Cellulolytic potential under environmental changes in microbial communities from grassland litter

In many ecosystems, global changes are likely to profoundly affect microorganisms. In Southern California, changes in precipitation and nitrogen deposition may influence the composition and functional potential of microbial communities and their resulting ability to degrade plant material. To test whether such environmental changes impact the distribution of functional groups involved in leaf litter degradation, we determined how the genomic diversity of microbial communities in a semi-arid grassland ecosystem changed under reduced precipitation or increased N deposition. We monitored communities seasonally over a period of 2 years to place environmental change responses into the context of natural variation. Fungal and bacterial communities displayed strong seasonal patterns, Fungi being mostly detected during the dry season whereas Bacteria were common during wet periods. Most putative cellulose degraders were associated with 33 bacterial genera and predicted to constitute 18% of the microbial community. Precipitation reduction reduced bacterial abundance and cellulolytic potential whereas nitrogen addition did not affect the cellulolytic potential of the microbial community. Finally, we detected a strong correlation between the frequencies of genera of putative cellulose degraders and cellulase genes. Thus, microbial taxonomic composition was predictive of cellulolytic potential. This work provides a framework for how environmental changes affect microorganisms responsible for plant litter deconstruction

Targeted metatranscriptomics of compost derived consortia reveals a GH11 exerting an unusual exo-1,4-β-xylanase activity

Background: Using globally abundant crop residues as a carbon source for energy generation and renewable chemicals production stands out as a promising solution to reduce current dependency on fossil fuels. In nature, such as in compost habitats, microbial communities efficiently degrade the available plant biomass using a diverse set of synergistic enzymes. However, deconstruction of lignocellulose remains a challenge for industry due to recalcitrant nature of the substrate and the inefficiency of the enzyme systems available, making the economic production of lignocellulosic biofuels difficult. Metatranscriptomic studies of microbial communities can unveil the metabolic functions employed by lignocellulolytic consortia and identify new biocatalysts that could improve industrial lignocellulose conversion. Results: In this study, a microbial community from compost was grown in minimal medium with sugarcane bagasse sugarcane bagasse as the sole carbon source. Solid-state nuclear magnetic resonance was used to monitor lignocellulose degradation; analysis of metatranscriptomic data led to the selection and functional characterization of several target genes, revealing the first glycoside hydrolase from Carbohydrate Active Enzyme family 11 with exo-1,4-β-xylanase activity. The xylanase crystal structure was resolved at 1.76 Å revealing the structural basis of exo-xylanase activity. Supplementation of a commercial cellulolytic enzyme cocktail with the xylanase showed improvement in Avicel hydrolysis in the presence of inhibitory xylooligomers. Conclusions: This study demonstrated that composting microbiomes continue to be an excellent source of biotechnologically important enzymes by unveiling the diversity of enzymes involved in in situ lignocellulose degradation

Dissimilar responses of fungal and bacterial communities to soil transplantation simulating abrupt climate changes.

Both fungi and bacteria play essential roles in regulating soil carbon cycling. To predict future carbon stability, it is imperative to understand their responses to environmental changes, which is subject to large uncertainty. As current global warming is causing range shifts toward higher latitudes, we conducted three reciprocal soil transplantation experiments over large transects in 2005 to simulate abrupt climate changes. Six years after soil transplantation, fungal biomass of transplanted soils showed a general pattern of changes from donor sites to destination, which were more obvious in bare fallow soils than in maize cropped soils. Strikingly, fungal community compositions were clustered by sites, demonstrating that fungi of transplanted soils acclimatized to the destination environment. Several fungal taxa displayed sharp changes in relative abundance, including Podospora, Chaetomium, Mortierella and Phialemonium. In contrast, bacterial communities remained largely unchanged. Consistent with the important role of fungi in affecting soil carbon cycling, 8.1%-10.0% of fungal genes encoding carbon-decomposing enzymes were significantly (p < 0.01) increased as compared with those from bacteria (5.7%-8.4%). To explain these observations, we found that fungal occupancy across samples was mainly determined by annual average air temperature and rainfall, whereas bacterial occupancy was more closely related to soil conditions, which remained stable 6 years after soil transplantation. Together, these results demonstrate dissimilar response patterns and resource partitioning between fungi and bacteria, which may have considerable consequences for ecosystem-scale carbon cycling

Evidence for Ecological Flexibility in the Cosmopolitan Genus Curtobacterium

Assigning ecological roles to bacterial taxa remains imperative to understanding how microbial communities will respond to changing environmental conditions. Here we analyze the genus Curtobacterium, as it was found to be the most abundant taxon in a leaf litter community in southern California. Traditional characterization of this taxon predominantly associates it as the causal pathogen in the agricultural crops of dry beans. Therefore, we sought to investigate whether the abundance of this genus was because of its role as a plant pathogen or another ecological role. By collating >24,000 16S rRNA sequences with 120 genomes across the Microbacteriaceae family, we show that Curtobacterium has a global distribution with a predominant presence in soil ecosystems. Moreover, this genus harbors a high diversity of genomic potential for the degradation of carbohydrates, specifically with regards to structural polysaccharides. We conclude that Curtobacterium may be responsible for the degradation of organic matter within litter communities.United States. Dept. of Energy. Office of Biological and Environmental Research (Award DE-PS02-09ER09-25)United States. Dept. of Energy (Grant DESC0008743

Nitrogen Cycling Potential of a Grassland Litter Microbial Community.

Because microorganisms have different abilities to utilize nitrogen (N) through various assimilatory and dissimilatory pathways, microbial composition and diversity likely influence N cycling in an ecosystem. Terrestrial plant litter decomposition is often limited by N availability; however, little is known about the microorganisms involved in litter N cycling. In this study, we used metagenomics to characterize the potential N utilization of microbial communities in grassland plant litter. The frequencies of sequences associated with eight N cycling pathways differed by several orders of magnitude. Within a pathway, the distributions of these sequences among bacterial orders differed greatly. Many orders within the Actinobacteria and Proteobacteria appeared to be N cycling generalists, carrying genes from most (five or six) of the pathways. In contrast, orders from the Bacteroidetes were more specialized and carried genes for fewer (two or three) pathways. We also investigated how the abundance and composition of microbial N cycling genes differed over time and in response to two global change manipulations (drought and N addition). For many pathways, the abundance and composition of N cycling taxa differed over time, apparently reflecting precipitation patterns. In contrast to temporal variability, simulated global change had minor effects on N cycling potential. Overall, this study provides a blueprint for the genetic potential of N cycle processes in plant litter and a baseline for comparisons to other ecosystems

Contribution of various techniques to U(VI) and Pu(IV) mass transfer kinetics in liquid-liquid extraction: towards the kinetics regime determination thanks to 3 technics

International audienceIn the frame of the development of Generation IV reactors, CEA is developing an advanced liquidliquid extraction process for the multirecycling of plutonium from the spent nuclear fuels. Thermodynamic data have already been acquired for the modeling of the extraction equilibriums in this process, but accurate kinetic data are also required to simulate the process in short-time contactors and for its scale-up in industrial contactors such as pulsed columns. This paper summarizes the acquisition of mass transfer coefficients of uranium(VI) and plutonium(IV) between nitric acid and a monoamide-based solvent upon extraction with three different techniques: the single drop technique, the Nitsch cell and the rotating membrane cell (RMC). The influence of temperature, nitric acidity, viscosity of the organic phase, the drop size and the nature of the continuous phase (aqueous or organic) on the transfer of uranium and plutonium during the extraction step was studied. The results obtained by the single drop technique showed that U(VI) and Pu(IV) mass transfer constants are quite similar. These data were compared with the literature as with results obtained in similar conditions with the TBP solvent currently used in the PUREX process. They revealed that the kinetics of U(VI) extraction with this monoamide solvent is about three times slower than with TBP, probably because of the higher viscosity of the monoamide-based solvent. The single drop method allowed the most complete study but the other methods brought some qualitative information to better understand the phenomena involved in the transfer of uranium and plutonium with this system. The global results point out that the resistance to the transfer is essentially located in the organic phase and the diffusion process would mainly control the kinetics. An attempt to estimate the chemical and the diffusionnal kinetic constants based on experimental results led also to the same conclusion. These results lead to a better understanding of this extraction system and will help to simulate experimental profiles of uranium and plutonium concentrations measured in continuous tests performed in mixer-settlers or pulsed columns with this monoamide solvent

Study of precision of transverse evenness measurements in FILTER experiment - Forum of European National Highway Research Laboratories Investigation on Longitudinal and Transverse Evenness of Roads Experiment

The results of an analysis of the transverse profile measurement data collected in the FILTER Experiment are presented. The purpose of the analysis was to determine the repeatabilities, reproducibilities, and accuracies of the measurements. Application of the International Organization for Standardization 5725 standard resulted in the detection of a significant proportion of outlying results with most if not all devices. After removal of the outliers, average standard deviations (SDs) for repeatability were typically 0.1 percent for cross fall, 0.5 to 0.9 nun for rut depth, and 0.25 mm for water depth: cross-fall measurements exhibited an average SD for reproducibility of 0.5 percent, for rut depth measurements the values were 1.7 to 2.7 mm, and for water depth measurements the values were 2.1 to 2.2 mm. The overall SD for the accuracies of the profile measurements was found to be 1.9 mm. The rather wide range of (in)accuracy (0.8 to 3.2 mm) among the different test sections is explained by the influence of longitudinal unevenness (international roughness index). Operating speed in the speed range used in the experiment had no significant influence on most measurements obtained. Moreover, speed had no significant influence on the repeatabilities or the reproducibilities of the indices or on profile measurement accuracy. Averaging distance had a significant influence on the SD for repeatability, which decreased by a factor of 2 to 4 when the averaging distance increased from 50 to 500 m. The reproducibilities of the indices did not significantly depend on the averaging distance in any systematic way

Three-colour CARS spectroscopy of the OH radical at triple resonance

Molecular Physics, vol. 70, Number 1, May 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.103 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc