Extracellular polymeric substance induces biogenesis of vivianite under inorganic phosphate-free conditions.

Vivianite is often found in reducing environments rich in iron and phosphorus from organic debris degradation or phosphorus mineral dissolution. The formation of vivianite is essential to the geochemical cycling of phosphorus and iron elements in natural environments. In this study, extracellular polymeric substances (EPS) were selected as the source of phosphorus. Microcosm experiments were conducted to test the evolution of mineralogy during the reduction of polyferric sulfate flocs (PFS) by Shewanella oneidensis MR-1 (S. oneidensis MR-1) at EPS concentrations of 0, 0.03, and 0.3 g/L. Vivianite was found to be the secondary mineral in EPS treatment when there was no phosphate in the media. The EPS DNA served as the phosphorus source and DNA-supplied phosphate could induce the formation of vivianite. EPS impedes PFS aggregation, contains redox proteins and stores electron shuttle, and thus greatly promotes the formation of minerals and enhances the reduction of Fe(III). At EPS concentration of 0, 0.03, and 0.3 g/L, the produced HCl-extractable Fe(II) was 107.9, 111.0, and 115.2 mg/L, respectively. However, when the microcosms remained unstirred, vivianite can be formed without the addition of EPS. In unstirred systems, the EPS secreted by S. oneidensis MR-1 could agglomerate at some areas, resulting in the formation of vivianite in the proximity of microbial cells. It was found that vivianite can be generated biogenetically by S. oneidensis MR-1 strain and EPS may play a key role in iron reduction and concentrating phosphorus in the oligotrophic ecosystems where quiescent conditions prevail.

Whey protein supplementation improves postprandial glycemia in persons with type 2 diabetes mellitus: A systematic review and meta-analysis of randomized controlled trials.

Whey protein (WP) can increase insulin secretion, produce an incretin effect, delay gastric emptying, and regulate appetite, resulting in improved glycemic control. We hypothesized that WP supplementation is associated with postprandial glycemia regulation in persons with type 2 diabetes mellitus (T2DM) and conducted a quantitative meta-analysis of randomized controlled trials (RCTs) to test this hypothesis. We searched PubMed, Embase, Cochrane Library, Scopus databases, and the ClinicalTrials.gov registry for relevant RCTs published before March 2022. We assessed the pooled effects using a random-effects model on glucose and insulin levels at 60 and 120 minutes, total glucagon-like peptide-1 (tGLP-1) at 30 and 60 minutes, and the incremental area under the curve (iAUC) of glucose, insulin, tGLP-1, and glucose-dependent insulinotropic polypeptide. Five RCTs involving 134 persons were included. Postprandial glycemia was significantly lower at 60 minutes (weighted mean difference: -2.67 mmol/L; 95% confidence interval, -3.62 to -1.72 mmol/L) and 120 minutes (-1.59 mmol/L; -2.91 to -0.28 mmol/L) in WP group than in placebo group. The iAUC of insulin was significantly higher in WP group (24.66 nmol/L × min, 1.65-47.66 nmol/L × min) than in placebo group. Although other results favored the WP group, differences between the groups were not statistically significant. The present study showed that premeal WP supplementation is beneficial for postprandial glycemia in persons with mild or well-controlled T2DM without substantial adverse effects. However, the level of certainty of current evidence is not high enough. Further larger and well-designed clinical trials are warranted for evaluating optimal dose and long-term effects of WP supplementation.

Black carbon and kerogen in soils and sediments. 2. Their roles in equilibrium sorption of less-polar organic pollutants.

The first paper of this series reported that soil/sediment organic matter (SOM) can be fractionated into four fractions with a combined wet chemical procedure and that kerogen and black carbon (BC) are major SOM components in soil/sediment samples collected from the industrialized suburban areas of Guangzhou, China. The goal of this study was to determine the sorptive properties forthe four SOM fractions for organic contaminants. Sorption isotherms were measured with a batch technique using phenanthrene and naphthalene as the sorbates and four original and four Soxhlet-extracted soil/sediment samples, 15 isolated SOM fractions, and a char as the sorbents. The results showed that the sorption isotherms measured for all the sorbents were variously nonlinear. The isolated humic acid (HA) exhibited significantly nonlinear sorption, but its contribution to the overall isotherm nonlinearity and sorption capacity of the original soil was insignificant because of its low content in the tested soils and sediments. The particulate kerogen and black carbon (KB) fractions exhibited more nonlinear sorption with much higher organic carbon-normalized capacities for both sorbates. They dominate the observed overall sorption by the tested soils and sediments and are expected to be the most important soil components affecting bioavailability and ultimate fate of hydrophobic organic contaminants (HOCs). The fact that the isolated KB fractions exhibited much higher sorption capacities than when they were associated with soil/sediment matrixes suggested that a large fraction of the particulate kerogen and BC was not accessible to sorbing HOCs. Encapsulation within soil aggregates and surface coverage by inorganic and organic coatings may have caused large variations in the accessibility of fine kerogen and BC particles to HOCs and hence lowered the sorption capacity of the soil. This variability posts an ultimate challenge for precisely predicting HOC sorption by soils from the contents of different types of SOM.

Black carbon and kerogen in soils and sediments. 1. Quantification and characterization.

A comprehensive wet chemical procedure was developed by combining acid demineralization, base extraction, and dichromate oxidation for fractionation and quantitative isolation of soil/sediment organic matter (SOM) into four fractions: (1) humic acids + kerogen + BC (HKB); (2) kerogen + BC (KB); (3) humic acid (HA); and (4) BC. The soil/sediment samples tested were collected from the suburban areas of Guangzhou, a rapidly developing city of China. The results show that BC and kerogen constitute 57.8-80.6% of the total organic carbon (TOC) and that the relative content of BC ranges from 18.3% to 41.0% of the TOC, indicating that both BC and kerogen are major organic components in soils and sediments from this industrialized region. Systematic characterization of the isolated SOMs shows that both BC and kerogen have sizes ranging from a few microns to above 100 microm, relatively low O/C and H/C atomic ratios, and low contents of oxygen-containing functional groups. The isolated BC has unique fusinite and semifusinite macerals, highly porous nature, and structures indicative of its possible origins. The study indicates that SOM is highly heterogeneous and that humin, the nonextractable humus fraction, consists mainly of kerogen and BC materials in the tested soil/sediment samples. The presence of these materials in soils and sediments may have significant impacts on pollutant mass transfer and transformation processes such as desorption and bioavailability of less polar organic chemicals in surface aquatic and groundwater environments.