409 research outputs found
Higher yields of cyclodepsipetides from Scopulariopsis brevicaulis by random mutagenesis
The ascomycete Scopulariopsis brevicaulis, which was isolated from the marine sponge
Tethya aurantium, produces two cyclodepsipeptides, scopularides A and B [1]. Both peptides
exhibit activity against several tumor cell lines. Within the EU-project MARINE FUNGI (EU
FP7, 265926) one of our aims is to enhance the production of these secondary metabolites.
We are in the process to establish two ways of random mutagenesis by both UV radiation
and transposon-mediated. To this end we created UV-mutants and a miniaturised screening
method was developed. UV-radiation was performed at 312 nm and the survival rate was set
to 1 %. With this method a mutant library was established. To screen these mutants for
higher secondary metabolites production, we developed a miniaturised screening method
which includes decreased cultivation volume, fast extraction and an optimised LC-MS
analysis format. Using the UV mutagenesis, we were able to identify several mutants with a
higher scopularide production in comparison to the wild type. One of these mutants, which
produces three times more biomass and more than double the amount of scopularide A, has
been used for another round of mutation. Next generation sequencing is being employed to
identify the molecular genetic basis of the observed mutations. In parallel we employ
transposable elements to introduce mutants [2]. The impact of transposons on gene
expression as well as their ability to cause major mutations within the genome or single
genes makes them an interesting tool for random mutagenesis [3, 4, 5]. We employ the
Vader transposon in its homologous host and found that Vader mostly integrates within or
very close to genes. Thus it appears to be a useful tool for transposon-mediated
mutagenesis in A. niger (6). At current we try to enhance its usability by modifying the Vader
element
Influence of coating on the thermal resistance of a Ni-Based superalloy
In this paper, the influence of M-CrAlY polycrystalline coating on the thermal fatigue behavior of a Nickel-base superalloy has been investigated. A special device using a rotating bending machine and two thermal sources has been used to perform thermo-mechanical tests. The two thermal sources have been set to obtain temperature variations between 750 and 1120 °C in the central part of the specimens, with a frequency of 0.1 Hz. The results showed a deleterious effect of the coating on the fatigue resistance. Numerical simulations have been carried out on SAMCEF to determine the thermo-mechanical field of the so-tested specimens. Calculated thermo-mechanical cycles of critical sites are associated with microstructure evolution and damage by cracking observed on the specimens. Damage mechanisms related to the presence of coating are discussed
Simplified and yet Turing universal spiking neural P systems with communication on request
The file attached to this record is the author's final peer reviewed version.Spiking neural P systems are a class of third generation neural networks belonging to the framework of membrane computing. Spiking neural P systems with communication on request (SNQ P systems) are a type of spiking neural P system where the spikes are requested from neighbouring neurons. SNQ P systems have previously been proved to be universal (computationally equivalent to Turing machines)
when two types of spikes are considered.
This paper studies a simpli ed version of SNQ P systems, i.e. SNQ P systems with one type of spike.
It is proved that one type of spike is enough to guarantee the Turing universality of SNQ P systems.
Theoretical results are shown in the cases of the SNQ P system used in both generating and accepting modes. Furthermore, the influence of the number of unbounded neurons (the number of spikes in a neuron is not bounded) on the computation power of SNQ P systems with one type of spike is investigated. It is found that SNQ P systems functioning as number generating devices with one type of spike and four unbounded neurons are Turing universal
Development and Validation of a Fast and Optimized Screening Method for Enhanced Production of Secondary Metabolites Using the Marine Scopulariopsis brevicaulis Strain LF580 Producing Anti-Cancer Active Scopularide A and B
Natural compounds from marine fungi are an excellent source for the discovery and development of new drug leads. The distinct activity profiles of the two cyclodepsipeptides scopularide A and B against cancer cell lines set their marine producer strain Scopulariopsis brevicaulis LF580 into the focus of the EU project MARINE FUNGI. One of the main goals was the development of a sustainable biotechnological production process for these compounds. The secondary metabolite production of strain LF580 was optimized by random mutagenesis employing UV radiation. For a fast and reliable detection of the intracellular secondary metabolite production level, a miniaturized bioactivity-independent screening method was developed, as the random mutagenesis yielded a large number of mutants to be analysed quantitatively and none of the existing hyphenated bioassay-dependent screening systems could be applied. The method includes decreased cultivation volume, a fast extraction procedure as well as an optimized LC-MS analysis. We show that deviation could be specifically reduced at each step of the process: The measuring deviation during the analysis could be minimized to 5% and technical deviation occurring in the downstream part to 10–15%. Biological variation during the cultivation process still has the major influence on the overall variation. However, the approach led to a 10-fold reduction of time and similar effects on costs and effort compared to standard reference screening methods. The method was applied to screen the UV-mutants library of Scopulariopsis brevicaulis LF580. For validation purposes, the occurring variations in the miniaturized scale were compared to those in the classical Erlenmeyer flask scale. This proof of concept was performed using the wild type strain and 23 randomly selected mutant strains. One specific mutant strain with an enhanced production behavior could be obtained
Crack fronts and damage in glass at the nanometer scale
We have studied the low speed fracture regime for different glassy materials
with variable but controlled length scales of heterogeneity in a carefully
mastered surrounding atmosphere. By using optical and atomic force microscopy
(AFM) techniques we tracked in real-time the crack tip propagation at the
nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence
of the heterogeneities on this velocity is presented and discussed. Our
experiments reveal also -for the first time- that the crack progresses through
nucleation, growth and coalescence of nanometric damage cavities within the
amorphous phase. This may explain the large fluctuations observed in the crack
tip velocities for the smallest values. This behaviour is very similar to what
is involved, at the micrometric scale, in ductile fracture. The only difference
is very likely due to the related length scales (nanometric instead of
micrometric). Consequences of such a nano-ductile fracture mode observed at a
temperature far below the glass transition temperature in glass is finally
discussed.Comment: 12 pages, 8 figures, submitted to Journal of Physics: Condensed
Matter; Invited talk at Glass and Optical Materials Division Fall 2002
Meeting, Pittsburgh, Pa, US
Hybridization and speciation in angiosperms: a role for pollinator shifts?
The majority of convincingly documented cases of hybridization in angiosperms has involved genetic introgression between the parental species or formation of a hybrid species with increased ploidy; however, homoploid (diploid) hybridization may be just as common. Recent studies, including one in BMC Evolutionary Biology, show that pollinator shifts can play a role in both mechanisms of hybrid speciation
Spiking Neural P Systems: A Short Introduction and New Normal Forms
Spiking neural P systems are a class of P systems inspired from the way
the neurons communicate with each other by means of electrical impulses (called
\spikes"). In the few years since this model was introduced, many results related
to the computing power and e ciency of these computing devices were reported.
The present paper quickly surveys the basic ideas of this research area and the basic
results, then, as typical proofs about the universality of spiking neural P systems,
we present some new normal forms for them. Speci cally, we consider a natural
restriction in the architecture of a spiking neural P system, to have neurons of a
small number of types (i.e., using a small number of sets of rules). We prove that
three types of neurons are su cient in order to generate each recursively enumerable
set of numbers as the distance between the rst two spikes emitted by the system;
the problem remains open for accepting SN P systems. The paper ends with the
complete bibliography of this domain, at the level of April 2009.Ministerio de Educación y Ciencia TIN2006-13452Junta de Andalucía P08-TIC-0420
The Critical Exponent is Computable for Automatic Sequences
The critical exponent of an infinite word is defined to be the supremum of
the exponent of each of its factors. For k-automatic sequences, we show that
this critical exponent is always either a rational number or infinite, and its
value is computable. Our results also apply to variants of the critical
exponent, such as the initial critical exponent of Berthe, Holton, and Zamboni
and the Diophantine exponent of Adamczewski and Bugeaud. Our work generalizes
or recovers previous results of Krieger and others, and is applicable to other
situations; e.g., the computation of the optimal recurrence constant for a
linearly recurrent k-automatic sequence.Comment: In Proceedings WORDS 2011, arXiv:1108.341
Recurrent allopolyploidizations diversify ecophysiological traits in marsh orchids (Dactylorhiza majalis s.l.).
Whole-genome duplication has shaped the evolution of angiosperms and other organisms, and is important for many crops. Structural reorganization of chromosomes and repatterning of gene expression are frequently observed in allopolyploids, with physiological and ecological consequences. Recurrent origins from different parental populations are widespread among polyploids, resulting in an array of lineages that provide excellent models to uncover mechanisms of adaptation to divergent environments in early phases of polyploid evolution. We integrate here transcriptomic and ecophysiological comparative studies to show that sibling allopolyploid marsh orchid species (Dactylorhiza, Orchidaceae) occur in different habitats (low nutrient fens vs. meadows with mesic soils) and are characterized by a complex suite of intertwined, pronounced ecophysiological differences between them. We uncover distinct features in leaf elemental chemistry, light-harvesting, photoprotection, nutrient transport and stomata activity of the two sibling allopolyploids, which appear to match their specific ecologies, in particular soil chemistry differences at their native sites. We argue that the phenotypic divergence between the sibling allopolyploids has a clear genetic basis, generating ecological barriers that maintain distinct, independent lineages, despite pervasive interspecific gene flow. This suggests that recurrent origins of polyploids bring about a long-term potential to trigger and maintain functional and ecological diversity in marsh orchids and other groups
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