Force and Stepwise Movements of Gliding Motility in Human Pathogenic Bacterium Mycoplasma pneumoniae

Integrated Information for Pathogenicity and Treatment of Spiroplasma

Spiroplasma, belonging to the class Mollicutes, is a small, helical, motile bacterium lacking a cell wall. Its host range includes insects, plants, and aquatic crustaceans. Recently, a few human cases of Spiroplasma infection have been reported. The diseases caused by Spiroplasma have brought about serious economic losses and hindered the healthy development of agriculture. The pathogenesis of Spiroplasma involves the ability to adhere, such as through the terminal structure of Spiroplasma, colonization, and invasive enzymes. However, the exact pathogenic mechanism of Spiroplasma remains a mystery. Therefore, we systematically summarize all the information about Spiroplasma in this review article. This provides a reference for future studies on virulence factors and treatment strategies of Spiroplasma.

Tahara Y, Nakane D, Miyata M. Internal structure of Mycoplasma mobile gliding machinery analyzed by negative staining electron tomography

Mycoplasma mobile is a parasitic bacterium that forms gliding machinery on the cell pole and glides on a solid surface in the direction of the cell pole. The gliding machinery consists of both internal and surface structures. The internal structure is divided into a bell at the front and chain structure extending from the bell. In this study, the internal structures prepared under several conditions were analyzed using negative-staining electron microscopy and electron tomography. The chains were constructed by linked motors containing two complexes similar to ATP synthase. A cylindrical spacer with a maximum diameter of 6 nm and a height of 13 nm, and anonymous linkers with a diameter of 0.9-8.3 nm and length of 14.7±6.9 nm were found between motors. The bell is bowl-shaped and features a honeycomb surface with a periodicity of 8.4 nm. The chains of the motor are connected to the rim of the bell through a wedge-shaped structure. These structures may play roles in the assembly and cooperation of gliding machinery units.

Propulsive cell entry diverts pathogens from immune degradation by remodeling the phagocytic synapse

Phagocytosis is a critical immune function for infection control and tissue homeostasis. During phagocytosis, pathogens are internalized and degraded in phagolysosomes. For pathogens that evade immune degradation, the prevailing view is that virulence factors are required to disrupt the biogenesis of phagolysosomes. In contrast, we present here that physical forces from motile pathogens during cell entry divert them away from the canonical degradative pathway. This altered fate begins with the force-induced remodeling of the phagocytic synapse formation. We used the parasite Toxoplasma gondii as a model because live Toxoplasma actively invades host cells using gliding motility. To differentiate the effects of physical forces from virulence factors in phagocytosis, we employed magnetic forces to induce propulsive entry of inactivated Toxoplasma into macrophages. Experiments and computer simulations show that large propulsive forces hinder productive activation of receptors by preventing their spatial segregation from phosphatases at the phagocytic synapse. Consequently, the inactivated parasites are engulfed into vacuoles that fail to mature into degradative units, similar to the live motile parasite's intracellular pathway. Using yeast cells and opsonized beads, we confirmed that this mechanism is general, not specific to the parasite used. These results reveal new aspects of immune evasion by demonstrating how physical forces during active cell entry, independent of virulence factors, enable pathogens to circumvent phagolysosomal degradation.

Rheotaxis in Mycoplasma gliding

This review describes the upstream-directed movement in the small parasitic bacterium Mycoplasma. Many Mycoplasma species exhibit gliding motility, a form of biological motion over surfaces without the aid of general surface appendages such as flagella. The gliding motility is characterized by a constant unidirectional movement without changes in direction or backward motion. Unlike flagellated bacteria, Mycoplasma lacks the general chemotactic signaling system to control their moving direction. Therefore, the physiological role of directionless travel in Mycoplasma gliding remains unclear. Recently, high-precision measurements under an optical microscope have revealed that three species of Mycoplasma exhibited rheotaxis, that is, the direction of gliding motility is lead upstream by the water flow. This intriguing response appears to be optimized for the flow patterns encountered at host surfaces. This review provides a comprehensive overview of the morphology, behavior, and habitat of Mycoplasma gliding, and discusses the possibility that the rheotaxis is ubiquitous among them.

Propulsive cell entry diverts pathogens from immune degradation by remodeling the phagocytic synapse

Phagocytosis is a critical immune function for infection control and tissue homeostasis. This process is typically described as non-moving pathogens being internalized and degraded in phagolysosomes. For pathogens that evade immune degradation, the prevailing view is that virulence factors that biochemically disrupt the biogenesis of phagoslysosomes are required. In contrast, here we report that physical forces exerted by pathogens during cell entry divert them away from the canonical phagolysosomal degradation pathway, and this altered intracellular fate is determined at the time of phagocytic synapse formation. We used the eukaryotic parasite Toxoplasma gondii as a model because live Toxoplasma uses gliding motility to actively invade into host cells. To differentiate the effect of physical forces from that of virulence factors in phagocytosis, we developed a strategy that used magnetic forces to induce propulsive entry of inactivated Toxoplasma into macrophage cells. Experiments and computer simulations collectively reveal that large propulsive forces suppress productive activation of receptors by hindering their spatial segregation from phosphatases at the phagocytic synapse. Consequently, the inactivated parasites, instead of being degraded in phagolysosomes, are engulfed into vacuoles that fail to mature into degradative units, following an intracellular pathway strikingly similar to that of the live motile parasite. Using opsonized beads, we further confirmed that this mechanism is general, not specific to the parasite used. These results reveal previously unknown aspects of immune evasion by demonstrating how physical forces exerted during active cell entry, independent of virulence factors, can help pathogens circumvent phagolysosomal degradation.

Direct Measurement of Kinetic Force Generated by Mycoplasma

Optical tweezers enable us to measure the force generated by bacterial motility and motor proteins. Here, we describe a method, using optical tweezers and related techniques, to measure the force generated during Mycoplasma gliding. An avidin-conjugated polystyrene bead trapped by a focused laser beam is bound to the surface-biotinylated Mycoplasma cell, which pulls the bead from the trap center of the laser. The force generated by Mycoplasma is calculated from a displacement measured and a spring constant of the laser trap.