Nitrification and nitrifiers in acidic soils Li, Yaying; Chapman, Stephen J.; Nicol, Graeme W. ...
Soil biology & biochemistry,
January 2018, 2018-01-00, 2018-01, Letnik:
116
Journal Article
Recenzirano
Nitrification, as a crucial step in nitrogen cycling and plant nutrition, is a biologically mediated process responsible for enormous losses of nitrogen fertilizer and a contributor to environmental ...pollution. The recent progress in our understanding of nitrification and nitrifiers, specifically in acidic soils, is discussed and reviewed. At one time it was assumed that rates of nitrification are relatively low in acidic soils. However, more recent studies have demonstrated nitrification down to pH 3.0 and that the rate of nitrification can equal, or even exceed, that found in neutral soils. Studies on acidic forest soils in Europe noted that they have a high potential for nitrate production. Furthermore, using the 15N isotope-dilution technique it was shown that net nitrification measurements can markedly underestimate gross nitrification in these natural and highly organic systems. Using selective inhibitors it has been demonstrated that heterotrophic nitrifiers can contribute to nitrification. While heterotrophic nitrification can be performed by a wide range of bacteria and fungi, inhibitor studies point to fungi to be mainly responsible. Autotrophic ammonia-oxidizing bacteria (AOB), such as Nitrosomonas and Nitrosospira, have been known for some considerable time but have generally found to be inactive in acidic conditions. The discovery of ammonia monooxygenase in uncultured archaea that were functionally active at low pH pointed to an autotrophic microbial group (ammonia oxidizing archaea, AOA) that might be adapted to low substrate (ammonia) concentrations and responsible for nitrification in the wider range of acidic grassland and cultivated soils. Obligately acidophilic AOA have more recently been cultivated while stable isotope probing has been used to confirm the dominance of AOA over AOB in acidic soils. Detailed molecular studies using both 16S rRNA and amoA (ammonia monooxygenase sub-unit A) gene sequencing are continuing to expand our appreciation of the diversity of both AOB and AOA and how this varies over different pH ranges and in different ecosystems. Similar work is being directed towards nitrite oxidizing bacteria (NOB) but to date we do not fully know the role of pH in controlling NOB activity. Such understanding of nitrification and nitrifiers will help develop new effective nitrification inhibitors and aid the management of nitrogen cycling in acidic soils.
•AOA generally make a greater contribution than AOB in acidic soils.•Heterotrophic nitrifiers play an important role in acidic forest soils.•Isotope labelling techniques have improved the detection of nitrification rates.•Pure culture studies have advanced our understanding of nitrification processes.
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•Oxytetracycline can be degraded effectively by black soldier fly larvae.•Intestinal microorganisms facilitate the bioremediation of antibiotic contamination.•This is the first report ...of ARGs and MGEs in the gut of black soldier fly larvae.
As a saprophytic insect, the black soldier fly can digest organic waste efficiently in an environmentally friendly way. However, the ability and efficiency of this insect, and the microbial mechanisms involved, in the degradation of antibiotics are largely uncharacterized. To obtain further details during the degradation of OTC (oxytetracycline) by black soldier fly larvae (larvae), the changes in intestinal bacterial communities were examined. Both ARGs (antibiotic resistance genes) and MGEs (mobile genetic elements) were found within the larval guts. At the end of the degradation period, 82.7%, 77.6% and 69.3% of OTC was degraded by larvae when the initial concentrations were 100, 1000 and 2000 mg kg−1 (dry weight), respectively, which was much higher than the degradation efficiencies (19.3–22.2%) without larvae. There was no obvious effect of OTC on the development of the larvae. Although the larval gut microorganisms were affected by OTC, they adapted to the altered environment. Enterococcus, Ignatzschineria, Providencia, Morganella, Paenalcaligenes and Actinomyces in the gut responded strongly to antibiotic exposure. Interestingly, numerous ARGs (specifically, 180 ARGs and 10 MGEs) were discovered, and significantly correlated with those of both integron-integrase gene and transposases in the larval gut. Of all the detected ARGs, tetracycline resistance genes expressed at relatively high levels and accounted for up to 67% of the total ARGs. In particular, Enterococcus, Ignatzschineria, Bordetella, Providencia and Proteus were all hosts of enzymatic modification genes of tetracycline in the guts that enabled effective degradation of OTC. These findings demonstrate that OTC can be degraded effectively and prove that the bioremediation of antibiotic contamination is enhanced by larvae. In addition, the abundance of ARGs and MGEs formed should receive attention and be considered in environmental health risk assessment systems.
The anaerobic oxidation of methane (AOM) mediated by microorganisms is a key process in the reduction of methane emissions, and AOM-coupled electron acceptors have been shown to regulate methane ...emissions into the atmosphere in marine systems. Paddy fields are a significant source of methane and account for 20% of global methane emissions, but the effect of electron acceptors on the methane emission process in flooded paddy fields has been poorly characterized. This study aimed to determine whether the electron acceptors ferric iron and nitrate, and biochar, acting as an electron shuttle, can regulate the AOM process in paddy soil, with or without interaction between biochar and these two electron acceptors. We also aimed to characterize which microorganisms are actively involved. Here, we added 13C-labeled CH4 (13CH4) into anaerobic microcosms to evaluate the role of electron acceptors by measuring the methane oxidation rate and the enrichment of 13C-labeled CO2 (13CO2). We then combined DNA-stable isotope probing with amplicon sequencing to study the active microorganisms. We found for the first time that, in addition to nitrate, ferric iron can also effectively promote AOM in paddy soil. However, there was no significant effect of biochar. Ferric iron-dependent AOM was mainly carried out by iron-reducing bacteria (Geobacter, Ammoniphilus and Clostridium), and nitrate-dependent AOM was mainly by nitrate-reducing bacteria (Rhodanobacter, Paenibacillus and Planococcus). Our results demonstrate that the AOM process, regulated by the electron acceptors ferric iron and nitrate, can alleviate methane emission from paddy soil. The potentially active microorganisms related to electron acceptor reduction may be crucial for this methane sink and deserve further research.
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•Fe3+ and NO3− can stimulate the anaerobic oxidation of methane (AOM) process.•Biochar has no obvious effect on the AOM process.•Iron/nitrate-reducing bacteria are active microorganisms involved in the AOM process.•Electron acceptors coupled with AOM is a key process to reduce methane emissions.
In this trial, intravascular ultrasonography was used to compare the effects of atorvastatin versus rosuvastatin on regression of coronary atherosclerosis. Both statins led to regression in two ...thirds of patients, with no significant difference between their effects.
Randomized clinical trials have consistently shown that inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) reduce cardiovascular event rates.
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The favorable effects of statins extend across a range of levels of low-density lipoprotein (LDL) cholesterol, with no apparent lower threshold for a benefit.
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In parallel, imaging trials have shown that intensive statin regimens slow the progression of coronary atherosclerosis and may even result in disease regression in some patients.
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Accordingly, guidelines for cardiovascular disease prevention have increasingly emphasized that lowering LDL cholesterol levels with statins is the primary goal of lipid-modulating therapy.
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Available statins differ considerably . . .
IMPORTANCE: Triglycerides and cholesterol are both carried in plasma by apolipoprotein B (ApoB)–containing lipoprotein particles. It is unknown whether lowering plasma triglyceride levels reduces the ...risk of cardiovascular events to the same extent as lowering low-density lipoprotein cholesterol (LDL-C) levels. OBJECTIVE: To compare the association of triglyceride-lowering variants in the lipoprotein lipase (LPL) gene and LDL-C–lowering variants in the LDL receptor gene (LDLR) with the risk of cardiovascular disease per unit change in ApoB. DESIGN, SETTING, AND PARTICIPANTS: Mendelian randomization analyses evaluating the associations of genetic scores composed of triglyceride-lowering variants in the LPL gene and LDL-C–lowering variants in the LDLR gene, respectively, with the risk of cardiovascular events among participants enrolled in 63 cohort or case-control studies conducted in North America or Europe between 1948 and 2017. EXPOSURES: Differences in plasma triglyceride, LDL-C, and ApoB levels associated with the LPL and LDLR genetic scores. MAIN OUTCOMES AND MEASURES: Odds ratio (OR) for coronary heart disease (CHD)—defined as coronary death, myocardial infarction, or coronary revascularization—per 10-mg/dL lower concentration of ApoB-containing lipoproteins. RESULTS: A total of 654 783 participants, including 91 129 cases of CHD, were included (mean age, 62.7 years; 51.4% women). For each 10-mg/dL lower level of ApoB-containing lipoproteins, the LPL score was associated with 69.9-mg/dL (95% CI, 68.1-71.6; P = 7.1 × 10−1363) lower triglyceride levels and 0.7-mg/dL (95% CI, 0.03-1.4; P = .04) higher LDL-C levels; while the LDLR score was associated with 14.2-mg/dL (95% CI, 13.6-14.8; P = 1.4 × 10−465) lower LDL-C and 1.9-mg/dL (95% CI, 0.1-3.9; P = .04) lower triglyceride levels. Despite these differences in associated lipid levels, the LPL and LDLR scores were associated with similar lower risk of CHD per 10-mg/dL lower level of ApoB-containing lipoproteins (OR, 0.771 95% CI, 0.741-0.802, P = 3.9 × 10−38 and OR, 0.773 95% CI, 0.747-0.801, P = 1.1 × 10−46, respectively). In multivariable mendelian randomization analyses, the associations between triglyceride and LDL-C levels with the risk of CHD became null after adjusting for differences in ApoB (triglycerides: OR, 1.014 95% CI, 0.965-1.065, P = .19; LDL-C: OR, 1.010 95% CI, 0.967-1.055, P = .19; ApoB: OR, 0.761 95% CI, 0.723-0.798, P = 7.51 × 10−20). CONCLUSIONS AND RELEVANCE: Triglyceride-lowering LPL variants and LDL-C–lowering LDLR variants were associated with similar lower risk of CHD per unit difference in ApoB. Therefore, the clinical benefit of lowering triglyceride and LDL-C levels may be proportional to the absolute change in ApoB.
Rice straw is considered as a renewable biomass energy source and its efficient utilization is still a topic worthy of attention. Black soldier fly larvae, Hermetia illucens (L.), (Diptera: ...Stratiomydiae) is a kind of saprophytic insect, which can effectively digest organic wastes. Here we report that alkaline peroxide-pretreatment improves the digestion of rice straw by these larvae, especially the decomposition of cellulose, which was at 70.9% compared to 58.2% without pretreatment. After conversion, the effective conversion rates of rice straw to larvae were 10.7% and 11.4%, for raw rice straw and rice straw with pretreatment, respectively. With pretreatment the composition of larval gut microorganisms was altered where Actinomyces, Dysgonomonas, Devosia and Pelagibacterium were the dominant flora for digesting rice straw. In addition, metabolism, environmental information processing and genetic information processing were the major gut microbial functions. These findings demonstrate that chemical pretreatment for the removal of lignin and hemicellulose was an effective measure for the digestion and consumption of rice straw by black soldier fly larvae.
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•Hermetia illucens can digest and consume rice straw.•Alkaline peroxide-pretreatment is more conductive to the digestion of rice straw.•Alkaline peroxide-pretreatment increased the decomposition of cellulose significantly.•Metabolism is the major potential gut microbial function.•Larval gut microorganisms play a key role for the degradation of rice straw.
A substantial challenge facing multicentre audit and research projects is timely recruitment of collaborators and their study centres. Cost-effective strategies are required and fee-free social media ...has previously been identified as a potential conduit. We investigated and evaluated the effectiveness of a novel multi-format social media and Internet strategy for targeted recruitment to a national multicentre cohort study.
Interventions involved a new Twitter account, including weekly live question-and-answer sessions, a new Facebook group page, online YouTube presentations and an information page on a national association website. Link tracking analysis was undertaken using Google Analytics, which was then related to subsequent registration. Social influence was calculated using the proprietary Klout score.
Internet traffic analysis identified a total of 1562 unique registration site views, of which 285 originated from social media (18.2%). Some 528 unique registrations were received, with 96 via social media platforms (18.2%). Traffic source analysis identified a separate national association webpage as resulting in the majority of registration page views (15.8%), followed by Facebook (11.9%), Twitter (4.8%) and YouTube (1.5%). A combination of publicity through Facebook, Twitter and the dedicated national association webpage contributed to the greatest rise in registration traffic and accounted for 312 (48%) of the total registrations within a 2-week period. A Twitter 'social influence' (Klout) score of 42/100 was obtained during this period.
Targeted social media substantially aided study dissemination and collaborator recruitment. It acted as an adjunct to traditional methods, accounting for 18.2% of collaborator registration in a short time period with no associated financial costs. We provide a practical model for designing future recruitment campaigns, and recommend Facebook, Twitter and targeted websites as the most effective adjuncts for maximising cost-effective study recruitment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
To appraise the clinical and genetic evidence that low-density lipoproteins (LDLs) cause atherosclerotic cardiovascular disease (ASCVD).
We assessed whether the association between LDL and ASCVD ...fulfils the criteria for causality by evaluating the totality of evidence from genetic studies, prospective epidemiologic cohort studies, Mendelian randomization studies, and randomized trials of LDL-lowering therapies. In clinical studies, plasma LDL burden is usually estimated by determination of plasma LDL cholesterol level (LDL-C). Rare genetic mutations that cause reduced LDL receptor function lead to markedly higher LDL-C and a dose-dependent increase in the risk of ASCVD, whereas rare variants leading to lower LDL-C are associated with a correspondingly lower risk of ASCVD. Separate meta-analyses of over 200 prospective cohort studies, Mendelian randomization studies, and randomized trials including more than 2 million participants with over 20 million person-years of follow-up and over 150 000 cardiovascular events demonstrate a remarkably consistent dose-dependent log-linear association between the absolute magnitude of exposure of the vasculature to LDL-C and the risk of ASCVD; and this effect appears to increase with increasing duration of exposure to LDL-C. Both the naturally randomized genetic studies and the randomized intervention trials consistently demonstrate that any mechanism of lowering plasma LDL particle concentration should reduce the risk of ASCVD events proportional to the absolute reduction in LDL-C and the cumulative duration of exposure to lower LDL-C, provided that the achieved reduction in LDL-C is concordant with the reduction in LDL particle number and that there are no competing deleterious off-target effects.
Consistent evidence from numerous and multiple different types of clinical and genetic studies unequivocally establishes that LDL causes ASCVD.
Various carbon sources as substrates and electron donors can produce methane via different metabolic pathways. In particular, the methane produced by rice cultivation has a severe impact on climate ...change. However, how Fe3+, the most abundant oxide in paddy soil, mediates the methanogenesis of different carbon sources is unknown. In this study, we investigated the effect of four carbon sources with different chain lengths (acetate, glucose, nonanoate, and starch) on CH4 production and associated methanogens in iron-rich paddy soil over 90 days of anaerobic incubation. We found that glucose and starch were the more preferential substrates for liberating methane compared to acetate, and the rate was also faster. Nonanoate was unable to support methane production. Methanosarcinales and Methanobacteriales were the most predominant methanogenic archaea as shown by 16S rRNA gene sequencing, though their abundance changed over time. Additionally, a significantly higher content of iron-reducing bacteria was observed in the glucose and starch treatments, and it was significantly positively correlated with the copy number of the methanogenic mcrA gene. Together, we confirmed the methanogenic capacity of different carbon sources and their related microorganisms. We also showed that iron oxides play a central role in regulating methane emissions from paddy soils and need more attention to be paid to them.
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•The methanogenic capacity of glucose and starch were stronger than acetate.•Methanosarcinales and Methanobacteriales were mainly responsible for CH4 production.•The type and abundance of methanogens changed with the incubation time.•mcrA gene copies positively correlated with the reduction of Fe(III).
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