Biology subjects

Jonas, K.

Publications and source records attributed to Jonas, K..

8 recordsLinked to original sources

bioRxiv2026

Functional diversification of two Lon homologs enhances stress adaptation in Pseudomonas aeruginosa

The Lon protease is a highly conserved ATP-dependent protease that contributes to protein quality control and regulatory processes across all domains of life. The opportunistic pathogen Pseudomonas aeruginosa, along with other members of the Pseudomonadales, encodes AsrA (aminoglycoside-induced stress response ATP-dependent protease), a second LonA-type protease in addition to canonical Lon. Although AsrA is upregulated by aminoglycoside stress, its biochemical activity, substrate spectrum, and cellular functions have remained elusive. Here, we demonstrate that AsrA is a temperature- and antimicrobial stress-induced protease with specialized functions and partial redundancy with Lon. Quantitative proteomics revealed a distinct AsrA substrate profile, while comparative biochemical analyses showed that AsrA and Lon share a substantial number of substrates in vitro but differ in their degradation kinetics, indicating divergent substrate preferences. Among the proteins preferentially degraded by AsrA is the quorum-sensing anti-activator QslA, and we show that AsrA-dependent QslA degradation under tobramycin stress induces quorum-sensing gene expression. Together, our findings demonstrate how duplication of a conserved protease can generate specialized regulatory functions through differential expression and substrate preference, expanding the proteolytic network that enables bacterial adaptation to stress.

microbiology↗

bioRxiv2025

Widespread potential for phototrophy and convergent reduction of lifecycle complexity in the dimorphic order Caulobacterales

Model bacteria are fundamental for research, but knowledge about their ecology and evolution is often limited. Here we establish evolutionary and ecological context for the model organism Caulobacter crescentus--an alphaproteobacterium intensively studied for its dimorphic lifecycle. By analyzing the species relationships and genetic potential of hundreds of Caulobacterales species, we reveal striking diversity regarding their environmental distribution, morphology, cell development, and metabolism. Our work provides insights into the evolutionary history of morphological features such as the cell curvature determinant crescentin and uncovers a striking case of convergent loss of traits for cellular dimorphism among close relatives of C. crescentus. Moreover, we find that genes for phototrophy are widespread across Caulobacterales and that the new genus Acaudatibacter, described here, includes the first reported Caulobacterales lineage with photoautotrophic potential. Our study advances our understanding of an environmentally widespread bacterial order and sheds light onto the evolution of fundamental prokaryotic features.

microbiology↗

bioRxiv2023

Phosphate starvation decouples cell differentiation from DNA replication control in the dimorphic bacterium Caulobacter crescentus

Upon nutrient depletion, bacteria stop proliferating and undergo physiological and morphological changes to ensure their survival. Yet, how these processes are coordinated in response to distinct starvation conditions is poorly understood. Here we compare the cellular responses of Caulobacter crescentus to carbon (C), nitrogen (N) and phosphorus (P) starvation conditions. We find that DNA replication initiation and abundance of the replication initiator DnaA are, under all three starvation conditions, regulated by a common mechanism involving the inhibition of DnaA translation. By contrast, cell differentiation from a motile swarmer cell to a sessile stalked cell is regulated differently under the three starvation conditions. During C and N starvation, production of the signaling molecules (p)ppGpp is required to arrest cell development in the motile swarmer stage. By contrast, our data suggest that low (p)ppGpp levels under P starvation allow P-starved swarmer cells to differentiate into sessile stalked cells. Further, we show that limited DnaA abundance, and consequently absence of DNA replication initiation, is the main reason that prevents P-starved stalked cells from completing the cell cycle. Together, our findings demonstrate that C. crescentus decouples cell differentiation from DNA replication initiation under certain starvation conditions, two otherwise intimately coupled processes. We hypothesize that arresting the developmental program either as motile swarmer cells or as sessile stalked cells improves the chances of survival of C. crescentus during the different starvation conditions. Author SummaryBacteria frequently encounter periods of nutrient limitation. To ensure their survival, they dynamically modulate their own proliferation and cellular behaviors in response to nutrient availability. In many Alphaproteobacteria, progression through the cell cycle is tightly coupled to morphological transitions generating distinct cell types. Here, we show how starvation for either of the major nutrients carbon, nitrogen, or phosphorus affects this coupling between key cell cycle events and cell differentiation in the model bacterium Caulobacter crescentus. All three starvation conditions prevent cell proliferation by blocking DNA replication initiation. However, while carbon and nitrogen exhaustion cause cells to arrest the cell cycle as non-replicating motile cells, phosphorus starvation leads to accumulation of non-replicating sessile stalked cells. Our data demonstrate that starvation-dependent differences in (p)ppGpp signaling account for these different starvation responses. Together, our work provides insights into the mechanisms that allow bacteria to modulate their developmental program in response to changing environmental conditions.

microbiology↗

bioRxiv2022

The heat shock protein LarA activates the Lon protease at the onset of proteotoxic stress.

The Lon protease is a highly conserved protein degradation machine that has critical regulatory and protein quality control functions in cells from the three domains of life. Here, we report the discovery of a -proteobacterial heat shock protein, LarA, that functions as a dedicated Lon regulator. We show that LarA accumulates at the onset of proteotoxic stress and allosterically activates Lon-catalysed degradation of a large group of substrates through a five amino acid sequence at its C-terminus. Further, we find that LarA is regulated by Lon itself, which is critical to prevent toxic overactivation of Lon. We suggest that the temporal LarA-dependent activation of Lon helps to meet an increased proteolysis demand at the onset of protein unfolding stress. Our study defines a regulatory interaction of a conserved protease with a heat shock protein, serving as a paradigm of how protease activity can be tuned under changing environmental conditions.

molecular biology↗

bioRxiv2021

The Lon protease temporally restricts polar cell differentiation events during the Caulobacter cell cycle

The highly conserved protease Lon has important regulatory and protein quality control functions in cells from the three domains of life. Despite many years of research on Lon, only few specific protein substrates are known in most organisms. Here, we used a quantitative proteomics approach to identify novel substrates of Lon in the dimorphic bacterium Caulobacter crescentus. We focused our study on proteins involved in polar cell differentiation and investigated the developmental regulator StaR and the flagella hook length regulator FliK as specific Lon substrates in detail. We show that Lon recognizes these proteins at their C-termini, and that Lon-dependent degradation ensures their temporally restricted accumulation in the cell cycle phase when their function is needed. Disruption of this precise temporal regulation of StaR and FliK levels in a{Delta} lon mutant contributes to defects in stalk biogenesis and motility, respectively, revealing a critical role of Lon in coordinating developmental processes with cell cycle progression. Our work underscores the importance of Lon in the regulation of complex temporally controlled processes by adjusting the concentrations of critical regulatory proteins. Furthermore, this study includes the first characterization of FliK in C. crescentus and uncovers a dual role of the C-terminal amino acids of FliK in protein function and degradation.

microbiology↗

bioRxiv2021

A nascent polypeptide sequence modulates DnaA translation elongation in response to nutrient availability

The ability to regulate DNA replication initiation in response to changing nutrient conditions is an important feature of most cell types. In bacteria, DNA replication is triggered by the initiator protein DnaA, which has long been suggested to respond to nutritional changes, nevertheless the underlying mechanisms remain poorly understood. Here, we report a novel mechanism that adjusts DnaA synthesis in response to nutrient availability in Caulobacter crescentus. By performing a detailed biochemical and genetic analysis of the dnaA mRNA we identified a sequence downstream of the dnaA start codon that inhibits DnaA translation elongation upon carbon exhaustion. Our data show that the corresponding peptide sequence, but not the mRNA secondary structure or the codon choice, are critical for this response, suggesting that specific amino acids in the growing DnaA nascent chain tune translational efficiency. Our study provides new insights into DnaA regulation and highlights the importance of translation elongation as a regulatory target. We propose that nascent chain sequences, like the one described, might constitute a general strategy for modulating the synthesis rate of specific proteins under changing conditions.

microbiology↗

bioRxiv2020

The chaperonin GroESL facilitates Caulobacter crescentus cell division by supporting the function of the actin homologue FtsA

The highly conserved chaperonin GroESL performs a crucial role in protein folding, however the essential cellular pathways that rely on this chaperone are underexplored. Loss of GroESL leads to severe septation defects in diverse bacteria, suggesting the folding function of GroESL may be integrated with the bacterial cell cycle at the point of cell division. Here, we describe new connections between GroESL and the bacterial cell cycle, using the model organism Caulobacter crescentus. Using a proteomics approach, we identify candidate GroESL client proteins that become insoluble or are degraded specifically when GroESL folding is insufficient, revealing several essential proteins that participate in cell division and peptidoglycan biosynthesis. We demonstrate that other cell cycle events such as DNA replication and chromosome segregation are able to continue when GroESL folding is insufficient, and find that deficiency of the bacterial actin homologue FtsA function mediates the GroESL-dependent block in cell division. Our data suggest that a GroESL-FtsA interaction is required to maintain normal dynamics of the FtsZ scaffold and divisome functionality in C. crescentus. In addition to supporting FtsA function, we show that GroESL is required to maintain the flow of peptidoglycan precursors into the growing cell wall. Linking a chaperone to cell division may be a conserved way to coordinate environmental and internal cues that signal when it is safe to divide. ImportanceAll organisms depend on mechanisms that protect proteins from misfolding and aggregation. GroESL is a highly conserved molecular chaperone that functions to prevent protein aggregation in organisms ranging from bacteria to humans. Despite detailed biochemical understanding of GroESL function, the in vivo pathways that strictly depend on this chaperone remain poorly defined in most species. This study provides new insights into how GroESL is linked to the bacterial cell division machinery, a crucial target of current and future antimicrobial agents. We identify a functional interaction between GroESL and FtsA, a conserved bacterial actin homologue, suggesting that as in eukaryotes, some bacteria exhibit a connection between cytoskeletal actin proteins and chaperonins. Our work further defines how GroESL is integrated with cell wall synthesis, and illustrates how highly conserved folding machines ensure the functioning of fundamental cellular processes during stress.

microbiology↗

bioRxiv2018

Growth-driven displacement of protein aggregates along the cell length ensures partitioning to both daughter cells in Caulobacter crescentus

All living cells must deal with protein aggregation, which can occur as a result of experiencing stress. In the bacteria Escherichia coli and Mycobacterium smegmatis, aggregates collect at the cell poles and are retained over consecutive cell divisions only in the daughter cell that inherits the old pole, resulting in aggregation-free progeny within a few generations. Here we have studied the in vivo kinetics of aggregate formation and clearance following heat and antibiotic stress in Caulobacter crescentus, which divides by a pre-programmed asymmetric cell cycle. Unexpectedly, we find that aggregates do not preferentially collect at the cell poles, but form as multiple distributed foci throughout the cell volume. Time-lapse microscopy revealed that under moderate stress, the majority of protein aggregates are short-lived and rapidly dissolved by the major chaperone DnaK and the disaggregase ClpB. Severe stress or genetic perturbation of the protein quality machinery results in long-lived protein aggregates, which individual cells can only clear by passing on to their progeny. Importantly, these persistent aggregates are neither collected at the old pole over multiple generations nor inherited exclusively by the old pole-inheriting stalked cell, but instead are partitioned between both daughter cells during successive division events in the same ratio. Our data indicate that this symmetric mode of aggregate inheritance is driven by the elongation and division of the growing mother cell. In conclusion, our study revealed a new pattern of aggregate inheritance in bacteria.

microbiology↗