This dissertation seeks to document observations, statistics, and physical processes relating to warm, salty mesoscale anticyclonic eddies in the Irminger Sea and their impact on the properties of the region. Anticyclones are studied with a variety of platforms including a mooring, a glider, Argo floats, satellite altimetry, and a regional model. They are found to be widespread throughout the central Irminger gyre, and are similar to anticyclones documented in the neighboring Labrador Sea and Lofoten Basin. Two anticyclone formation regions are found along the boundary current, producing two size classes of anticylones. Over the period between 2002 and 2009, anticyclone transport makes an important contribution to the heat and salt budgets of the gyre upper (<460 m) layer. Along with surface fluxes, they dominate the heat and salt balance on this time scale. The eddy contribution is relatively steady over the 7-year period and presumably over longer timescales as well. Changes in the temperature and salinity in the central gyre can be explained by anomalies in surface forcing. Over yearly time scales, the eddy contribution plays a minimal role in the heat and salt budgets, and the dominant terms include surface forcing and non-eddy horizontal advection. The assumption was made that anticyclones decay in the basin interior, motivated by the observed absence of eddies in the winter, and we explore the hypothesis that winter mixing can lead to eddy decay. To study this, a 1D mixing model is used to show that the barotropic component of velocity can be weakened during a period of sustained surface heat loss, with little change in the baroclinic component. This can push the eddy toward a counter-rotating state, which has been shown by theoretical studies to be unstable for similar anticyclonic vortices, and may thus be a mechanism for eddy decay. Observations of anticyclones are compared to a 1/20 degree resolution regional model (VIKING20). The model reproduces many features of the circulation and water masses, and similar salty anticyclones as observed. However, it cannot resolve the smallest eddies that we detected, and the long-term evolution of the eddies in the model appears to be dominated by numerical diffusivity and viscosity. Therefore, the model cannot be used for studying the processes of eddy decay

Gliding motility in Myxococcus xanthus is powered by flagella stator homologs that move in helical trajectories using proton motive force. The Frz chemosensory pathway regulates the cell polarity axis through MglA, a Ras family GTPase; however, little is known about how MglA establishes the polarity of gliding, because the gliding motors move simultaneously in opposite directions. Here we examined the localization and dynamics of MglA and gliding motors in high spatial and time resolution. We determined that MglA localizes not only at the cell poles, but also along the cell bodies, forming a decreasing concentration gradient toward the lagging cell pole. MglA directly interacts with the motor protein AglR, and the spatial distribution of AglR reversals is positively correlated with the MglA gradient. Thus, the motors moving toward lagging cell poles are less likely to reverse, generating stronger forward propulsion. MglB, the GTPase-activating protein of MglA, regulates motor reversal by maintaining the MglA gradient. Our results suggest a mechanism whereby bacteria use Ras family proteins to modulate cellular polarity.

MreB is a bacterial actin that is important for cell shape and cell wall biosynthesis in many bacterial species. MreB also plays crucial roles in Myxococcus xanthus gliding motility, but the underlying mechanism remains unknown. Here we tracked the dynamics of single MreB particles in M. xanthus using single-particle tracking photoactivated localization microscopy. We found that a subpopulation of MreB particles moves rapidly along helical trajectories, similar to the movements of the MotAB-like gliding motors. The rapid MreB motion was stalled in the mutants that carried truncated gliding motors. Remarkably, M. xanthus MreB moves one to two orders of magnitude faster than its homologs that move along with the cell wall synthesis machinery in Bacillus subtilis and Escherichia coli, and this rapid movement was not affected by the inhibitors of cell wall biosynthesis. Our results show that in M. xanthus, MreB provides a scaffold for the gliding motors while the gliding machinery drives the movement of MreB filaments, analogous to the interdependent movements of myosin motors and actin in eukaryotic cells.

MreB is a bacterial actin that is important for cell shape and cell wall biosynthesis in many bacterial species. MreB also plays crucial roles in Myxococcus xanthus gliding motility, but the underlying mechanism remains unknown. Here we tracked the dynamics of single MreB particles in M. xanthus using single-particle tracking photoactivated localization microscopy. We found that a subpopulation of MreB particles moves rapidly along helical trajectories, similar to the movements of the MotAB-like gliding motors. The rapid MreB motion was stalled in the mutants that carried truncated gliding motors. Remarkably, M. xanthus MreB moves one to two orders of magnitude faster than its homologs that move along with the cell wall synthesis machinery in Bacillus subtilis and Escherichia coli, and this rapid movement was not affected by the inhibitors of cell wall biosynthesis. Our results show that in M. xanthus, MreB provides a scaffold for the gliding motors while the gliding machinery drives the movement of MreB filaments, analogous to the interdependent movements of myosin motors and actin in eukaryotic cells.