Size exclusion experiment in a grassland field unravels top-down control of the soil fauna on microbial community assembly.

Highly diverse and abundant organisms coexist in soils. However, the contribution of biotic interactions between soil organisms to microbial community assembly remains to be explored. Here, we assess the extent to which soil fauna can shape microbial community assembly using an exclusion experiment in a grassland field to sort soil biota based on body size. After 1 year, the exclusion of larger fauna favoured phagotrophic protists, with increases up to 32% in their proportion compared to the no-mesh treatment. In contrast, members of the bacterial community and to a lesser extent of the fungal community were negatively impacted. Shifts in bacterial but not in fungal communities were best explained by the response of the protistan community to exclusion. Our findings provide empirical evidence of top-down control on the soil microbial communities and underline the importance of integrating higher trophic levels for a better understanding of the soil microbiome assembly.

Soil microbial community fragmentation reveals indirect effects of fungicide exposure mediated by biotic interactions between microorganisms.

Fungicides are used worldwide to improve crop yields, but they can affect non-target soil microorganisms which are essential for ecosystem functioning. Microorganisms form complex communities characterized by a myriad of interspecies interactions, yet it remains unclear to what extent non-target microorganisms are indirectly affected by fungicides through biotic interactions with sensitive taxa. To quantify such indirect effects, we fragmented a soil microbial community by filtration to alter biotic interactions and compared the effect of the fungicide hymexazol between fractions in soil microcosms. We postulated that OTUs which are indirectly affected would exhibit a different response to the fungicide across the fragmented communities. We found that hymexazol primarily affected bacterial and fungal communities through indirect effects, which were responsible for more than 75% of the shifts in relative abundance of the dominant microbial OTUs after exposure to an agronomic dose of hymexazol. However, these indirect effects decreased for the bacterial community when hymexazol doses increased. Our results also suggest that N-cycling processes such as ammonia oxidation can be impacted indirectly by fungicide application. This work sheds light on the indirect impact of fungicide exposure on soil microorganisms through biotic interactions, which underscores the need for higher-tier risk assessment. ENVIRONMENTAL IMPLICATION: In this study, we used a novel approach based on the fragmentation of the soil microbial community to determine to which extent fungicide application could indirectly affect fungi and bacteria through biotic interactions. To assess off-target effects of fungicide on soil microorganisms, we selected hymexazol, which is used worldwide to control a variety of fungal plant pathogens, and exposed arable soil to the recommended field rate, as well as to higher rates. Our findings show that at least 75% of hymexazol-impacted microbial OTUs were indirectly affected, therefore emphasizing the importance of tiered risk assessment.

Manipulating the physical distance between cells during soil colonization reveals the importance of biotic interactions in microbial community assembly.

BACKGROUND: Microbial communities are of tremendous importance for ecosystem functioning and yet we know little about the ecological processes driving the assembly of these communities in the environment. Here, we used an unprecedented experimental approach based on the manipulation of physical distance between neighboring cells during soil colonization to determine the role of bacterial interactions in soil community assembly. We hypothesized that experimentally manipulating the physical distance between bacterial cells will modify the interaction strengths leading to differences in microbial community composition, with increasing distance between neighbors favoring poor competitors. RESULTS: We found significant differences in both bacterial community diversity, composition and co-occurrence networks after soil colonization that were related to physical distancing. We show that reducing distances between cells resulted in a loss of bacterial diversity, with at least 41% of the dominant OTUs being significantly affected by physical distancing. Our results suggest that physical distancing may differentially modulate competitiveness between neighboring species depending on the taxa present in the community. The mixing of communities that assembled at high and low cell densities did not reveal any "home field advantage" during coalescence. This confirms that the observed differences in competitiveness were due to biotic rather than abiotic filtering. CONCLUSIONS: Our study demonstrates that the competitiveness of bacteria strongly depends on cell density and community membership, therefore highlighting the fundamental role of microbial interactions in the assembly of soil communities.

Experimental community coalescence sheds light on microbial interactions in soil and restores impaired functions.

BACKGROUND: Microbes typically live in communities where individuals can interact with each other in numerous ways. However, knowledge on the importance of these interactions is limited and derives mainly from studies using a limited number of species grown in coculture. Here, we manipulated soil microbial communities to assess the contribution of interactions between microorganisms for assembly of the soil microbiome. RESULTS: By combining experimental removal (taxa depletion in the community) and coalescence (mixing of manipulated and control communities) approaches, we demonstrated that interactions between microorganisms can play a key role in determining their fitness during soil recolonization. The coalescence approach not only revealed the importance of density-dependent interactions in microbial community assembly but also allowed to restore partly or fully community diversity and soil functions. Microbial community manipulation resulted in shifts in both inorganic nitrogen pools and soil pH, which were related to the proportion of ammonia-oxidizing bacteria. CONCLUSIONS: Our work provides new insights into the understanding of the importance of microbial interactions in soil. Our top-down approach combining removal and coalescence manipulation also allowed linking community structure and ecosystem functions. Furthermore, these results highlight the potential of manipulating microbial communities for the restoration of soil ecosystems. Video Abstract.

Fate and impact of wastewater-borne micropollutants in lettuce and the root-associated bacteria.

The reuse of water for agricultural practices becomes progressively more important due to increasing demands for a transition to a circular economy. Treated wastewater can be an alternative option of blue water used for the irrigation of crops but its risks need to be evaluated. This study assesses the uptake and metabolization of pharmaceuticals and personal care products (PPCPs) derived from treated wastewater into lettuce as well as the impact on root-associated bacteria under a realistic and worst-case scenario. Lettuce was grown in a controlled greenhouse and irrigated with water or treated wastewater spiked with and without a mixture of fourteen different PPCPs at 10 µg/L or 100 µg/L. After harvesting the plants, the same soil was reused for a consecutive cultivation campaign to test for the accumulation of PPCPs. Twelve out of fourteen spiked PPCPs were detected in lettuce roots, and thirteen in leaves. In roots, highest concentrations were measured for sucralose, sulfamethoxazole and citalopram, while sucralose, acesulfame and carbamazepine were the highest in leaves. Higher PPCP concentrations were found in lettuce roots irrigated with spiked treated wastewater than in those irrigated with spiked water. The absolute bacterial abundance remained stable over both cultivation campaigns and was not affected by any of the treatments (type of irrigation water (water vs. wastewater) nor concentration of PPCPs). However, the irrigation of lettuce with treated wastewater had a significant effect on the microbial α-diversity indices at the end of the second cultivation campaign, and modified the structure and community composition of root-associated bacteria at the end of both campaigns. Five and fourteen bacterial families were shown to be responsible for the observed changes at the end of the first and second cultivation campaign, respectively. Relative abundance of Haliangium and the clade Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium was significantly affected in response to PCPPs exposure. Caulobacter, Cellvibrio, Hydrogenophaga and Rhizobacter were significantly affected in microcosms irrigated with wastewater.

Land-use intensification differentially affects bacterial, fungal and protist communities and decreases microbiome network complexity.

BACKGROUND: Soil microbial communities are major drivers of cycling of soil nutrients that sustain plant growth and productivity. Yet, a holistic understanding of the impact of land-use intensification on the soil microbiome is still poorly understood. Here, we used a field experiment to investigate the long-term consequences of changes in land-use intensity based on cropping frequency (continuous cropping, alternating cropping with a temporary grassland, perennial grassland) on bacterial, protist and fungal communities as well as on their co-occurrence networks. RESULTS: We showed that land use has a major impact on the structure and composition of bacterial, protist and fungal communities. Grassland and arable cropping differed markedly with many taxa differentiating between both land use types. The smallest differences in the microbiome were observed between temporary grassland and continuous cropping, which suggests lasting effects of the cropping system preceding the temporary grasslands. Land-use intensity also affected the bacterial co-occurrence networks with increased complexity in the perennial grassland comparing to the other land-use systems. Similarly, co-occurrence networks within microbial groups showed a higher connectivity in the perennial grasslands. Protists, particularly Rhizaria, dominated in soil microbial associations, as they showed a higher number of connections than bacteria and fungi in all land uses. CONCLUSIONS: Our findings provide evidence of legacy effects of prior land use on the composition of the soil microbiome. Whatever the land use, network analyses highlighted the importance of protists as a key element of the soil microbiome that should be considered in future work. Altogether, this work provides a holistic perspective of the differential responses of various microbial groups and of their associations to agricultural intensification.

Unraveling negative biotic interactions determining soil microbial community assembly and functioning.

Microbial communities play important roles in all ecosystems and yet a comprehensive understanding of the ecological processes governing the assembly of these communities is missing. To address the role of biotic interactions between microorganisms in assembly and for functioning of the soil microbiota, we used a top-down manipulation approach based on the removal of various populations in a natural soil microbial community. We hypothesized that removal of certain microbial groups will strongly affect the relative fitness of many others, therefore unraveling the contribution of biotic interactions in shaping the soil microbiome. Here we show that 39% of the dominant bacterial taxa across treatments were subjected to competitive interactions during soil recolonization, highlighting the importance of biotic interactions in the assembly of microbial communities in soil. Moreover, our approach allowed the identification of microbial community assembly rule as exemplified by the competitive exclusion between members of Bacillales and Proteobacteriales. Modified biotic interactions resulted in greater changes in activities related to N- than to C-cycling. Our approach can provide a new and promising avenue to study microbial interactions in complex ecosystems as well as the links between microbial community composition and ecosystem function.

Domestication-driven changes in plant traits associated with changes in the assembly of the rhizosphere microbiota in tetraploid wheat.

Despite the large morphological and physiological changes that plants have undergone through domestication, little is known about their impact on their microbiome. Here we characterized rhizospheric bacterial and fungal communities as well as the abundance of N-cycling microbial guilds across thirty-nine accessions of tetraploid wheat, Triticum turgidum, from four domestication groups ranging from the wild subspecies to the semi dwarf elite cultivars. We identified several microbial phylotypes displaying significant variation in their relative abundance depending on the wheat domestication group with a stronger impact of domestication on fungi. The relative abundance of potential fungal plant pathogens belonging to the Sordariomycetes class decreased in domesticated compared to wild emmer while the opposite was found for members of the Glomeromycetes, which are obligate plant symbionts. The depletion of nitrifiers and of arbuscular mycorrhizal fungi in elite wheat cultivars compared to primitive domesticated forms suggests that the Green Revolution has decreased the coupling between plant and rhizosphere microbes that are potentially important for plant nutrient availability. Both plant diameter and fine root percentage exhibited the highest number of associations with microbial taxa, highlighting their putative role in shaping the rhizosphere microbiota during domestication. Aside from domestication, significant variation of bacterial and fungal community composition was found among accessions within each domestication group. In particular, the relative abundances of Ophiostomataceae and of Rhizobiales were strongly dependent on the host accession, with heritability estimates of ~ 27% and ~ 25%, indicating that there might be room for genetic improvement via introgression of ancestral plant rhizosphere-beneficial microbe associations.

Impact of phages on soil bacterial communities and nitrogen availability under different assembly scenarios.

BACKGROUND: Bacteriophages, the viruses infecting bacteria, are biological entities that can control their host populations. The ecological relevance of phages for microbial systems has been widely explored in aquatic environments, but the current understanding of the role of phages in terrestrial ecosystems remains limited. Here, our objective was to quantify the extent to which phages drive the assembly and functioning of soil bacterial communities. We performed a reciprocal transplant experiment using natural and sterilized soil incubated with different combinations of two soil microbial communities, challenged against native and non-native phage suspensions as well as against a cocktail of phage isolates. We tested three different community assembly scenarios by adding phages: (a) during soil colonization, (b) after colonization, and (c) in natural soil communities. One month after inoculation with phage suspensions, bacterial communities were assessed by 16S rRNA amplicon gene sequencing. RESULTS: By comparing the treatments inoculated with active versus autoclaved phages, our results show that changes in phage pressure have the potential to impact soil bacterial community composition and diversity. We also found a positive effect of active phages on the soil ammonium concentration in a few treatments, which indicates that increased phage pressure may also be important for soil functions. CONCLUSIONS: Overall, the present work contributes to expand the current knowledge about soil phages and provide some empirical evidence supporting their relevance for soil bacterial community assembly and functioning. Video Abstract.

Cover Crop Management Practices Rather Than Composition of Cover Crop Mixtures Affect Bacterial Communities in No-Till Agroecosystems.

Cover cropping plays a key role in the maintenance of arable soil health and the enhancement of agroecosystem services. However, our understanding of how cover crop management impacts soil microbial communities and how these interactions might affect soil nutrient cycling is still limited. Here, we studied the impact of four cover crop mixtures varying in species richness and functional diversity, three cover crop termination strategies (i.e., frost, rolling, and glyphosate) and two levels of irrigation at the cover crop sowing on soil nitrogen and carbon dynamics, soil microbial diversity, and structure as well as the abundance of total bacteria, archaea, and N-cycling microbial guilds. We found that total nitrogen and soil organic carbon were higher when cover crops were killed by frost compared to rolling and glyphosate termination treatments, while cover crop biomass was positively correlated to soil carbon and C:N ratio. Modifications of soil properties due to cover crop management rather than the composition of cover crop mixtures were related to changes in the abundance of ammonia oxidizers and denitrifiers, while there was no effect on the total bacterial abundance. Unraveling the underlying processes by which cover crop management shapes soil physico-chemical properties and bacterial communities is of importance to help selecting optimized agricultural practices for sustainable farming systems.

Compounded Disturbance Chronology Modulates the Resilience of Soil Microbial Communities and N-Cycle Related Functions.

There is a growing interest of overcoming the uncertainty related to the cumulative impacts of multiple disturbances of different nature in all ecosystems. With global change leading to acute environmental disturbances, recent studies demonstrated a significant increase in the possible number of interactions between disturbances that can generate complex, non-additive effects on ecosystems functioning. However, how the chronology of disturbances can affect ecosystems functioning is unknown even though there is increasing evidence that community assembly history dictates ecosystems functioning. Here, we experimentally examined the importance of the disturbances chronology in modulating the resilience of soil microbial communities and N-cycle related functions. We studied the impact of 3-way combinations of global change related disturbances on total bacterial diversity and composition, on the abundance of N-cycle related guilds and on N-cycle related activities in soil microcosms. The model pulse disturbances, i.e., short-term ceasing disturbances studied were heat, freeze-thaw and anaerobic cycles. We determined that repeated disturbances of the same nature can either lead to the resilience or to shifts in N-cycle related functions concomitant with diversity loss. When considering disturbances of different nature, we demonstrated that the chronology of compounded disturbances impacting an ecosystem determines the aggregated impact on ecosystem properties and functions. Thus, after 3 weeks the impact of the 'anoxia/heat/freeze-thaw' sequence was almost two times stronger than that of the 'heat/anoxia/freeze-thaw' sequence. Finally, we showed that about 29% of the observed variance in ecosystem aggregated impact caused by series of disturbances could be attributed to changes in the microbial community composition measured by weighted UniFrac distances. This indicates that surveying changes in bacterial community composition can help predict the strength of the impact of compounded disturbances on N-related functions and properties.

Depth matters: effects of precipitation regime on soil microbial activity upon rewetting of a plant-soil system.

Changes in frequency and amplitude of rain events, that is, precipitation patterns, result in different water conditions with soil depth, and likely affect plant growth and shape plant and soil microbial activity. Here, we used 18O stable isotope probing (SIP) to investigate bacterial and fungal communities that actively grew or not upon rewetting, at three different depths in soil mesocosms previously subjected to frequent or infrequent watering for 12 weeks (equal total water input). Phylogenetic marker genes for bacteria and fungi were sequenced after rewetting, and plant-soil microbial coupling documented by plant 13C-CO2 labeling. Soil depth, rather than precipitation pattern, was most influential in shaping microbial response to rewetting, and had differential effects on active and inactive bacterial and fungal communities. After rewetting, active bacterial communities were less rich, more even and phylogenetically related than the inactive, and reactivated throughout the soil profile. Active fungal communities after rewetting were less abundant and rich than the inactive. The coupling between plants and soil microbes decreased under infrequent watering in the top soil layer. We suggest that differences in fungal and bacterial abundance and relative activity could result in large effects on subsequent soil biogeochemical cycling.

Peaks of in situ N2 O emissions are influenced by N2 O-producing and reducing microbial communities across arable soils.

Agriculture is the main source of terrestrial N2 O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2 O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2 O-reducers (nosZII) was related to the potential capacity of the soil to act as a N2 O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N2 O-producers and N2 O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2 O emissions. The abundance of both ammonia-oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N2 O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N2 O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N2 O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of in situ N2 O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2 O-reducing bacteria to agricultural practices and how it may ultimately affect N2 O emissions.

Effectiveness of ecological rescue for altered soil microbial communities and functions.

Soil ecosystems worldwide are subjected to marked modifications caused by anthropogenic disturbances and global climate change, resulting in microbial diversity loss and alteration of ecosystem functions. Despite the paucity of studies, restoration ecology provides an appropriate framework for testing the potential of manipulating soil microbial communities for the recovery of ecosystem functioning. We used a reciprocal transplant design in experimentally altered microbial communities to investigate the effectiveness of introducing microbial communities in degraded soil ecosystems to restore N-cycle functioning. Microbial diversity loss resulted in alternative compositional states associated with impaired N-cycle functioning. Here, the addition of complex microbial communities to these altered communities revealed a pivotal role of deterministic community assembly processes. The diversity of some alternative compositional states was successfully increased but without significant restoration of soil N-cycle functioning. However, in the most degraded alternative state, the introduction of new microbial communities caused an overall decrease in phylogenetic diversity and richness. The successful soil colonization by newly introduced species for some compositional states indicates that priority effects could be overridden when attempting to manipulate microbial communities for soil restoration. Altogether, our result showed consistent patterns within restoration treatments with minor idiosyncratic effects. This suggests the predominance of deterministic processes and the predictability of restoration trajectories, which could be used to guide the effective management of microbial community assemblages for ecological restoration of soils.

Relevance of Self-reported Behavioral Changes Before Bariatric Surgery to Predict Success After Surgery.

BACKGROUND: International guidelines emphasize the need for multidisciplinary preparation to improve the safety and effectiveness of bariatric surgery (BS), but whether the patient is ready for surgery is difficult to assess. The objective of this study was to explore whether inquiries on dietary habits and physical activity before surgery are predictive of postoperative weight loss. METHODS: We prospectively assessed in 78 candidates for BS (age, 43 ± 12 years; M/F, 15/63; weight, 122 ± 17 kg; IMC, 44 ± 5 kg/m2) anthropometric parameters, food intake, and physical activity (Baecke questionnaire) at the beginning and the end of a systematized preoperative preparation (7 ± 2 months) including consultations (mean number 7 ± 2) with a nutritionist, dietician, psychologist, and sports coach. RESULTS: During the preparation, weight change was zero (±5 kg). In contrast, self-reported caloric intake decreased from 2143 ± 640 to 1906 ± 564 kcal/24 h (p < 0.001) and snacking from 68 to 13% during the preparation. Self-reported physical activity increased (p < 0.05). The decrease in reported caloric intake was positively correlated with the mean number of preoperative consultations attended (R = 0.2885, p < 0.05) but not with the changes in preoperative weight. Postsurgical weight loss (recorded at 6 and 12 months) was correlated with preoperative changes in weight and physical activity but not with preoperative dietary changes. CONCLUSIONS: Self-reported improvement of dietary habits is not a good reflection of actual changes in dietary behavior among candidates for bariatric surgery, as illustrated by the absence of weight changes on average during the preoperative preparation. In contrast to dietary inquiry, self-reported changes in physical activity are predictive of postoperative weight loss after bariatric surgery.

The diversity of the N2O reducers matters for the N2O:N2 denitrification end-product ratio across an annual and a perennial cropping system.

Agriculture is the main source of terrestrial emissions of N2O, a potent greenhouse gas and the main cause of ozone layer depletion. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only biological process known to eliminate this greenhouse gas. Recent studies showed that a previously unknown clade of N2O-reducers was related to the capacity of the soil to act as an N2O sink, opening the way for new strategies to mitigate emissions. Here, we investigated whether the agricultural practices could differently influence the two N2O reducer clades with consequences for denitrification end-products. The abundance of N2O-reducers and producers was quantified by real-time PCR, and the diversity of both nosZ clades was determined by 454 pyrosequencing. Potential N2O production and potential denitrification activity were used to calculate the denitrification gaseous end-product ratio. Overall, the results showed limited differences between management practices but there were significant differences between cropping systems in both the abundance and structure of the nosZII community, as well as in the [rN2O/r(N2O+N2)] ratio. More limited differences were observed in the nosZI community, suggesting that the newly identified nosZII clade is more sensitive than nosZI to environmental changes. Potential denitrification activity and potential N2O production were explained mainly by the soil properties while the diversity of the nosZII clade on its own explained 26% of the denitrification end-product ratio, which highlights the importance of understanding the ecology of this newly identified clade of N2O reducers for mitigation strategies.

N2O production, a widespread trait in fungi.

N2O is a powerful greenhouse gas contributing both to global warming and ozone depletion. While fungi have been identified as a putative source of N2O, little is known about their production of this greenhouse gas. Here we investigated the N2O-producing ability of a collection of 207 fungal isolates. Seventy strains producing N2O in pure culture were identified. They were mostly species from the order Hypocreales order-particularly Fusarium oxysporum and Trichoderma spp.-and to a lesser extent species from the orders Eurotiales, Sordariales, and Chaetosphaeriales. The N2O (15)N site preference (SP) values of the fungal strains ranged from 15.8‰ to 36.7‰, and we observed a significant taxa effect, with Penicillium strains displaying lower SP values than the other fungal genera. Inoculation of 15 N2O-producing strains into pre-sterilized arable, forest and grassland soils confirmed the ability of the strains to produce N2O in soil with a significant strain-by-soil effect. The copper-containing nitrite reductase gene (nirK) was amplified from 45 N2O-producing strains, and its genetic variability showed a strong congruence with the ITS phylogeny, indicating vertical inheritance of this trait. Taken together, this comprehensive set of findings should enhance our knowledge of fungi as a source of N2O in the environment.

Comparison of nutritional status during the first year after sleeve gastrectomy and Roux-en-Y gastric bypass.

Sleeve gastrectomy (SG) is supposed to induce fewer nutritional deficiencies than gastric bypass (GBP). However, few studies have compared nutritional status after these two procedures, and the difference in weight loss (WL) between procedures may alter the results. Thus, our aim was to compare nutritional status after SG and GBP in subjects matched for postoperative weight. Forty-three subjects who underwent SG were matched for age, gender, and 6-month postoperative weight with 43 subjects who underwent GBP. Dietary intakes (DI), metabolic (MP), and nutritional parameters (NP) were recorded before and at 6 and 12 months after both procedures. Multivitamin supplements were systematically prescribed after surgery. Before surgery, BMI, DI, MP, and NP were similar between both groups. After surgery, LDL cholesterol, serum prealbumin, vitamin B12, urinary calcium, and vitamin D concentrations were lower after GBP than after SG, whereas WL and DI were similar after both procedures. However, the total number of deficiencies did not increase after surgery regardless of the procedure. In addition, we found a significant increase in liver enzymes and a greater decrease in C-reactive protein after GBP. In conclusion, during the first year after surgery, in patients with the same WL and following the same strategy of vitamin supplementation, global nutritional status was only slightly impaired after SG and GBP. However, some nutritional parameters were specifically altered after GBP, which could be related to malabsorption or other mechanisms, such as alterations in liver metabolism.

Serum vitamin D increases with weight loss in obese subjects 6 months after Roux-en-Y gastric bypass.

BACKGROUND: Malabsorptive surgical procedures lead to deficiencies in fat-soluble vitamins. However, results concerning serum vitamin D (25OHD) after gastric bypass (GBP) are controversial. The aim of the study was to assess the influence of GBP on 25OHD and calcium metabolism. METHODS: Parameters of calcium metabolism were evaluated in 202 obese subjects before and 6 months after GBP. Thirty of them were matched for age, gender, weight, skin color, and season with 30 subjects who underwent sleeve gastrectomy (SG). A multivitamin preparation that provides 200 to 500 IU vitamin D3 per day was systematically prescribed after surgery. RESULTS: In the 202 patients after GBP, serum 25OHD significantly increased from 13.4 ± 9.1 to 22.8 ± 11.3 ng/ml (p < 0.0001), whereas parathyroid hormone (PTH) did not change. Despite a decrease in calcium intake (p < 0.0001) and urinary calcium/creatinine ratio (p = 0.015), serum calcium increased after GBP (p < 0.0001). Preoperatively, 91 % of patients had 25OHD insufficiency (< 30 ng/ml), 80% deficiency (< 20 ng/ml), and 19% secondary hyperparathyroidism (> 65 pg/ml) vs. 76, 44, and 17%, respectively, following GBP. Serum 25OHD was negatively correlated with BMI at 6 months after GBP (R = -0.299, p < 0.0001). In the two groups of 30 subjects, serum 25OHD and PTH did not differ at 6 months after GBP or SG. CONCLUSIONS: At 6 months after GBP, serum 25OHD significantly increased in subjects supplemented with multivitamins containing low doses of vitamin D. These data suggest that weight loss at 6 months after surgery has a greater influence on vitamin D status than malabsorption induced by GBP.

Distribution of bacteria and nitrogen-cycling microbial communities along constructed Technosol depth-profiles.

Technosol construction through assemblage of treated soil and recycled wastes is an innovative option for the restoration of degraded lands and re-use of industrial wastes. Recent studies have evidenced that Technosols could support soil functions such as primary production but the knowledge about other ecosystemic services, such as nutrient cycling, is limited. We investigated how the total bacterial community and key functional microbial communities involved in nitrogen cycling were influenced by the depth and type of Technosol. We found that despite being artificially constructed, Technosols exhibited a gradual change in microbial activity and abundance along the soil profile. Both nitrification and denitrification rates decreased with increasing depth as previously observed in other soil systems. Potential denitrification and nitrification were correlated with Technosol physico-chemical properties but also with abundances of nirS denitrifiers and bacterial amoA gene, respectively. The correlation between nitrification rates and bacterial ammonia-oxidizers suggests that bacteria are driving nitrification in Technosols. A-RISA fingerprints showed a distinct community structure along different Technosol layers. Technosol properties affected denitrification strongly than nitrification underlining the importance of better understanding the microbial communities in Technosols to maximize their potential for nutrient cycling, an essential ecosystem function.