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81.
Paris Laskaris Sahar Tolba Leo Calvo‐Bado Liz Wellington 《Environmental microbiology》2010,12(3):783-796
We present evidence for the coexistence and coevolution of antibiotic resistance and biosynthesis genes in soil bacteria. The distribution of the streptomycin (strA) and viomycin (vph) resistance genes was examined in Streptomyces isolates. strA and vph were found either within a biosynthetic gene cluster or independently. Streptomyces griseus strains possessing the streptomycin cluster formed part of a clonal complex. All S. griseus strains possessing solely strA belonged to two clades; both were closely related to the streptomycin producers. Other more distantly related S. griseus strains did not contain strA. S. griseus strains with only vph also formed two clades, but they were more distantly related to the producers and to one another. The expression of the strA gene was constitutive in a resistance‐only strain whereas streptomycin producers showed peak strA expression in late log phase that correlates with the switch on of streptomycin biosynthesis. While there is evidence that antibiotics have diverse roles in nature, our data clearly support the coevolution of resistance in the presence of antibiotic biosynthetic capability within closely related soil dwelling bacteria. This reinforces the view that, for some antibiotics at least, the primary role is one of antibiosis during competition in soil for resources. 相似文献
82.
Cytosolic phospholipase A(2)α (cPLA(2)α) up-regulation has been reported in human colorectal cancer cells, thus we aimed to elucidate its role in the proliferation of the human colorectal cancer cell line, HT-29. EGF caused a rapid activation of cPLA(2)α which coincided with a significant increase in cell proliferation. The inhibition of cPLA(2)α activity by pyrrophenone or by antisense oligonucleotide against cPLA(2)α (AS) or inhibition of prostaglandin E(2) (PGE(2)) production by indomethacin resulted with inhibition of cell proliferation, that was restored by addition of PGE(2). The secreted PGE(2) activated both protein kinase A (PKA) and PKB/Akt pathways via the EP2 and EP4 receptors. Either, the PKA inhibitor (H-89) or the PKB/Akt inhibitor (Ly294002) caused a partial inhibition of cell proliferation which was restored by PGE(2). But, inhibited proliferation in the presence of both inhibitors could not be restored by addition of PGE(2). AS or H-89, but not Ly294002, inhibited CREB activation, suggesting that CREB activation is mediated by PKA. AS or Ly294002, but not H-89, decreased PKB/Akt activation as well as the nuclear localization of β-catenin and cyclin D1 and increased the plasma membrane localization of β-catenin with E-cadherin, suggesting that these processes are regulated by the PKB pathway. Similarly, Caco-2 cells exhibited cPLA(2)α dependent proliferation via activation of both PKA and PKB/Akt pathways. In conclusion, our findings suggest that the regulation of HT-29 proliferation is mediated by cPLA(2)α-dependent PGE(2) production. PGE(2)via EP induces CREB phosphorylation by the PKA pathway and regulates β-catenin and cyclin D1 cellular localization by PKB/Akt pathway. 相似文献
83.
Finnon P Robertson N Dziwura S Raffy C Zhang W Ainsbury L Kaprio J Badie C Bouffler S 《Human genetics》2008,123(5):485-493
Genetic factors are likely to affect individual cancer risk, but few quantitative estimates of heritability are available.
Public health radiation protection policies do not in general take this potentially important source of variation in risk
into account. Two surrogate cellular assays that relate to cancer susceptibility have been developed to gain an insight into
the role of genetics in determining individual variation in radiosensitivity. These flow cytometric assays for apoptosis induction
and cell cycle delay following radiation are sufficiently sensitive to distinguish lymphocytes from a healthy donor population
from those of a sample of obligate carriers of ATM mutations (P = 0.01 and P = 0.02, respectively). Analysis of 54 unselected twin pairs (38 dizygotic, 16 monozygotic) indicated much greater intrapair
correlation in response in monozygotic than in dizygotic pairs. Structural equation modelling indicated that models including
unique environmental factors only fitted the data less well than those incorporating two or more of additive genetic factors,
common environmental factors and unique environmental factors. A model incorporating additive genetic factors and unique environmental
factors yielded estimates of heritability for the two traits of 68% (95% CI 40–82%, cell cycle) and 59% (95% CI 22–79%, apoptosis).
Thus, these data suggest that genetic factors contribute significantly to human variation in these two measures of radiosensitivity
that relate to cancer susceptibility. 相似文献
84.
Soil microbial communities can have an important role in the adaptation of plants to their local abiotic soil conditions and in mediating plant responses to environmental stress. This has been clearly demonstrated for individual plant species, but it is unknown how locally adapted microbes may affect plant communities. It is possible that the adaptation of microbial communities to local conditions can shape plant community composition. Additionally, it is possible that the effects of locally adapted microorganisms on individual plant species could be altered by co-occurring plant species. We tested these possibilities in plant community mesocosms with soils and mycorrhizal fungi (AMF) from three locations. We found that plant community biomass responded positively to local adaptation of AMF to soil conditions. Plant community composition also changed in response to local adaptation of AMF. Unexpectedly, the strongest benefits of locally adapted AMF went to early successional plant species that have the highest relative growth rates and the lowest responsiveness to the presence of AMF. Late successional plants that responded positively overall to the presence of AMF were often suppressed in communities with local AMF, perhaps because of strong competition from fast growing plant species. These results show that local adaptation of soil microbial communities can shape plant community composition, and the benefits that plants derive from locally adapted microorganisms can be reshaped by the competitive context in which these associations occur. 相似文献
85.
David G. Alberg Thomas B. Poulsen Søren Bertelsen Kasper L. Christensen Rune D. Birkler Mogens Johannsen Karl Anker Jørgensen 《Bioorganic & medicinal chemistry letters》2009,19(14):3888-3891
The aldol reaction of the endogeneous compounds acetone and methylglyoxal has been studied using organocatalysis in relation to biologically relevant non-enzymatic reactions. Under preparative conditions, 3-hydroxy-2,5-hexadione, known as Henze’s ketol, is formed in high yield and with enantioselectivities up to 88% ee. Furthermore, Henze’s ketol is also formed under simulated physiological conditions at micromolar scale, indicating that this reaction might take place in living organisms. 相似文献
86.
87.
Calcium limitation in Daphnia magna 总被引:1,自引:0,他引:1
The role of ambient calcium concentrations on survival, moulting,growth and egg production was assessed in the cladoceran Daphniamagna. A threshold for survival was found in the range 0.10.5mg Ca l1, even when ionic strength of the medium waskept constant. Accumulated length and length specific dry weightwas retarded at low Ca (0.51.0 mg Ca l1) at foodconcentrations above incipient limiting level. For lower foodlevels, the effect of Ca on growth was less clear. The effectof low Ca on growth rate was most manifest during the firstdays after hatching, reflecting the higher Ca demands of theearly juveniles. Age-specific egg production was strongly reducedat Ca concentrations <10 mg Ca l1. This was partlyan indirect effect of reduced growth rates, but could also bean effect of higher energetic costs associated with Ca uptakein a Ca-poor medium. The high Ca demands in D.magna may notbe representative of other Daphnia species. Nevertheless, highspecific Ca content seems to be a common property of Daphniaspp. and Ca deficiency could be a major determinant of speciessuccess and community structure among crustacean zooplankton;it also puts constraints on carbon sequestration in the pelagicfood web of softwater lakes. 相似文献
88.
Teichert Nils Lizé Anne Tabouret Hélène Gérard Claudia Bareille Gilles Acou Anthony Carpentier Alexandre Trancart Thomas Virag Laure-Sarah Robin Emma Druet Morgan Prod’Homme Jordan Feunteun Eric 《Hydrobiologia》2022,849(8):1885-1903
Hydrobiologia - River fragmentation is expected to impact not only movement patterns and distribution of eels within catchment, but also their life-history traits. Here, we used otolith... 相似文献
89.
Heather M. Kraus William E. Jensen Gregory R. Houseman Mary Liz Jameson Molly M. Reichenborn D. Fraser Watson Esben L. Kjaer 《The Journal of wildlife management》2022,86(2):e22152
Bird populations in grasslands have experienced declines coinciding with loss and fragmentation of prairies. The United States Department of Agriculture (USDA)-administered Conservation Reserve Program (CRP) is the most extensive grassland restoration program in North America and it has especially benefitted grassland birds. Grazing by domestic cattle has been restricted in CRP during avian nesting seasons despite the potential improvements in structuring habitat for a greater diversity of grassland bird species. Potential negative consequences of grazing in CRP grasslands include trampling of nests by cattle, reductions in nest concealment from predators, and attraction of brood-parasitic brown-headed cowbirds (Molothrus ater). We designed an experiment to test for effects of cattle grazing in CRP fields during the nesting season on nest survival and brood parasitism of 5 bird species that commonly nest in CRP grasslands: mourning dove (Zenaida macroura), grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern (Sturnella magna) and western (S. neglecta) meadowlarks. Grazing was implemented during summers 2017 and 2018 on 17 of 36 fields followed by a year of rest on all fields in 2019. Of the 879 nests on grazed fields, only 4 were likely trampled by cattle (vs. 54% of all nests estimated as failing because of depredation). Experimental grazing (grazed vs. ungrazed fields) had variable effects on nest survival and cowbird parasitism among the bird species analyzed. Negative effects of grazing on daily nest survival of dickcissel and meadowlarks were apparent, at least in some years. We found no direct effects of grazing on nest survival of mourning dove or grasshopper sparrow. Probability and intensity (cowbird offspring/nest) of cowbird parasitism in dickcissel nests was higher on grazed versus ungrazed sites but only in conservation practice (CP) CP2 (vs. CP25 fields). Parasitism probability of grasshopper sparrow nests by cowbirds was higher on grazed fields in the 2 years after introduction of cattle in 2017. Greater vegetative concealment around nest sites was associated with reduced cowbird parasitism of meadowlark and grasshopper sparrow nests and higher nest survival for grasshopper sparrows. Reductions in vegetative height caused by longer-term or high-intensity grazing might therefore have negative consequences for some grassland birds by increasing nest site visibility and exposure to cowbird parasitism. Our results indicate that cattle grazing in CRP fields during the nesting season might have some negative effects on reproductive success of some grassland bird species, at least in the short term; however, the potential improvements of structuring habitat to accommodate more grassland bird species and increasing landowner participation in the CRP are considerable. 相似文献
90.
Liz Stevenson Erik Laursen Graeme J. Cowan Betty Bandoh Lea Barfod David R. Cavanagh Gregers R. Andersen Lars Hviid 《PLoS pathogens》2015,11(7)
Rosetting, the adhesion of Plasmodium falciparum-infected erythrocytes to uninfected erythrocytes, involves clonal variants of the parasite protein P. falciparum erythrocyte membrane protein 1 (PfEMP1) and soluble serum factors. While rosetting is a well-known phenotypic marker of parasites associated with severe malaria, the reason for this association remains unclear, as do the molecular details of the interaction between the infected erythrocyte (IE) and the adhering erythrocytes. Here, we identify for the first time a single serum factor, the abundant serum protease inhibitor α2-macroglobulin (α2M), which is both required and sufficient for rosetting mediated by the PfEMP1 protein HB3VAR06 and some other rosette-mediating PfEMP1 proteins. We map the α2M binding site to the C terminal end of HB3VAR06, and demonstrate that α2M can bind at least four HB3VAR06 proteins, plausibly augmenting their combined avidity for host receptors. IgM has previously been identified as a rosette-facilitating soluble factor that acts in a similar way, but it cannot induce rosetting on its own. This is in contrast to α2M and probably due to the more limited cross-linking potential of IgM. Nevertheless, we show that IgM works synergistically with α2M and markedly lowers the concentration of α2M required for rosetting. Finally, HB3VAR06+ IEs share the capacity to bind α2M with subsets of genotypically distinct P. falciparum isolates forming rosettes in vitro and of patient parasite isolates ex vivo. Together, our results are evidence that P. falciparum parasites exploit α2M (and IgM) to expand the repertoire of host receptors available for PfEMP1-mediated IE adhesion, such as the erythrocyte carbohydrate moieties that lead to formation of rosettes. It is likely that this mechanism also affects IE adhesion to receptors on vascular endothelium. The study opens opportunities for broad-ranging immunological interventions targeting the α2M—(and IgM-) binding domains of PfEMP1, which would be independent of the host receptor specificity of clinically important PfEMP1 antigens. 相似文献