627 research outputs found
Studies on the relationship between genes and enzymes
The experimental work and theoretical discussion presented
here suggests the following main conclusions.1. Argininosuccinase may be detected in extracts of a standard
wild -type (SLA) and measurements may be made of some of the kinetics
of its catalysis. I:t is considered likely, from these kinetic data
and from the information on the behaviour of the enzyme on hydroxylapatite
gel and on electrophoresis, that the enzyme is a single protein species.2. A report is given of an examination of some of the arg-10 mutants
and of a heterokaryon between two of them.3.. The production and genetics of revertants of some of these arg-10
mutants, is described and it is suggested that at least two of the revertants
(362r-1 and 362r-2) are the result of mutation(s) at or close to the
arg-10 locus.4. The argininosuccinase formed by 362r-1 is described and it is
proposed that the differences between this enzyme and that of the
original wild-type (SLA) may be explained as the result of an alteration
to the structure of the enzyme involving the active site.5. The argininosuccinase formed by 362r-2 is described and it is
proposed that this enzyme differs both from that found in SLA and in
362r-1 and that this is also a reflection of an alteration in the
structure of the active site of the enzyme.6. Some of the properties of argininosuccinase from K32 3-revertants are described and it is suggested that they may not differ in any
way from the enzyme of SLA.7. A discussion is given of the growth of Neurospora crassa in
culture and it is concluded that the growth -curves of the organism
are complex and depend on the culture conditions.8. Measurements of argininosuccinase, argininosuccinic acid and
arginine in cultures of SLA and 362r-1 are reported and the results
obtained are explained in terms of a kinetic model of the arginine
pathway in vivo. It is suggested that the concentration of arginine
must always be independent of argininosuccinase concentration (at
steady-state).9. In a discussion of the experiments and theory presented, the
thesis is proposed that there are at least two major classes of
catalyses, 'buffered" and "unbuffered", and that the genes affecting
the enzymes concerned with these two types of catalyses will have
distinct properties
Preparing for animal health emergencies: considerations for economic evaluation
Livestock production systems and the societies in which they are embedded face a set of risks presented by infectious diseases and natural and human-made disasters which compromise animal health. Within this set, threats are posed by natural, deliberate and accidental actions that can cause sudden changes in animal health status, requiring the allocation of additional resources to manage animal health. Determining the benefit of preparing for such emergencies is a challenge when the total set of risks includes the unknown. Any method for analysing the economic costs and benefits of animal health emergencies must not only accommodate this uncertainty, but make it a central feature of the analysis. Cost-benefit analysis is a key approach to economically evaluating animal health interventions. However, the value of this approach in dealing with uncertainty is often called into question. This paper makes the case that, by restricting the outcomes of an emergency event to specified states of nature, boundaries can be placed on the uncertainty space, allowing cost-benefit analysis to be performed. This method, which merges state-contingent analysis with cost-benefit analysis, is presented here. Further discussion on the economic characteristics of emergency events, and the nature of the threats posed to animal health systems, is also provided.D. Adamson, W. Gilbert, K. Hamilton, D. Donachie and J. Rushto
Cultivation and Complete Genome Sequencing of Gloeobacter kilaueensis sp. nov., from a Lava Cave in KÄ«lauea Caldera, Hawai'i
The ancestor of Gloeobacter violaceus PCC 7421T is believed to have diverged from that of all known cyanobacteria before the evolution of thylakoid membranes and plant plastids. The long and largely independent evolutionary history of G. violaceus presents an organism retaining ancestral features of early oxygenic photoautotrophs, and in whom cyanobacteria evolution can be investigated. No other Gloeobacter species has been described since the genus was established in 1974 (Rippka et al., Arch Microbiol 100:435). Gloeobacter affiliated ribosomal gene sequences have been reported in environmental DNA libraries, but only the type strain's genome has been sequenced. However, we report here the cultivation of a new Gloeobacter species, G. kilaueensis JS1T, from an epilithic biofilm in a lava cave in Kīlauea Caldera, Hawai'i. The strain's genome was sequenced from an enriched culture resembling a low-complexity metagenomic sample, using 9 kb paired-end 454 pyrosequences and 400 bp paired-end Illumina reads. The JS1T and G. violaceus PCC 7421T genomes have little gene synteny despite sharing 2842 orthologous genes; comparing the genomes shows they do not belong to the same species. Our results support establishing a new species to accommodate JS1T, for which we propose the name Gloeobacter kilaueensis sp. nov. Strain JS1T has been deposited in the American Type Culture Collection (BAA-2537), the Scottish Marine Institute's Culture Collection of Algae and Protozoa (CCAP 1431/1), and the Belgian Coordinated Collections of Microorganisms (ULC0316). The G. kilaueensis holotype has been deposited in the Algal Collection of the US National Herbarium (US# 217948). The JS1T genome sequence has been deposited in GenBank under accession number CP003587. The G+C content of the genome is 60.54 mol%. The complete genome sequence of G. kilaueensis JS1T may further understanding of cyanobacteria evolution, and the shift from anoxygenic to oxygenic photosynthesis. © 2013 Saw et al
Pivotal Roles for pH, Lactate, and Lactate-Utilizing Bacteria in the Stability of a Human Colonic Microbial Ecosystem.
Lactate can be produced by many gut bacteria, but in adults its accumulation in the colon is often an indicator of microbiota perturbation. Using continuous culture anaerobic fermentor systems, we found that lactate concentrations remained low in communities of human colonic bacteria maintained at pH 6.5, even when dl-lactate was infused at 10 or 20âmM. In contrast, lower pH (5.5) led to periodic lactate accumulation following lactate infusion in three fecal microbial communities examined. Lactate accumulation was concomitant with greatly reduced butyrate and propionate production and major shifts in microbiota composition, with Bacteroidetes and anaerobic Firmicutes being replaced by Actinobacteria, lactobacilli, and Proteobacteria Pure-culture experiments confirmed that Bacteroides and Firmicutes isolates were susceptible to growth inhibition by relevant concentrations of lactate and acetate, whereas the lactate-producer Bifidobacterium adolescentis was resistant. To investigate system behavior further, we used a mathematical model (microPop) based on 10 microbial functional groups. By incorporating differential growth inhibition, our model reproduced the chaotic behavior of the system, including the potential for lactate infusion both to promote and to rescue the perturbed system. The modeling revealed that system behavior is critically dependent on the proportion of the community able to convert lactate into butyrate or propionate. Communities with low numbers of lactate-utilizing bacteria are inherently less stable and more prone to lactate-induced perturbations. These findings can help us to understand the consequences of interindividual microbiota variation for dietary responses and microbiota changes associated with disease states.IMPORTANCE Lactate is formed by many species of colonic bacteria, and can accumulate to high levels in the colons of inflammatory bowel disease subjects. Conversely, in healthy colons lactate is metabolized by lactate-utilizing species to the short-chain fatty acids butyrate and propionate, which are beneficial for the host. Here, we investigated the impact of continuous lactate infusions (up to 20âmM) at two pH values (6.5 and 5.5) on human colonic microbiota responsiveness and metabolic outputs. At pH 5.5 in particular, lactate tended to accumulate in tandem with decreases in butyrate and propionate and with corresponding changes in microbial composition. Moreover, microbial communities with low numbers of lactate-utilizing bacteria were inherently less stable and therefore more prone to lactate-induced perturbations. These investigations provide clear evidence of the important role these lactate utilizers may play in health maintenance. These should therefore be considered as potential new therapeutic probiotics to combat microbiota perturbations
Invariant Distribution of Promoter Activities in Escherichia coli
Cells need to allocate their limited resources to express a wide range of genes. To understand how Escherichia coli partitions its transcriptional resources between its different promoters, we employ a robotic assay using a comprehensive reporter strain library for E. coli to measure promoter activity on a genomic scale at high-temporal resolution and accuracy. This allows continuous tracking of promoter activity as cells change their growth rate from exponential to stationary phase in different media. We find a heavy-tailed distribution of promoter activities, with promoter activities spanning several orders of magnitude. While the shape of the distribution is almost completely independent of the growth conditions, the identity of the promoters expressed at different levels does depend on them. Translation machinery genes, however, keep the same relative expression levels in the distribution across conditions, and their fractional promoter activity tracks growth rate tightly. We present a simple optimization model for resource allocation which suggests that the observed invariant distributions might maximize growth rate. These invariant features of the distribution of promoter activities may suggest design constraints that shape the allocation of transcriptional resources
A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291
We present the analysis of planetary microlensing event MOA-2011-BLG-291,
which has a mass ratio of and a source star that
is redder (or brighter) than the bulge main sequence. This event is located at
a low Galactic latitude in the survey area that is currently planned for NASA's
WFIRST exoplanet microlensing survey. This unusual color for a microlensed
source star implies that we cannot assume that the source star is in the
Galactic bulge. The favored interpretation is that the source star is a lower
main sequence star at a distance of kpc in the Galactic disk.
However, the source could also be a turn-off star on the far side of the bulge
or a sub-giant in the far side of the Galactic disk if it experiences
significantly more reddening than the bulge red clump stars. However, these
possibilities have only a small effect on our mass estimates for the host star
and planet. We find host star and planet masses of and from a Bayesian
analysis with a standard Galactic model under the assumption that the planet
hosting probability does not depend on the host mass or distance. However, if
we attempt to measure the host and planet masses with host star brightness
measurements from high angular resolution follow-up imaging, the implied masses
will be sensitive to the host star distance. The WFIRST exoplanet microlensing
survey is expected to use this method to determine the masses for many of the
planetary systems that it discovers, so this issue has important design
implications for the WFIRST exoplanet microlensing survey
The First Neptune Analog or Super-Earth with Neptune-like Orbit: MOA-2013-BLG-605Lb
We present the discovery of the first Neptune analog exoplanet or super-Earth
with Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to
that of Neptune or a super-Earth and it orbits at times the expected
position of the snow-line, , which is similar to Neptune's
separation of from the Sun. The planet/host-star mass ratio
is and the projected separation normalized by the
Einstein radius is . There are three degenerate physical
solutions and two of these are due to a new type of degeneracy in the
microlensing parallax parameters, which we designate "the wide degeneracy". The
three models have (i) a Neptune-mass planet with a mass of orbiting a low-mass M-dwarf with a mass of , (ii) a mini-Neptune with orbiting a brown dwarf host with and (iii) a super-Earth with orbiting a low-mass brown dwarf host with which is slightly favored. The 3-D
planet-host separations are 4.6 AU, 2.1 AU and
0.94 AU, which are , or
times larger than for these models,
respectively. The Keck AO observation confirm that the lens is faint. This
discovery suggests that low-mass planets with Neptune-like orbit are common. So
processes similar to the one that formed Neptune in our own Solar System or
cold super-Earth may be common in other solar systems.Comment: 54 pages, 10 figures, 13 tables, Accepted for publication in the Ap
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