Project description:Arsenic (As) bioavailability in the rice rhizosphere is influenced by many microbial interactions, particularly by metal-transforming functional groups at the root-soil interface. This study was conducted to examine As-transforming microbes and As-speciation in the rice rhizosphere compartments, in response to two different water management practices (continuous and intermittently flooded), established on fields with high to low soil-As concentration. Microbial functional gene composition in the rhizosphere and root-plaque compartments were characterized using the GeoChip 4.0 microarray. Arsenic speciation and concentrations were analyzed in the rhizosphere soil, root-plaque, porewater and grain samples. Results indicated that intermittent flooding significantly altered As-speciation in the rhizosphere, and reduced methyl-As and AsIII concentrations in the pore water, root-plaque and rice grain. Ordination and taxonomic analysis of detected gene-probes indicated that root-plaque and rhizosphere assembled significantly different metal-transforming functional groups. Taxonomic non-redundancy was evident, suggesting that As-reduction, -oxidation and -methylation processes were performed by different microbial groups. As-transformation was coupled to different biogeochemical cycling processes establishing functional non-redundancy of rice-rhizosphere microbiome in response to both rhizosphere compartmentalization and experimental treatments. This study confirmed diverse As-biotransformation at root-soil interface and provided novel insights on their responses to water management, which can be applied for mitigating As-bioavailability and accumulation in rice grains.
Project description:Microbial communities in the rhizosphere make significant contributions to crop health and nutrient cycling. However, their ability to perform important biogeochemical processes remains uncharacterized. Important functional genes, which characterize the rhizosphere microbial community, were identified to understand metabolic capabilities in the maize rhizosphere using GeoChip 3.0-based functional gene array method.
Project description:Elevated atmospheric CO2 can influence the structure and function of rhizosphere microorganisms by altering root growth and the quality and quantity of compounds released into the rhizosphere via root exudation. In these studies we investigated the transcriptional responses of Bradyrhizobium japonicum cells growing in the rhizosphere of soybean plants exposed to elevated atmospheric CO2. The results of microarray analyses indicated that atmospheric elevated CO2 concentration indirectly influences on expression of large number of Bradyrhizobium genes through soybean roots. In addition, genes involved in C1 metabolism, denitrification and FixK2-associated genes, including those involved in nitrogen fixation, microanaerobic respiration, respiratory nitrite reductase, and heme biosynthesis, were significantly up-regulated under conditions of elevated CO2 in the rhizosphere, relative to plants and bacteria grown under ambient CO2 growth conditions. The expression profile of genes involved in lipochitinoligosaccharide Nod factor biosynthesis and negative transcriptional regulators of nodulation genes, nolA and nodD2, were also influenced by plant growth under conditions of elevated CO2. Taken together, results of these studies indicate that growth of soybeans under conditions of elevated atmospheric CO2 influences gene expressions in B. japonicum in the soybean rhizosphere, resulting in changes to carbon/nitrogen metabolism, respiration, and nodulation efficiency.
Project description:Microbial communities in the rhizosphere make significant contributions to crop health and nutrient cycling. However, their ability to perform important biogeochemical processes remains uncharacterized. Important functional genes, which characterize the rhizosphere microbial community, were identified to understand metabolic capabilities in the maize rhizosphere using GeoChip 3.0-based functional gene array method. Triplicate samples were taken for both rhizosphere and bulk soil, in which each individual sample was a pool of four plants or soil cores. To determine the abundance of functional genes in the rhizosphere and bulk soils, GeoChip 3.0 was used.
Project description:Microbial communities in the rhizosphere make significant contributions to crop health and nutrient cycling. However, their ability to perform important biogeochemical processes remains uncharacterized. Important functional genes, which characterize the rhizosphere microbial community, were identified to understand metabolic capabilities in the maize rhizosphere using GeoChip 3.0-based functional gene array method. Triplicate samples were taken for both rhizosphere and bulk soil, in which each individual sample was a pool of four plants or soil cores. To determine the abundance of functional genes in the rhizosphere and bulk soils, GeoChip 3.0 was used.
Project description:Elevated atmospheric CO2 can influence the structure and function of rhizosphere microorganisms by altering root growth and the quality and quantity of compounds released into the rhizosphere via root exudation. In these studies we investigated the transcriptional responses of Bradyrhizobium japonicum cells growing in the rhizosphere of soybean plants exposed to elevated atmospheric CO2. Transciptomic expression profiles indicated that genes involved in carbon/nitrogen metabolism, and FixK2-associated genes, including those involved in nitrogen fixation, microanaerobic respiration, respiratory nitrite reductase, and heme biosynthesis, were significantly up-regulated under conditions of elevated CO2, relative to plants and bacteria grown under ambient CO2 growth conditions. The expression profile of genes involved in lipochitinoligosaccharide Nod factor biosynthesis and negative transcriptional regulators of nodulation genes, nolA and nodD2, were also influenced by plant growth under conditions of elevated CO2. Taken together, results of these studies indicate that growth of soybeans under conditions of elevated atmospheric CO2 influences gene expressions in B. japonicum in the soybean rhizosphere, resulting in changes to carbon/nitrogen metabolism, respiration, and nodulation efficiency. Bradyrhizobium japonicum strains were grown in the soybean rhizosphere under two different CO2 concentrations. Transcriptional profiling of B. japonicum was compared between cells grown under elevated CO2 and ambient conditions. Four biological replicates of each treatment were prepared, and four microarray slides were used for each strain.
Project description:Plants and rhizosphere microbes rely closely on each other, with plants supplying carbon to bacteria in root exudates, and bacteria mobilizing soil-bound phosphate for plant nutrition. When the phosphate supply becomes limiting for plant growth, the composition of root exudation changes, affecting rhizosphere microbial communities and microbially-mediated nutrient fluxes. To evaluate how plant phosphate deprivation affects rhizosphere bacteria, Lolium perenne seedlings were root-inoculated with Pseudomonas aeruginosa 7NR, and grown in axenic microcosms under different phosphate regimes (330 uM vs 3-6 uM phosphate). The effect of biological nutrient limitation was examined by DNA microarray studies of rhizobacterial gene expression.