The existence of ferric hydroxide links the carbon and nitrogen cycles by promoting nitrite-coupled methane anaerobic oxidation.

Microorganism-mediated anaerobic oxidation of methane can efficiently mitigate methane atmospheric emissions and is a key process linking the biogeochemical cycles of carbon, nitrogen, and iron. The results showed that methane oxidation and nitrite removal rates in the CF were 1.12 and 1.28 times higher than those in CK, respectively, suggesting that ferric hydroxide can enhance nitrite-driven AOM. The biochemical process was mediated by the enrichment of methanogens, methanotrophs, and denitrifiers. Methanobacterium and Methanosarcina were positively correlated with Fe3+ and Fe2+, whereas Methylocystis and Methylocaldum were positively correlated with methane, and denitrifiers were positively correlated with nitrite. Metagenomic analysis revealed that the genes related to methane oxidation, nitrogen reduction, and heme c-type cytochrome were upregulated in CF, indicating that a synergistic action of bacteria and methanogens drove AOM via diverse metabolic pathways, within which ferric hydroxide played a crucial role. This study provides novel insights into the synergistic mechanism of ferric iron and nitrite-driven AOM.

The synergy of Fe(III) and NO2- drives the anaerobic oxidation of methane.

The anaerobic oxidation of methane (AOM) driven by NO2- or Fe(III) alone was limited by slow electron delivery and ineffective enrichment of microbes. The flexible coupling between Fe(III) and NO2- potentially cooperated to accelerate AOM. One negative control was fed CH4 and NO2-, and four treatment reactors were supplemented with CH4, NO2- and ferric citrate (FC)/ferric chloride (FCH)/ chelate iron (FCI)/ferric hydroxide (FH) and were anaerobically operated for 1200 days to verify the synergy and promicrobial roles of Fe(III) and NO2- in improving AOM. The changes in gas and ion profiles were observed in the reactors, and microbial development was studied using 16S rRNA gene sequencing with the Illumina platform. The results indicated that the combined Fe(III) and NO2- treatment improved AOM, and their synergy followed the order of FC > FCI > FCH > FH. The biochemical reaction of Fe3+ with NO2- and its secondary process accelerated electron transfer to microbial cells and subsequently enhanced AOM in the reactors. The total organic carbon (TOC) content, NH4+ content, NO3- content, and pH value altered the dominant bacteria the most in the FC reactor, FCI, FCH, and FH groups, respectively. Several dominant bacterial species were enriched, whereas only two archaea were highly concentrated in the FC and FCI groups. Only bacteria were detected in the FCH group, and archaea contributed substantially to the FH group. These findings contribute to an improved understanding of the interactions among nitrogen, iron and CH4 that are paramount to accelerating the process of AOM for engineering applications.

Determination of Morphine in Human Urine by the Novel Competitive Fluorescence Immunoassay.

A competitive fluorescence immunoassay for the identification and quantification of morphine has been developed on the basis of hapten-coated plate format. Hapten was prepared through covalent conjugating a morphine derivative with albumin bovine. In the immunoassay, the hapten was inoculated on a 96-well plate and then bound with monoclonal antibodies labeled with a signal indicating dye, fluorescein isothiocyanate (FITC). Unbound FITC-antibodies were rinsed off from the plate. The fluorescein intensity decreases in the presence of morphine molecules due to the competitively binding to antibodies against hapten. The intensity is inversely correlated with the concentration of morphine. In quantitative analysis for urine samples, we obtained a linearity range of 0.2 µg/mL∼2.5 µg/mL, along with a detection limit of c.a. 1 ng/mL. The fluorescence immunoassay shows low cross-reactivity (below 10%) to 6-acetylmorphine, 3-acetylmorphine, and heroine. The developed method produced comparable results to the standard GC-MS/MS method. In conclusion, a rapid and efficient screening tool for morphine in clinical human urine has been established.