Exponential Growth Stage Research Articles

Growth-phase-dependent control of rRNA synthesis in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is one of the most well-studied model organisms used in the scientific community. Its ease of manipulation, accessible growth conditions, short life cycle, and conserved eukaryotic metabolic pathways make it a useful model organism. Consequently, yeast has been used to investigate a myriad of phenomena, from microbial to human studies. Most of the research performed using this model organism utilizes yeast cell populations when they are growing exponentially, a growth phase aptly termed exponential or log phase. However, log phase encompasses several yeast generations and ranges several hours of yeast growth, meaning that there is a potential for variability during this "homogenous" growth phase. Cells in log phase require robust ribosome biogenesis to support their rapid growth and cell division. Interestingly, during log phase, ribosomal RNA (rRNA) synthesis (which is the first and rate limiting step in ribosome biosynthesis) has been shown to decrease prior to growth rate decline in stationary phase. In this study, we utilized several genomic and biochemical methods to elucidate the relationship between subphases of log phase and rRNA synthesis. Our results indicate that as yeast cells progress through subphases of log growth, both polymerase I transcription and rRNA processing are repressed. Overall, this study establishes a growth-phase-dependent control of rRNA synthesis that unexpectedly begins prior to the switch to stationary phase (i.e., pre-diauxic shift) as a putative mechanism of anticipating nutrient starvation.IMPORTANCESaccharomyces cerevisiae is a ubiquitously used model organism in a wide range of scientific research fields. The conventional practice when performing yeast studies is to investigate its properties during logarithmic growth phase. This growth phase is defined as the period during which the cell population doubles at regular intervals, and nutrients are not limiting. However, this growth phase lasts hours and encompasses several yeast cell generations which consequently introduce heterogeneity to log growth phase depending on their time of harvest. This study reveals significant changes in the transcriptomic landscape even in early stages of exponential growth. The overall significance of this work is the revelation that even the seemingly homogenous log growth phase is far more diverse than was previously believed.

Impact of the expansion ratio on the properties of hydrogen recirculation ejectors

Exploring the development characteristics and influencing factors of the mixing layer (ML) inside the hydrogen recirculation ejector is of great importance for enhancing the recirculation properties of the ejector and promoting green and sustainable energy development. However, the evolution of ML in the ejector and the transport and diffusion characteristics of the fluid are problematic, in particular, the influence of the expansion ratio on the properties of the ejector is unclear. Therefore, in this study, a CFD numerical model of an ejector was established to simulate the flow of fluids in the ejector. The evolution of ML was elucidated, and the interaction mechanism between the mixing and the recirculation performance of the ejector was revealed. The findings showed that the velocity difference is a significant driving force for the development of ML, and the formation of an adverse pressure gradient contributes to the diffusion of hydrogen and the rapid development of ML. The development process of ML in the ejector can be divided into three stages under the interaction of the velocity difference and the convective Mach number: the rapid growth stage, the slow growth stage, and the exponential growth stage. By studying the evolution of ML at different expansion ratios, it was found that there exists a critical expansion ratio for the ejector, which results in the largest of the non-mixing length ratio and the effective mixing thickness, the strongest relative mass transfer capability of the entrained flow, the fullest development of ML, and the optimal hydrogen recirculation performance.

Regulation of the PFK1 gene on the interspecies microbial competition behavior of Saccharomyces cerevisiae

Saccharomyces cerevisiae is a widely used strain for ethanol fermentation; meanwhile, efficient utilization of glucose could effectively promote ethanol production. The PFK1 gene is a key gene for intracellular glucose metabolism in S. cerevisiae. Our previous work suggested that although deletion of the PFK1 gene could confer higher oxidative tolerance to S. cerevisiae cells, the PFK1Δ strain was prone to contamination by other microorganisms. High interspecies microbial competition ability is vital for the growth and survival of microorganisms in co-cultures. The result of our previous studies hinted us a reasonable logic that the EMP (i.e., the Embden-Meyerhof-Parnas pathway, the glycolytic pathway) key gene PFK1 could be involved in regulating interspecies competitiveness of S. cerevisiae through the regulation of glucose utilization and ethanol production efficiency. The results suggest that under 2% and 5% glucose, the PFK1Δ strain showed slower growth than the S288c wild-type and TDH1Δ strains in the lag and exponential growth stages, but realized higher growth in the stationary stage. However, relative high supplement of glucose (10%) eliminated this phenomenon, suggesting the importance of glucose in the regulation of PFK1 in yeast cell growth. Furthermore, during the lag growth phase, the PFK1Δ strain displayed a decelerated glucose consumption rate (P < 0.05). The expression levels of the HXT2, HXT5, and HXT6 genes decreased by approximately 0.5-fold (P < 0.05) and the expression level of the ZWF1 exhibited a onefold increase in the PFK1Δ strain compared to that in the S. cerevisiae S288c wild-type strain (P < 0.05).These findings suggested that the PFK1 inhibited the uptake and utilization of intracellular glucose by yeast cells, resulting in a higher amount of residual glucose in the medium for the PFK1Δ strain to utilize for growth during the reverse overshoot stage in the stationary phase. The results presented here also indicated the potential of ethanol as a defensive weapon against S. cerevisiae. The lower ethanol yield in the early stage of the PFK1Δ strain (P < 0.001) and the decreased expression levels of the PDC5 and PDC6 (P < 0.05), which led to slower growth, resulted in the strain being less competitive than the wild-type strain when co-cultured with Escherichia coli. The lower interspecies competitiveness of the PFK1Δ strain further promoted the growth of co-cultured E. coli, which in turn activated the ethanol production efficiency of the PFK1Δ strain to antagonize it from E. coli at the stationary stage. The results presented clarified the regulation of the PFK1 gene on the growth and interspecies microbial competition behavior of S. cerevisiae and would help us to understand the microbial interactions between S. cerevisiae and other microorganisms.Key points• PFK1Δ strain could realize reverse growth overshoot at the stationary stage• PFK1 deletion decreased ethanol yield and interspecific competitiveness• Proportion of E. coli in co-culture affected ethanol yield capacity of yeast cells

Effect of a cyclonic eddy on phytoplankton: A bioassay experiment

AbstractCyclonic eddies often increase the primary productivity of marine ecosystems. However, the study of their influence on the taxonomic structure and productivity of plankton is complex due to the short‐term and mesoscale nature of the action of eddies. In a laboratory bioassay experiment, we simulated two mechanisms of eddy's effect on the deep phytoplankton maximum: an increase in the upward flow of deep nutrients and illumination. Doubling of nutrient additions compared to control increased chlorophyll's specific growth rate (SGR) 1.7‐fold over 12 days while doubling the light intensity increased SGR by 3.5 times. During the first 4 days of the experiment, at the exponential growth stage, SGR of carbon biomass was maximum with the simultaneous doubling of nutrients and light (0.44 day−1). It was statistically significantly higher than at increased nutrients but not light. These results suggest that nutrient deficiencies were less crucial for phytoplankton growth than light. The increase in the phytoplankton biomass was mainly due to the growth of a large‐celled diatom Pseudosolenia calcar‐avis. It showed the highest SGR (1.15–1.28 day−1) at increased nutrients and/or light, resulting in high wet biomass of 2–3 g m−3 over 4 days. The ecological meaning of the obtained results is as follows. First, in the eddy, where the deep phytoplankton maximum is located close to the nutricline, its rise to more illuminated layers results in higher phytoplankton growth than the shortening distance to the nutricline. Second, increases in the upward flow of nutrients and light intensity, separate or simultaneous, stimulate the rapid reproduction of large‐celled diatoms that increase the carbon‐to‐chlorophyll ratio by 2–4 times. Third, exposure to a typical Black Sea mesoscale cyclonic eddy can lead to phytoplankton blooms in the thermocline within a few days.

Explosive Growth of Asymmetric Disturbances in a Flow with Vertical Shear

The classical problem of geophysical hydrodynamics is the problem of the instability of a zonal geostrophic flow with a vertical velocity shear. At present, the instability with respect to symmetric perturbations that do not depend on the coordinate along the flow has been most thoroughly studied. For a symmetric instability to arise, the two-dimensional perturbation wave vector must lie inside a certain sector in the vertical plane of the wave numbers. In this paper, we study the instability with respect to asymmetric perturbations oriented at an angle to the flow. Fundamentally new features of the temporal dynamics of the amplitudes of such perturbations are found. The main feature is associated with the existence of a stage of exponential explosive growth of finite duration. A kinematic interpretation of this stage is given, which is related to the passage of the vertical projection of the perturbation wave vector through the sector of symmetric instability.

Combining AFM, XPS and chemical hydrolysis to understand the complexity and dynamics of C. vulgaris cell wall composition and architecture

The microalgae cell wall represents its interface with its environment, and is a dynamic and complex structure that evolves depending on the growth phase or culture conditions. To apprehend this complexity, an experimental approach combining AFM, XPS, and chemical hydrolysis followed by HPAEC-PAD was developed to understand the cell wall of Chlorella vulgaris, a biotechnologically-relevant green microalgae species. Exponential and stationary growth stages were investigated, as well as saline stress condition inducing lipid production. Results showed that both the cell wall composition and architecture changes in stationary phase, with an increase of the lipidic fraction at the expense of the proteic fraction, changes in the polysaccharidic composition, and a significant increase of its rigidity. Under saline stress, cell wall architecture seems to be affected as importantly, its rigidity is reduced. Altogether, this study demonstrates the power of combining these three techniques to give new insights into C. vulgaris cell wall, in terms of composition and architecture, and of its dynamics in different conditions.

Shear Flow Instability over a Finite Time Interval

Within the framework of a discrete quasi-geostrophic model with two vertical levels, the problem of linear stability of the flow of a stratified rotating fluid with constant vertical and horizontal velocity shifts is solved. It is shown that taking into account the horizontal shear leads to a qualitative change in the dynamics of unstable wave disturbances. The main feature is related to the effect of temporary exponential growth of unstable perturbations, i.e. growth over a finite time period. This effect manifests itself in the alternation of stages of smooth oscillating behavior (in time) with stages of exponential (explosive) growth of finite duration. A kinematic interpretation of the effect of temporal exponential growth is given, which is associated with the passage of a time-dependent perturbation wave vector through the region of exponential instability that exists in the absence of a horizontal shear. It is shown that mathematically this effect is described by solutions of a second-order differential equation containing turning points. Asymptotic solutions of the equation are given for weak horizontal shifts.

Predicting the evolution of static yield stress with time of blended cement paste through a machine learning approach

Predicting the static yield stress (τ0S) is relevant to design innovative concrete technologies. This paper evaluated three machine learning methods to choose the most accurate model to predict the growth of τ0S of blended cement pastes. Eight input parameters were used, including supplementary cementitious material (SCM) properties, cement reactivity, mixture design parameters, and resting time. Among the evaluated methods, the multilayer perceptron was the most accurate. Results showed that τ0S during the initial linear growth stage is controlled by the SCM properties. However, the τ0S during the later exponential growth stage is controlled by the amount of pseudo-contact zones.

Constitutive Expression of a Cytotoxic Anticancer Protein in Tumor-Colonizing Bacteria.

Bacterial cancer therapy is a promising next-generation modality to treat cancer that often uses tumor-colonizing bacteria to deliver cytotoxic anticancer proteins. However, the expression of cytotoxic anticancer proteins in bacteria that accumulate in the nontumoral reticuloendothelial system (RES), mainly the liver and spleen, is considered detrimental. This study examined the fate of the Escherichia coli strain MG1655 and an attenuated strain of Salmonella enterica serovar Gallinarum (S. Gallinarum) with defective ppGpp synthesis after intravenous injection into tumor-bearing mice (~108 colony forming units/animal). Approximately 10% of the injected bacteria were detected initially in the RES, whereas approximately 0.01% were in tumor tissues. The bacteria in the tumor tissue proliferated vigorously to up to 109 colony forming units/g tissue, whereas those in the RES died off. RNA analysis revealed that tumor-associated E. coli activated rrnB operon genes encoding the rRNA building block of ribosome needed most during the exponential stage of growth, whereas those in the RES expressed substantially decreased levels of this gene and were cleared soon presumably by innate immune systems. Based on this finding, we engineered ΔppGpp S. Gallinarum to express constitutively a recombinant immunotoxin comprising TGFα and the Pseudomonas exotoxin A (PE38) using a constitutive exponential phase promoter, the ribosomal RNA promoter rrnB P1. The construct exerted anticancer effects on mice grafted with mouse colon (CT26) or breast (4T1) tumor cells without any notable adverse effects, suggesting that constitutive expression of cytotoxic anticancer protein from rrnB P1 occurred only in tumor tissue.

Minimizing the Lag Phase of Cupriavidus necator Growth under Autotrophic, Heterotrophic, and Mixotrophic Conditions.

Cupriavidus necator has the unique metabolic capability to grow under heterotrophic, autotrophic, and mixotrophic conditions. In the current work, we examined the effect of growth conditions on the metabolic responses of C. necator. In our lab-scale experiments, autotrophic growth was rapid, with a short lag phase as the exponential growth stage was initiated in 6 to 12 h. The lag phase extended significantly (>22 h) at elevated O2 and CO2 partial pressures, while the duration of the lag phase was independent of the H2 or N2 partial pressure. Under heterotrophic conditions with acetate as the organic substrate, the lag phase length was short (<12 h), but it increased with increasing acetate concentrations. When glucose and glycerol were provided as the organic substrate, the lag phase was consistently long (>12 h) regardless of the examined substrate concentrations (up to 10.0 g/L). In the transition experiments, C. necator cells showed rapid transitions from autotrophic to heterotrophic growth in less than 12 h and vice versa. Our experimental results indicate that C. necator can rapidly grow with both autotrophic and heterotrophic substrates, while the lag time substantially increases with nonacetate organic substrates (e.g., glucose or glycerol), high acetate concentrations, and high O2 and CO2 partial pressures. IMPORTANCE The current work investigated the inhibition of organic and gaseous substrates on the microbial adaption of Cupriavidus necator under several metabolic conditions commonly employed for commercial polyhydroxyalkanoate production. We also proposed a two-stage cultivation system to minimize the lag time required to change over between the heterotrophic, autotrophic, and mixotrophic pathways.

Regulation of Lysozyme Activity by Human Hormones

Lysozyme is a part of human and animal noncellular immunity. The regulation of its activity by hormones is poorly studied. The aim of this study was to test the in vitro activity of lysozyme in the presence of catecholamines, natriuretic hormones, and estradiol (E2). Hormones were incubated with lysozyme, and the activity of lysozome was further determined using a test culture of Micrococcus luteus in the early exponential growth stage. The activity of lysozyme was assessed based on the rate of change in the OD of the test culture. Molecular docking was performed using SwissDock server http://www.swissdock.ch/docking), and molecular structures were further analyzed and visualized in the UCSF Chimera 1.15rc software. According to the results, epinephrine and norepinephrine increased lysozyme activity up to 180% compared to the hormone-free enzyme. Changing the pH of the medium from 6.3 to 5.5, increased the lysozyme activity in the presence of E2 up to 150-200 %. The results also showed that exposure to hormones could modify lysozyme ctivity, and this effect depends on the temperature and pH value. The molecular docking revealed a decrease in the activation energy of the active site of enzyme during the interaction of catecholamines with the amino acid residues, asp52 and glu35 of the active site. Our findings demonstrate an additional mechanism for the involvement of lysozyme in humoral regulation of nonspecific immunity with respect to human pathogenic microflora and bacterial skin commensals by direct modulation of its activity using human hormones.

Recycling of Glass Waste by Deposition of TiO2 for the Intensification of the Photocatalytic Effect in the Purification of Wastewater

In this study, the photocatalytic effect of TiO2 (1 wt. % and 3 wt. %) deposited on the surface of sintered cathode ray tube glass was examined, as well as its effect on an E. coli strain (BL21(DE3)). DTA analysis indicated the sintering temperature for samples to be 820 °C while scanning electron microscopy (SEM)showed an intimate contact and a strong interface between the support and photocatalyst. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was employed to establish the chemical and bonding environment of the samples. The investigations of the bacterial viability were conducted using flow cytometry, a specific cellular viability assay, while bacterial growth was measured using the turbidimetric method. The experimental results show the influence of the TiO2 concentration on the bacterial inactivation process: higher concentrations (3% wt.) have a bactericidal effect in the long term, whereas lower concentrations (1% wt.) render them inactive for a shorter time in the exponential growth stage. The preliminary results were used to calculate the efficiency of microbial inactivation and the parameters of the kinetics of inactivation using ANOVA software. The results indicate that this material could be an effective solution for water disinfection.

Effect of free ammonia shock on Chlorella sp. in wastewater: Concentration-dependent activity response and enhanced settleability

The unstable microbial activity and unsatisfactory settling performance impede the development and implementation of microalgal wastewater treatment, especially in high-ammonium wastewater in the presence of free ammonia (FA). The shock of FA due to the nutrient fluctuation in wastewater was demonstrated as the primary stress factor suppressing microalgal activities. Recent study has clearly revealed the inhibition mechanism of FA at a specific high level (110.97 mg/L) by inhibiting the genetic information processing, photosynthesis, and nutrient metabolism. However, the effects of various FA shock concentrations on microalgal activities and settling performance remain unknown, limiting the wastewater bioremediation efficiencies improvement and the process development. Herein, a concentration-dependent shock FA (that was employed on microalgae during their exponential growth stages) effect on microalgal growth and photosynthesis was observed. Results showed that the studied five FA shock concentrations ranging from 25 to 125 mg/L significantly inhibited biomass production by 14.7–57.0%, but sharp reductions in photosynthesis with the 36.0–49.0% decreased Fv/Fm values were only observed when FA concentration was above 75.0 mg/L. On the other hand, FA shock enhanced microalgal settling efficiency by 12.8-fold, which was believed to be due to the stimulated intra- and extracellular protein contents and thereby the enhanced extracellular polymer substances (EPS) secretion. Specifically, FA shock induced 40.2 ± 2.3% higher cellular protein content at the cost of the decreased carbohydrates (22.6 ± 1.3%) and fatty acid (39.0 ± 0.8%) contents, further improving the protein secretion by 1.21-fold and the EPS production by 40.2 ± 2.3%. These FA shock-induced variations in intra- and extracellular biomolecules were supported by the up-regulated protein processing and export at the assistance of excessive energy generated from fatty acid degradation and carbohydrates consumption. In addition, FA shock significantly decreased the biomass nutritional value as indicated by the 1.86-fold lower essential amino acid score and nearly 50% reduced essential to non-essential amino acids ratio, while slightly decreased the biodiesel quality. This study is expected to enrich the knowledge of microalgal activities and settling performance in response to fluctuant ammonium concentrations in wastewater and to promote the development of microalgal wastewater treatment.

ОСОБЕННОСТИ ОПУХОЛЕВЫХ КЛЕТОК ЧЕЛОВЕКА ЛИНИИ HeLa,ВЫЖИВШИХ И ДАВШИХ УСТОЙЧИВЫЙ РОСТ ПОСЛЕ ОСТРОГО РЕНТГЕНОВСКОГО ОБЛУЧЕНИЯ

Purpose: The evaluation of the repair efficiency of DNA double-strand breaks (DSB), proliferative activity and the yield of cytogenetic disorders in human tumor HeLa cells which survived and gave stable growth after acute irradiation at a dose of 15 Gy. Material and methods: HeLa human tumor cell line (cervical carcinoma) was used. Cells were irradiated on an X-ray biological installation RUST-M1 (Russia), equipped with two X-ray emitters, at a dose rate of 0.85 Gy / min, a voltage of 200 kV, a total current of 10 mA, and a 1.5 mm Al filter. To obtain clones of surviving cells (HeLaRR), after acute irradiation at a dose of 15 Gy, cell cultures were incubated under standard CO2 incubator conditions (37 °C, 5 % CO2) for several weeks until well proliferating cells were obtained. Immunocytochemical staining of the foci of the phosphorylated H2AX protein (γH2AX) was used to quantitatively evaluate the residual foci of DNA DSB repair. The micronuclei number was assessed in cytochalasin-B cytokinesis-blocked binucleated cells stained with acridine orange with luminescence microscopy. The doubling time of the cell population was analyzed by the cell growth curves obtained by daily cell counting for five days. The cell cycle stages distribution was assessed by flow cytometry using the propidium iodide dye. All quantitative indicators of the studies were processed using the Student’s t-test for independent samples and the Kolmogorov – Smirnov test. Results: It was revealed that acute irradiation at a high dose leads to the selection of cells with a higher reparative capacity which is confirmed by the low yield of residual foci of DNA DSB repair and MN after testing irradiation at doses of 5 and 10 Gy. A significant decrease in the proliferative activity of cells that survived after acute X-ray irradiation at a dose of 15 Gy was revealed. The doubling time of the population of unirradiated cells at the stage of exponential growth was ~18 hours while for cells that survived after irradiation at a dose of 15 Gy ~42 hours. A change in the cell cycle phases distribution was observed. Conclusion: Thus, acute irradiation at a high dose leads to the selection of cells with a higher reparative capacity which is confirmed by the low yield of residual γH2AX foci and MN after testing irradiation at doses of 5 and 10 Gy. The decrease in proliferative activity was accompanied by a change in the cell cycle phases distribution.

Discrete Boltzmann modeling of Rayleigh-Taylor instability: Effects of interfacial tension, viscosity, and heat conductivity.

The two-dimensional Rayleigh-Taylor instability (RTI) in compressible flow with intermolecular interactions is probed via the discrete Boltzmann method. The effects of interfacial tension, viscosity, and heat conduction are investigated. It is found that the influences of interfacial tension on the perturbation amplitude, bubble velocity, and two kinds of entropy production rates all show differences at different stages of RTI evolution. It inhibits the RTI evolution at the bubble acceleration stage, while at the asymptotic velocity stage, it first promotes and then inhibits the RTI evolution. Viscosity and heat conduction inhibit the RTI evolution. Viscosity shows a suppressive effect on the entropy generation rate related to heat flow at the early stage but a first promotive and then suppressive effect on the entropy generation rate related to heat flow at a later stage. Heat conduction shows a promotive effect on the entropy generation rate related to heat flow at an early stage. Still, it offers a first promotive and then suppressive effect on the entropy generation rate related to heat flow at a later stage. By introducing the morphological boundary length, we find that the stage of exponential growth of the interface length with time corresponds to the bubble acceleration stage. The first maximum point of the interface length change rate and the first maximum point of the change rate of the entropy generation rate related to viscous stress can be used as a criterion for RTI to enter the asymptotic velocity stage.

Model of pulsar pair cascades in non-uniform electric fields: Growth rate, density profile, and screening time

Time-dependent cascades of electron–positron pairs are thought to be the main source of plasma in pulsar magnetospheres and a primary ingredient to explain the nature of pulsar radio emission, a long-standing open problem in high-energy astrophysics. During these cascades—positive feedback loops of gamma-ray photon emission via curvature radiation by TeV electrons and positrons and pair production—the plasma self-consistently develops inductive waves that couple to electromagnetic modes capable of escaping the pulsar dense plasma. In this work, we present an analytical description of pair cascades relevant in pulsars, including their onset, exponential growth, and saturation stages. We study this problem in the case of a background linear electric field, relevant in pulsar polar caps, and using an heuristic model of the pair production process. The analytical results are confirmed with particle-in-cell simulations performed with the OSIRIS code that include heuristic pair production.

Tribological behaviour of AISI 1045 carbon steel in metalworking fluid containing Pseudomonas pseudoalcaligenes

AbstractThe microbial contamination of metalworking fluid (MWF) has been increasingly recognised as an issue in the machining industry. To investigate the effects of microbes on the tribological behaviour of AISI 1045 carbon steel in the MWF, a strain of Pseudomonas pseudoalcaligenes was isolated from waste metalworking fluid (WMWF). The biodegradation of MWF and the tribological behaviour of carbon steel in MWF in the presence of bacteria and its extracellular polymeric substances (EPS) were studied. The results showed that the buffer agent and emulsifier were severely biodegraded. The lubricity of the MWF increased first and then dramatically decreased, resulting in a similar trend for the wear of carbon steel in MWF upon prolonging the culture time. The wear mechanism of carbon steel involved a transformation from abrasive wear into tribo‐corrosion wear. Remarkably, the lubricity of the MWF was enhanced during the exponential microbial growth stage due to the synergistic reduction in friction by the layer of adsorbed EPS and the additive layer.

Aggregation Kinetics of Polysorbate 80/m-Cresol Solutions: A Small-Angle Neutron Scattering Study.

Polysorbate 80 (PS80), a nonionic surfactant used in pharmaceutical formulation, is known to be incompatible with m-cresol, an antimicrobial agent for multi-dose injectable formulations. This incompatibility results in increased turbidity caused by micelle aggregation progressing over weeks or longer, where storage temperature, ionic strength, and component concentration influence the aggregation kinetics. Small-angle neutron scattering (SANS) analysis of PS80/m-cresol solutions over a pharmaceutically relevant concentration range of each component reveals the cause of aggregation, the coalescence mechanism, and aggregate structure. PS80 solutions containing m-cresol concentrations below ≈2.0 mg/mL and above ≈4.5 mg/mL are kinetically stable and do not aggregate over a 50 h period. At 5 mg/mL of m-cresol, the mixture forms a kinetically stable microemulsion phase, despite being well below the aqueous solubility limit of m-cresol. Solutions containing intermediate m-cresol concentrations (2.0-4.5 mg/mL) are unstable, resulting in aggregation, coalescence, and eventual phase separation. In unstable solutions, two stages of aggregate growth (nucleation and power-law growth) are observed at m-cresol concentrations at or below ≈3.6 mg/mL. At higher m-cresol concentrations, aggregates experience a third stage of exponential growth. A single kinetic model is developed to explain the stages of aggregate growth observed in both kinetic mechanisms. This work establishes the phase diagram of PS80/m-cresol solution stability and identifies component concentrations necessary for producing stable formulations.

Microbiome Associated With Gambierdiscus balechii Cultures Under Different Toxicity Conditions

Dinoflagellates, including harmful algal bloom species, are known to co-exist with and rely upon bacteria but how the microbiome changes with the physiologies of the cognate dinoflagellates is poorly understood. Here, we used 16S rRNA gene meta-barcoding to characterize the bacterial community in the cultures of Gambierdiscus balechii, a ciguatoxin-producing benthic dinoflagellate, under different nitrogen (N)-nutrient conditions and at different ciguatoxin-producing growth. The high-throughput sequencing of a total of 12 libraries generated 926,438 reads which were classified into 16 phyla. We observed a shift of the G. balechii-associated microbiome from N-replete to low-N conditions and from the early (low toxin) to the late exponential (high toxin) growth stage. Common across these conditions were species from families Rhodobacteraceae and Flavobacteriaceae. Species abundant in the low-N condition mainly included Planctomyces, Ekhidna, and Lactobacillus. Dominant or highly abundant microbial taxa in the high toxin-producing stage (N-replete, late exponential stage) were Oceanococcus and Marinoscillum. Under this condition, one Rhizobiales bacterium, Oricola, also increased in relative abundance. Our study documents the high diversity and dynamics of the G. balechii-associated microbiome, and identifies condition-specific sub-communities: the core (constitutive) microbiome that stably co-exists with G. balechii, the bacterial lineages that are responsive to N-nutrient variations, and species whose abundances are correlated with toxin content of the dinoflagellate. These findings demonstrate that particular bacterial groups are responsive to N-nutrient or toxicity changes of G. balechii and thus will be useful for further investigations on the associated microbiome’s interactions with benthic dinoflagellates and functions in the course of benthic harmful algae blooms.

In situ experimental study on the solubility and crystallization of zabuyelite (Li2CO3) in aqueous solution under igneous conditions

Zabuyelite (Li2CO3) was discovered in sedimentary environments, but it can form in igneous environments (e.g., rare-element pegmatites). This experiment extends the solubility and crystallization behaviors of Li2CO3 in an aqueous solution to igneous conditions (up to 783 °C and 8.24 kbar) from sedimentary conditions using a Bassett-type hydrothermal diamond-anvil cell. The solubility of Li2CO3 in an aqueous solution increases with temperature and pressure above the vapor-liquid critical pressure–temperature (P–T) condition. This is in contrast to its negative temperature coefficient in vapor-saturated water. The solubility data are fitted with the eq. R × T × lnxLi2CO3 = −3.0328 × 104–16.6486 × T + 3.3252 × 103 × P (r2 = 0.9643), where xLi2CO3 is the mole fraction (mol/mol) of Li2CO3, 714 ≤ T (K) ≤ 1056, 3.28 ≤ P (kbar) ≤ 8.24, and R is the gas constant. Zabuyelite grows quickly when nucleated from complete Li2CO3-dissolved aqueous solutions during cooling (at average rates of 0.2–3.0 μm2/s), especially in the initial exponential growth stage with approximately 18.7–34.2 μm2/s. This is orders of magnitude faster than other pegmatite minerals (e.g., spodumene), forming tabular crystals with the pseudo-hexagonal outlines of monoclinic systems in an aqueous solution. Nevertheless, zabuyelite forms microcrystals in Li2CO3 melt. In addition, zabuyelite crystallization (exhibiting significant temperature dependence) dominantly occurs at ~450–600 °C. The aforementioned crystallization features are identical with the features of zabuyelite contained in crystal-rich fluid inclusions from pegmatite, proving the zabuyelite's daughter-mineral nature in the fluid inclusions, hence indicating the primary origin of the crystal-rich inclusions in pegmatite. In the future, the solubility model of Li2CO3 in an aqueous solution can infer pegmatite formation conditions based on the analysis of the Li2CO3 content dissolved in the pegmatite crystallization media.