Multiple-phase equilibration headspace analysis for the determination of N2O and N2 during bacterial denitrification

A gas-handling manifold for the preparation, introduction and analysis by gas chromatography (GC) system of the gaseous products of denitrification is described. A procedure of multiple-phase equilibration is adopted which allows the quantitative determination of the total gas present in sample vials. Assumptions of solubility coefficients are not required as these are determined during the analysis. The method is particularly suited to gases of appreciable solubilities as a significant proportion of the gas will be found in the liquid phase. This method was used for the determination of the stoichiometry of denitrification, in washed cells of Rhodopseudomonas sphaeroides f. sp. denitrificans, namely NO2-:N2 and N2O:N2, which were found to be 2:1 and 1:1, respectively.     

Role of the coat in resistance of bacterial spores to inactivation by ethylene oxide

A study of spore morphology revealed an association between resistance to ethylene oxide and abnormal spore coat development and both characteristics were enhanced by selection and propagation of resistant survivors. After rupture of the coat, spores were sensitized to lysozyme but not to ethylene oxide. Resistance to ethylene oxide was increased following treatment of spores with ureamercaptoethanol-alkali and decreased after treatment with urea. Germinated spores retained resistance to the sterilant and loss of resistance coincided with emergence of the vegetative cells.     

Rhizosphere processes in nitrate-rich barley soil tripled both N2O and N2 losses due to enhanced bacterial and fungal denitrification

Plant and Soil - Plants can directly affect nitrogen (N) transformation processes at the micro-ecological scale when soil comes into contact with roots. Due to the methodological limitations in...     

Microbial N2O consumption in and above marine N2O production hotspots

The ocean is a net source of N₂O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N₂O via microbial N₂O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N₂O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O₂ tolerance, and community composition of N₂O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N₂O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N₂O cycling. Microbes from the oxic layer consume N₂O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N₂O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O₂ and N₂O gradients right above the ODZ is a previously ignored potential gatekeeper of N₂O and should be accounted for in the marine N₂O budget.Subject terms: Water microbiology, Biogeochemistry, Microbial ecology     

Surface appendages of bacterial spores

Bacilli and Clostridia generate dormant, highly resistant cells, called spores, in response to stress. Spores of many species are decorated by morphologically diverse structures of unknown function called appendages that have yet to be studied at the molecular level. In this issue, Walker et al. employ reverse genetics to identify genes encoding protein components of the ornate ribbon-like appendages of the spores of Clostridium taeniosporum. Their results reveal striking commonalities between these genes and those encoding outer structures in phylogenetically and taxonomically distinct spore-forming species. The insights gained from this work demonstrate the value of analysis of non-model spore formers.     

The kinetics of germination in bacterial spores

The entire absorbance vs. time curve of a sample of germinating bacterial spores can be accurately described by a model which considers that the spores rate of entry into the phase initiation of germination is determined by transitions between three spore states. The first of these transitions is easily identified with the triggering event, while the existence of the intermediate state, and its identification with the triggered spore, can be established from theoretical as well as experimental considerations. The observed sample lag time is seen to arise from the position of the measured event in the single spore in the sequence of indices of germination. Consideration that the single spore may effect the measured change in a complex way over a finite interval of time leads to a mathematical formulation of our model which can describe the germination process whatever the endpoint chosen for its observation.     

Photometric immersion refractometry of bacterial spores

Photometric immersion refractometry was used to determine the average apparent refractive index (n) of five types of dormant Bacillus spores representing a 600-fold range in moist-heat resistance determined as a D100 value. The n of a spore type increased as the molecular size of various immersion solutes decreased. For comparison of the spore types, the n of the entire spore and of the isolated integument was determined by use of bovine serum albumin, which is excluded from permeating into them. The n of the sporoplast (the structures bounded by the outer pericortex membrane) was determined by use of glucose, which was shown to permeate into the spore only as deeply as the pericortex membrane. Among the various spore types, an exponential increase in the heat resistance correlated with the n of the entire spore and of the sporoplast, but not of the isolated perisporoplast integument. Correlation of the n with the solids content of the entire spore provided a method of experimentally obtaining the refractive index increment (dn/dc), which was constant for the various spore types and enables the calculation of solids and water content from an n. Altogether, the results showed that the total water content is distributed unequally within the dormant spore, with less water in the sporoplast than in the perisporoplast integument, and that the sporoplast becomes more refractile and therefore more dehydrated as the heat resistance becomes greater among the various spore types.     

The antigenic properties of bacterial spores

Summary 1°. Bacterial spores are antigenic.2°. Spore-antigen is distinct and separate from the antigens of the bacillary forms to which the spores give rise on germination.3°. Antigens of the spores of various kinds of spore-bearing bacilli are also mutually distinct.I am greatly indebted to Miss A.de Groot for her technical assistence.     

过量施肥对设施菜田土壤菌群结构及N2O产生的影响

【背景】N_2O是一种很强的温室气体,其温室效应强度大约是CO_2的265倍。土壤氮肥施加量是影响N_2O排放的重要因素,而厌氧条件下微生物反硝化则是N_2O产生的重要途径。【目的】研究过量施肥条件下蔬菜大棚土壤菌群结构变化及其对N_2O气体排放的影响。【方法】利用自动化培养与实时气体检测系统(Robot)监测土壤厌氧培养过程中N_2O和N_2排放通量,比较过量施肥和减氮施肥模式下土壤N_2O排放模式的差异。通过Illumina二代测序平台对这2种不同施肥处理的土壤微生物群落进行高通量测序,研究不同施肥量对土壤菌群组成的影响。【结果】过量施肥土壤中硝酸盐的含量大约是减氮施肥土壤的2倍,通过添加硝酸盐使2种土壤的硝酸盐含量均为60 mg/kg或为200 mg/kg时,过量施肥土壤在厌氧培养前期N_2O气体的产生量及产生速度都明显高于减氮施肥土壤。另外,过量施肥导致土壤菌群结构发生显著改变,并且降低了土壤微生物的多样性。相对于减氮施肥,过量施肥方式富集了Rhodanobacter属的微生物。PICRUSt预测结果显示,传统施肥没有显著改变反硝化功能基因相对丰度。【结论】长期过量氮肥施用显著增加了土壤N_2O的排放,可能原因是施肥改变了包括氮转化相关微生物在内的土壤菌群组成,从而影响了土壤N_2O气体的形成与还原过程。