Genome-Scale Modeling of Light-Driven Reductant Partitioning and Carbon Fluxes in Diazotrophic Unicellular Cyanobacterium Cyanothece sp. ATCC 51142

Genome-scale metabolic models have proven useful for answering fundamental questions about metabolic capabilities of a variety of microorganisms, as well as informing their metabolic engineering. However, only a few models are available for oxygenic photosynthetic microorganisms, particularly in cyanobacteria in which photosynthetic and respiratory electron transport chains (ETC) share components. We addressed the complexity of cyanobacterial ETC by developing a genome-scale model for the diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142. The resulting metabolic reconstruction, iCce806, consists of 806 genes associated with 667 metabolic reactions and includes a detailed representation of the ETC and a biomass equation based on experimental measurements. Both computational and experimental approaches were used to investigate light-driven metabolism in Cyanothece sp. ATCC 51142, with a particular focus on reductant production and partitioning within the ETC. The simulation results suggest that growth and metabolic flux distributions are substantially impacted by the relative amounts of light going into the individual photosystems. When growth is limited by the flux through photosystem I, terminal respiratory oxidases are predicted to be an important mechanism for removing excess reductant. Similarly, under photosystem II flux limitation, excess electron carriers must be removed via cyclic electron transport. Furthermore, in silico calculations were in good quantitative agreement with the measured growth rates whereas predictions of reaction usage were qualitatively consistent with protein and mRNA expression data, which we used to further improve the resolution of intracellular flux values

The image of the American businessman in the popular press, 1928-1941

Historians frequently make statements which, superficially or fundamentally, seem to be gross generalizations without obvious foundations. The suggestion that one of America’s heroes of the twenties, the businessman, became a devil of the thirties struck this author as one of those generalizations. Since it was impossible to measure "public opinion" on the subject, the study examined the image of businessmen as presented in the periodical press.Businessmen are an integral part of American society; however, historical writing has tended to favor political and military exploits. The businessman's ability to influence societal decisions and his role as a major functioning and determining element within society require in-depth study.The general hypothesis for the study was based on a perception held by the author. It was assumed that historians had projected an image of businessmen held by the American people which was at a high level prior to the 1929 Stock Market Crash, plunged drastically following the Crash and remained at a low level through 1.934; in 1935, that image rose through the 1937 recession, when it fell again, and then, as recovery began and foreign war materials orders were filled, the image rose but never reached the level of the pre-Crash period. This assumption of the historical attitude was based on the writing of several historians.The project classified businessmen in several categories: retail, construction, and services; wholesale; chain store and mail order; local, small manufacturing; national, corporate manufacturing; local financial and real estate; national financial, insurance, stock brokerage and Wall Street; extractive industry; and, transportation, communication, power, publishing, and entertainment. The popular press was defined as those periodicals with a circulation greater than 0.1 percent of the population of the United States (±125,000) for at least 6 of the 14 years covered by the study. A random sample of one-sixth of the articles published, regardless of subject matter, was content analyzed for attitudes assigned by the study to the vocabulary pertaining to businessmen. Of 293 businessmen who appeared in magazine articles by name, 21 were selected for specific mention and comparison in the study. The great quantity of data was subjected to computer programs to determine precise and systematic measurement.The results indicated that the popular press did not reflect the variations in image suggested by historians. Indeed, the numerical image of businessmen in the period represented a very even, medium, or neutral, position. Mean attitudes toward businessmen for the five periods of the study were clustered around the mean attitude for the entire study (3.31973 on a scale of 1 to 5), and in only two periods did the numerical image differ significantly from the mean for the entire study. The wide variations suggested by historians did not develop when businessmen were in the twenties as a hero and that he fell from that position examined by business classification, by type of article, or by the magazines' subject/interest areas. Finally, the suggested variations did not emerge from examination of individual periodicals or examination of individual businessmen.The study, then, throws into doubt conclusions reached by many historians that the businessman was regarded by many citizens into disrepute during the thirties. Further study of other periodicals and other sources will be required.Thesis (Ph. D.

Daphnia magna’s sense of competition: intra-specific interactions (ISI) alter life history strategies and increase metals toxicity

This work investigates whether the scale-up to multi-animal exposures that is commonly applied in genomics studies provides equivalent toxicity outcomes to single-animal experiments of standard Daphnia magna toxicity assays. Specifically, we tested the null hypothesis that intraspecific interactions (ISI) among D. magna have neither effect on the life history strategies of this species, nor impact toxicological outcomes in exposure experiments with Cu and Pb. The results show that ISI significantly increased mortality of D. magna in both Cu and Pb exposure experiments, decreasing 14 day LC50 s and 95 % confidence intervals from 14.5 (10.9–148.3) to 8.4 (8.2–8.7) µg Cu/L and from 232 (156–4810) to 68 (63–73) µg Pb/L. Additionally, ISI potentiated Pb impacts on reproduction eliciting a nearly 10-fold decrease in the no-observed effect concentration (from 236 to 25 µg/L). As an indication of environmental relevance, the effects of ISI on both mortality and reproduction in Pb exposures were sustained at both high and low food rations. Furthermore, even with a single pair of Daphnia, ISI significantly increased (p < 0.05) neonate production in control conditions, demonstrating that ISI can affect life history strategy. Given these results we reject the null hypothesis and conclude that results from scale-up assays cannot be directly applied to observations from single-animal assessments in D. magna. We postulate that D. magna senses chemical signatures of conspecifics which elicits changes in life history strategies that ultimately increase susceptibility to metal toxicity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10646-016-1667-1) contains supplementary material, which is available to authorized users

Histone tyrosine phosphorylation comes of age

Histones were discovered over a century ago and have since been found to be the most extensively post-translationally modified proteins, although tyrosine phosphorylation of histones had remained elusive until recently. The year 2009 proved to be a landmark year for histone tyrosine (Y) phosphorylation as five research groups independently discovered this modification. Three groups describe phosphorylation of Y142 in the variant histone H2A.X, where it may be involved in the cellular decision making process to either undergo DNA repair or apoptosis in response to DNA damage. Further, one group suggests that phosphorylation of histone H3 on Y99 is crucial for its regulated proteolysis in yeast, while another found that Y41 phosphorylation modulates chromatin architecture and oncogenesis in mammalian cells. These pioneering studies provide the initial conceptual framework for further analyses of the diverse roles of tyrosine phosphorylation on different histones, with far reaching implications for human health and disease