Filamentous structures in adherent Mycoplasma pneumoniae cells treated with nonionic detergents.

Abstract

Mycoplasma pneumoniae cells adhering to glass or Parlodion-coated grids were extracted with Triton X-100. The extracted cells showed a cytoskeleton consisting of a rodlike tip structure and a filamentous network in the cytoplasm. The tip structure was up to 300 nm long and -40 nm wide ending at the distal end in a bleb-like structure, and seemed to consist of filaments arranged in parallel, 4.8 ± 0.5 nm wide . In the cytoplasm the filaments formed an irregular lattice. Similar filaments were found in platinum replicated critical-point dried extracted cells. An actinlike nature of the filaments is suggested by some of their properties, but the degree of homology with respect to eucaryotic actin is still unknown . The filaments were sensitive to protease treatment but stable in high molar KCI solutions . They were apparently destroyed by incubation in high molar KI solution, leaving only some parts of the tip structure. Formaldehyde-fixed M. pneumoniae cells treated with Triton X-100 bound rhodamine-labeled phalloidin specifically . Furthermore, they could be stained with antiactin antibodies . Binding of myosin subfragment 1 to the filaments was not observed .In animal and plant cells, microfilaments are involved in motile processes such as cell contraction, cytoplasmic streaming, and pseudopod or filopod formation during amoeboid movement, Information about the arrangement of microfilaments within the cell, their biochemical characteristics, and their role in maintenance of cell shape and cell motility is accumulating (1,25,26) .In contrast to eucaryotic cells, the molecular basis of motility in procaryotic cells is only poorly understood . In the mycoplasmas, the smallest procaryotes known to grow in a cell-free medium, several observations suggest the presence of contractile elements : (a) specialized tip structures and gliding movement in the species M. gallisepticum, M. pneumoniae, and M. pulmonis (7, 9, 27), (b) contractile processes in M . hominis and M. orale, as revealed in microcinematographic studies (7, 8), (c) the possible presence of actin-like proteins in several species including Spiroplasma citri (6,21,24,32).In the present study we use M. pneumoniae to demonstrate the presence and the in situ arrangement of actin-like microfilaments. MATERIALS AND METHODS MycoplasmasU . GOBEL, V. SPETH, and W. BREDT Institute for General Hygiene and Bacteriology, Center for Hygiene, University of Freiburg, and MaxPlanck-Institute for Immunobiology, Freiburg, Federal Republic of Germany M. pneumoniae strain FH was grown in a modified Hayflick medium containing 20% inactivated horse serum, 0.1% glucose, 0.05% thallium acetate and 1000 U/ml penicillin (27) .

The proline-rich P65 protein of Mycoplasma pneumoniae is a component of the Triton X-100-insoluble fraction and exhibits size polymorphism in the strains M129 and FH

“…An insoluble protein network remains after treatment of whole M. pneumoniae cells with Triton X-100 (22,41). This cell fraction still has a complex protein composition and also contains the cytadherence-associated proteins HMW1 to HMW5 (30,31,(51)(52)(53).…”

“…Both proteins are located mainly in a tip structure that functions as the attachment organelle of the bacterium. It could be demonstrated, by nearestneighbor analysis with a hydrophilic chemical cross-linker, that the product of open reading frame 6 (ORF6) of the P1 operon (28), a 40-kDa protein and 90-kDa protein (9, 34, 50) are located in close proximity to the P1 adhesin on the cell surface (35).Scanning and transmission electron microscope analyses of M. pneumoniae cells grown on grids and pretreated with Triton X-100 revealed a rodlike tip structure and a network of filamentous strands (22,41). Krause and coworkers identified a set of high-molecular-weight proteins (HMW1 to HMW5) which play an important role in cytadherence (30,31,(51)(52)(53) and appear to be involved in formation of a cytoskeletonlike structure (38).…”

“…Scanning and transmission electron microscope analyses of M. pneumoniae cells grown on grids and pretreated with Triton X-100 revealed a rodlike tip structure and a network of filamentous strands (22,41). Krause and coworkers identified a set of high-molecular-weight proteins (HMW1 to HMW5) which play an important role in cytadherence (30,31,(51)(52)(53) and appear to be involved in formation of a cytoskeletonlike structure (38).…”

Role of Mycoplasma genitalium MG218 and MG317 cytoskeletal proteins in terminal organelle organization, gliding motility and cytadherence

“…genitalium cells display a differentiated tip structure, commonly known as the terminal organelle (TO), that gives them a flask-shaped appearance. The TO plays a key role in mycoplasma cytadherence and further parasitism of host target cells and it is defined by an electron-dense core (EDC) that is a component of the Triton X-100-insoluble fraction (Gobel et al, 1981;Meng & Pfister, 1980). The intriguing complexity and the multifunctional role of the TO have attracted the interest of many researchers.…”

Terminal organelle development in the cell wall-less bacterium Mycoplasma pneumoniae

“…Nevertheless, a remarkable level of structural complexity underlies what are otherwise considered minimal cells (4). Thus, experimental evidence indicated the presence of cytoskeletal structure and function in M. pneumoniae well before cytoskeleton-like elements were described in walled bacteria (5,6). Furthermore, M. pneumoniae cells possess a complex, differentiated polar extension of the cell body that mediates both adherence to host cells (cytadherence) and gliding motility (7,8).…”