The Mycoplasma pneumoniae cluster is a clade of eight described species which all exhibit cellular polarity. Their polar attachment organelle is a hub of cellular activities including cytadherence and gliding motility, and its duplication in the species M. pneumoniae is coordinated with cell division and DNA replication. The attachment organelle houses a detergent-insoluble, electron-dense core whose presence is required for structural integrity. Although mutant analysis has led to the identification of attachment organelle proteins, the mechanistic basis for the activities of the attachment organelle remains poorly understood, with gliding motility attributed alternatively to the core or to the adhesins. In this study we investigated attachment organelle-associated phenotypes, including gliding motility characteristics and ultrastructural details, in seven species of the M. pneumoniae cluster under identical conditions, allowing direct comparison. We identified gliding ability in three species in which it has not previously been reported, Mycoplasma imitans, Mycoplasma pirum and Mycoplasma testudinis. Across species, ultrastructural features of attachment organelles and their cores do not correlate with gliding speed, and morphological features of cores are inconsistent with predictions about how these structures are involved in the gliding process, disfavouring a prominent, direct role for the electron-dense core in gliding. In addition, we found M. pneumoniae to be an outlier in terms of cell structure with respect to its close relatives, suggesting that it has acquired a special set of adaptations during its evolution.

Despite their small size and reduced genomes, many mycoplasma cells have complex structures involved in virulence. Mycoplasma pneumoniae has served as a model for the study of virulence factors of a variety of mycoplasma species that cause disease in humans and animals. These cells feature an attachment organelle, which mediates cytadherence and gliding motility and is required for virulence. An essential component of the architecture of the attachment organelle is an internal detergent-insoluble structure, the electron-dense core. Little information is known regarding its underlying mechanisms. Mycoplasma amphoriforme, a close relative of both M. pneumoniae and the avian pathogen Mycoplasma gallisepticum, is a recently discovered organism associated with chronic bronchitis in immunosuppressed individuals. This work describes both the ultrastructure of M. amphoriforme strain A39T as visualized by scanning electron microscopy and the gliding motility characteristics of this organism on glass. Though externally resembling M. gallisepticum, M. amphoriforme cells were found to have a Triton X-100-insoluble structure similar to the M. pneumoniae electron-dense core but with different dimensions. M. amphoriforme also exhibited gliding motility using time-lapse microcinematography; its movement was slower than that of either M. pneumoniae or M. gallisepticum.

We explored the differences in course level, personality, and cognitive factors among students who did and did not do extra credit. A total of 276 undergraduate students enrolled in introductory or upper-level psychology and biology courses were surveyed following their final exams to determine levels of academic self-efficacy, metacognitive ability, and a variety of other demographic factors. We conducted a 2 (Extra Credit: Completed or Not Completed) x 2 (Course Level: Introductory or Upper-level) x 4 (Final Course Grade: "A", "B", "C", or "D/F") between-subjects MANOVA with academic self-efficacy and measures of metacognitive ability as dependent variables. Our results indicated that Academic self-efficacy and Regulation of Cognition metacognition scores differed based on these factors. The implications for how course-specific feedback and improved awareness of metacognition can improve student achievement related to our findings and future research directions are discussed.