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971.
Stukenbrock EH Banke S Javan-Nikkhah M McDonald BA 《Molecular biology and evolution》2007,24(2):398-411
The Fertile Crescent represents the center of origin and earliest known place of domestication for many cereal crops. During the transition from wild grasses to domesticated cereals, many host-specialized pathogen species are thought to have emerged. A sister population of the wheat-adapted pathogen Mycosphaerella graminicola was identified on wild grasses collected in northwest Iran. Isolates of this wild grass pathogen from 5 locations in Iran were compared with 123 M. graminicola isolates from the Middle East, Europe, and North America. DNA sequencing revealed a close phylogenetic relationship between the pathogen populations. To reconstruct the evolutionary history of M. graminicola, we sequenced 6 nuclear loci encompassing 464 polymorphic sites. Coalescence analyses indicated a relatively recent origin of M. graminicola, coinciding with the known domestication of wheat in the Fertile Crescent around 8,000-9,000 BC. The sympatric divergence of populations was accompanied by strong genetic differentiation. At the present time, no genetic exchange occurs between pathogen populations on wheat and wild grasses although we found evidence that gene flow may have occurred since genetic differentiation of the populations. 相似文献
972.
We develop a kinetic model that builds on the foundation of classic Monod kinetics, but incorporates new phenomena such as substrate thresholds and survival mode observed in experiments with the H2-oxidizing methanogen Methanobacterium bryantii M.o.H. We apply our model to the experimental data presented in our companion paper on H2 thresholds. The model accurately describes H2 consumption, CH4 generation, biomass growth, substrate thresholds, and survival state during batch experiments. Methane formation stops when its Gibbs free energy is equal zero, although this does not interrupt H2 oxidation. The thermodynamic threshold for H2 oxidation occurs when the free energy for oxidizing H2 and transferring electrons to biomass is no longer negative, at approximately 0.4 nM. This threshold is not controlled by the Gibbs free energy equation of methanogenesis from H2 + HCO3- as we show in our companion paper. Beyond this threshold, the microorganisms shift to a low-maintenance metabolism called "the survival state" in response to extended H2 starvation; adding the starvation response as another new feature of the kinetic model. A kinetic threshold (or S (min)), a natural feature of the Monod kinetics, is also captured by the model at H2 concentration of around approximately 2,400 nM. S (min) is the minimum substrate concentration to maintain steady-state biomass concentration. Our model will be useful for interpreting threshold results and designing new studies to understand thresholds and their ecological implications. 相似文献
973.
We develop a comprehensive biogeochemical framework for understanding and quantitatively evaluating metals bio-protection
in sulfidic microbial systems. We implement the biogeochemical framework in CCBATCH by expanding its chemical equilibrium
and biological sub-models for surface complexation and the formation of soluble and solid products, respectively. We apply
the expanded CCBATCH to understand the relative importance of the various key ligands of sulfidic systems in Zn detoxification.
Our biogeochemical analysis emphasizes the relative importance of sulfide over other microbial products in Zn detoxification,
because the sulfide yield is an order of magnitude higher than that of other microbial products, while its reactivity toward
metals also is highest. In particular, metal-titration simulations using the expanded CCBATCH in a batch mode illustrate how
sulfide detoxifies Zn, controlling its speciation as long as total sulfide is greater than added Zn. Only in the absence of
sulfide does complexation of Zn to biogenic organic ligands play a role in detoxification. Our biogeochemical analysis conveys
fundamental insight on the potential of the key ligands of sulfidic systems to effect Zn detoxification. Sulfide stands out
for its reactivity and prevalence in sulfidic systems. 相似文献
974.
We tested the hypothesis that the H2-based membrane biofilm reactor (MBfR) is capable of reducing multiple oxidized contaminants, a common situation for groundwater
contamination. We conducted bench-scale experiments with three groundwater samples collected from California’s San Joaquin
Valley and on two synthetic groundwaters containing selenate and chromate. The actual groundwater sources had nitrate levels
exceeding 10 mg-N l−1 and different combinations of anthropogenic perchlorate + chlorate, arsenate, and dibromochloropropane (DBCP). For all actual
groundwaters, the MBfR reduced nitrate to less than 0.01 mg-N l−1. Present in two groundwaters, perchlorate + chlorate was reduced to below the California Notification Level, 6 μg-ClO4 l−1. As(V) was substantially reduced to As(III) for two groundwaters samples, which had influent As(V) concentrations from 3
to 8.8 μg-As l−1. DBCP, present in one groundwater at 1.4 μg l−1, was reduced to below its detection limit of 0.01 μg l−1, which is well below California’s 0.2 μg l−1 MCL for DBCP. For the synthetic groundwaters, two MBfRs initially reduced Se(VI) or Cr(VI) stably to Se° or Cr(III). When
we switched the influent oxidized contaminants, the new oxidized contaminant was reduced immediately, and its reduction soon
was approximately the same or greater than it had been reduced in its original MBfR. These results support that the H2-based MBfR can reduce multiple oxidized contaminants simultaneously. 相似文献
975.
Characterization of Streptococcus pneumoniae isolated from children with otitis media 总被引:2,自引:0,他引:2
Onwubiko C Shires C Quin LR Swiatlo E McDaniel LS 《FEMS immunology and medical microbiology》2007,50(1):119-125
Streptococcus pneumoniae is the main causative agent of acute otitis media in children. Serotype-based vaccines have provided some protection against otitis media, but not as much as anticipated, demonstrating the need for alternative vaccine options. Pneumococcal otitis media isolates were obtained from children 5 years old or younger from hospitals around Mississippi in the prevaccine era (1999-2000). These isolates were compared by capsular typing, pneumococcal surface protein A (PspA) family typing, antibiotic susceptibility, and DNA fingerprinting. Our study shows that there is great genetic variability among pneumococcal clinical isolates of otitis media, except with regard to PspA. Therefore, efforts focused on the development of a PspA-based pneumococcal vaccine would be well placed. 相似文献
976.
Gealy EC Kerr BC Young RD Tudor D Hayes AJ Hughes CE Caterson B Quantock AJ Ralphs JR 《Histochemistry and cell biology》2007,128(6):551-555
Keratan sulphate (KS) proteoglycans (PGs) are key molecules in the connective tissue matrix of the cornea of the eye, where
they are believed to have functional roles in tissue organisation and transparency. Keratocan, is one of the three KS PGs
expressed in cornea, and is the only one that is primarily cornea-specific. Work with the developing chick has shown that
mRNA for keratocan is present in early corneal embryogenesis, but there is no evidence of protein synthesis and matrix deposition.
Here, we investigate the tissue distribution of keratocan in the developing chick cornea as it becomes compacted and transparent
in the later stages of development. Indirect immunofluorescence using a new monoclonal antibody (KER-1) which recognises a
protein epitope on the keratocan core protein demonstrated that keratocan was present at all stages investigated (E10–E18),
with distinct differences in localisation and organisation observed between early and later stages. Until E13, keratocan appeared
both cell-associated and in the stromal extracellular matrix, and was particularly concentrated in superficial tissue regions.
By E14 when the cornea begins to become transparent, keratocan was located in elongate arrays, presumably associated along
collagen fibrils in the stroma. This fibrillar label was still concentrated in the anterior stroma, and persisted through
E15–E18. Presumptive Bowman’s layer was evident as an unlabelled subepithelial zone at all stages. Thus, in embryonic chick
cornea, keratocan, in common with sulphated KS chains in the E12–E14 developmental period, exhibits a preferential distribution
in the anterior stroma. It undergoes a striking reorganisation of structure and distribution consistent with a role in relation
to stromal compaction and corneal transparency.
E. Claire Gealy and Briedgeen C. Kerr were joint first authors. 相似文献
977.
Hair cells of the inner ear develop from an equivalence group marked by expression of the proneural gene Atoh1. In mouse, Atoh1 is necessary for hair cell differentiation, but its role in specifying the equivalence group (proneural function) has been questioned and little is known about its upstream activators. We have addressed these issues in zebrafish. Two zebrafish homologs, atoh1a and atoh1b, are together necessary for hair cell development. These genes crossregulate each other but are differentially required during distinct developmental periods, first in the preotic placode and later in the otic vesicle. Interactions with the Notch pathway confirm that atoh1 genes have early proneural function. Fgf3 and Fgf8 are upstream activators of atoh1 genes during both phases, and foxi1, pax8 and dlx genes regulate atoh1b in the preplacode. A model is presented in which zebrafish atoh1 genes operate in a complex network leading to hair cell development. 相似文献
978.
Coral microbial communities, zooxanthellae and mucus along gradients of seawater depth and coastal pollution 总被引:3,自引:0,他引:3
The high incidence of coral disease in shallow coastal marine environments suggests seawater depth and coastal pollution have an impact on the microbial communities inhabiting healthy coral tissues. A study was undertaken to determine how bacterial communities inhabiting tissues of the coral Montastraea annularis change at 5 m, 10 m and 20 m water depth in varying proximity to the urban centre and seaport of Willemstad, Cura?ao, Netherlands Antilles. Analyses of terminal restriction fragment length polymorphisms (TRFLP) of 16S rRNA gene sequences show significant differences in bacterial communities of polluted and control localities only at the shallowest seawater depth. Furthermore, distinct differences in bacterial communities were found with increasing water depth. Comparisons of TRFLP peaks with sequenced clone libraries indicate the black band disease cyanobacterium clone CD1C11 is common and most abundant on healthy corals in less than 10 m water depth. Similarly, sequences belonging to a previously unrecognized group of likely phototrophic bacteria, herein referred to as CAB-I, were also more common in shallow water. To assess the influence of environmental and physiologic factors on bacterial community structure, canonical correspondence analysis was performed using explanatory variables associated with: (i) light availability; (ii) seawater pollution; (iii) coral mucus composition; (iv) the community structure of symbiotic algae; and (v) the photosynthetic activity of symbiotic algae. Eleven per cent of the variation in bacterial communities was accounted for by covariation with these variables; the most important being photosynthetically active radiation (sunlight) and the coral uptake of sewage-derived compounds as recorded by the delta(15)N of coral tissue. 相似文献
979.
980.
James M Wells Farzad Esni Gregory P Boivin Bruce J Aronow William Stuart Chelsea Combs Angela Sklenka Steven D Leach Andrew M Lowy 《BMC developmental biology》2007,7(1):4