scholarly journals Bacterial evolution in high osmolarity environments

2020 ◽  
Author(s):  
Spencer Cesar ◽  
Maya Anjur-Dietrich ◽  
Brian Yu ◽  
Ethan Li ◽  
Enrique Rojas ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Carbon Source ◽  
Cell Size ◽  
Metagenomic Sequencing ◽  
Evolutionary Mechanisms ◽  
Nutrient Quality ◽  
Mean Cell Volume ◽  
High Osmolarity ◽  
Orthogonal Relationship

AbstractBacteria must maintain a cytosolic osmolarity higher than that of their environment in order to take up water. High osmolarity environments therefore present a formidable stress to bacteria. To explore the evolutionary mechanisms by which bacteria adapt to high osmolarity environments, we selected Escherichia coli in media with a variety of osmolytes and concentrations for 250 generations. Adaptation was osmolyte-dependent, with sorbitol stress generally resulting in increased fitness in conditions with higher osmolarity, while selection in high concentrations of proline resulted in increased fitness specifically on proline. Consistent with these phenotypes, sequencing of the evolved populations showed that passaging in proline resulted in specific mutations in an associated metabolic pathway that increases the ability to utilize proline for growth, while evolution in sorbitol resulted in mutations in many different genes that generally improve growth in high osmolarity conditions at the expense of growth at low osmolarity. High osmolarity decreased growth rate but increased mean cell volume compared with growth on proline as the sole carbon source, demonstrating that osmolarity-induced changes in growth rate and cell size follow an orthogonal relationship from the classical Growth Law relating cell size and nutrient quality. Isolates from a sorbitol-evolved population that capture the likely temporal sequence of mutations revealed by metagenomic sequencing demonstrate a tradeoff between growth at high and low osmolarity. Our study highlights the utility of experimental evolution for dissecting complex cellular networks and environmental interactions, particularly in the case of behaviors that can involve both specific and general metabolic stressors.ImportanceFor bacteria, maintaining higher internal solute concentrations than the environment allows cells to take up water. As a result, survival is challenging in high osmolarity environments. To investigate how bacteria adapt to high osmolarity environments, we evolved Escherichia coli in a variety of high osmolarity solutions for hundreds of generations. We found that evolved populations adopted different strategies to improve their growth depending on the osmotic passaging condition, either generally adapting to high osmolarity conditions or better metabolizing the osmolyte as carbon source. Single-cell imaging demonstrated that enhanced fitness was coupled to faster growth, and metagenomic sequencing revealed mutations that reflect growth tradeoffs across osmolarities. Our study demonstrates the utility of long-term evolution experiments for probing adaptation during environmental stress.

scholarly journals Bacterial Evolution in High-Osmolarity Environments

mBio ◽  
2020 ◽  
Vol 11 (4) ◽  
Author(s):  
Spencer Cesar ◽  
Maya Anjur-Dietrich ◽  
Brian Yu ◽  
Ethan Li ◽  
Enrique Rojas ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Carbon Source ◽  
Cell Size ◽  
Metagenomic Sequencing ◽  
Evolutionary Mechanisms ◽  
Mean Cell Volume ◽  
Content Type ◽  
High Osmolarity ◽  
Trade Offs

ABSTRACT Bacteria must maintain a cytosolic osmolarity higher than that of their environment in order to take up water. High-osmolarity environments therefore present formidable stress to bacteria. To explore the evolutionary mechanisms by which bacteria adapt to high-osmolarity environments, we selected Escherichia coli in media with a variety of osmolytes and concentrations for 250 generations. Adaptation was osmolyte dependent, with sorbitol stress generally resulting in increased fitness under conditions with higher osmolarity, while selection in high concentrations of proline resulted in increased fitness specifically on proline. Consistent with these phenotypes, sequencing of the evolved populations showed that passaging in proline resulted in specific mutations in an associated metabolic pathway that increased the ability to utilize proline for growth, while evolution in sorbitol resulted in mutations in many different genes that generally resulted in improved growth under high-osmolarity conditions at the expense of growth at low osmolarity. High osmolarity decreased the growth rate but increased the mean cell volume compared with growth on proline as the sole carbon source, demonstrating that osmolarity-induced changes in growth rate and cell size follow an orthogonal relationship from the classical Growth Law relating cell size and nutrient quality. Isolates from a sorbitol-evolved population that captured the likely temporal sequence of mutations revealed by metagenomic sequencing demonstrated a trade-off between growth at high osmolarity and growth at low osmolarity. Our report highlights the utility of experimental evolution for dissecting complex cellular networks and environmental interactions, particularly in the case of behaviors that can involve both specific and general metabolic stressors. IMPORTANCE For bacteria, maintaining higher internal solute concentrations than those present in the environment allows cells to take up water. As a result, survival is challenging in high-osmolarity environments. To investigate how bacteria adapt to high-osmolarity environments, we maintained Escherichia coli in a variety of high-osmolarity solutions for hundreds of generations. We found that the evolved populations adopted different strategies to improve their growth rates depending on the osmotic passaging condition, either generally adapting to high-osmolarity conditions or better metabolizing the osmolyte as a carbon source. Single-cell imaging demonstrated that enhanced fitness was coupled to faster growth, and metagenomic sequencing revealed mutations that reflected growth trade-offs across osmolarities. Our study demonstrated the utility of long-term evolution experiments for probing adaptation occurring during environmental stress.

scholarly journals H-NS Controls pap and daaFimbrial Transcription in Escherichia coli in Response to Multiple Environmental Cues

2000 ◽  
Vol 182 (22) ◽  
pp. 6391-6400 ◽  
Author(s):  
Christine A. White-Ziegler ◽  
Anuradha Villapakkam ◽  
Karla Ronaszeki ◽  
Sarah Young
Keyword(s):  
Escherichia Coli ◽  
Low Temperature ◽  
Carbon Source ◽  
Iron Concentration ◽  
Environmental Cues ◽  
Rich Medium ◽  
High Osmolarity ◽  
E Coli ◽  
Transcriptional Fusions

ABSTRACT A comparative study was completed to determine the influence of various environmental stimuli on the transcription of three different fimbrial operons in Escherichia coli and to determine the role of the histone-like protein H-NS in this environmental regulation. The fimbrial operons studied included the pap operon, which encodes pyelonephritis-associated pili (P pili), the daaoperon, which encodes F1845 fimbriae, and the fan operon, which encodes K99 fimbriae. Using lacZYA transcriptional fusions within each of the fimbrial operons, we tested temperature, osmolarity, carbon source, rich medium, oxygen levels, pH, amino acids, solid medium, and iron concentration for their effects on fimbrial gene expression. Low temperature, high osmolarity, glucose as a carbon source, and rich medium repressed transcription of all three operons. High iron did not alter transcription of any of the operons tested, whereas the remaining stimuli had effects on individual operons. For the pap and daa operons, introduction of thehns651 mutation relieved the repression, either fully or partially, due to low temperature, glucose as a carbon source, rich medium, and high osmolarity. Taken together, these data indicate that there are common environmental cues that regulate fimbrial transcription in E. coli and that H-NS is an important environmental regulator for fimbrial transcription in response to several stimuli.

scholarly journals Threshold effect of growth rate on population variability of Escherichia coli cell lengths

2017 ◽  
Vol 4 (2) ◽  
pp. 160417 ◽  
Author(s):  
Manasi S. Gangan ◽  
Chaitanya A. Athale
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Cell Size ◽  
Growth Rates ◽  
Threshold Effect ◽  
Cell Length ◽  
Replication Forks ◽  
E Coli ◽  
Cell Size Distributions ◽  
Rate Threshold

A long-standing question in biology is the effect of growth on cell size. Here, we estimate the effect of Escherichia coli growth rate ( r ) on population cell size distributions by estimating the coefficient of variation of cell lengths (CV L ) from image analysis of fixed cells in DIC microscopy. We find that the CV L is constant at growth rates less than one division per hour, whereas above this threshold, CV L increases with an increase in the growth rate. We hypothesize that stochastic inhibition of cell division owing to replication stalling by a RecA-dependent mechanism, combined with the growth rate threshold of multi-fork replication (according to Cooper and Helmstetter), could form the basis of such a threshold effect. We proceed to test our hypothesis by increasing the frequency of stochastic stalling of replication forks with hydroxyurea (HU) treatment and find that cell length variability increases only when the growth rate exceeds this threshold. The population effect is also reproduced in single-cell studies using agar-pad cultures and ‘mother machine’-based experiments to achieve synchrony. To test the role of RecA, critical for the repair of stalled replication forks, we examine the CV L of E. coli ΔrecA cells. We find cell length variability in the mutant to be greater than wild-type, a phenotype that is rescued by plasmid-based RecA expression. Additionally, we find that RecA-GFP protein recruitment to nucleoids is more frequent at growth rates exceeding the growth rate threshold and is further enhanced on HU treatment. Thus, we find growth rates greater than a threshold result in increased E. coli cell lengths in the population, and this effect is, at least in part, mediated by RecA recruitment to the nucleoid and stochastic inhibition of division.

Effect of carbon source on growth rate and phospholipid composition of Escherichia coli 15T− and an unsaturated fatty acid auxotroph

1981 ◽  
Vol 27 (12) ◽  
pp. 1283-1289 ◽  
Author(s):  
James E. Urban ◽  
W. E. Klopfenstein ◽  
K. Ahmad ◽  
J. D. Baines
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Fatty Acid Composition ◽  
Oleic Acid ◽  
Fatty Acid ◽  
Carbon Source ◽  
Acid Composition ◽  
Doubling Time ◽  
Phospholipid Composition ◽  
Acid Supplementation

Escherichia coli 15T− was grown with glucose, succinic acid, aspartic acid, oleic acid, and oleic plus aspartic acids as carbon sources, and a fatty acid auxotroph derived from 15T− was grown on oleic acid and oleic plus aspartic acids. The doubling time, phospholipid composition, phosphorus content, and the fatty acid composition of the phospholipids of cells in each of the media were determined. In all cases, phosphatidylethanolamine was the major phospholipid present; but with 15T− its concentration was inversely proportional to the doubling time in unsupplemented media. With the auxotroph the phosphatidylethanolamine concentration was essentially unchanged with growth. Total lipid phosphorus was inversely proportional to doubling time, an effect particularly evident with the auxotroph. Without oleic acid supplementation, the major effects of carbon source on fatty acid composition are decreases in the content of palmitoleic acid and increases in the content of cis-9,10-methylene hexadecanoic acid as growth rate decreases. Oleic acid supplementation elevated 18:1 fatty acid content in both 15T− and the auxotroph.

scholarly journals Quantitative Connection between Cell Size and Growth Rate by Phospholipid Metabolism

Cells ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 391 ◽  
Author(s):  
Zhichao Zhang ◽  
Qing Zhang ◽  
Shaohua Guan ◽  
Hualin Shi
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Cell Size ◽  
Flux Balance Analysis ◽  
Phospholipid Metabolism ◽  
Cell Length ◽  
Synthesis Rate ◽  
Phospholipid Synthesis ◽  
Flux Balance ◽  
Balance Analysis

The processes involved in cell growth are extremely complicated even for a single cell organism such as Escherichia coli, while the relationship between growth rate and cell size is simple. We aimed to reveal the systematic link between them from the aspect of the genome-scale metabolic network. Since the growth rate reflects metabolic rates of bacteria and the cell size relates to phospholipid synthesis, a part of bacterial metabolic networks, we calculated the cell length from the cardiolipin synthesis rate, where the cardiolipin synthesis reaction is able to represent the phospholipid metabolism of Escherichia coli in the exponential growth phase. Combined with the flux balance analysis, it enables us to predict cell length and to examine the quantitative relationship between cell length and growth rate. By simulating bacteria growing in various nutrient media with the flux balance analysis and calculating the corresponding cell length, we found that the increase of the synthesis rate of phospholipid, the cell width, and the protein fraction in membranes caused the increase of cell length with growth rate. Different tendencies of phospholipid synthesis rate changing with growth rate result in different relationships between cell length and growth rate. The effects of gene deletions on cell size and growth rate are also examined. Knocking out the genes, such as Δ tktA, Δ tktB, Δ yqaB, Δ pgm, and Δ cysQ, affects growth rate largely while affecting cell length slightly. Results of this method are in good agreement with experiments.

scholarly journals Genome-wide phenotypic analysis of growth, cell morphogenesis and cell cycle events in Escherichia coli.

2017 ◽  
Author(s):  
Manuel Campos ◽  
Sander K Govers ◽  
Irnov Irnov ◽  
Genevieve S Dobihal ◽  
Francois Cornet ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Cycle ◽  
Growth Rate ◽  
Cell Division ◽  
Cell Size ◽  
Gene Knockout ◽  
Single Gene ◽  
Cell Morphogenesis ◽  
Phenotypic Analysis ◽  
New Genes

Cell size, cell growth and the cell cycle are necessarily intertwined to achieve robust bacterial replication. Yet, a comprehensive and integrated view of these fundamental processes is lacking. Here, we describe an image-based quantitative screen of the single-gene knockout collection of Escherichia coli, and identify many new genes involved in cell morphogenesis, population growth, nucleoid (bulk chromosome) dynamics and cell division. Functional analyses, together with high-dimensional classification, unveil new associations of morphological and cell cycle phenotypes with specific functions and pathways. Additionally, correlation analysis across ~4,000 genetic perturbations shows that growth rate is surprisingly not predictive of cell size. Growth rate was also uncorrelated with the relative timings of nucleoid separation and cell constriction. Rather, our analysis identifies scaling relationships between cell size and nucleoid size and between nucleoid size and the relative timings of nucleoid separation and cell division. These connections suggest that the nucleoid links cell morphogenesis to the cell cycle.

scholarly journals A conserved Lkb1 signaling axis modulates TORC2 signaling in budding yeast

2018 ◽  
Author(s):  
Maria Alcaide-Gavilán ◽  
Rafael Lucena ◽  
Katherine Schubert ◽  
Karen Artiles ◽  
Jessica Zapata ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Growth ◽  
Carbon Source ◽  
Cell Size ◽  
Nutrient Availability ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Small Cells ◽  
Cycle Progression

ABSTRACTNutrient availability, growth rate and cell size are closely linked. For example, in budding yeast, the rate of cell growth is proportional to nutrient availability, cell size is proportional to growth rate, and growth rate is proportional to cell size. Thus, cells grow slowly in poor nutrients and are nearly half the size of cells growing in rich nutrients. Moreover, large cells grow faster than small cells. A signaling network that surrounds Tor kinase complex 2 (TORC2) plays an important role in enforcing these proportional relationships. Cells that lack components of the TORC2 network fail to modulate their growth rate or size in response to changes in nutrient availability. Here, we show that budding yeast homologs of the Lkb1 tumor suppressor kinase are required for normal modulation of TORC2 signaling and in response to changes in carbon source. Lkb1 kinases activate Snf1/AMPK to initiate transcription of genes required for utilization of poor carbon sources. However, Lkb1 influences TORC2 signaling via a novel pathway that is independent of Snf1/AMPK. Of the three Lkb1 homologs in budding yeast, Elm1 plays the most important role in modulating TORC2. Elm1 activates a pair of related kinases called Gin4 and Hsl1. Previous work found that loss of Gin4 and Hsl1 causes cells to undergo unrestrained growth during a prolonged mitotic arrest, which suggests that play a role in linking cell cycle progression to cell growth. We found that Gin4 and Hsl1 also control the TORC2 network. In addition, Gin4 and Hsl1 are themselves influenced by signals from the TORC2 network, consistent with previous work showing that the TORC2 network constitutes a feedback loop. Together, the data suggest a model in which the TORC2 network sets growth rate in response to carbon source, while also relaying signals via Gin4 and Hsl1 that set the critical amount of growth required for cell cycle progression. This kind of close linkage between control of cell growth and size would suggest a simple mechanistic explanation for the proportional relationship between cell size and growth rate.

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