Biomedical subjects

J Ignacio Rangel-Castro

Publications and source records attributed to J Ignacio Rangel-Castro.

5 recordsLinked to original sources

PubMed2006

Studying plant-microbe interactions using stable isotope technologies.

Interactions between plants and microorganisms in the rhizosphere are complex and varied. They include the general transfer of nutrients and specific interactions mediated by the release of signalling molecules from plant roots. Until recently, understanding the nature of these interactions was limited by a reliance on traditional, cultivation-based techniques. Stable isotope probing provides the potential for cultivation-independent characterisation of organisms actively assimilating carbon derived from plant root exudate or added to the soil. Current applications have focused on interactions with relatively low-level specificity, but there is significant potential for mechanistic studies of more specific interactions, particularly if the sensitivity of the technique can be increased.

Bacteria↗

PubMed2005

Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystem.

The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with (13)CO(2) for a 3-day period. In plots that had been limed (CaCO(3) amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of (13)C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated (13)C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of (13)C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of (13)C fixed and allocated within the plant-soil system.

Biomass↗

PubMed2005

Stable isotope probing analysis of the influence of liming on root exudate utilization by soil microorganisms.

Rhizosphere microorganisms play an important role in soil carbon flow, through turnover of root exudates, but there is little information on which organisms are actively involved or on the influence of environmental conditions on active communities. In this study, a 13CO2 pulse labelling field experiment was performed in an upland grassland soil, followed by RNA-stable isotope probing (SIP) analysis, to determine the effect of liming on the structure of the rhizosphere microbial community metabolizing root exudates. The lower limit of detection for SIP was determined in soil samples inoculated with a range of concentrations of 13C-labelled Pseudomonas fluorescens and was found to lie between 10(5) and 10(6) cells per gram of soil. The technique was capable of detecting microbial communities actively assimilating root exudates derived from recent photo-assimilate in the field. Denaturing gradient gel electrophoresis (DGGE) profiles of bacteria, archaea and fungi derived from fractions obtained from caesium trifluoroacetate (CsTFA) density gradient ultracentrifugation indicated that active communities in limed soils were more complex than those in unlimed soils and were more active in utilization of recently exuded 13C compounds. In limed soils, the majority of the community detected by standard RNA-DGGE analysis appeared to be utilizing root exudates. In unlimed soils, DGGE profiles from 12C and 13C RNA fractions differed, suggesting that a proportion of the active community was utilizing other sources of organic carbon. These differences may reflect differences in the amount of root exudation under the different conditions.

Bacteria↗

PubMed2002

Use of different nitrogen sources by the edible ectomycorrhizal mushroom Cantharellus cibarius.

The growth of three strains of Cantharellus cibarius on liquid media containing ammonium, nitrate and bovine serum albumin (BSA) in different combinations was determined. The most readily utilisable source of N was ammonium. BSA utilisation was limited compared with media containing ammonium. Growth on nitrate was also poor, suggesting a limited capacity of C. cibarius to metabolise this nitrogen source. There was some indication of considerable intraspecific variation within C. cibarius in the utilisation of nitrogen sources. Possible links between atmospheric nitrogen deposition and the observed decrease of sporocarp formation by C. cibarius in Europe are discussed. We highlight the potential ecological significance of bacteria associated with C. cibarius which may circumvent the need for fungal extracellular enzymes to access complex nitrogen sources.

Agaricales↗

PubMed2002

Physiological and genetic characterization of fluorescent Pseudomonas associated with Cantharellus cibarius.

Fluorescent Pseudomonas spp. isolated from fruiting bodies (FB) of Cantharellus cibarius were characterized physiologically and genetically and were compared with fluorescent Pseudomonas from forest soil and with sequences from the GenBank database. Pseudomonas spp. from FB differed physiologically from isolates from soil lacking FB and had some similarities with the strains obtained from soil underneath the FB. Analyses of the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) patterns and partial sequencing analysis of the 16S-rDNA region indicated that the bacteria isolated from these environments were different. However, there was no specific Pseudomonas genotype restricted to the FB environment. Utilization of the reported fungal exudates trehalose and mannitol may explain how millions of bacteria survive in the C. cibarius FB without deteriorating the fungal mycelium. The importance of the metabolic characterization of bacteria and the possible mechanisms involved in the association with C cibarius are discussed. Our study showed that standard processes for bacterial identification, e.g., Biolog and 16S-rDNA are insufficient until databases for different ecosystems are created.

Base Sequence↗