Improving soil fertility by driving microbial community changes in saline soils of Yellow River Delta under petroleum pollution.

It is promising to use indigenous microorganisms for fertility improvement in petroleum-contaminated coastal soil. As a result, the microbial community and physicochemical property are the base for the restoration. For the detailed information, the Phragmites Communis (P), Chinese Tamarisk (C), Suaeda salsa (S), and new Bare Land (B) soil of Yellow River Delta was 90 g in 100 mL sterile bottles simulated at 25 °C with soil: petroleum = 10:1 in the incubator for four months. The samples were detected at 60 and 120 days along with untreated soil and aged Oil Sludge (O) as control. The results showed that all the samples were alkaline (pH 7.99-8.83), which the salinity and NO3- content of incubate soil followed the in situ samples as P (1.09-1.72‰, 8.02-8.17 mg kg-1), C (10.61-13.79‰, 5.99-6.07 mg kg-1), S (10.19-12.43‰, 3.64-4.22 mg kg-1), B (31.85-32.45‰, 3.56-3.72 mg kg-1) and O (31.61-34.30‰, 0.89-0.90 mg kg-1). NO3- and organic carbon decreased after incubation, which the polluted samples (86.63-92.63 g kg-1) still had higher organic carbon than untreated ones with more NH4+ consumption. The high-throughput sequence results showed that the Gammaproteobacteria and Alphaproteobacteria were dominant in all samples, while sulfate reducting bacteria Alphaproteobacteria decreased at 120 days. Meanwhile, the electroactive Gammaproteobacteria might symbiosis with Methanosaetaceae and Methanosarcinaceae, degrading petroleum after electron receptors depletion. Nitrososphaeraceae and Nitrosopumilaceae oxidise NH4+ to NO2- for intra-aerobic anaerobes and denitrifying bacteria producing oxygen for biodegradation in polluted Phragmites Communis soil. The halotolerant Halomicrobiaceae and Haloferacaceae predominated in saline Chinese Tamarisk, Suaeda Salsa and Bare Land, which were potential electroactive degradater. As the ageing sludge formed, the hydrogen trophic methanogens Methanothermobacteraceae (73.90-92.72%) was prevalent with the petroleum pollution. In conclusion, petroleum initiated two-phase in the sludge forming progress: electron acceptor consumption and electron transfer between degradater and methanogens. Based on the results, the domestic sewage N, P removal coupling and electron transport will be the basement for polluted soils fertility improvement.

Magnetite production and transformation in the methanogenic consortia from coastal riverine sediments.

Minerals that contain ferric iron, such as amorphous Fe(III) oxides (A), can inhibit methanogenesis by competitively accepting electrons. In contrast, ferric iron reduced products, such as magnetite (M), can function as electrical conductors to stimulate methanogenesis, however, the processes and effects of magnetite production and transformation in the methanogenic consortia are not yet known. Here we compare the effects on methanogenesis of amorphous Fe (III) oxides (A) and magnetite (M) with ethanol as the electron donor. RNA-based terminal restriction fragment length polymorphism with a clone library was used to analyse both bacterial and archaeal communities. Iron (III)-reducing bacteria including Geobacteraceae and methanogens such as Methanosarcina were enriched in iron oxide-supplemented enrichment cultures for two generations with ethanol as the electron donor. The enrichment cultures with A and non-Fe (N) dominated by the active bacteria belong to Veillonellaceae, and archaea belong to Methanoregulaceae and Methanobacteriaceae, Methanosarcinaceae (Methanosarcina mazei), respectively. While the enrichment cultures with M, dominated by the archaea belong to Methanosarcinaceae (Methanosarcina barkeri). The results also showed that methanogenesis was accelerated in the transferred cultures with ethanol as the electron donor during magnetite production from A reduction. Powder X-ray diffraction analysis indicated that magnetite was generated from microbial reduction of A and M was transformed into siderite and vivianite with ethanol as the electron donor. Our data showed the processes and effects of magnetite production and transformation in the methanogenic consortia, suggesting that significantly different effects of iron minerals on microbial methanogenesis in the iron-rich coastal riverine environment were present.