Ileosigmoidal knotting: a case report and literature review of a rare cause of acute abdomen in children.

Ileosigmoidal knotting (ISK) is a rare, possibly fatal cause of intestinal obstruction. ISK is a compound volvulus that is more common in Africa and Asia. ISK is mostly seen in adults, pediatric cases reported in the literature are much rarer. In this report, we present the first reported case of ISK in a pediatric patient from Nepal. An 8-year-old male child presented with symptoms of abdominal pain, vomiting, and obstipation. The abdomen was distended with generalized tenderness. Erect abdominal X-ray showed multiple air-fluid levels. Intraoperatively, gangrenous ileum loops were entangled around the sigmoid, and resection of the gangrenous ileum and sigmoid was performed. An end-to-end colo-colic anastomosis from the descending colon to the remaining sigmoid with a double-loop ileostomy was performed. Pediatric ISK is a rare fatal form of intestinal obstruction that progresses quickly to gangrene. Clinical signs and symptoms are nonspecific, making preoperative diagnosis challenging.

Biogeochemical fate of ferrihydrite-model organic compound complexes during anaerobic microbial reduction.

Associations of organic carbon (OC) with iron (Fe) oxide minerals play an important role in regulating the stability of OC in soil environments. Knowledge about the fate and stability of Fe-OC complexes is impaired by the heterogeneity of OC. Additional biogeochemical variables in soil environments, such as redox conditions and microbes, further increase complexity in understanding the stability of mineral-associated soil OC. This study investigated the fate and stability of model organic compounds, including glucose (GL), glucosamine (GN), tyrosine (TN), benzoquinone (BQ), amylose (AM), and alginate (AL), complexed with an Fe oxide mineral, ferrihydrite (Fh), during microbial reduction. During a 25-d anaerobic incubation with Shewanella putrefaciens CN32, the reduction of Fe followed the order of Fh-BQ > Fh-GL > Fh-GN > Fh-TN > Fh-AL > Fh-AM. In terms of OC released during the anaerobic incubation, Fh-GN complexes released the highest amount of OC while Fh-AM complexes released the lowest. Organic carbon regulated the reduction of Fe by acting as an electron shuttle, affecting microbial activities, and associating with Fh. Benzoquinone had the highest electron accepting capacity, but potentially can inhibit microbial activity. These findings provide insights into the roles of different organic functional groups in regulating Fe reduction and the stability of Fh-bound OC under anaerobic conditions.

Aerobic respiration of mineral-bound organic carbon in a soil.

Associations with minerals can potentially augment soil organic carbon (SOC) stability by reducing the bioavailability and degradation of SOC. However, few studies have directly measured aerobic respiration of mineral-bound SOC. In this study, we investigated the microbial aerobic respiration and bioavailability of ferrihydrite-sorbed glucose (Fh-GLU) and ferrihydrite-sorbed formic acid (Fh-FA) by adding 13C-labeled compounds to a soil. During an 11-day incubation, 30.2% of free, non-Fh-sorbed glucose (GLU) and 61.8% of free formic acid (FA) were respired, whereas 4.2% and 27.9% of Fh-GLU and Fh-FA were respired, respectively. Our results demonstrated that Fh-bound GLU/FA had lower bioavailability compared to free organic compounds. Associations with Fh led to greater inhibition in the bioavailability of GLU than that for FA. The priming effects of added compounds on the respiration of native SOC were decreased by their association with Fh. Our results demonstrated that the bioavailability and priming effect of organic compounds depend on their interactions with minerals.

Spatial Associations and Chemical Composition of Organic Carbon Sequestered in Fe, Ca, and Organic Carbon Ternary Systems.

Organo-mineral associations of organic carbon (OC) with iron (Fe) oxides play a major role in environmental OC sequestration, a process crucial to mitigating climate change. Calcium has been found to have high coassociation with OC in soils containing high Fe content, increase OC sorption extent to poorly crystalline Fe oxides, and has long been suspected to form bridging complexes with Fe and OC. Due to the growing realization that Ca may be an important component of C cycling, we launched a scanning transmission X-ray microscopy (STXM) investigation, paired with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, in order to spatially resolve Fe, Ca, and OC relationships and probe the effect of Ca on sorbed OC speciation. We performed STXM-NEXAFS analysis on 2-line ferrihydrite reacted with leaf litter-extractable dissolved OC and citric acid in the absence and presence of Ca. Organic carbon was found to highly associate with Ca ( R2 = 0.91). Carboxylic acid moieties were dominantly sequestered; however, Ca facilitated the additional sequestration of aromatic and phenolic moieties. Also, C NEXAFS revealed polyvalent metal ion complexation. Our results provide evidence for the presence of Fe-Ca-OC ternary complexation, which has the potential to significantly impact how organo-mineral associations are modeled.

Relationship among Phosphorus Circulation Activity, Bacterial Biomass, pH, and Mineral Concentration in Agricultural Soil.

Improvement of phosphorus circulation in the soil is necessary to enhance phosphorus availability to plants. Phosphorus circulation activity is an index of soil's ability to supply soluble phosphorus from organic phosphorus in the soil solution. To understand the relationship among phosphorus circulation activity; bacterial biomass; pH; and Fe, Al, and Ca concentrations (described as mineral concentration in this paper) in agricultural soil, 232 soil samples from various agricultural fields were collected and analyzed. A weak relationship between phosphorus circulation activity and bacterial biomass was observed in all soil samples (R² = 0.25), and this relationship became significantly stronger at near-neutral pH (6.0-7.3; R² = 0.67). No relationship between phosphorus circulation activity and bacterial biomass was observed at acidic (pH < 6.0) or alkaline (pH > 7.3) pH. A negative correlation between Fe and Al concentrations and phosphorus circulation activity was observed at acidic pH (R² = 0.72 and 0.73, respectively), as well as for Ca at alkaline pH (R² = 0.64). Therefore, bacterial biomass, pH, and mineral concentration should be considered together for activation of phosphorus circulation activity in the soil. A relationship model was proposed based on the effects of bacterial biomass and mineral concentration on phosphorus circulation activity. The suitable conditions of bacterial biomass, pH, and mineral concentration for phosphorus circulation activity could be estimated from the relationship model.

Biochar-Facilitated Microbial Reduction of Hematite.

As an important component of soil organic matter (SOM), the transformation of pyrogenic carbon plays a critical role in the biogeochemical cycles of carbon and other redox-active elements such as iron (Fe). Herein, we studied the influences of wheat straw-derived biochars on the microbial reduction of 100 mM of hematite by the dissimilatory metal reducing bacteria Shewanella oneidensis MR-1 under anoxic conditions. The long-term microbial reduction extent and initial reduction rate of hematite were accelerated by more than 2-fold in the presence of 10 mg L(-1) biochar. Soluble leachate from 10 mg L(-1) biochar enhanced Fe(III) reduction to a similar degree. Microbially prereduced biochar leachate abiotically reduced hematite, consistent with the apparent electron shuttling capacity of biochar leachate. Electron paramagnetic resonance (EPR) analysis suggested that biochar leachate-associated semiquinone functional groups were likely involved in the redox reactions. In addition to electron shuttling effects, biochar particles sorbed 0.5-1.5 mM biogenic Fe(II) and thereby increased the long-term extent of hematite reduction by 1.4-1.7 fold. Our results suggest that Fe redox cycling may be strongly impacted by pyrogenic carbon in soils with relatively high content of indigenous pyrogenic carbon or substantial application of biochar.

Selective stabilization of aliphatic organic carbon by iron oxide.

Stabilization of organic matter in soil is important for natural ecosystem to sequestrate carbon and mitigate greenhouse gas emission. It is largely unknown what factors govern the preservation of organic carbon in soil, casting shadow on predicting the response of soil to climate change. Iron oxide was suggested as an important mineral preserving soil organic carbon. However, ferric minerals are subject to reduction, potentially releasing iron and decreasing the stability of iron-bound organic carbon. Information about the stability of iron-bound organic carbon in the redox reaction is limited. Herein, we investigated the sorptive interactions of organic matter with hematite and reductive release of hematite-bound organic matter. Impacts of organic matter composition and conformation on its sorption by hematite and release during the reduction reaction were analyzed. We found that hematite-bound aliphatic carbon was more resistant to reduction release, although hematite preferred to sorb more aromatic carbon. Resistance to reductive release represents a new mechanism that aliphatic soil organic matter was stabilized by association with iron oxide. Selective stabilization of aliphatic over aromatic carbon can greatly contribute to the widely observed accumulation of aliphatic carbon in soil, which cannot be explained by sorptive interactions between minerals and organic matter.

Isolation and identification of phytate-degrading bacteria and their contribution to phytate mineralization in soil.

To better understand the phosphorus (P) cycling in an agricultural soil environment, amounts of total, organic and inorganic P in 10 agricultural soil samples were analyzed. Since a large proportion (57.8%) of the total P in the soils was in organic form, a method was developed to evaluate the mineralization rate of organic P in the soil by adding phytate to the soil and analyzing the change in water-soluble P (WSP) content after incubating it for 3 days. Moreover, the relationship between the phytate mineralization activity and bacterial biomass in 60 agricultural soils was also investigated, where the phytate mineralization activity ranged from 0 to 61.7% (average: 18.8%), and the R² value between phytate mineralization activity and indigenous bacterial biomass was 0.11 only. Phytate-degrading bacteria were isolated from the soil environment, and identified as Pseudomonas rhodesiae JT29, JT32, JT33, JT34, JT35, Pseudomonas sp. JT30, and Flavobacterium johnsoniae JT31. When P. rhodesiae JT29 and F. johnsoniae JT31 were inoculated into the agricultural soils, the phytate mineralization activities were increased up to 16 and 27 times, respectively. It was concluded that promotion of effective phytate-degrading bacterial strains could improve the sustainable P management in the agricultural soils.