58 research outputs found
Physiological responses to folate overproduction in lactobacillys plantarum WCFS1.
<p>Abstract</p> <p>Background</p> <p>Using a functional genomics approach we addressed the impact of folate overproduction on metabolite formation and gene expression in <it>Lactobacillus plantarum </it>WCFS1. We focused specifically on the mechanism that reduces growth rates in folate-overproducing cells.</p> <p>Results</p> <p>Metabolite formation and gene expression were determined in a folate-overproducing- and wild-type strain. Differential metabolomics analysis of intracellular metabolite pools indicated that the pool sizes of 18 metabolites differed significantly between these strains. The gene expression profile was determined for both strains in pH-regulated chemostat culture and batch culture. Apart from the expected overexpression of the 6 genes of the folate gene cluster, no other genes were found to be differentially expressed both in continuous and batch cultures. The discrepancy between the low transcriptome and metabolome response and the 25% growth rate reduction of the folate overproducing strain was further investigated. Folate production per se could be ruled out as a contributing factor, since in the absence of folate production the growth rate of the overproducer was also reduced by 25%. The higher metabolic costs for DNA and RNA biosynthesis in the folate overproducing strain were also ruled out. However, it was demonstrated that folate-specific mRNAs and proteins constitute 8% and 4% of the total mRNA and protein pool, respectively.</p> <p>Conclusion</p> <p>Folate overproduction leads to very little change in metabolite levels or overall transcript profile, while at the same time the growth rate is reduced drastically. This shows that <it>Lactobacillus plantarum </it>WCFS1 is unable to respond to this growth rate reduction, most likely because the growth-related transcripts and proteins are diluted by the enormous amount of gratuitous folate-related transcripts and proteins.</p
The alcohol acetyltransferase Eat1 is located in yeast mitochondria
Eat1 is a recently discovered alcohol acetyltransferase responsible for bulk ethyl acetate production in yeasts such as Wickerhamomyces anomalus and Kluyveromyces lactis. These yeasts have the potential to become efficient biobased ethyl acetate producers. However, some fundamental features of Eat1 are still not understood, which hampers the rational engineering of efficient production strains. The cellular location of Eat1 in yeast is one of these features. To reveal its location, Eat1 was fused with yEGFP to allow intracellular tracking. Despite the current assumption that bulk ethyl acetate production occurs in the yeast cytosol, most of Eat1 localised to the mitochondria of K. lactis CBS 2359 Îku80. We then compared five bulk ethyl acetate-producing yeasts in iron-limited chemostats with glucose as carbon source. All yeasts produced ethyl acetate under these conditions. This strongly suggests that the mechanism and location of bulk ethyl acetate synthesis are similar in these yeast strains. Furthermore, an in silico analysis showed that Eat1 proteins from various yeasts were mostly predicted as mitochondrial. Altogether, it is concluded that Eat1-catalyzed ethyl acetate production occurs in yeast mitochondria. This study has added new insights to bulk ethyl acetate synthesis in yeast, which is relevant for developing efficient production strains
What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earthâs âSisterâ Planet
Venus is Earthâs closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earthâs sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years.The oxygen isotope composition of Venus is currently unknown. However, this single measurement (Î17O) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Î17O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide.Determining the Î17O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Î17O, this would favour the classic, lower energy, giant impact scenario.We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered.Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a âGrab and Goâ strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, âvacuum-cleanerâ device) to ensure success. Surface operations would take no longer than one hour.Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earthâs planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE Δ4 allele
Primary production of seagrass beds in south Sulawesi (Indonesia): a comparison of habitats, methods and species
Primary production of tropical seagrass meadows was studied between April and August 1990 in South Sulawesi, Indonesia. Oxygen evolution studies in enclosures over seagrass vegetation revealed gross community production values between 900 and 4400 mg C mâ2 dayâ1. Assumed community respiration ranged from 800 to 1800 mg C mâ2 dayâ1 in non-vegetated areas and from 1400 to 5100 mg C mâ2 dayâ1 for areas with varying amounts of seagrass. Benthic community respiration varied considerably in response to diurnal fluctuations in the dissolved oxygen concentration in the water column. Net production was small (less than 500 mg C mâ2 dayâ1) and slightly negative on seven of 12 occasions. Light compensation points ranged from 50 to 340 ÎŒE mâ2 sâ1. Bell jar measurements revealed no significant differences in seagrass production between coastal and reef island habitats. Leaf marking experiments with Enhalus acoroides (L.f.) Royle revealed significantly higher leaf growth in a coastal muddy area (3.1 ± 0.8 cm per shoot dayâ1) than at an offshore sandy reef site (1.6 ± 0.5 cm per shoot dayâ1), but relative growth rates were comparable between the two habitats (0.019 ± 0.005 g gâ1 leaf biomass (AFDW) dayâ1 and 0.012 ± 0.003 g gâ1 AFDW dayâ1, respectively). Leaf marking and plastochrone interval methods revealed similar results for net leaf production in a monospecific stand of Thalassia hemprichii (Ehrenb.) Aschers. at a reef site which averaged 1.6 g C mâ2 dayâ1. Rhizome tagging experiments revealed net rhizome production values of 0.1â0.3 g C mâ2 dayâ1 for Thalassia hemprichii at this reef site. Relative growth rate of leaves of Thalassia hemprichii (0.039 ± 0.010 g gâ1 AFDW dayâ1) at the reef site was significantly higher than that of E. acoroides (0.012 ± 0.003 g gâ1 AFDW dayâ1). The pioneering seagrass species Halodule uninervis (Forssk.) Aschers. and Cymodocea rotundata Ehrenb. & Hempr. ex Aschers. had considerably higher horizontal apical rhizome growth rates (0.7â0.9 cm per apex dayâ1) than the constant species Thalassia hemprichii (0.1 cm per apex dayâ1). The suitability of different methods to measure seagrass productivity is evaluated.
Bioconversion of limonene to increased concentrations of perillic acid by Pseudomonas putida GS1 in a fed-batch reactor
Bioconversion of limonene to increased concentrations of perillic acid by Pseudomonas putida GS1 in a fed-batch reactor
Method for the combined production of butanol and hydrogen
The invention relates to a process for the combined production of butanol and hydrogen from biomass, comprising the steps of fermenting biomass to obtain butanol in a first reaction mixture; removing the butanol and hydrogen from the first reaction mixture to obtain effluent; and using the effluent as a substrate in a second reaction mixture in a process using low substrate concentrations, in particular a hydrogen production process. Preferably, the process using low substrate concentrations is a hydrogen production process and at least part of the end products of the hydrogen production process is removed from the second reaction mixture for obtaining an effluent that comprises organic acid, which effluent is returned to the first reaction mixture
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