Exploration of the hydrogen producing potential of Rhodobacter capsulatus chemostat cultures: The application of deceleration‐stat and gradient‐stat methodology

In this work, the dependency of the volumetric hydrogen production rate of ammonium‐limited Rhodobacter capsulatus chemostat cultures on their imposed biomass concentration and dilution rate was investigated. A deceleration‐stat experiment was performed by lowering the dilution rate from 1.0 d^?1 to zero aimed at a constant biomass concentration of 4.0 g L^?1 at constant incident light intensity. The results displayed a maximal volumetric hydrogen production rate of 0.6 mmol m^?3 s^?1, well below model predictions. Possibly the high cell density limited the average light availability, resulting in a sub‐optimal specific hydrogen production rate. To investigate this hypothesis, a gradient‐stat experiment was conducted at constant dilution rate of 0.4 d^?1 at constant incident light intensity. The biomass concentration was increased from 0.7 to 4.0 g L^?1 by increasing the influent ammonium concentration. Up to a biomass concentration of 1.5 g L^?1, the volumetric hydrogen production rate of the system increased according to model predictions, after which it started to decline. The results obtained provide strong evidence that the observed decline in volumetric hydrogen production rate at higher biomass concentrations was at least partly caused by a decrease in light availability. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Optimization of biomass, vitamins, and carotenoid yield on light energy in a flat-panel reactor using the A-stat technique

Acceleration-stat (A-stat) cultivations in which the dilution rate is continuously changed at a constant acceleration rate, leading to different average light intensities inside the photobioreactor, can supply more information and reduce experimental time compared with chemostat cultivations. The A-stat was used to optimize the biomass and product yield of continuous cultures of the microalgae D. tertiolecta in a flat-panel reactor. In this study, four different accelerations were studied, a pseudo steady state was maintained at acceleration rates of 0.00016 and 0.00029 h(-2) and results were similar to those of the chemostat. An increase in the acceleration rate led to an increase in the deviation between results obtained in the A-stat and in the chemostats. We concluded that it is advantageous to use the A-stat instead of chemostats to determine culture characteristics and optimize a specific photobioreactor. The effect of average light intensity inside the photobioreactor on the production of vitamins C and E, lutein, and beta-carotene was studied using the A-stat. The highest concentrations of these products were 3.48 +/- 0.46, 0.33 +/- 0.06, 5.65 +/- 0.24, and 2.36 +/- 0.38 mg g(-1), respectively. These results were obtained at different average light intensities, showing the importance of optimizing each product on light intensity.     

Theory of pH-stat titration

Innovative techniques are being studied to assess the activity of bioreactors and to improve the performance and operational stability of biological processes. Among these techniques, the pH-stat titration is applicable to any bioreaction involving pH variations. Up to now, the main application of the pH-stat titration has been for nitrification monitoring. In this article, we present a theoretical model of pH-stat titration, which predicts the response to any reaction involving the production or consumption of protons, hydroxyl ions, or inorganic carbon chemical species (CO(2), HCO(3)(-), CO(3)(=)). This model is a useful tool to understand pH-stat titrations, to define their applicability and limits, and to select the best experimental conditions for specific applications. Tests have been performed to compare experimental pH-stat titration rates in the presence of carbon dioxide and HCO(3)(-) producing reactions to the values predicted by the model and a very satisfying correspondence was found.     

Estimation of steady-state culture characteristics during acceleration-stats with yeasts

Steady-state culture characteristics are usually determined in chemostat cultivations, which are very time-consuming. In contrast, acceleration-stat (A-stat) cultivations in which the dilution rate is continuously changed with a constant acceleration rate are not so time-consuming, especially at high acceleration rates. Therefore, the A-stat could be advantageous to use instead of the chemostat. However, the highest acceleration rate, meaning the fastest A-stat that can be applied for estimating steady-state culture characteristics, is not known yet. Experimental results obtained with Zygosaccharomyces rouxii, an important yeast in soy sauce processes, showed that the culture characteristics during the A-stat with an acceleration rate of 0.001 h(-2) were roughly comparable to those of the chemostat. For higher acceleration rates the deviation between the culture characteristics in the A-stat and those in the chemostat obtained at the same dilution rate generally started to increase. The source of these deviations was examined by simulation for Saccharomyces cerevisiae. The simulations demonstrated that this deviation was not only dependent on the metabolic adaptation rate of the yeast, but also on the rate of change in environmental substrate concentrations during A-stats. From this work, it was concluded that an A-stat with an acceleration rate of 0.001 h(-2) is attractive to be used instead of chemostat whenever a rough estimation of steady-state culture characteristics is acceptable.     

Monitoring denitrification by pH-Stat titration

An improved pH-stat titrimetric procedure was developed, validated, and extensively applied to monitor biological heterotrophic denitrification in a lab-scale sequencing batch reactor (SBR). So far, titrimetric procedures were not successful in monitoring denitrification processes in full-scale wastewater (WW) treatment plants, mainly because the stoichiometric ratio between proton production and nitrate reduction is highly variable due to variability of both biomass and influent WW characteristics. In this article, a new titration procedure is proposed where a simple calibration step is performed before each experimental test. This procedure allows for the assessment of (i) nitrate content in a sample of mixed liquor; (ii) the maximum denitrification rate of sludge when fed on acetate; and (iii) the denitrification potential (DNP) of different substrates. As for (i), validation by comparison with spectrophotometric measures indicated an average discrepancy of less than 3% on more than 40 samples; as for (ii) and (iii) collected values compared well with literature data. The titrimetric method proposed here is also capable of assessing the biomass anoxic yield in a very simple way, since it does not require any analytical nitrate determination. According to the results of this experimentation, titrimetry appeared to be a simple, inexpensive, and powerful tool for monitoring and operating denitrification processes in WW treatment plants.     

Acetoclastic methanogenic activity measurement by a titration bioassay.

A titration bioassay, designed to accurately determine the activity of acetoclastic methanogens, is described that also allows evaluation of inhibition due to potential toxicants on the active biomass. The instrument is made of a pH-stat connected to an anaerobic batch reactor. Acetate is blended and mixed with anaerobic sludge in the reactor where a 1:1 N2 and CO2 mixture is sparged at the beginning of each test. As the acetoclastic methanogens consume acetate, the pH increase, and the titration unit adds acetic acid and keeps the pH constant. The rate of titrant addition is directly proportional to the methanogenic activity. A very useful feature of the system is its potential to operate for long periods (days) at constant pH and substrate (acetate) concentration. The theoretical background and principle of operation are described as well as some of the practical problems encountered with the use of the instrument. Estimation of kinetic constants for an anaerobic culture according to the Michaelis-Menten model is presented. Examples of inhibition by inorganics (NaCl) and chlorinated solvents (chloroform) are also given.     

苦参碱对肝癌细胞增殖凋亡及stat3、stat5基因的影响

观察苦参碱对SMMC-7721细胞增殖、凋亡及stat3s、tat5基因的影响。用MTT法检测不同浓度苦参碱对SMMC-7721细胞增殖的抑制作用,双荧光染色观察细胞凋亡率,RT-PCR半定量检测stat3s、tat5基因的表达。结果发现苦参碱有抑制细胞增殖促进凋亡的作用,并呈时间剂量依赖性;不同浓度苦参碱作用于SMMC-7721细胞后stat3s、tat5的mRNA水平明显下调(P<0.01),其中高浓度苦参碱的作用更强。苦参碱能显著抑制SMMC-7721细胞增殖、促进其凋亡,其机制可能与下调stat3s、tat5的基因表达有关。     

pH-stat fed-batch process to enhance the production of cis, cis-muconate from benzoate by Pseudomonas putida KT2440-JD1

Pseudomonas putida KT2440-JD1 is able to cometabolize benzoate to cis, cis-muconate in the presence of glucose as growth substrate. P. putida KT2440-JD1 was unable to grow in the presence of concentrations above 50 mM benzoate or 600 mM cis, cis-muconate. The inhibitory effects of both compounds were cumulative. The maximum specific uptake rate of benzoate was higher than the specific production rate of cis, cis-muconate during growth on glucose in the presence of benzoate, indicating that a benzoate derivative accumulated in the cells, which is likely to be catechol. Catechol was shown to reduce the expression level of the ben operon, which encodes the conversion of benzoate to cis, cis-muconate. To prevent overdoses of benzoate, a pH-stat fed-batch process for the production of cis, cis-muconate from benzoate was developed, in which the addition of benzoate was coupled to the acidification of the medium. The maximum specific production rate during the pH-stat fed-batch process was 0.6 g (4.3 mmol) g dry cell weight(-1) h(-1), whereas 18.5 g L(-1) cis, cis-muconate accumulated in the culture medium with a molar product yield of close to 100%. Proteome analysis revealed that the outer membrane protein H1 was upregulated during the pH-stat fed-batch process, whereas the expression of 10 other proteins was reduced. The identified proteins are involved in energy household, transport, translation of RNA, and motility.     

Phylogenetic analyses suggest that Psammomitra (Ciliophora,Urostylida) should represent an urostylid family,based on small subunit rRNA and alpha‐tubulin gene sequence information

The morphologically unique ciliate Psammomitra has long been considered as a systematically uncertain stichotrich. This is mainly because of its highly specialized morphology and a lack of either detailed information concerning its ontogenesis, or molecular data. Based on the small subunit rRNA (SSrRNA) gene and alpha‐tubulin gene sequences, we re‐evaluated the phylogenetic position of Psammomitra retractilis using multiple algorithms. Phylogenetic trees inferred from the SSrRNA gene sequences representing a total of 53 spirotrichs demonstrated the closest relationship of Psammomitra was with Holosticha‐like taxa, with strong support, which clearly suggested that Psammomitra should be placed into the order Urostylida although it branched at a rather deep level, and is likely to be closely related to Holostichidae. With consideration to molecular evidence and morphological characters, Psammomitra should be a clearly outlined taxon at about the rank of family, i.e. Psammomitridae stat. nov. , within the order Urostylida. The improved diagnosis for this family is as follows: Urostylida possessing extremely contractile, elongated body which consists of three parts: head, trunk, and slender tail; midventral complex composed of midventral pairs only and restricted to about anterior 1/3 of ventral surface; frontal, frontoterminal, and transverse cirri present; one left and one right marginal rows which commence near proximal end of adoral zone and extend to near rear body end.     

Effects of Ni2+ on proton extrusion, dark CO2 fixation and malate synthesis in maize roots

The presence of Ni²⁺ in the incubation medium of maize root segments ( Zen mays L. cv. Dekalb XL 640) induces an early and significant enhancement of the rate of proton extrusion both in the absence and presence of fusicoccin; with time, an inhibition of proton extrusion and a leakage of K⁺ appear. The inhibition of proton extrusion is accompanied by a decrease in the dark CO₂ fixation and by a decrease in the level of malate in the cells. Ni²⁺ inhibits in vitro phosphoenolpyruvale carboxylase activity of maize roots. The data indicate a correlation between the operativity of the proton pump and that of the malate-pH stat mechanism for the homeostasis of cytoplasmic pH.     

Morphometric variation of Seminavis pusilla (Bacillariophyceae) and its relationship to salinity in inter‐dune lakes of the Badain Jaran Desert,Inner Mongolia,China

We used light and scanning electron microscope analyses to quantify morphometric features (valve length, width, stria density, lineola density and valve curvature) from the observation of valves representing Seminavis pusilla. Cluster analysis based on Gaussian mixture models and the expectation‐maximization algorithm was used for delineating two species, Seminavis pusilla sensu stricto and Seminavis lata (Krammer) Rioual comb. et stat. nov. By comparison with S. pusilla, S. lata is characterized by wider valves and lower stria density. The two species have also markedly different ecology. S. pusilla is most abundant in the most saline lakes of the dataset, while S. lata is most abundant in the less saline lakes. Our results indicate that combining the two species into S. pusilla sensu lato would lead to a loss of ecological information and a decrease of the performance of transfer functions developed for quantitative reconstruction of past salinity from fossil diatom assemblages in sediment cores.     

Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pH

The processes responsible for maintenance of cation-anion balance in plants and their relation to active ion accumulation and changes in rhizosphere pH are outlined and discussed. The major processes involved are: (1) accumulation and degradation of organic acids which occur in the plant mainly as organic acid anions (and their transfer within the plant) and (2) extrusion of H⁺ or OH^– into the rhizosphere. The relative importance of the two processes is determined by the size of the excess anion or cation uptake. Indeed, plants typically absorb unequal quantities of nutritive cations (NH₄ ⁺+Ca²⁺+ Mg²⁺+K⁺+Na⁺) and anions (NO₃ ^–+Cl^–+SO₄ ^2–+H₂PO₄ ^–) and charge balance is maintained by excretion of an amount of H⁺ or OH^– which is stoichiometrically equal to the respective excess cation or anion uptake. The mechanisms and processes by which H⁺ and in particular OH^– ions are excreted in response to unequal cation-anion uptake are, however, poorly understood.The contemporary view is that primary active extrusion of H⁺, catalyzed by a membrane-located ATPase, is the major driving force for secondary transport of cations and anions across the plasma membrane. However, the fact that net OH^– extrusion often occurs (since excess anion absorption commonly takes place) implies there is a yet-to-be characterized OH^– ion efflux mechanism at the plasma membrane that is associated with anion uptake. There is, therefore, a need for future studies of the uptake mechanisms and stoichiometry of anion uptake; particularly that of NO₃ ^– which is often the predominant anion absorbed. Another related phenonenon which requires detailed study in terms of cation-anion balance is localized rhizosphere acidification which can occur in response to deficiencies of Fe and P.     

激光诱变无核沙田柚的染色体研究

选摘经激光诱变得到的第二代无核(少核)沙田柚叶片,和未经激光处理的对照组进行染色体的对比分析,实验分析发现染色体数目发生了改变,出现了非整倍体。本文对染色体数目进行了统计分析,并讨论了非整倍体与无核化之间的关系。     

Observations on Aulacoseira nipponica from Lake Biwa, Japan, and Aulacoseira solida from North America (Bacillariophyceae)

A recent diatom, Aulacoseira nipponica (Skvortzow) Tuji comb. et stat. nov., is described from Lake Biwa, Japan, where they had been identified previously as Aulacoseira solida (Eulenstein) Krammer. These forms are compared with populations of A. solida from North America. The Japanese species differs from the North American specimens in characteristics related to the density of striae and form of the rimoportulae.     

Bovine milk-derived extracellular vesicles enhance doxorubicin sensitivity in triple negative breast cancer cells by targeting metabolism and STAT signalling

Metastatic triple-negative breast cancer (TNBC) has a low 5-year survival rate of below 30% with systemic chemotherapy being the most widely used treatment. Bovine milk-derived extracellular vesicles (MEVs) have been previously demonstrated to have anti-cancer attributes. In this study, we isolated bovine MEVs from commercial milk and characterised them according to MISEV guidelines. Bovine MEVs sensitised TNBC cells to doxorubicin, resulting in reduced metabolic potential and cell-viability. Label-free quantitative proteomics of cells treated with MEVs and/or doxorubicin suggested that combinatorial treatment depleted various pro-tumorigenic interferon-inducible gene products and proteins with metabolic function, previously identified as therapeutic targets in TNBC. Combinatorial treatment also led to reduced abundance of various STAT proteins and their downstream oncogenic targets with roles in cell-cycle and apoptosis. Taken together, this study highlights the ability of bovine MEVs to sensitise TNBC cells to standard-of-care therapeutic drug doxorubicin, paving the way for novel treatment regimens.     

Preliminary observations on differences of scale morphology at various stages in the life cycle of ‘Apistonema-Syracosphaera’ Sensu von Stosch

A preliminary study of the fine structure of various stages in the life cycle of von Stosch's solate of ‘Syracosphaera carterae’ has been made by means of sections and whole mounts. Protoplast structure appears to be similar throughout the cycle. However, the Apistonema thallus possesses a cell wall composed of numerous layers of closely adpressed rimless unmineralised scales. Two types of asexual swarmers are shown to be covered with one or two layers of somewhat similar scales. One type of swarmer possesses a short haptonema which is covered with small scales. In addition the coccolith-bearing stages are shown to be identical with Hymenomonas carterae sensu Manton and Peterfi (1969) and this isolate has therefore been transferred to H. carterae.