Biology subjects

Vecchiarelli, A. G.

Publications and source records attributed to Vecchiarelli, A. G..

At least 19 recordsLinked to original sources

bioRxiv2026

Fluorescent Biosensors for Cryogenic Correlative Light and Electron Microscopy

Cryogenic electron tomography provides nanometer-scale views of subcellular structures but lacks essential physiological context, such as the metabolic state or ion concentration. To bridge this gap, we incorporated fluorescent biosensors into a cryogenic correlative light and electron microscopy workflow, enabling direct measurement of physiological conditions alongside structural data. Here, we focused on establishing and calibrating biosensors for calcium, pH, and osmotic stress at cryogenic conditions through an in vitro workflow in which biosensors were frozen in defined chemical environments and then imaged ratiometrically. We then applied these biosensors across a range of sample types: an osmotic stress sensor in Saccharomyces cerevisiae, a calcium sensor in human U2OS cells, and a pH sensor in the bacterium Halothiobacillus neapolitanus. This approach links localized physiological changes to the 3D structures of macromolecules and their organization in situ.

biophysics↗

bioRxiv2026

Engineering modular cargo loading strategies for carboxysome-derived protein particles

Bacterial microcompartments (BMCs) are a diverse and widespread class of protein-based organelle consisting of a semi-permeable protein shell encapsulating an enzymatic core. Along with their native assembly pathway, isolated BMC shell proteins have been shown to assemble into alternative superstructures such as flat sheets and nanotubes. The self-assembly and modularity of BMC shell proteins make them of great interest as modular platforms for applications involving scaffolding, immobilization and compartmentalization. While the assembly of BMC shell proteins into higher-order structures has been well-studied, the design of controllable and modular cargo loading is underdeveloped in comparison. Recently, we reported the pH-controlled assembly of CcmK2 - the major hexameric shell protein of the {beta}-carboxysome BMC - into monodisperse mesh-like microscale particles. Here, we develop a suite of encapsulation strategies for stochastic or targeted loading of various cargos, as well as the direct conjugation of cargo to CcmK2 particles. Our systematic analysis demonstrates that cargo loading and particle assembly can be modulated by the choice of recruitment strategy and the order of cargo introduction. Our findings also reveal a cooperative cargo loading mechanism during assembly that influences particle sizing and apparent morphology. Our study serves as a blueprint for the rational design of tunable cargo loading into engineered BMC-derived microcompartment systems for diverse biotechnological applications.

biochemistry↗

bioRxiv2026

Polyphosphate acts as an architectural regulator of carbon fixation and nucleoid structure in cyanobacteria

Polyphosphate (polyP) is a conserved inorganic polymer traditionally viewed as a stress-induced phosphate and energy reserve. In cyanobacteria, however, polyP granules are constitutively present and frequently observed in proximity to carboxysomes, the bacterial microcompartments that mediate CO2 fixation. Here we show that polyP functions as a spatially organized regulator of the photosynthetic cytoplasm in Synechococcus elongatus. PolyP granules localize to the nucleoid and are periodically arranged along the cell axis, independently of the McdAB carboxysome positioning system. Despite this independence, polyP and carboxysomes associate non-randomly, and this association is enhanced when active carboxysome positioning by the McdAB system is disrupted. Loss of polyP synthesis leads to nucleoid expansion, an increased number of smaller carboxysomes with high mobility, and severe defects in growth under ambient CO2. Perturbation of polyP turnover further reveals structural connections to both carboxysomes and thylakoid membranes. Together, these findings identify polyP as an architectural integrator that couples chromosome organization, metabolic compartmentalization, and photosynthetic fitness.

microbiology↗

bioRxiv2026

The kinetics and mobility of a ParA ATPase drive carboxysome distribution in Halothiobacillus neapolitanus

Carboxysomes are bacterial microcompartments that drive efficient carbon fixation in autotrophic bacteria. Critical to their function and inheritance is their spatial organization by the ParA-type ATPase, McdA, and its partner protein, McdB. Here, we investigate the -carboxysome McdAB system in Halothiobacillus neapolitanus using biochemical assays, quantitative fluorescence imaging, and mathematical modeling. We find that, unlike most ParA-type ATPases, the ATPase activity of McdA is only stimulated by DNA rather than by its partner protein McdB. Despite this difference, McdB conserves the ability to displace McdA from DNA, suggesting that ATP hydrolysis and DNA unbinding by McdA are not strictly coupled. Together with its ability to diffuse while bound to DNA, McdA forms gradients on the nucleoid that prevent carboxysome aggregation via a Brownian ratchet mechanism. Overall, these findings reveal key differences in a ParA-type ATPase that may be specific for the spatial organization of protein-based organelles in bacteria.

biophysics↗

bioRxiv2025

Engineering Spatial Control of Bacterial Organelles

Bacteria were once thought to lack organelles, but it is now clear they confine cellular reactions using an array of membrane- and protein-based compartments. A central question, however, is how bacterial organelles are organized in the cell, and whether their spatial control can be engineered. Here, we show that a two-protein system (McdAB) that positions carboxysomes - CO2-fixing organelles found in autotrophic bacteria - can be repurposed to provide programmable spatial control to diverse organelles in Escherichia coli. McdAB not only restores proper assembly and positioning of heterologously produced carboxysomes in E. coli, but can also be reprogrammed to spatially organize all other known types of bacterial organelles, including encapsulins, biomolecular condensates, and even membrane-bound organelles. Programmable spatial organization of bacterial organelles establishes a new design principle for synthetic biology, where the location of reactions is as tunable as their content. Our work paves the way for more efficient biocatalysis in engineered microbes.

microbiology↗

bioRxiv2025

Tuning the interaction of a ParA-type ATPase with its partner separates bacterial organelle positioning from partitioning

The maintenance of carboxysome distribution (Mcd) system comprises the proteins McdA and McdB, which spatially organize carboxysomes to promote efficient carbon fixation and ensure their equal inheritance during cell division. McdA, a member of the ParA/MinD family of ATPases, forms dynamic gradients on the nucleoid that position McdB-bound carboxysomes. McdB belongs to a widespread but poorly characterized class of ParA/MinD partner proteins, and the molecular basis of its interaction with McdA remains unclear. Here, we demonstrate that the N-terminal 20 residues of H. neapolitanus McdB are both necessary and sufficient for interaction with McdA. Within this region, we identify three lysine residues whose individual substitution modulates McdA binding and leads to distinct carboxysome organization phenotypes. Notably, lysine 7 (K7) is critical for McdA interaction: substitutions at this site result in the formation of a single carboxysome aggregate positioned at mid-nucleoid. This phenotype contrasts with that of an McdB deletion, in which carboxysome aggregates lose their nucleoid association and become sequestered at the cell poles. These findings suggest that weakened McdA-McdB interactions are sufficient to maintain carboxysome aggregates on the nucleoid but inadequate for partitioning individual carboxysomes across it. We propose that, within the ParA/MinD family of ATPases, cargo positioning and partitioning are mechanistically separable: weak interactions with the cognate partner can mediate positioning, whereas effective partitioning requires stronger interactions capable of overcoming cargo self-association forces.

microbiology↗

bioRxiv2025

Nucleoid Compaction Influences Carboxysome Localization and Dynamics in Synechococcus elongatus PCC 7942

The bacterial nucleoid is not just a genetic repository--it serves as a dynamic scaffold for spatially organizing key cellular components. ParA-family ATPases exploit this nucleoid matrix to position a wide range of cargos, yet how nucleoid compaction influences these positioning reactions remains poorly understood. We previously characterized the Maintenance of Carboxysome Distribution (Mcd) system in the cyanobacterium Synechococcus elongatus PCC 7942, where the ParA-like ATPase McdA binds the nucleoid and interacts with its partner protein, McdB, to generate dynamic gradients that distribute carboxysomes for optimal carbon fixation. Here, we investigate how nucleoid compaction impacts carboxysome positioning, particularly during metabolic dormancy when McdAB activity is downregulated. We demonstrate that a compacted nucleoid maintains carboxysome organization in the absence of active McdAB-driven positioning. This finding reveals that the nucleoid is not merely a passive substrate for positioning, but an active player in spatial organization. Given the widespread role of ParA-family ATPases in the positioning of diverse cellular cargos, our study suggests that nucleoid compaction state is a fundamental, yet underappreciated, determinant of mesoscale organization across bacteria.

microbiology↗

bioRxiv2024

A robust synthetic biology toolkit to advance carboxysome study and design

Carboxysomes are polyhedral protein organelles that microorganisms use to facilitate carbon dioxide assimilation. They are composed of a modular protein shell which envelops an enzymatic core mainly comprised of physically coupled Rubisco and carbonic anhydrase. While the modular construction principles of carboxysomes make them attractive targets as customizable metabolic platforms, their size and complexity can be a hinderance. In this work, we design and validate a plasmid set - the pXpressome toolkit -in which -carboxysomes are robustly expressed and remain intact and functional after purification. We tested this toolkit by introducing mutations which influence carboxysome structure and performance. We find that deletion of vertex-capping genes results in formation of larger carboxysomes while deletion of facet forming genes produces smaller particles, suggesting that adjusting the ratio of these proteins can rationally affect morphology. Through a series of fluorescently labeled constructs, we observe this toolkit leads to more uniform expression and better cell health than previously published carboxysome expression systems. Overall, the pXpressome toolkit facilitates the study and redesign of carboxysomes with robust performance and improved phenotype uniformity. The pXpressome toolkit will support efforts to remodel carboxysomes for enhanced carbon fixation or serve as a platform for other nanoencapsulation goals.

synthetic biology↗

bioRxiv2023

An invariant C-terminal tryptophan in McdB mediates its interaction and positioning function with carboxysomes

Bacterial microcompartments (BMCs) are widespread, protein-based organelles that regulate metabolism. The model for studying BMCs is the carboxysome, which facilitates carbon-fixation in several autotrophic bacteria. Carboxysomes can be distinguished as type or {beta}, which are structurally and phyletically distinct. We recently characterized the Maintenance of Carboxysome Distribution (Mcd) systems responsible for spatially regulating - and {beta}-carboxysomes, consisting of the proteins McdA and McdB. McdA is an ATPase that drives carboxysome positioning, and McdB is the adaptor protein that directly interacts with carboxysomes to provide cargo specificity. The molecular features of McdB proteins that specify their interactions with carboxysomes, and whether these are similar between - and {beta}-carboxysomes, remain unknown. Here, we identify C-terminal motifs containing an invariant tryptophan necessary for - and {beta}-McdBs to associate with - and {beta}-carboxysomes, respectively. Substituting this tryptophan with other aromatic residues reveals corresponding gradients of carboxysome colocalization and positioning by McdB in vivo. Intriguingly, these gradients also correlate with the ability of McdB to form condensates in vitro. The results reveal a shared mechanism underlying McdB adaptor protein binding to carboxysomes, and potentially other BMCs. Our findings also implicate condensate formation as playing a key role in this association. SIGNIFICANCE STATEMENTO_LIMaintenance of carboxysome distribution protein B (McdB) is necessary for positioning a widespread class of protein-based organelles in bacteria that regulate metabolism. Without McdB, these organelles aggregate and lose functionality. How McdB interacts with and positions these organelles is unknown. C_LIO_LIWe determine that an invariant tryptophan is necessary for McdB to interact with and position its organelle. A similar mechanism occurs in two diverse bacterial cell types, both relying on the invariant tryptophan. C_LIO_LIThis class of bacterial organelle includes compartments involved in bacterial pathogenesis and carbon fixation. Our results therefore advance our understanding and applications of these organelles. C_LI

microbiology↗

bioRxiv2023

An experimental framework to assess biomolecular condensates in bacteria

High-resolution imaging of biomolecular condensates in living cells is essential for correlating their properties to those observed through in vitro assays. However, such experiments are limited in bacteria due to resolution limitations. Here we present an experimental framework that probes the formation, reversibility, and dynamics of condensate-forming proteins in Escherichia coli as a means to determine the nature of biomolecular condensates in bacteria. We demonstrate that condensates form after passing a threshold concentration, maintain a soluble fraction, dissolve upon shifts in temperature and concentration, and exhibit dynamics consistent with internal rearrangement and exchange between condensed and soluble fractions. We also discovered that an established marker for insoluble protein aggregates, IbpA, has different colocalization patterns with bacterial condensates and aggregates, demonstrating its applicability as a reporter to differentiate the two in vivo. Overall, this framework provides a generalizable, accessible, and rigorous set of experiments to probe the nature of biomolecular condensates on the sub-micron scale in bacterial cells.

microbiology↗

bioRxiv2022

Cell Surface-localized CsgF Condensate is a Gatekeeper in Bacterial Curli Subunit Secretion

Curli are functional amyloids present on the outer membrane of E. coli. Cell-surface aggregation of CsgA, the major subunit of curli, is a well-orchestrated process. CsgB, the minor subunit of curli, nucleates the aggregation of CsgA while CsgF, a curli accessory protein, ensures proper anchoring of CsgB to the cell surface. The molecular basis of the interactions between CsgF and curli subunits is unclear. Here, we show that CsgF undergoes phase separation in vitro and that the ability of CsgF variants to phase separate tightly correlated with CsgF function in cells during curli biogenesis. Substitution of phenylalanine residues in the CsgF N-terminus both reduced the propensity of CsgF to phase-separate and impaired curli biogenesis. Exogenous addition of purified CsgF complemented csgF - cells. This exogenous addition assay was used to assess the ability of CsgF variants to complement csgF - cells. The presence of CsgF on the cell surface modulated the secretion of CsgA to the cell surface. We also found that the CsgB nucleator protein is a CsgF client. CsgB can form SDS-insoluble aggregates within the dynamic CsgF condensate, and we propose that these multi-component CsgF-B condensates form a nucleation-competent complex that templates CsgA amyloid formation on the cell surface. Together, our study provides insight into the ability of CsgF to phase separate, regulate CsgA secretion, and promote CsgB aggregation in curli assembly.

biochemistry↗

bioRxiv2022

Multiple ParA/MinD ATPases coordinate the positioning of disparate cargos in a bacterial cell

In eukaryotes, linear motor proteins govern intracellular transport and organization. In bacteria, where linear motors are absent, the ParA/MinD (A/D) family of ATPases spatially organize an array of genetic- and protein-based cellular cargos. ParA is well known to segregate plasmids and chromosomes, as is MinD for its role in divisome positioning. Less studied is the growing list of ParA/MinD-like ATPases found across prokaryotes and involved in the spatial organization of diverse protein-based organelles, such as Bacterial Microcompartments (BMCs), flagella, chemotaxis clusters, and conjugation machinery. Given the fundamental nature of these processes in both cell survival and pathogenesis, the positioning of these cargos has been independently investigated to varying degrees in several organisms. However, it remains unknown whether multiple A/D ATPases can coexist and coordinate the positioning of such a diverse set of fundamental cargos in the same cell. If so, what are the mechanistic commonalities, variation, and specificity determinants that govern the positioning reaction for each cargo? Here, we find that over a third of sequenced bacteria encode multiple A/D ATPases. Among these bacteria, we identified several human pathogens as well as the experimentally tractable organism, Halothiobacillus neapolitanus, which encodes seven A/D ATPases. We directly demonstrate that five of these A/D ATPases are each dedicated to the spatial regulation of a single cellular cargo: the chromosome, the divisome, the carboxysome BMC, the flagellum, and the chemotaxis cluster. We identify putative specificity determinants that allow each A/D ATPase to position its respective cargo. Finally, we show how the deletion of one A/D ATPase can have indirect effects on the inheritance of a cargo actively positioned by another A/D ATPase, stressing the importance of understanding how organelle trafficking, chromosome segregation, and cell division are coordinated in bacterial cells. Together, our data show how multiple A/D ATPases coexist and function to position a diverse set of fundamental cargos in the same bacterial cell. With this knowledge, we anticipate the design of minimal autonomous positioning systems for natural- and synthetic-cargos in bacteria for synthetic biology and biomedical applications.

microbiology↗

bioRxiv2022

The disordered N-terminus of McdB modulates phase separation via pH-sensitive hydration and folds upon interaction with McdA

Across bacteria, protein-based organelles called bacterial microcompartments (BMCs) encapsulate key enzymes to regulate their activities. The model BMC is the carboxysome that encapsulates enzymes for CO2 fixation to increase efficiency and is found in many autotrophic bacteria, such as cyanobacteria. Despite their importance in the global carbon cycle, little is known about how carboxysomes are spatially regulated. We recently identified the two-factor system required for the maintenance of carboxysome distribution (McdAB). McdA drives the equal spacing of carboxysomes via interactions with McdB, which associates with carboxysomes. McdA is a ParA/MinD ATPase, a protein family well-studied in positioning diverse cellular structures in bacteria. However, the adaptor proteins like McdB that connect these ATPases to their cargos are extremely diverse. In fact, McdB represents a completely unstudied class of proteins. Despite the diversity, many adaptor proteins undergo phase separation, but functional roles remain unclear. Here, we define the domain architecture of McdB from the model cyanobacterium Synechococcus elongatus PCC 7942, and dissect its mode of biomolecular condensate formation. We identify an N-terminal intrinsically disordered region (IDR) that modulates condensate solubility, a central coiled-coil dimerizing domain that drives condensate formation, and a C-terminal domain that trimerizes McdB dimers and provides increased valency for condensate formation. We then identify critical basic residues in the IDR, which we mutate to fine-tune condensate solubility. Finally, we find that a condensate-defective mutant of McdB has altered association with carboxysomes and influences carboxysome enzyme content. The results have broad implications for understanding spatial organization of BMCs and the molecular grammar of protein condensates.

biochemistry↗

bioRxiv2021

Rho and F-actin self-organize within an artificial cell cortex

The cell cortex, comprised of the plasma membrane and underlying cytoskeleton, undergoes dynamic reorganizations during a variety of essential biological processes including cell adhesion, cell migration, and cell division1,2. During cell division and cell locomotion, for example, waves of filamentous-actin (F-actin) assembly and disassembly develop in the cell cortex in a process termed "cortical excitability"3-7. In developing frog and starfish embryos, cortical excitability is generated through coupled positive and negative feedback, with rapid activation of Rho-mediated F-actin assembly followed in space and time by F-actin-dependent inhibition of Rho8,9. These feedback loops are proposed to serve as a mechanism for amplification of active Rho signaling at the cell equator to support furrowing during cytokinesis, while also maintaining flexibility for rapid error correction in response to movement of the mitotic spindle during chromosome segregation10. In this paper, we develop an artificial cortex based on Xenopus egg extract and supported lipid bilayers (SLBs), to investigate cortical Rho and F-actin dynamics11. This reconstituted system spontaneously develops two distinct dynamic patterns: singular excitable Rho and F-actin waves and non-traveling oscillatory Rho and F-actin patches. Both types of dynamic patterns have properties and dependencies similar to the cortical excitability previously characterized in vivo9. These findings directly support the longstanding speculation that the cell cortex is a self-organizing structure and present a novel approach for investigating mechanisms of Rho-GTPase-mediated cortical dynamics. HighlightsO_LIAn artificial cell cortex comprising Xenopus egg extract on a supported lipid bilayer self-organizes into complex, dynamic patterns of active Rho and F-actin C_LIO_LIWe identified two types of reconstituted cortical dynamics - excitable waves and coherent oscillations C_LIO_LIReconstituted waves and oscillations require Rho activity and F-actin polymerization C_LI

cell biology↗

bioRxiv2021

Dissection of the ATPase active site of McdA reveals the sequential steps essential for carboxysome distribution

Carboxysomes, the most prevalent and well-studied anabolic bacterial microcompartment, play a central role in efficient carbon fixation by cyanobacteria and proteobacteria. In previous studies, we identified the two-component system called McdAB that spatially distributes carboxysomes across the bacterial nucleoid. McdA, a ParA-like ATPase, forms a dynamic oscillating gradient on the nucleoid in response to carboxysome-localized McdB. As McdB stimulates McdA ATPase activity, McdA is removed from the nucleoid in the vicinity of carboxysomes, propelling these proteinaceous cargos toward regions of highest McdA concentration via a Brownian-ratchet mechanism. However, how the ATPase cycle of McdA governs its in vivo dynamics and carboxysome positioning remains unresolved. Here, by strategically introducing amino acid substitutions in the ATP-binding region of McdA, we sequentially trap McdA at specific steps in its ATP cycle. We map out critical events in the ATPase cycle of McdA that allows the protein to bind ATP, dimerize, change its conformation into a DNA-binding state, interact with McdB-bound carboxysomes, hydrolyze ATP and release from the nucleoid. We also find that McdA is a member of a previously unstudied subset of ParA family ATPases, harboring unique interactions with ATP and the nucleoid for trafficking their cognate intracellular cargos.

microbiology↗

bioRxiv2020

The McdAB system positions α-carboxysomes in proteobacteria

Carboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is utilized as a surface for the equidistant-spacing of {beta}-carboxysomes across cell lengths by a two-component system (McdAB) in the model cyanobacterium Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among {beta}-cyanobacteria, which possess {beta}-carboxysomes, but are absent in -cyanobacteria, which possess structurally distinct -carboxysomes. Since cyanobacterial -carboxysomes are thought to have arisen in proteobacteria and were subsequently horizontally transferred into cyanobacteria, this raised the question whether -carboxysome containing proteobacteria possess a McdAB system for positioning -carboxysomes. Here, using the model chemoautotrophic proteobacterium H. neapolitanus, we show that a McdAB system distinct from that of {beta}-cyanobacteria operates to position -carboxysomes across cell lengths. We further show that this system is widespread among -carboxysome containing proteobacteria and that cyanobacteria likely inherited an -carboxysome operon from a proteobacterium lacking the mcdAB locus. These results demonstrate that McdAB is a cross-phylum two-component system necessary for positioning - and {beta}-carboxysomes. The findings have further implications for understanding the positioning of other bacterial protein-based organelles involved in diverse metabolic processes.

microbiology↗

bioRxiv2020

The emergence of phase separation as an organizing principle in bacteria

Recent investigations in bacteria suggest that membraneless organelles play a crucial role in the subcellular organization of bacterial cells. However, the biochemical functions and assembly mechanisms of these compartments have not yet been completely characterized. This Review assesses the current methodologies used in the study of membraneless organelles in bacteria, highlights the limitations in determining the phase of complexes in cells that are typically an order of magnitude smaller than a eukaryotic cell, and identifies gaps in our current knowledge about the functional role of membraneless organelles in bacteria. Liquid-liquid phase separation (LLPS) is one proposed mechanism for membraneless organelle assembly. Overall, we outline the framework to evaluate LLPS in vivo in bacteria, we describe the bacterial systems with proposed LLPS activity, and we comment on the general role LLPS plays in bacteria and how it may regulate cellular function. Lastly, we provide an outlook for super-resolution microscopy and single-molecule tracking as tools to assess condensates in bacteria. Statement of SignificanceThough membraneless organelles appear to play a crucial role in the subcellular organization and regulation of bacterial cells, the biochemical functions and assembly mechanisms of these compartments have not yet been completely characterized. Furthermore, liquid-liquid phase separation (LLPS) is one proposed mechanism for membraneless organelle assembly, but it is difficult to determine subcellular phases in tiny bacterial cells. Thus, we outline the framework to evaluate LLPS in vivo in bacteria and we describe the bacterial systems with proposed LLPS activity in the context of these criteria.

biophysics↗

bioRxiv2020

Cyanobacterial growth and morphology are influenced by carboxysome positioning and temperature

Cyanobacteria are the prokaryotic group of phytoplankton responsible for a significant fraction of global CO2 fixation. Like plants, cyanobacteria use the enzyme Ribulose 1,5-bisphosphate Carboxylase/Oxidase (RuBisCO) to fix CO2 into organic carbon molecules via the Calvin-Benson-Bassham cycle. Unlike plants, cyanobacteria evolved a carbon concentrating organelle called the carboxysome - a proteinaceous compartment that encapsulates and concentrates RuBisCO along with its CO2 substrate. In the rod-shaped cyanobacterium Synechococcus elongatus PCC7942, we recently identified the McdAB system responsible for uniformly distributing carboxysomes along the cell length. It remains unknown what role carboxysome positioning plays with respect to cellular physiology. Here, we show for the first time that a failure to distribute carboxysomes leads to a temperature-dependent decrease in cell growth rate, cell division arrest, cell elongation, asymmetric cell division, and a significant reduction in cellular levels of RuBisCO. Unexpectedly, we also report that even wild-type S. elongatus undergoes filamentous growth at the cool, but environmentally-relevant, growth temperature of 20{degrees}C. The findings suggest that carboxysome positioning by the McdAB system functions to maintain the carbon-fixation efficiency of RuBisCO by preventing carboxysome aggregation, which is particularly important at temperatures where rod-shaped cyanobacteria adopt a filamentous morphology. IMPORTANCEPhotosynthetic cyanobacteria are responsible for almost half of global CO2 fixation. Due to eutrophication, rising temperatures, and increasing atmospheric CO2 concentrations, cyanobacteria have recently gained notoriety for their ability to form massive blooms in both freshwater and marine ecosystems across the globe. Like plants, cyanobacteria use the most abundant enzyme on Earth, RuBisCO, to provide the sole source of organic carbon required for its photosynthetic growth. Unlike plants, cyanobacteria have evolved a carbon-concentrating organelle called the carboxysome that encapsulates and concentrates RuBisCO with its CO2 substrate to significantly increase carbon-fixation efficiency and cell growth. We recently identified the positioning system that distributes carboxysomes in cyanobacteria. However, the physiological consequence of carboxysome mispositioning in the absence of this distribution system remains unknown. Here we find that carboxysome mispositioning triggers temperature-dependent changes in cell growth and morphology as well as a significant reduction in cellular levels of RuBisCO.

cell biology↗