILTRATE AS AN AID TO THE ISOLATION AND GROWTH OF ANEROBIC SPIROCHETES

Hardy, Paul H., Jr. (The Johns Hopkins University School of Medicine, Baltimore, Md.), Young C. Lee, and E. Ellen Nell. Use of a bacterial culture filtrate as an aid to the isolation and growth of anaerobic spirochetes. J. Bacteriol. 87:1521-1525. 1964.-A previously described procedure that permits colonial growth of laboratory-adapted anaerobic spirochetes on surface streaked media was applied to the isolation of new spirochetal strains from human oral microflora. Primary isolates were readily cultivable as colonies, but they were found to be nutritionally dependent upon other microorganisms with which they are normally associated in vivo. Spirochetal growth was first noted around colonies of oral bacteria; pure cultures were then grown on media fortified with the culture filtrate of one such organism-a microaerophilic diphtheroid.

Effects of SR-spirochete infection on Drosophila melanogaster carrying intersex genes

Three sex-transforming genes (ix, tra-D, and dsx) in D. melanogaster were examined with respect to possible interactions with the NSR strain SR-spirochetes. The SR-spirochetes exerted a lethal effect on XY but not on XX individuals, regardless of whether they were phenotypically males, intersexes, or females. These results, taken together with those reported by Sakaguchi and Poulson (1963)on tra and 2X3A intersexes, both of which are resistant to the androcidal action of SR-spirochetes, support the interpretation that male susceptibility is a consequence of the single X condition.

Ultrastructural identification of spirochetes and flagellated microbes at the brush border of the large intestinal epithelium of the rhesus monkey

Spiral-shaped organisms exclusively and intimately populate the brush border of the cecal and colonic epithelium of healthy monkeys (Macaca mulatta). These organisms replace the glycocalyx, destroy most microvilli, and attenuate the terminal web of the brush border. Despite these remarkable alterations, the remaining host cellular structure is unchanged. Two structurally distinct microbes, a spirochete and a flagellate, were recognized by electron microscopy. These spirochetes share the general characteristics of other known spirochetes: they are 3 to 6 mum long and 0.2 to 0.4 mum wide, spiral 2 to 6 times, and have axial fibrils of 6-12-6 and 4-8-4 arrangements. Flagellated microbes are 4 to 6 mum long and 0.2 to 0.4 mum wide, spiral 2 to 4 times, and are characterized by a polar flagellum which originates from the terminal button at each end of the cytoplasmic body. This in vivo ultrastructural study of anaerobic spiral-shaped organisms bypasses the difficulties of in vitro culture techniques and provides a detailed description and identification of these organisms in their host environment.

A virus associated with SR-spirochetes of Drosophila nebulosa

A virus is associated with a strain of transovarially-transmitted SR-spirochetes, NSR, of Drosophila. This virus, designated spv-1, is able to infect and to multiply in another strain of SR-spirochetes, WSR, thereby eliminating the SR condition from the host flies. Spv-1 contains DNA, has a buoyant density of 1.480 in CsCl, and is spherical in shape, measuring 50-60 nm in diameter.