Project description:Microbial enzymes alter marine biogeochemical cycles by catalyzing chemical transformations that bring elements into and out of particulate organic pools. These processes are traditionally studied through enzyme rate-based estimates and nutrient-amendment bioassays, but these approaches lack the ability to resolve species-level contributions to enzymatic rates. Molecular methods including proteomics have the potential to link the contributions of specific populations to the overall community enzymatic rate; this is important because organisms will have distinct enzyme characteristics, feedbacks, and responses to perturbations. Integrating molecular methods with rate measurements can be achieved quantitatively through absolute quantitative proteomics. Here, we use the subtropical North Atlantic as a model system to probe how absolute quantitative proteomics can provide a more comprehensive understanding of nutrient limitation in marine environments. The experimental system is characterized by phosphorus stress and potential metal-phosphorus co-limitation due to dependence of the organic phosphorus scavenging enzyme alkaline phosphatase on metal cofactors; we performed nutrient amendment incubation experiments to investigate how alkaline phosphatase abundance and activity is affected by trace metal additions. We show that the two most abundant picocyanobacteria, Prochlorocccus and Synechococcus are minor contributors to total alkaline phosphatase activity as assessed by a widely used enzyme assay. This was true even when trace metals were added, despite both species having the genetic potential to utilize both the Fe and Zn containing enzymes, PhoX and PhoA respectively. Serendipitously, we also found that the alkaline phosphatases responded to cobalt additions suggesting possible substitution of the metal center by Co in natural populations of Prochloroccocus (substitution for Fe in PhoX) and Synechococcus (substitution for Zn in PhoA). This integrated approach allows for a nuanced interpretation of how nutrient limitation affects marine biogeochemical cycles and highlights the benefit of building quantitative connections between rate and “-omics” based measurements.
Project description:Aeolian soil erosion, exacerbated by anthropogenic perturbations, has become one of the most alarming processes of land degradation and desertification. By contrast, dust deposition might confer a potential fertilization effect. To examine how they affect topsoil microbial community, we conducted a study GeoChip techniques in a semiarid grassland of Inner Mongolia, China. We found that microbial communities were significantly (P<0.039) altered and most of microbial functional genes associated with carbon, nitrogen, phosphorus and potassium cycling were decreased or remained unaltered in relative abundance by both erosion and deposition, which might be attributed to acceleration of organic matter mineralization by the breakdown of aggregates during dust transport and deposition. As a result, there were strong correlations between microbial carbon and nitrogen cycling genes. amyA genes encoding alpha-amylases were significantly (P=0.01) increased by soil deposition, reflecting changes of carbon profiles. Consistently, plant abundance, total nitrogen and total organic carbon were correlated with functional gene composition, revealing the importance of environmental nutrients to soil microbial function potentials. Collectively, our results identified microbial indicator species and functional genes of aeolian soil transfer, and demonstrated that functional genes had higher susceptibility to environmental nutrients than taxonomy. Given the ecological importance of aeolian soil transfer, knowledge gained here are crucial for assessing microbe-mediated nutrient cyclings and human health hazard. The experimental sites comprised of three treatments of control, soil erosion and deposition, with 5 replicates of each treatment.
Project description:Aeolian soil erosion, exacerbated by anthropogenic perturbations, has become one of the most alarming processes of land degradation and desertification. By contrast, dust deposition might confer a potential fertilization effect. To examine how they affect topsoil microbial community, we conducted a study GeoChip techniques in a semiarid grassland of Inner Mongolia, China. We found that microbial communities were significantly (P<0.039) altered and most of microbial functional genes associated with carbon, nitrogen, phosphorus and potassium cycling were decreased or remained unaltered in relative abundance by both erosion and deposition, which might be attributed to acceleration of organic matter mineralization by the breakdown of aggregates during dust transport and deposition. As a result, there were strong correlations between microbial carbon and nitrogen cycling genes. amyA genes encoding alpha-amylases were significantly (P=0.01) increased by soil deposition, reflecting changes of carbon profiles. Consistently, plant abundance, total nitrogen and total organic carbon were correlated with functional gene composition, revealing the importance of environmental nutrients to soil microbial function potentials. Collectively, our results identified microbial indicator species and functional genes of aeolian soil transfer, and demonstrated that functional genes had higher susceptibility to environmental nutrients than taxonomy. Given the ecological importance of aeolian soil transfer, knowledge gained here are crucial for assessing microbe-mediated nutrient cyclings and human health hazard.
Project description:Cropping soils vary in extent of natural suppression of soil-borne plant diseases. However, it is unknown whether similar variation occurs across pastoral agricultural systems. We examined soil microbial community properties known to be associated with disease suppression across 50 pastoral fields varying in management intensity. The composition and abundance of the disease-suppressive community were assessed from both taxonomic and functional perspectives.