Backreaction in Axion Monodromy, 4-forms and the Swampland

Axion monodromy models can always be described in terms of an axion coupled to 3-form gauge fields with non-canonical kinetic terms. The presence of the saxions parametrising the kinetic metrics of the 3-form fields leads to backreaction effects in the inflationary dynamics. We review the case in which saxions backreact on the K\"ahler metric of the inflaton leading to a logarithmic scaling of the proper field distance at large field. This behaviour is universal in Type II string flux compactifications and consistent with a refinement of the Swampland Conjecture. The critical point at which this behaviour appears depends on the mass hierarchy between the inflaton and the saxions. However, in tractable compactifications, such a hierarchy cannot be realised without leaving the regime of validity of the effective theory, disfavouring transplanckian excursions in string theory.Comment: Proceedings prepared for the "Workshop on Geometry and Physics", November 2016, Ringberg Castl

LVD_v1_95-85.fna

Land use viromes</p

Biochar Impacts Soil Microbial Community Composition and Nitrogen Cycling in an Acidic Soil Planted with Rape

Biochar has been suggested to improve acidic soils and to mitigate greenhouse gas emissions. However, little has been done on the role of biochar in ameliorating acidified soils induced by overuse of nitrogen fertilizers. In this study, we designed a pot trial with an acidic soil (pH 4.48) in a greenhouse to study the interconnections between microbial community, soil chemical property changes, and N₂O emissions after biochar application. The results showed that biochar increased plant growth, soil pH, total carbon, total nitrogen, C/N ratio, and soil cation exchange capacity. The results of high-throughput sequencing showed that biochar application increased α-diversity significantly and changed the relative abundances of some microbes that are related with carbon and nitrogen cycling at the family level. Biochar amendment stimulated both nitrification and denitrification processes, while reducing N₂O emissions overall. Results of redundancy analysis indicated biochar could shift the soil microbial community by changing soil chemical properties, which modulate N-cycling processes and soil N₂O emissions. The significantly increased <i>nosZ</i> transcription suggests that biochar decreased soil N₂O emissions by enhancing its further reduction to N₂

Application of Struvite Alters the Antibiotic Resistome in Soil, Rhizosphere, and Phyllosphere

Struvite recovered from wastewater is a renewable source of phosphorus and nitrogen and can be used as fertilizer for plant growth. However, antibiotics and resistome can be enriched in the struvite derived from wastewater. Robust understanding of the potential risks after struvite application to soils has remained elusive. Here, we profiled antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in struvite, soil, rhizosphere and phyllosphere of <i>Brassica</i> using high-throughput quantitative PCR. A total of 165 ARGs and 10 MGEs were detected. Application of struvite was found to increase both the abundance and diversity of ARGs in soil, rhizosphere and phyllosphere. In addition, ARGs shared exclusively between <i>Brassica</i> phyllosphere and struvite were identified, indicating that struvite was an important source of ARGs found in phyllosphere. Furthermore, OTUs shared between rhizosphere and phyllosphere were found to significantly correlate with ARGs, suggesting that microbiota in leaf and root could interconnect and ARGs might transfer from struvite to the surface of plants via rhizosphere using bacteria as spreading medium. These findings demonstrated that struvite as an organic fertilizer can facilitate the spread of antibiotic resistance into human food chain and this environment-acquired antibiotic resistance should be put into human health risk assessment system

Diversity and Abundance of Arsenic Biotransformation Genes in Paddy Soils from Southern China

Microbe-mediated arsenic (As) biotransformation in paddy soils determines the fate of As in soils and its availability to rice plants, yet little is known about the microbial communities involved in As biotransformation. Here, we revealed wide distribution, high diversity, and abundance of arsenite (As­(III)) oxidase genes (<i>aioA</i>), respiratory arsenate (As­(V)) reductase genes (<i>arrA</i>), As­(V) reductase genes (<i>arsC</i>), and As­(III) <i>S</i>-adenosylmethionine methyltransferase genes (<i>arsM</i>) in 13 paddy soils collected across Southern China. Sequences grouped with As biotransformation genes are mainly from rice rhizosphere bacteria, such as some <i>Proteobacteria</i>, <i>Gemmatimonadales</i>, and <i>Firmicutes</i>. A significant correlation of gene abundance between <i>arsC</i> and <i>arsM</i> suggests that the two genes coexist well in the microbial As resistance system. Redundancy analysis (RDA) indicated that soil pH, EC, total C, N, As, and Fe, C/N ratio, SO₄^2–-S, NO₃^–-N, and NH₄⁺-N were the key factors driving diverse microbial community compositions. This study for the first time provides an overall picture of microbial communities involved in As biotransformation in paddy soils, and considering the wide distribution of paddy fields in the world, it also provides insights into the critical role of paddy fields in the As biogeochemical cycle

Antibiotic Resistome and Its Association with Bacterial Communities during Sewage Sludge Composting

Composting is widely used for recycling of urban sewage sludge to improve soil properties, which represents a potential pathway of spreading antibiotic resistant bacteria and genes to soils. However, the dynamics of antibiotic resistance genes (ARGs) and the underlying mechanisms during sewage sludge composting were not fully explored. Here, we used high-throughput quantitative PCR and 16S rRNA gene based illumina sequencing to investigate the dynamics of ARGs and bacterial communities during a lab-scale in-vessel composting of sewage sludge. A total of 156 unique ARGs and mobile genetic elements (MGEs) were detected encoding resistance to almost all major classes of antibiotics. ARGs were detected with significantly increased abundance and diversity, and distinct patterns, and were enriched during composting. Marked shifts in bacterial community structures and compositions were observed during composting, with Actinobacteria being the dominant phylum at the late phase of composting. The large proportion of Actinobacteria may partially explain the increase of ARGs during composting. ARGs patterns were significantly correlated with bacterial community structures, suggesting that the dynamic of ARGs was strongly affected by bacterial phylogenetic compositions during composting. These results imply that direct application of sewage sludge compost on field may lead to the spread of abundant ARGs in soils

Electron Shuttles Enhance Anaerobic Ammonium Oxidation Coupled to Iron(III) Reduction

Anaerobic ammonium oxidation coupled to iron­(III) reduction, termed Feammox, is a newly discovered nitrogen cycling process. However, little is known about the roles of electron shuttles in the Feammox reactions. In this study, two forms of Fe­(III) (oxyhydr)­oxide ferrihydrite (ex situ ferrihydrite and in situ ferrihydrite) were used in dissimilatory Fe­(III) reduction (DIR) enrichments from paddy soil. Evidence for Feammox in DIR enrichments was demonstrated using the ¹⁵N-isotope tracing technique. The extent and rate of both the ³⁰N₂–²⁹N₂ and Fe­(II) formation were enhanced when amended with electron shuttles (either 9,10-anthraquinone-2,6-disulfonate (AQDS) or biochar) and further simulated when these two shuttling compounds were combined. Although the Feammox-associated Fe­(III) reduction accounted for only a minor proportion of total Fe­(II) formation compared to DIR, it was estimated that the potentially Feammox-mediated N loss (0.13–0.48 mg N L^–1 day^–1) was increased by 17–340% in the enrichments by the addition of electron shuttles. The addition of electron shuttles led to an increase in the abundance of unclassified Pelobacteraceae, Desulfovibrio, and denitrifiers but a decrease in Geobacter. Overall, we demonstrated a stimulatory effect of electron shuttles on Feammox that led to higher N loss, suggesting that electron shuttles might play a crucial role in Feammox-mediated N loss from soils

Long-Term Impact of Field Applications of Sewage Sludge on Soil Antibiotic Resistome

Land applications of municipal sewage sludge may pose a risk of introducing antibiotic resistance genes (ARGs) from urban environments into agricultural systems. However, how the sewage sludge recycling and application method influence soil resistome and mobile genetic elements (MGEs) remains unclear. In the present study, high through-put quantitative PCR was conducted on the resistome of soils from a field experiment with past (between 1994 and 1997) and annual (since 1994) applications of five different sewage sludges. Total inputs of organic carbon were similar between the two modes of sludge applications. Intrinsic soil resistome, defined as the ARGs shared by the soils in the control and sludge-amended plots, consisted of genes conferring resistance to multidrug, β-lactam, Macrolide-Lincosamide-Streptogramin B (MLSB), tetracycline, vancomycin, and aminoglycoside, with multidrug resistance genes as the most abundant members. There was a strong correlation between the abundance of ARGs and MGE marker genes in soils. The composition and diversity of ARGs in the five sludges were substantially different from those in soils. Considerable proportions of ARGs and MGE marker genes in the sludges attenuated following the application, especially aminoglycoside and tetracycline resistance genes. Annual applications posed a more significant impact on the soil resistome, through both continued introduction and stimulation of the soil intrinsic ARGs. In addition, direct introduction of sludge-specific ARGs into soil was observed especially from ARG-rich sludge. These results provide a better insight into the characteristics of ARG dissemination from urban environment to the agricultural system through sewage sludge applications

Functional Single-Cell Approach to Probing Nitrogen-Fixing Bacteria in Soil Communities by Resonance Raman Spectroscopy with ¹⁵N₂ Labeling

Nitrogen (N) fixation is the conversion of inert nitrogen gas (N₂) to bioavailable N essential for all forms of life. N₂-fixing microorganisms (diazotrophs), which play a key role in global N cycling, remain largely obscure because a large majority are uncultured. Direct probing of active diazotrophs in the environment is still a major challenge. Herein, a novel culture-independent single-cell approach combining resonance Raman (RR) spectroscopy with ¹⁵N₂ stable isotope probing (SIP) was developed to discern N₂-fixing bacteria in a complex soil community. Strong RR signals of cytochrome c (Cyt c, frequently present in diverse N₂-fixing bacteria), along with a marked ¹⁵N₂-induced Cyt c band shift, generated a highly distinguishable biomarker for N₂ fixation. ¹⁵N₂-induced shift was consistent well with ¹⁵N abundance in cell determined by isotope ratio mass spectroscopy. By applying this biomarker and Raman imaging, N₂-fixing bacteria in both artificial and complex soil communities were discerned and imaged at the single–cell level. The linear band shift of Cyt c versus ¹⁵N₂ percentage allowed quantification of N₂ fixation extent of diverse soil bacteria. This single-cell approach will advance the exploration of hitherto uncultured diazotrophs in diverse ecosystems

16S analysis

R script for analysis of 16S rRNA gene sequence