Connectivity of centermost chromatophores in Rhodobacter sphaeroides bacteria

Abstract

The size of whole Rhodobacter sphaeroides prevents 3D visualization of centermost chromatophores in their native environment. This study combines cryo-focused ion beam milling with cryo-electron tomography to probe vesicle architecture both in situ and in 3D. Developing chromatophores are membrane-bound buds that remain in topological continuity with the cytoplasmic membrane and detach into vesicles when mature. Mature chromatophores closest to the cell wall are typically isolated vesicles, whereas centermost chromatophores are either linked to neighboring chromatophores or contain smaller, budding structures. Isolated chromatophores comprised a minority of centermost chromatophores. Connections between vesicles in growing bacteria are through ~10 nm-long, ~5 nm-wide linkers, and are thus physical rather than functional in terms of converting photons to ATP. In cells in the stationary phase, chromatophores fuse with neighboring vesicles, lose their spherical structure, and greatly increase in volume. The fusion and morphological changes seen in older bacteria are likely a consequence of the aging process, and are not representative of connectivity in healthy R. sphaeroides. Our results suggest that chromatophores can adopt either isolated or connected morphologies within a single bacterium. Revealing the organization of chromatophore vesicles throughout the cell is an important step in understanding the photosynthetic mechanisms in R. sphaeroides.

Atoms to Phenotypes: Molecular Design Principles of Cellular Energy Metabolism

“…sphaeroides (Frese et al, 2008;Olsen et al, 2008), are packed together into a spherical arrangement (Chandler et al, 2008), whereas those agnostic to curvature (bc 1 ) are sequestered within isolated domains that become locally flat. Thus, deviation of the membrane from an ideal sphere (Noble et al, 2018) allows co-localization of groups of proteins into neighborhoods with distinct curvature-dependent functions.…”

Atoms to Phenotypes: Molecular Design Principles of Cellular Energy Metabolism

“…sphaeroides (Olsen et al, 2008), are packed together into a spherical arrangement (Chandler et al, 2008), whereas the ones agnostic to curvature, namely bc1, are sequestered within isolated membrane domains that become locally flat. Thus, deviation of the membrane from an ideal sphere (Noble et al, 2018) allows co-localization of groups of proteins into neighborhoods with distinct curvature-dependent functions. Zoom-in view of two proximal bc1 complexes that are found to induce the highest degree of local membrane curvature change.…”

Nonvolatile molecular memory with the multilevel states based on MoS2 nanochannel field effect transistor through tuning gate voltage to control molecular configurations

“…Cryogenic sample temperatures in the FIB have previously been utilized to improve milling characteristics for a variety of materials, such as III-V semiconductor devices 15 , minerals 16 , thin film solar cells 17 , and human dentin/enamel 18,19 , and initial demonstrations of cryo-FIB techniques that enable imaging of larger volumes of deposited lithium have recently been shown 14,20,21 . In addition, cryo-FIB has become a valuable tool in biology, where it enables frozen-hydrated biological specimens to be either directly milled and characterized 22,23 in the FIB/SEM or prepared for cryo-TEM [24][25][26][27][28][29] . Here, we illustrate the benefits of cryogenic sample preparation and transfer for characterization of devices containing solid-liquid interfaces and reactive materials in the FIB/SEM and extend the capabilities of cryo-FIB/SEM to nanoscale spectroscopic mapping.…”