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181.
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183.
Escherichia coli serotype-39 capsular polysaccharide: primary structure and depolymerisation by a bacteriophage-associated glycanase 总被引:1,自引:0,他引:1
The acidic capsular polysaccharide isolated from Escherichia coli O9:K39:H9 was investigated, using n.m.r. spectroscopy, methylation analysis, uronic acid degradation of the native and methylated polysaccharides, and bacteriophage-associated enzyme degradation. The structure of the repeating unit, which is shown below, is identical to that reported for Klebsiella serotype-61 capsular polysaccharide. (formula; see text) 相似文献
184.
Xiao Ma Fabián E. Vaistij Yi Li Willem S. Jansen van Rensburg Sarah Harvey Michael W. Bairu Sonja L. Venter Sydney Mavengahama Zemin Ning Ian A. Graham Allen Van Deynze Yves Van de Peer Katherine J. Denby 《The Plant journal : for cell and molecular biology》2021,107(2):613-628
Traditional crops have historically provided accessible and affordable nutrition to millions of rural dwellers but have been neglected, with most modern agricultural systems over-reliant on a small number of internationally traded crops. Traditional crops are typically well-adapted to local agro-ecological conditions and many are nutrient-dense. They can play a vital role in local food systems through enhanced nutrition (particularly where diets are dominated by starch crops), food security and livelihoods for smallholder farmers, and a climate-resilient and biodiverse agriculture. Using short-read, long-read and phased sequencing technologies, we generated a high-quality chromosome-level genome assembly for Amaranthus cruentus, an under-researched crop with micronutrient- and protein-rich leaves and gluten-free seed, but lacking improved varieties, with respect to productivity and quality traits. The 370.9 Mb genome demonstrates a shared whole genome duplication with a related species, Amaranthus hypochondriacus. Comparative genome analysis indicates chromosomal loss and fusion events following genome duplication that are common to both species, as well as fission of chromosome 2 in A. cruentus alone, giving rise to a haploid chromosome number of 17 (versus 16 in A. hypochondriacus). Genomic features potentially underlying the nutritional value of this crop include two A. cruentus-specific genes with a likely role in phytic acid synthesis (an anti-nutrient), expansion of ion transporter gene families, and identification of biosynthetic gene clusters conserved within the amaranth lineage. The A. cruentus genome assembly will underpin much-needed research and global breeding efforts to develop improved varieties for economically viable cultivation and realization of the benefits to global nutrition security and agrobiodiversity. 相似文献
185.
This study examines the effect of female presence on the amount of ‘strippable’ sperm, and the relationship between male sexual activity and the amount of ‘ready’ sperm in the male guppy Poecilia reticulata. The amount of strippable sperm was greater in males paired for one week with females than in isolated males. We separated these ‘paired’ males from females by a clear partition and thus exposed males to visual and possibly olfactory stimuli. In the second experiment, control males spent more time attending females and performed more sexual acts during a 15-min test period than males previously stripped of spermatophores. These results indicate that females play an important role in stimulating sperm availability in males and that the amount of ready sperm influences male sexual behaviour. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved. 相似文献
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187.
Cliff characteristics,neighbour requirements and breeding success of the colonial Cape Vulture Gyps coprotheres
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The breeding success of endangered colonial nesting species is important for their conservation. Many species of Gyps vultures form large breeding colonies that are the foci of conservation efforts. The Cape Vulture is a globally threatened species that is endemic to southern Africa and has seen a major reduction in its population size (≥ 50% over 48 years). There is evidence that breeding colonies are prone to desertion as a result of human disturbance. Factors that influence the occupancy and breeding success of individual nest‐sites is not fully understood for any African vulture species. We investigated cliff characteristics and neighbour requirements of the Msikaba Cape Vulture colony, a major breeding colony in the southern node of the population in the Eastern Cape, South Africa, together with their nest‐site occupation and breeding success over 13 years. In total, 1767 breeding attempts were recorded. Nest‐sites that had a higher elevation, smaller ledge depth, greater total productivity and were surrounded by conspecifics were more likely to be occupied, although the amount of overhang above the nest was not an important predictor of occupancy. In accordance with occupation, nest‐sites with a smaller ledge depth had higher breeding success; however, nests with a greater overhang were also more successful and height of the nest‐site was not an important predictor of breeding success. The breeding success of a nest‐site in a given year was positively influenced by the number of direct nest neighbours, and nests in the middle of high‐density areas had greater breeding success. This suggests that maintaining a high nest density may be an important consideration if declines of reproducing adults continue. Breeding success declined over the study period, highlighting the effects of a temporal variation or observer bias. Our results identified optimal nest‐site locations (ledge depths of 1 m, at a height of 180 m) and their effects on breeding success. This information can be used for planning reintroduction efforts of the endangered Cape Vulture and for their ongoing conservation. 相似文献
188.
Optimal climate for large trees at high elevations drives patterns of biomass in remote forests of Papua New Guinea
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Michelle Venter John Dwyer Wouter Dieleman Anurag Ramachandra David Gillieson Susan Laurance Lucas A. Cernusak Bruce Beehler Rigel Jensen Michael I. Bird 《Global Change Biology》2017,23(11):4873-4883
Our ability to model global carbon fluxes depends on understanding how terrestrial carbon stocks respond to varying environmental conditions. Tropical forests contain the bulk of the biosphere's carbon. However, there is a lack of consensus as to how gradients in environmental conditions affect tropical forest carbon. Papua New Guinea (PNG) lies within one of the largest areas of contiguous tropical forest and is characterized by environmental gradients driven by altitude; yet, the region has been grossly understudied. Here, we present the first field assessment of aboveground biomass (AGB) across three main forest types of PNG using 193 plots stratified across 3,100‐m elevation gradient. Unexpectedly, AGB had no direct relationship to rainfall, temperature, soil, or topography. Instead, natural disturbances explained most variation in AGB. While large trees (diameter at breast height > 50 cm) drove altitudinal patterns of AGB, resulting in a major peak in AGB (2,200–3,100 m) and some of the most carbon‐rich forests at these altitudes anywhere. Large trees were correlated to a set of climatic variables following a hump‐shaped curve. The set of “optimal” climatic conditions found in montane cloud forests is similar to that of maritime temperate areas that harbor the largest trees in the world: high ratio of precipitation to evapotranspiration (2.8), moderate mean annual temperature (13.7°C), and low intra‐annual temperature range (7.5°C). At extreme altitudes (2,800–3,100 m), where tree diversity elsewhere is usually low and large trees are generally rare or absent, specimens from 18 families had girths >70 cm diameter and maximum heights 20–41 m. These findings indicate that simple AGB‐climate‐edaphic models may not be suitable for estimating carbon storage in forests where optimal climate niches exist. Our study, conducted in a very remote area, suggests that tropical montane forests may contain greater AGB than previously thought and the importance of securing their future under a changing climate is therefore enhanced. 相似文献
189.
Brink CB Pretorius A van Niekerk BP Oliver DW Venter DP 《Redox report : communications in free radical research》2008,13(2):87-100
Ozone is used to treat several medical conditions, while the underlying mechanisms of action are sometimes poorly understood. In the current study, we exposed cultured human epithelial (HeLa) cells acutely and repeatedly to ozone and investigated the effects thereof on cell viability. The involvement of anti-apoptotic pathways in observed adaptive responses to ozone were investigated by employing the Akt inhibitor (-)-deguelin. Cells were exposed to an ozone-saturated physiological solution using various dosing regimens, including acute exposure and various repetitive exposures. Cell viability was determined with Trypan Blue or MTT tests, or by a DNA-fragmentation (comet) assay. Acute ozone exposure compromised cell membrane integrity severely, while adaptation to reverse an initial reduction in mitochondrial activity was observed. Repetitive, short-duration exposures followed by a single long-duration exposure to ozone furnished a protective adaptation that was reversed by Akt inhibition. Extracellular and intracellular damage (and adaptation) occurs differentially. While acute ozone may decrease cell viability, multiple preexposures up-regulates cellular plasticity via induction of anti-apoptotic pathways in a treatment regimen-specific manner. 相似文献
190.
Aggressive assembly of pyrosequencing reads with mates 总被引:2,自引:0,他引:2
Miller JR Delcher AL Koren S Venter E Walenz BP Brownley A Johnson J Li K Mobarry C Sutton G 《Bioinformatics (Oxford, England)》2008,24(24):2818-2824