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11.
Manuel J. López-Nieto Filomena R. Ramos José M. Luengo Juan F. Martín 《Applied microbiology and biotechnology》1985,22(5):343-351
Summary The parameters affecting the formation in vivo of -aminoadipyl-cysteinyl-valine (ACV), an intermediate in penicillin biosynthesis, have been established in low- and high-penicillin producing strains ofPenicillium chrysogenum. ACV was found both in cell extracts and in the culture broth filtrates. (14C)valine, -(14C)aminoadipic acid and (14C)cysteine were efficiently incorporated into ACV. Formation of ACV was stimulated by phenylacetic acid when added during the growth of the culture. ACV biosynthesis was enhanced when protein synthesis was blocked with cycloheximide or anisomicin. The ACV-synthesising activity of the culture increased between 24 and 48 h of the culture preceeding penicillin biosynthesis, and remained constant thereafter. A decay of ACV-forming activity was observed when de novo protein synthesis was inhibited with cycloheximide. The apparent half-life of the ACV-synthesising enzyme system was 2.5 h. 相似文献
12.
Rhizobia are soil bacteria which symbiotically infect legume roots and generate nodules in which they fix atmospheric nitrogen for the plant in exchange for photosynthetically fixed carbon. A crucial aspect of signal exchange between these symbionts is the secretion of phenolic compounds by the host root which induce nodulation gene expression in the bacteria. Stimulation of nod gene expression by host phenolics is required for nodule formation, is biochemically specific at 10-6
M, and is mediated by nodD. We and others have shown that rhizobia display chemotaxis to 10-9
M of the same phenolic compounds. Chemotaxis to inducer phenolics is selectively reduced or abolished by mutations in certain nod genes governing nodulation efficiency or host specificity. Conversely, mutations in rhizobia that affect general motility or chemotaxis have substantial effects on nodulation efficiency and competitiveness. These findings suggest that microbes entering the rhizosphere environment may utilize minor, non-nutrient components in root exudates as signals to guide their movement towards the root surface and elicit changes in gene expression appropriate to this environment. 相似文献
13.
Caridad Rojas Susana Cadenas Mónica López-Torres Rosa Pérez-Campo Gustavo Barja 《Free radical biology & medicine》1996,21(7):907-915
Dietary treatment with three diets differing in vitamin E, Low E (15 mg of vitamin E/kg diet), Medium E (150 mg/kg), or High E (1,500 mg/kg), resulted in guinea pigs with low (but nondeficient), intermediate, or high heart a-tocopherol concentration. Neither the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, and reductase, nor the nonenzymatic antioxidants, GSH, ascorbate, and uric acid were homeostatically depressed by increases in heart a-tocopherol. Protection from both enzymatic (NADPH dependent) and nonenzymatic (ascorbate-Fe2+) lipid peroxidation was strongly increased by vitamin E supplementation from Low to Medium E Whereas no additional gain was obtained from the Medium E to the High E group. The GSH/GSSG and GSH/total glutathione ratios increased as a function of the vitamin E dietary concentration closely resembling the shape of the dependence of heart a-tocopherol on dietary vitamin E. The results show the capacity of dietary vitamin E to increase the global antioxidant capacity of the heart and to improve the heart redox status in both the lipid and water-soluble compartments. This capacity occurred at levels six times higher than the minimum daily requirement of vitamin E, even in the presence of optimum dietary vitamin C concentrations and basal unstressed conditions. The need for vitamin E dietary supplementation seems specially important in this tissue due to the low constitutive levels of endogenous enzymatic and nonenzymatic antioxidants present of the mammalian heart in comparison with those of other internal organs. 相似文献
14.
Gustavo Caetano-Anollés Brant J. Bassam Peter M. Gresshoff 《Molecular & general genetics : MGG》1993,241(1-2):57-64
Multiple endonuclease digestion of template DNA or amplification products can increase significantly the detection of polymorphic DNA in fingerprints generated by multiple arbitrary amplicon profiling (MAAP). This coupling of endonuclease cleavage and amplification of arbitrary stretches of DNA, directed by short oligonucleotide primers, readily allowed distinction of closely related fungal and bacterial isolates and plant cultivars. MAAP analysis of cleaved template DNA enabled the identification of molecular markers linked to a developmental locus of soybean (Glycine max L. Merrill). Ethyl methane sulfonate (EMS)-induced supernodulating, near-isogenic lines altered in the nts locus, which controls nodule formation, could be distinguished from each other and from the parent cultivar by amplification of template pre-digested with 2–3 restriction enzymes. A total of 42 DNA polymorphisms were detected using only 19 octamer primers. In the absence of digestion, 25 primers failed to differentiate these soybean genotypes. Several polymorphic products co-segregated tightly with the nts locus in F2 families from crosses between the allelic mutants nts382 and nts1007 and the ancestral G. soja Sieb. & Succ. PI468.397. Our results suggest that EMS is capable of inducing extensive DNA alterations, probably around discrete mutational hot-spots. EMS-induced DNA polymorphisms may constitute sequence-tagged markers diagnostic of specific genomic regions. 相似文献
15.
Honorina Martínez-Blanco Angel Reglero Dr. José M. Luengo 《Journal of industrial microbiology & biotechnology》1994,13(3):144-146
Summary The effect of phenylacetic acid (PAA) and several analogs on the activity of isopenicillin N synthase (IPNS) and acyl-CoA: 6-APA acyltransferase (AT) fromPenicillium chrysogenum Wis 54-1255 has been tested. Whereas the substitution on the ring of a hydrogen atom by hydroxy-, methyl- or methoxy- groups did not cause any effect, the presence of halogens (Cl or Br) at positions 3 and/or 4 of PAA strongly inhibited these two enzymes. The replacement of hydrogen atoms by fluorine in certain positions also caused inhibition, but to a lesser extent. 相似文献
16.
Gustavo A. Romero 《Brittonia》1993,45(3):237-239
A new Catasetum species from Brazil,Catasetum confusum, is described and illustrated. This widely cultivated species had been referred previously toCatasetum ornithoides Pabst. 相似文献
17.
Pereyra Paula Evelyn Rubira Hallwass Gustavo Begossi Alpina Giacomin Leandro Lacerda Silvano Renato Azevedo Matias 《Ecosystems》2023,26(5):1095-1107
Ecosystems - Frugivory and seed dispersal by fish is an important mutualistic interaction in complex and species-rich tropical rivers. The local ecological knowledge (LEK) held by fishers can... 相似文献
18.
19.
Franco M. Valdez Ovallez Rodrigo Gómez Alés Vanesa Astudillo Mariela Córdoba Gustavo Fava Rodrigo Acosta Graciela Blanco José Villavicencio Juan Carlos Acosta 《Acta zoologica》2023,104(4):561-574
Ectotherms thermoregulate to maintain their body temperature within the optimal range needed for performing vital functions. The effect of climate change on lizards has been studied as regards the sensitivity of locomotor performance to environmental temperatures. We studied thermoregulatory efficiency and locomotor performance for Liolaemus fitzgeraldi in the Central Andes of Argentina. We determined body temperature, micro-environmental temperatures and operative temperatures in the field. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. We estimated the thermal sensitivity of locomotion by measuring sprint speed (initial velocity and long sprint) and endurance at five different body temperatures. Body temperature was not associated with either micro-environmental temperature, nor did it show differences with preferred temperatures. Thermoregulatory efficiency was moderate (0.61). Initial velocity and long sprint trials showed differences at different temperatures; however, endurance did not. Moreover, the optimal temperatures for the performance trials showed no significant differences among themselves. We conclude that Liolaemus fitzgeraldi has thermal sensitivity in locomotor performance with respect to body temperature and that it is an eurythermic lizard that experiences a large variation in body temperature and that has thermal flexibility in the cold. 相似文献
20.
Gustavo A. Londoño Juan Pablo Gomez Manuel A. Sánchez-Martínez Douglas J. Levey Scott K. Robinson 《Ecology letters》2023,26(4):609-620
Tropical montane communities host the world's highest beta diversity of birds, a phenomenon usually attributed to community turnover caused by changes in biotic and abiotic factors along elevation gradients. Yet, empirical data on most biotic factors are lacking. Nest predation is thought to be especially important because it appears to be common and can change selective pressures underlying life history traits, which can alter competitive interactions. We monitored 2538 nests, 338 of which had known nest predators, to evaluate if nest predation changes along a tropical elevational gradient. We found that nest predation decreased with elevation, reflecting the loss of lowland predators that do not tolerate colder climates. We found different “super” nest predators at each elevation that accounted for a high percentage of events, suggesting that selection pressures exerted by nest predator communities may be less diffuse than has been hypothesized, at least for birds nesting in the understory. 相似文献