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

Arsenic Demethylation by a C·As Lyase in Cyanobacterium <i>Nostoc</i> sp. PCC 7120

Arsenic, a ubiquitous toxic substance, exists mainly as inorganic forms in the environment. It is perceived that organoarsenicals can be demethylated and degraded into inorganic arsenic by microorganisms. Few studies have focused on the mechanism of arsenic demethylation in bacteria. Here, we investigated arsenic demethylation in a typical freshwater cyanobacterium <i>Nostoc</i> sp. PCC 7120. This bacterium was able to demethylate monomethylarsenite [MAs­(III)] rapidly to arsenite [As­(III)] and also had the ability to demethylate monomethylarsenate [MAs­(V)] to As­(III). The <i>NsarsI</i> encoding a C·As lyase responsible for MAs­(III) demethylation was cloned from <i>Nostoc</i> sp. PCC 7120 and heterologously expressed in an As-hypersensitive strain Escherichia coli AW3110 (Δ<i>arsRBC</i>). Expression of <i>NsarsI</i> was shown to confer MAs­(III) resistance through arsenic demethylation. The purified NsArsI was further identified and functionally characterized in vitro. NsArsI existed mainly as the trimeric state, and the kinetic data were well-fit to the Hill equation with <i>K</i>_0.5 = 7.55 ± 0.33 μM for MAs­(III), <i>V</i>_max = 0.79 ± 0.02 μM min^–1, and <i>h</i> = 2.7. Both of the NsArsI truncated derivatives lacking the C-terminal 10 residues (ArsI10) or 23 residues (ArsI23) had a reduced ability of MAs­(III) demethylation. These results provide new insights for understanding the important role of cyanobacteria in arsenic biogeochemical cycling in the environment

Arsenic Speciation and Volatilization from Flooded Paddy Soils Amended with Different Organic Matters

Arsenic (As) methylation and volatilization in soil can be increased after organic matter (OM) amendment, though the factors influencing this are poorly understood. Herein we investigate how amended OM influences As speciation as well as how it alters microbial processes in soil and soil solution during As volatilization. Microcosm experiments were conducted on predried and fresh As contaminated paddy soils to investigate microbial mediated As speciation and volatilization under different OM amendment conditions. These experiments indicated that the microbes attached to OM did not significantly influence As volatilization. The arsine flux from the treatment amended with 10% clover (clover-amended treatment, CT) and dried distillers grain (DDG) (DDG-amended treatment, DT2) were significantly higher than the control. Trimethylarsine (TMAs) was the dominant species in arsine derived from CT, whereas the primary arsine species from DT2 was TMAs and arsine (AsH₃), followed by monomethylarsine (MeAsH₂). The predominant As species in the soil solutions of CT and DT2 were dimethylarsinic acid (DMAA) and As­(V), respectively. OM addition increased the activities of arsenite-oxidizing bacteria (harboring <i>aroA</i>-like genes), though they did not increase or even decrease the abundance of arsenite oxidizers. In contrast, the abundance of arsenate reducers (carrying the <i>arsC</i> gene) was increased by OM amendment; however, significant enhancement of activity of arsenate reducers was observed only in CT. Our results demonstrate that OM addition significantly increased As methylation and volatilization from the investigated paddy soil. The physiologically active bacteria capable of oxidization, reduction, and methylation of As coexisted and mediated the As speciation in soil and soil solution

Anthropogenic Cycles of Arsenic in Mainland China: 1990–2010

Arsenic (As) is a trace element in the global environment with toxicity to both humans and ecosystem. This study characterizes China’s historical anthropogenic arsenic cycles (AACs) from 1990 to 2010. Key findings include the following: (1) the scale of China’s AACs grew significantly during the studied period, making China the biggest miner, producer, and user of arsenic today; (2) the majority of arsenic flows into China’s anthroposphere are the impurity of domestically mined nonferrous metal ores, which far exceeds domestic intentional demands; (3) China has been a net exporter of arsenic trioxide and arsenic metalloid, thus suffering from the environmental burdens of producing arsenic products for other economies; (4) the growth of arsenic use in China is driven by simultaneous increases in many applications including glass making, wood preservatives, batteries, semiconductors, and alloys, implying the challenge for regulating arsenic uses in multiple applications/industries at the same time; (5) the dissipative arsenic emissions resulting from intentional applications are at the same order of magnitude as atmospheric emissions from coal combustion, and their threats to human and ecosystem health can spread widely and last years to decades. Our results demonstrate that the characterization of AACs is indispensable for developing a complete arsenic emission inventory

Surface-Enhanced Raman Spectroscopy Combined with Stable Isotope Probing to Monitor Nitrogen Assimilation at Both Bulk and Single-Cell Level

Microbe-mediated biogeochemical cycle of nitrogen is a critical process in the environment. In this study, surface-enhanced Raman spectroscopy combined with ¹⁵N stable isotope probing (SERS–¹⁵N SIP) was developed as a new, nondestructive, and robust approach to probe nitrogen assimilation by bacteria at both bulk and single-cell level, and from pure culture to environmental microbial community. Multiple distinguishable SERS band shifts were observed and displayed a linear relationship with ¹⁵N content, because of the substitution of “light” nitrogen by “heavier” ¹⁵N stable isotope. These shifts, especially in 730 cm^–1 band, were highly distinguishable and universal in different bacteria, providing a robust indicator for nitrogen assimilation in bacteria. SERS–¹⁵N SIP was also demonstrated in important N₂-fixing bacteria via ¹⁵N₂ incubations. The same prominent shifts as that induced by ¹⁵NH₄Cl were observed, indicating the applicability of SERS–¹⁵N SIP to different nitrogen sources. SERS–¹⁵N SIP was further applied to environmental microbial community via ¹⁵NH₄Cl, ¹⁵NO₃^–, and ¹⁵N₂ incubation. Bacteria- and nitrogen source-dependent activity in nitrogen assimilation were revealed in environmental microbial community, pointing to the bacterial diversity and necessity of single-cell level investigation. Finally, by mixing optimized ratio of bacteria with Ag NPs, explicit single-cell SERS–¹⁵N SIP was obtained. The nondestructive SERS–¹⁵N SIP approach will be useful not only to identify active nitrogen-assimilating cells, but also enable Raman activated cell sorting and downstream genomic analysis, which will bring in deep insights into nitrogen metabolism of environmental microorganisms

Quantifying Nanoplastics in Soil-Cultured Plants Based on a Microcombustion Calorimeter

Nanoplastics have been detected in a variety of plants and threaten plant growth. To further investigate the physiological damage of nanoplastics to plants and their translocation in plants, it is crucial to quantify the nanoplastics in the plant. However, until now, no studies have reported on how to quantify nanoplastics in soil-cultured plants. Here, we proposed to determine the polyethylene (PE) and poly(methyl methacrylate) (PMMA) contents in soil-cultured plants using a microcombustion calorimeter (MCC). Since the thermal properties of nanoplastics were different from those of plants and soil, this method was not affected by the environmental background. The linear relationships were developed between the sample total heat release (THR) and nanoplastic proportions. Generally, the application of MCC to quantify PE and PMMA resulted in low detection limits (LODs), quantification limits (LOQs), and high spiked recoveries. The method also achieved a high level of accuracy (relative standard deviation and A type uncertainty), demonstrating the feasibility of the proposed method. This is the first report to quantify nanoplastics in soil-cultured plants based on MCC. It provides the possibility for rapid quantification of nanoplastics in plants and thus allows in-depth research of the behavior of nanoplastics in a soil–plant system