RESUMEN
Paenibacillus sp. EJP73 has been previously demonstrated as a mycorrhization helper bacterium (MHB) for the Lactarius rufus-Pinus sylvestris symbiosis in both laboratory and glasshouse experiments. In the present study, the effect of Paenibacillus sp. EJP73 metabolites on L. rufus EO3 pre-symbiotic growth was tested in two agar plate-based systems. Specifically, volatile metabolites were investigated using a dual plate system, in which the presence of strain EJP73 resulted in a significant negative effect on L. rufus EO3 hyphal radial growth but enhanced hyphal branching and reduced internode distance. Soluble metabolites produced by strain EJP73 were tested on L. rufus EO3 growth in single-agar plate assays by incorporating bacterial cell-free whole or molecular weight fraction spent broth into the agar. Whole spent broth had a negative effect on hyphal growth, whereas a low molecular weight fraction (100-1,000) promoted colony radial growth. Headspace and spent broth analysis of strain EJP73 cultures revealed 2,5-diisopropylpyrazine to be the most significant component. Synthesised 2,5-diisopropylpyrazine and elevated CO2 (2,000 ppm) were tested as specific volatile metabolites in the dual plate system, but neither produced the response shown when strain EJP73 was present. Increased pre-symbiotic hyphal branching leading to increased likelihood of plant infection may be an important MHB mechanism for strain EJP73. Although the precise signal molecules could not be identified, the work suggests a number of metabolites may work synergistically to increase L. rufus root colonisation.
Asunto(s)
Basidiomycota/crecimiento & desarrollo , Factores Biológicos/metabolismo , Hifa/crecimiento & desarrollo , Micorrizas/crecimiento & desarrollo , Paenibacillus/metabolismo , Pinus sylvestris/microbiología , Compuestos Orgánicos Volátiles/metabolismo , Basidiomycota/efectos de los fármacos , Factores Biológicos/química , Factores Biológicos/farmacología , Hifa/efectos de los fármacos , Peso Molecular , Micorrizas/efectos de los fármacos , Paenibacillus/química , Raíces de Plantas/microbiología , Compuestos Orgánicos Volátiles/farmacologíaRESUMEN
The role of litter tannins in controlling soil nitrogen (N) cycling may explain the competitive ability of Kalmia relative to black spruce (Picea mariana), although this has not been demonstrated experimentally. Here, the protein-precipitation capacities of purified tannins and leaf extracts from Kalmia and black spruce were compared. The resistance to degradation of tannin-protein precipitates from both species were compared by monitoring carbon (C) and N dynamics in humus amended with protein, purified tannins or protein-tannin precipitates. The purity of the precipitates was verified using solid-state (13)C nuclear magnetic resonance (NMR) spectra. The ability of mycorrhizal fungi associated with both species to grow on media amended with tannin-protein complexes as the principal N source was also compared. The protein precipitation capacity of Kalmia tannins was superior to those of black spruce. Humus amended with protein increased both mineral and microbial N, whereas humus amended with tannin-protein precipitates increased dissolved organic N. Mycorrhizal fungi associated with Kalmia showed better growth than those associated with black spruce when N was provided as tannin-protein precipitates. These data suggest that Kalmia litter increases the amount of soil N sequestered as tannin-protein complexes, which may improve the competitive ability of Kalmia relative to black spruce by favouring N uptake by mycorrhizas associated with the former.
Asunto(s)
Ericaceae/crecimiento & desarrollo , Nitrógeno/metabolismo , Picea/crecimiento & desarrollo , Taninos/metabolismo , Adaptación Fisiológica , Ericaceae/metabolismo , Espectroscopía de Resonancia Magnética , Micorrizas/crecimiento & desarrollo , Picea/metabolismo , Suelo , Microbiología del SueloRESUMEN
The phyllosphere represents the habitat provided by the aboveground parts of plants, and on a global scale supports a large and complex microbial community. Microbial interactions in the phyllosphere can affect the fitness of plants in natural communities, the productivity of agricultural crops, and the safety of horticultural produce for human consumption. The structure of phyllosphere communities reflects immigration, survival and growth of microbial colonists, which is influenced by numerous environmental factors in addition to leaf physico-chemical properties. The recent use of culture-independent techniques has demonstrated considerable previously unrecognized diversity in phyllosphere bacterial communities. Furthermore, there is significant recent evidence that plant genotype can play a major role in determining the structure of phyllosphere microbial communities. The main aims of this review are: (i) to discuss the diversity of phyllosphere microbial populations; (ii) to consider the processes by which microbes colonize the phyllosphere; (iii) to address the leaf characteristics and environmental factors that determine the survival and growth of colonists; (iv) to discuss microbial adaptations that allow establishment in the phyllosphere habitat and (v) to evaluate evidence for plant genotypic control of phyllosphere communities. Finally, we suggest approaches and priority areas for future research on phyllosphere microbiology.
Asunto(s)
Biodiversidad , Ecosistema , Plantas/microbiología , Genotipo , Hojas de la Planta/microbiología , Plantas/genética , Microbiología del SueloRESUMEN
This review looks briefly at plants and their rhizosphere microbes, the chemical communications that exist, and the biological processes they sustain. Primarily it is the loss of carbon compounds from roots that drives the development of enhanced microbial populations in the rhizosphere when compared with the bulk soil, or that sustains specific mycorrhizal or legume associations. The benefits to the plant from this carbon loss are discussed. Overall the general rhizosphere effect could help the plant by maintaining the recycling of nutrients, through the production of hormones, helping to provide resistance to microbial diseases and to aid tolerance to toxic compounds. When plants lack essential mineral elements such as P or N, symbiotic relationships can be beneficial and promote plant growth. However, this benefit may be lost in well-fertilized (agricultural) soils where nutrients are readily available to plants and symbionts reduce growth. Since these rhizosphere associations are commonplace and offer key benefits to plants, these interactions would appear to be essential to their overall success.
Asunto(s)
Raíces de Plantas/microbiología , Raíces de Plantas/fisiología , Microbiología del Suelo , Ecosistema , Enfermedades de las Plantas , Transducción de Señal , Suelo/análisisRESUMEN
The nucleotide sequence of the internal transcribed spacer (ITS) 1 and 2 regions was determined for 22 Suillus isolates representing seven species. Analysis of the sequence data along with 12 related sequences from databases divided the 34 isolates into seven groups, and six of these were supported by 100% bootstrap values. Isolates belonging to Suillus granulatus (0-11 divergence) were divided into three groups (SG1, SG2 and SG3); SG1 and SG2 had 100% bootstrap values. SG2 was clustered with two Suillus collinitus isolates and a Suillus variegatus isolate; SG3 was linked to a previously characterised Suillus subluteus isolate. These results clearly indicate heterogeneity among the isolates described under these species. Intra- (0.4-11) and inter- (2.4-13.6) specific divergence varied considerably. Suillus laricinus showed a high level (0.5-4.4) of intra-specific divergence. Suillus bovinus showed maximum divergence (11.4-13.3) to all other species examined. The potential of the ITS region for understanding the intra- and inter-specific relationships among Suillus species and refining their taxonomy is discussed.
Asunto(s)
Basidiomycota/clasificación , ADN Espaciador Ribosómico/genética , Variación Genética , ARN Ribosómico 5.8S/genética , Análisis de Secuencia de ADN , Basidiomycota/genética , ADN de Hongos/análisis , ADN de Hongos/genética , ADN Espaciador Ribosómico/análisis , Europa (Continente) , Datos de Secuencia Molecular , Árboles/microbiologíaRESUMEN
Thirty samples of soil were taken at 50-m intersections on a grid pattern over an area of 250 x 200 m within a single field with nominally uniform soil characteristics. Incubations of isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) under standard conditions (15 degrees C; -33 kPa soil water potential) indicated considerable variation in degradation rate of the herbicide, with the time to 50% loss (DT50) varying from 6.5 to 30 days. The kinetics of degradation also varied between the sub-samples of soil. In many of them, there was an exponential decline in isoproturon residues; in others, exponential loss was followed by more rapid rates of decline; in a few soil samples, rapid rates of loss began shortly after the start of the incubations. In more detailed studies with soils from a smaller number of sub-sites (20), measurements were again made of isoproturon degradation rate, and the soils were analysed for organic matter content, pH, and nutrient status (N, P, K). Measurements were also made of isoproturon adsorption by the soils and of soil microbial biomass. Patterns of microbial metabolism were assessed using 95 substrates in Biolog GN plates. Soils showing rapid biodegradation were generally of higher pH and contained more available potassium than those showing slower degradation rates. They also had a larger microbial biomass and greater microbial metabolic diversity as determined by substrate utilisation on Biolog GN plates. The implications of the results for the efficacy and environmental behaviour of isoproturon are discussed.