Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition

Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size‐density fractionation and solid‐state ¹³C‐NMR spectroscopy to explore the extent to which declines in microbial decay in a long‐term (ca. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; oPOM); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N‐alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in oPOM at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because oPOM can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine‐texture forest soils.     

The early life of a leaf‐cutter ant colony constrains symbiont vertical transmission and favors horizontal transmission

Colonial organisms host a large diversity of symbionts (collectively, parasites, mutualists, and commensals) that use vertical transmission (from parent colony to offspring colony) and/or horizontal transmission to disperse between host colonies. The early life of some colonies, characterized by the dispersal and establishment of solitary individuals, may constrain vertical transmission and favor horizontal transmission between large established colonies. We explore this possibility with the miniature cockroach Attaphila fungicola, a symbiont of leaf‐cutter ants and the mutualist fungal gardens they cultivate. The early life of a leaf‐cutter colony is characterized by the dispersal of a female alate (winged “queen”) carrying a fungal pellet, and the subsequent establishment of a foundress (workerless “queen”) raising her incipient fungal garden and colony. Roaches hitchhike on female alates during leaf‐cutter nuptial flights, which strongly suggests that roaches are vertically transmitted to foundresses and their incipient colonies; however, weak compatibility between roaches and incipient gardens may constrain roach vertical transmission. Reciprocally, opportunities for horizontal transmission between large established colonies with abundant fungal gardens may weaken selection against roach‐induced harm (virulence) of incipient gardens. We use a laboratory experiment, behavioral observations, field surveys, and a transmission model to estimate the effect roaches have on the survivorship of incipient gardens and the frequency of roach vertical transmission. Contrary to traditional assumptions, our results indicate that roaches harm incipient gardens and predominantly use horizontal transmission between established leaf‐cutter colonies. Ultimately, “costs of generalism” associated with infecting disparate stages of a host''s lifecycle (e.g., incipient vs. established colonies) may constrain the vertical transmission of roaches and a broad range of symbionts.     

Purification of fatty acid methyl esters by high-performance liquid chromatography

The determination by gas chromatography (GC) of fatty acid methyl esters (FAMEs) prepared from complex biological samples is subject to interference from cholesterol. During sample injection on the GC system of FAMEs prepared from tissues that contain cholesterol, we observed a major contaminant that co-eluted with docosahexaenoic acid (DHA, 22:6n-3). To address this problem, FAMEs were purified on an amino-phase high-performance liquid chromatography (HPLC) column using a hexane–isopropanol gradient. The HPLC retention times for both the FAME fraction and cholesterol were stable and reproducible when the amino column was used for sample purification. The purified extracts were analyzed by GC without artifacts or impurity peaks after 50 analytical runs. The method described here will be useful for measurement of 22:6n-3 and other fatty acids important for studies of nutrition or pathology.     

Redrawing the US Obesity Landscape: Bias-Corrected Estimates of State-Specific Adult Obesity Prevalence

Background

State-level estimates from the Centers for Disease Control and Prevention (CDC) underestimate the obesity epidemic because they use self-reported height and weight. We describe a novel bias-correction method and produce corrected state-level estimates of obesity and severe obesity.

Methods

Using non-parametric statistical matching, we adjusted self-reported data from the Behavioral Risk Factor Surveillance System (BRFSS) 2013 (n = 386,795) using measured data from the National Health and Nutrition Examination Survey (NHANES) (n = 16,924). We validated our national estimates against NHANES and estimated bias-corrected state-specific prevalence of obesity (BMI≥30) and severe obesity (BMI≥35). We compared these results with previous adjustment methods.

Results

Compared to NHANES, self-reported BRFSS data underestimated national prevalence of obesity by 16% (28.67% vs 34.01%), and severe obesity by 23% (11.03% vs 14.26%). Our method was not significantly different from NHANES for obesity or severe obesity, while previous methods underestimated both. Only four states had a corrected obesity prevalence below 30%, with four exceeding 40%–in contrast, most states were below 30% in CDC maps.

Conclusions

Twelve million adults with obesity (including 6.7 million with severe obesity) were misclassified by CDC state-level estimates. Previous bias-correction methods also resulted in underestimates. Accurate state-level estimates are necessary to plan for resources to address the obesity epidemic.     

Microbial substrate preference and community dynamics during decomposition of Acer saccharum

The Guild Decomposition Model (GDM) hypothesized that temporal shifts in microbial “guilds,” each with distinct substrate preferences, drive decomposition dynamics and regulate soil carbon (C) losses and sequestration. To test this hypothesis, we established a laboratory incubation of Acer saccharum litter and monitored respiration, microbial biomass and enzyme activities, inorganic nutrients and shifts in functional groups of decomposers using phospholipid fatty acid (PLFA) analysis. Biomass and respiration peaked within the first 2 d of incubation, and the Gram negative PLFA biomarker 18:1ω7c predominated during the first 5 d. Hydrolytic enzyme activities and two fungal biomarkers (18:2ω6,9c and 18:3ω6c) increased by 25 d and lignolytic enzyme activity was detected at 68 d. Our results suggest that decomposers preferentially use labile substrates and that shifts in decomposer groups occur in response to changes in available substrates, which supports the GDM.     

Role for the Epidermal Growth Factor Receptor in Chemotherapy-Induced Alopecia

Treatment of cancer patients with chemotherapeutics like cyclophosphamide often causes alopecia as a result of premature and aberrant catagen. Because the epidermal growth factor receptor (EGFR) signals anagen hair follicles to enter catagen, we hypothesized that EGFR signaling may be involved in cyclophosphamide-induced alopecia. To test this hypothesis, skin-targeted Egfr mutant mice were generated by crossing floxed Egfr and Keratin 14 promoter-driven Cre recombinase mice. Cyclophosphamide treatment of control mice resulted in alopecia while Egfr mutant skin was resistant to cyclophosphamide-induced alopecia. Egfr mutant skin entered catagen normally, as indicated by dermal papilla condensation and decreased follicular proliferation, but did not progress to telogen as did Egfr wild type follicles. Egfr mutant follicles responded with less proliferation, apoptosis, and fewer p53-positive cells after cyclophosphamide. Treatment of control mice with the EGFR inhibitors erlotinib or gefitinib similarly suppressed alopecia and catagen progression by cyclophosphamide. Secondary analysis of clinical trials utilizing EGFR-targeted therapies and alopecia-inducing chemotherapy also revealed evidence for involvement of EGFR in chemotherapy-induced alopecia. Taken together, our results demonstrated the involvement of EGFR signaling in chemotherapy-induced alopecia, which will help in the design of novel therapeutic regimens to minimize chemotherapy-induced alopecia.     

Identification of a myosin VII-talin complex

Myosin VII (M7) plays a role in adhesion in both Dictyostelium and mammalian cells where it is a component of a complex of proteins that serve to link membrane receptors to the underlying actin cytoskeleton. The nature of this complex is not fully known, prompting a search for M7-binding proteins. Co-immunoprecipitation experiments reveal that Dictyostelium M7 (DdM7) interacts with talinA, an actin-binding protein with a known role in cell-substrate adhesion. No additional proteins are observed in the immunoprecipitate, indicating that the interaction is direct. The N-terminal region of the DdM7 tail that lies between the region of predicted coil and the first MyTH4 domain is found to harbor the talinA binding site. Localization experiments reveal that talinA does not serve as a membrane receptor for DdM7 and vice versa. These findings reveal that talinA is a major DdM7 binding partner and suggest that their interaction induces a conformational change in each that, in combination with membrane receptor binding, promotes the assembly of a high avidity receptor complex essential for adhesion of the cell to substrata.     

Nuclear lactate dehydrogenase modulates histone modification in human hepatocytes

It is becoming increasingly apparent that the nucleus harbors metabolic enzymes that affect genetic transforming events. Here, we describe a nuclear isoform of lactate dehydrogenase (nLDH) and its ability to orchestrate histone deacetylation by controlling the availability of nicotinamide adenine dinucleotide (NAD⁺), a key ingredient of the sirtuin-1 (SIRT1) deacetylase system. There was an increase in the expression of nLDH concomitant with the presence of hydrogen peroxide (H₂O₂) in the culture medium. Under oxidative stress, the NAD⁺ generated by nLDH resulted in the enhanced deacetylation of histones compared to the control hepatocytes despite no discernable change in the levels of SIRT1. There appeared to be an intimate association between nLDH and SIRT1 as these two enzymes co-immunoprecipitated. The ability of nLDH to regulate epigenetic modifications by manipulating NAD⁺ reveals an intricate link between metabolism and the processing of genetic information.     

Faster induction of photosynthesis increases biomass and grain yield in glasshouse-grown transgenic Sorghum bicolor overexpressing Rieske FeS

Sorghum is one of the most important crops providing food and feed in many of the world's harsher environments. Sorghum utilizes the C₄ pathway of photosynthesis in which a biochemical carbon-concentrating mechanism results in high CO₂ assimilation rates. Overexpressing the Rieske FeS subunit of the Cytochrome b₆f complex was previously shown to increase the rate of photosynthetic electron transport and stimulate CO₂ assimilation in the model C₄ plant Setaria viridis. To test whether productivity of C₄ crops could be improved by Rieske overexpression, we created transgenic Sorghum bicolor Tx430 plants with increased Rieske content. The transgenic plants showed no marked changes in abundances of other photosynthetic proteins or chlorophyll content. The steady-state rates of electron transport and CO₂ assimilation did not differ between the plants with increased Rieske abundance and control plants, suggesting that Cytochrome b₆f is not the only factor limiting electron transport in sorghum at high light and high CO₂. However, faster responses of non-photochemical quenching as well as an elevated quantum yield of Photosystem II and an increased CO₂ assimilation rate were observed from the plants overexpressing Rieske during the photosynthetic induction, a process of activation of photosynthesis upon the dark–light transition. As a consequence, sorghum with increased Rieske content produced more biomass and grain when grown in glasshouse conditions. Our results indicate that increasing Rieske content has potential to boost productivity of sorghum and other C₄ crops by improving the efficiency of light utilization and conversion to biomass through the faster induction of photosynthesis.