RESUMEN
Soil environments are dynamic and the plant rhizosphere harbours a phenomenal diversity of micro-organisms which exchange signals and beneficial nutrients. Bipartite beneficial or symbiotic interactions with host roots, such as mycorrhizae and various bacteria, are relatively well characterized. In addition, a tripartite interaction also exists between plant roots, arbuscular mycorrhizal fungi (AMF) and associated bacteria. Bacterial biofilms exist as a sheet of bacterial cells in association with AMF structures, embedded within a self-produced exopolysaccharide matrix. Such biofilms may play important functional roles within these tripartite interactions. However, the details about such interactions in the rhizosphere and their relevant functional relationships have not been elucidated. This review explores the current understanding of naturally occurring microbial biofilms, and their interaction with biotic surfaces, especially AMF. The possible roles played by bacterial biofilms and the potential for their application for a more productive and sustainable agriculture is discussed in this review.
Asunto(s)
Agricultura , Biopelículas , Rizosfera , Fenómenos Fisiológicos Bacterianos , Biopelículas/crecimiento & desarrollo , Micorrizas/fisiología , Raíces de Plantas/microbiología , Microbiología del Suelo , SimbiosisRESUMEN
The global biogeography of microorganisms remains largely unknown, in contrast to the well-studied diversity patterns of macroorganisms. We used arbuscular mycorrhizal (AM) fungus DNA from 1014 plant-root samples collected worldwide to determine the global distribution of these plant symbionts. We found that AM fungal communities reflected local environmental conditions and the spatial distance between sites. However, despite AM fungi apparently possessing limited dispersal ability, we found 93% of taxa on multiple continents and 34% on all six continents surveyed. This contrasts with the high spatial turnover of other fungal taxa and with the endemism displayed by plants at the global scale. We suggest that the biogeography of AM fungi is driven by unexpectedly efficient dispersal, probably via both abiotic and biotic vectors, including humans.
Asunto(s)
Ecosistema , Micorrizas , Raíces de Plantas/microbiología , Simbiosis , Animales , Biodiversidad , ADN de Hongos/análisis , Ambiente , Humanos , Micorrizas/genética , Micorrizas/aislamiento & purificación , Micorrizas/fisiología , Filogenia , Filogeografía , Agua , VientoRESUMEN
Pichia membranifaciens strain FY-101, isolated from grape skins, was found to be antagonistic to Botrytis cinerea, the causal organism of the grey mould disease of the grapevine. When grown together on solid as well as liquid media, the yeast brings about the inhibition of this parasitic fungus, coagulation and leakage of its cytoplasm, and suppression of its ability to produce the characteristic grey mould symptoms on the grapevine plantlets. In vitro experiments confirm that this yeast can be used as a biological control organism against B. cinerea. An account of the molecular characterisation of P. membranifaciens (complete sequence of the ITS region of its ribosomal DNA, GenBank accession No. AF 270935), as well as the interaction between B. cinerea and the yeast, are given here.
Asunto(s)
Antibiosis , Botrytis/fisiología , Pichia/fisiología , Rosales/microbiología , Secuencia de Bases , ADN Ribosómico/genética , Datos de Secuencia Molecular , Pichia/genética , Enfermedades de las Plantas/microbiología , Alineación de Secuencia , Homología de SecuenciaRESUMEN
Lyophilized vegetative mycelium of ectomycorrhizal fungi was subjected to various viability tests to confirm functional integrity. Physical integrity of freeze-dried cultures was comparable to that of non-lyophilized cultures. Inter- and intraspecific variations in morphology, physiology, and metabolic rate were maintained after lyophilization. Maintenance of total protein content confirmed metabolic stability. According to the assays of viability, a plating assay and determination of total biomass confirmed stable mitotic activity of the freeze-dried cultures.
Asunto(s)
Liofilización , Hongos/crecimiento & desarrollo , Proteínas Fúngicas/análisis , Hongos/química , Concentración de Iones de HidrógenoRESUMEN
Eucalyptus tereticornis was grown in a green house in a low phosphorus (0.67 ppm Olsen's P) soil (Typic Haplustalf) inoculated with mixed indigenous arbuscular mycorrhizal (AM) fungi. Soil was amended to achieve P levels of 10, 20, 25, 30 and 40 ppm to evaluate the growth response and dependence of E. tereticornis to inoculation with AM fungi. A positive response to mycorrhizal inoculation was evident at the first two levels of soil P, i.e., at 0.67 and 10 ppm but not at the higher levels of soil P. Dry matter yield of inoculated plants beyond 20 ppm soil P was similar or even less compared to their uninoculated counterparts. Inoculated plants produced maximum dry matter (root and shoot) at 10 ppm soil P, whereas uninoculated plants did not produce until the level reached 20 ppm. The percentage root length colonized by AM fungi decreased from 31% to 3% as the concentration of P increased beyond 10 ppm soil P. Higher levels of soil P depressed the AM colonization significantly. Inoculated plants had higher shoot P and N contents compared to their uninoculated counterparts at all levels of soil P. However, at the first two lower levels of soil P, inoculated plants showed significantly higher shoot P and N contents over their respective uninoculated counterparts. The increasing shoot P accumulation beyond 10 ppm did not enhance dry matter yields. Inoculated plants had lower values of phosphorus utilization efficiency (PUE) and nitrogen utilization efficiency (NUE) at all levels of soil P except at the unamended level (0.67 ppm) where the inoculated plants showed higher values of NUE compared to uninoculated control plants. Taking dry matter yield into consideration, Eucalyptus plants were found to be highly dependent on 10 ppm of soil P for maximum dry matter production. Any further amendment of P to soil was not beneficial neither for AM symbiosis nor plant growth.