Miguel Angel Quiñones

Bio: Miguel Angel Quiñones is an academic researcher from Spanish National Research Council. The author has contributed to research in topics: Nitrate & Lupinus. The author has an hindex of 9, co-authored 16 publications receiving 282 citations.

Mercury-resistant rhizobial bacteria isolated from nodules of leguminous plants growing in high Hg-contaminated soils

Abstract: A survey of symbiotic bacteria from legumes grown in high mercury-contaminated soils (Almaden, Spain) was performed to produce a collection of rhizobia which could be well adapted to the environmental conditions of this region and be used for restoration practices. Nineteen Hg-tolerant rhizobia were isolated from nodules of 11 legume species (of the genera Medicago, Trifolium, Vicia, Lupinus, Phaseolus, and Retama) and characterized. Based on their growth on Hg-supplemented media, the isolates were classified into three susceptibility groups. The minimum inhibitory concentrations (MICs) and the effective concentrations that produce 50% mortality identified the patterns of mercury tolerance and showed that 15 isolates were tolerant. The dynamics of cell growth during incubation with mercury showed that five isolates were unaffected by exposure to Hg concentrations under the MICs. Genetic analyses of the 16S rRNA gene assigned ten strains to Rhizobium leguminosarum, six to Ensifer medicae, two to Bradyrhizobium canariense, and one to Rhizobium radiobacter. Inoculation of host plants and analysis of the nodC genes revealed that most of them were symbiotically effective. Finally, three isolates were selected for bioremediation processes with restoration purposes on the basis of their levels of Hg tolerance, their response to high concentrations of this heavy metal, and their genetic affiliation and nodulation capacity.

Blue Light, a Positive Switch Signal for Nitrate and Nitrite Uptake by the Green Alga Monoraphidium braunii

Abstract: Blue light was shown to regulate the utilization of oxidized nitrogen sources by green algae, both by activating nitrate reductase and promoting nitrite reductase biosysnthesis (MA Quinones, PJ Aparicio [1990] Inorganic Nitrogen in Plants and Microorganisms, Springer-Verlag, Berlin, pp 171-177; MA Quinones, PJ Aparicio [1990] Photochem Photobiol 51: 681-692). The data reported herein show that, when cells of Monoraphidium braunii at pH 8, containing both active nitrate reductase and nitrite reductase, were sparged with CO(2)-free air and irradiated with strong background red light, they took up oxidized nitrogen sources only when PAR comprised blue light. The activation of the transport system(s) of either both nitrate and nitrite was very quick and elicited by low irradiance blue light. In fact, blue light appears to act as a switch signal from the environment, since the uptake of these anions immediately ceased when this radiation was turned off. The requirement of blue light for nitrate uptake was independent of the availability of CO(2) to cells. However, cells under high CO(2) tensions, although they showed an absolute blue light requirement to initially establish the uptake of nitrite, as they gained carbon skeletons to allocate ammonia, gradually increased their nitrite uptake rates in the subsequent red light intervals. Under CO(2)-free atmosphere, cells irradiated with strong background red light of 660 nanometers only evolved oxygen when they were additionally irradiated with low irradiance blue light and either nitrate or nitrite was present in the media to provide electron acceptors for the photosynthetic reaction.

Blue-light-induced pH changes associated with NO3−, NO2− and Cl− uptake by the green alga Monoraphidium braunii

Abstract: In M. braunii, the uptake of NO3− and NO2− is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO2-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO3− and NO2− reductases were active, the pH increased to values of around 10, since the NH4+ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H2SO4 of NO3− or NO2− uptake and reduction showed that two protons were consumed for every one NH4+ released. The uptake of Cl− was also triggered by blue light with a similar 10 s time response. However, the Cl− -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl−) taken up by the cells were released to the medium. When the cells lacked NO3− and NO2− reductases, the shape of the alkalinization traces in the presence of NO3− and NO2− was similar to that in the presence of Cl−, suggesting that NO3− or NO2− was also released to the medium. Both the NO3− and Cl−-dependent rates of alkalinization were independent of mono- and divalent cations.

Chlamydomonas as a model organism

Abstract: The unicellular green alga Chlamydomonas offers a simple life cycle, easy isolation of mutants, and a growing array of tools and techniques for molecular genetic studies. Among the principal areas of current investigation using this model system are flagellar structure and function, genetics of basal bodies (centrioles), chloroplast biogenesis, photosynthesis, light perception, cell-cell recognition, and cell cycle control. A genome project has begun with compilation of expressed sequence tag data and gene expression studies and will lead to a complete genome sequence. Resources available to the research community include wild-type and mutant strains, plasmid constructs for transformation studies, and a comprehensive on-line database.

A review of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions

Abstract: Emiliania huxleyi is numerically the most important coccolithophorid in the modern ocean and has been intensely studied in the contexts of biogeochemistry (especially relating to the global carbon cycle), plankton ecology, biomineralization, and cellular carbon transport. This paper reviews older as well as more recently acquired information on reproduction, morphology, ecophysiology, and cell physiology of E. huxleyi, emphasizing aspects that are relevant to coccolith formation and calcification–photosynthesis interactions. The existence of a number of ecotypes, which probably accounts for the wide distribution of this species in nature, complicates comparisons between laboratory studies in which different clones have been used. Coccolith formation is a strongly regulated process; use of mutants may be helpful in elucidating the control mechanisms involved. Conceptual models illustrating the role of calcification in photosynthetic carbon supply are supported by extensive experimental evidence, b...

List of new names and new combinations previously effectively, but not validly, published.

Abstract: The purpose of this announcement is to effect the valid publication of the following effectively published new names and new combinations under the procedure described in the Bacteriological Code (1990 Revision). Authors and other individuals wishing to have new names and/or combinations included in future lists should send three copies of the pertinent reprint or photocopies thereof, or an electronic copy of the published paper to the IJSEM Editorial Office for confirmation that all of the other requirements for valid publication have been met. It is also a requirement of IJSEM and the ICSP that authors of new species, new subspecies and new combinations provide evidence that types are deposited in two recognized culture collections in two different countries. It should be noted that the date of valid publication of these new names and combinations is the date of publication of this list, not the date of the original publication of the names and combinations. The authors of the new names and combinations are as given below. Inclusion of a name on these lists validates the publication of the name and thereby makes it available in the nomenclature of prokaryotes. The inclusion of a name on this list is not to be construed as taxonomic acceptance of the taxon to which the name is applied. Indeed, some of these names may, in time, be shown to be synonyms, or the organisms may be transferred to another genus, thus necessitating the creation of a new combination.

Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton

Abstract: We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations of nitrate (NO ) 2 3 during its assimilation by laboratory cultures of marine phytoplankton and derive the N and O kinetic isotope effects for nitrate assimilation by three species of diatoms ( Thalassiosira weissflogii, Thalassiosira oceanica,and Thalassiosira pseudonana) and a coccolithophorid (Emiliana huxleyi). Large interspecies and intraspecies variations in the N isotope effects were observed. The O isotope effect associated with nitrate consumption was consistently close to the N isotope effect, such that the 18 O/ 16 O and 15 N/ 14 N of nitrate varied in a ratio of ;1 : 1, regardless of species or of the magnitude of the isotope effect. In addition, the 18 O/ 16 O and 15 N/ 14 N of internal nitrate of T. weissflogii grown under various environmental conditions were elevated relative to the medium nitrate by a proportion of ; 1: 1. These findings are consistent with a nitrate isotopic fractionation mechanism that involves nitrate reduction as the chief fractionating step. The observed N : O isotopic coupling during nitrate assimilation suggests that combined N and O isotopic measurements of water column nitrate can provide new constraints on the ocean N cycle.

Nitrate and ammonium nutrition of plants: physiological and molecular perspectives

Abstract: Nitrogen is the mineral nutrient that plants need in the greatest quantities and the one that most frequently limits plant growth and crop yields. Most plants get their nitrogen (N) from the soil as either nitrate or ammonium, with some species showing a strong preference for one ionic form over the other. The uptake of nitrate and ammonium ions by roots involves a complex set of membrane transport systems that includes both high- and low-affinity transporters; net uptake rates can also be strongly influenced by the rate at which these ions efflux from root cells. Here we review our current picture of the mechanisms responsible for the uptake and efflux of nitrate and ammonium, attempting to integrate the large body of physiological data with the recent advances in the molecular biology of nitrate and ammonium transporters in bacteria and algae as well as in higher plants. We also review what is known at the physiological and molecular levels about the regulation of the N uptake systems, a process which involves both positive signals from soil nitrate or ammonium and feedback inhibitory signals that are generated by the plant's internal N status