Aquatic and terrestrial cyanobacteria produce methane.

Evidence is accumulating to challenge the paradigm that biogenic methanogenesis, considered a strictly anaerobic process, is exclusive to archaea. We demonstrate that cyanobacteria living in marine, freshwater, and terrestrial environments produce methane at substantial rates under light, dark, oxic, and anoxic conditions, linking methane production with light-driven primary productivity in a globally relevant and ancient group of photoautotrophs. Methane production, attributed to cyanobacteria using stable isotope labeling techniques, was enhanced during oxygenic photosynthesis. We suggest that the formation of methane by cyanobacteria contributes to methane accumulation in oxygen-saturated marine and limnic surface waters. In these environments, frequent cyanobacterial blooms are predicted to further increase because of global warming potentially having a direct positive feedback on climate change. We conclude that this newly identified source contributes to the current natural methane budget and most likely has been producing methane since cyanobacteria first evolved on Earth.

Online monitoring of stable carbon isotopes of methane in anaerobic digestion as a new tool for early warning of process instability.

Effective control of anaerobic digestion in biogas plants requires the monitoring of process sensitive and rapid response parameters in order to ensure efficient biogas production and to prevent potential process failure. In this study, stable carbon isotopes of methane (δ(13)CCH4) produced in a full-scale continuous stirred-tank reactor were investigated as a potential new monitoring tool for this purpose. Over a six-month period with variable organic loading rates, δ(13)CCH4-values were measured online by a portable high-precision laser absorption spectrometer. During a stress period of consecutive high organic loading, δ(13)CCH4-values early indicated process changes in contrast to traditionally monitored parameters where a change was observed some five to ten days later. Comparison of the stable isotope values with data from microbial analyses showed a distinct relationship between the quantity of potentially acetoclastic methanogens and δ(13)CCH4-values. This finding indicates an association between dominant methanogenic pathways and carbon isotope values.

Design and application of a synthetic DNA standard for real-time PCR analysis of microbial communities in a biogas digester.

A synthetic DNA fragment containing primer binding sites for the quantification of ten different microbial groups was constructed and evaluated as a reliable enumeration standard for quantitative real-time PCR (qPCR) analyses. This approach has been exemplary verified for the quantification of several methanogenic orders and families in a series of samples drawn from a mesophilic biogas plant. Furthermore, the total amounts of bacteria as well as the number of sulfate-reducing and propionic acid bacteria as potential methanogenic interaction partners were successfully determined. The obtained results indicated a highly dynamic microbial community structure which was distinctly affected by the organic loading rate, the substrate selection, and the amount of free volatile fatty acids in the fermenter. Methanosarcinales was the most predominant methanogenic order during the 3 months of observation despite fluctuating process conditions. During all trials, the modified quantification standard indicated a maximum of reproducibility and efficiency, enabling this method to open up a wide range of novel application options.

Carbon, hydrogen and oxygen stable isotope ratios of whole wood, cellulose and lignin methoxyl groups of Picea abies as climate proxies.

RATIONALE: Carbon, hydrogen and oxygen (C, H and O) stable isotope ratios of whole wood and components are commonly used as paleoclimate proxies. In this work we consider eight different proxies in order to discover the most suitable wood component and stable isotope ratio to provide the strongest climate signal in Picea abies in a southeastern Alpine region (Trentino, Italy). METHODS: δ(13)C, δ(18)O and δ(2)H values in whole wood and cellulose, and δ(13)C and δ(2)H values in lignin methoxyl groups were measured. Analysis was performed using an Isotopic Ratio Mass Spectrometer coupled with an Elemental Analyser for measuring (13)C/(12)C and a Pyrolyser for measuring (2)H/(1)H and (18)O/(16)O. The data were evaluated by Principal Component Analysis, and a simple Pearson's correlation between isotope chronologies and climatic features, and multiple linear regression were performed to evaluate the data. RESULTS: Each stable isotope ratio in cellulose and lignin methoxyl differs significantly from the same stable isotope ratio in whole wood, the values begin higher in cellulose and lignin except for the lignin δ(2)H values. Significant correlations were found between the whole wood and the cellulose fractions for each isotope ratio. Overall, the highest correlations with temperature were found with the δ(18)O and δ(2)H values in whole wood, whereas no significant correlations were found between isotope proxies and precipitation. CONCLUSIONS: δ(18)O and δ(2)H values in whole wood provide the best temperature signals in Picea abies in the northern Italian study area. Extraction of cellulose and lignin and analysis of other isotopic ratios do not seem to be necessary.

Halogen retention, organohalogens, and the role of organic matter decomposition on halogen enrichment in two Chilean peat bogs.

Natural formation of organohalogen compounds can be shown to occur in all natural environments. Peat bogs, which are built up exclusively of organic matter and cover approximately 3% of the total continental world area, are potentially significant reservoirs for organohalogen formation. Up to now, fluxes and retention rates of halogens and organohalogen formation in peat bogs were mostly unquantified. In our study, we investigated the retention of atmospheric derived halogens and the natural formation of organohalogens by differential halogen analysis in two peat bogs in southernmost Chile. Atmospheric wet deposition rates of chlorine, bromine, and iodine range between 600 and 36000, 6 and 160, and 1 and 3 mg m(-2) yr(-1), respectively. Mean annual net accumulation rates of these halogens in peat are calculated to be 12-72 mg of Cl m(-2), 1.7-12 mg of Br m(-2), and 0.4-1.2 mg of l m(-2). Retention rates are similarly high for iodine (36-46%) and bromine (7.5-50%), and substantially lower for chlorine (0.2-2%). To evaluate influences of peat decomposition processes on halogen enrichment, halogen concentrations were compared to carbon/nitrogen ratios (C/N). Our results indicate that up to 95% of chlorine, 91% of bromine, and 81% of iodine in peat exist in an organically bound form. The results also indicate that the concentrations of halogens, especially of bromine and iodine, in peat are largely determined by peat decomposition processes and that halogens are not conservative in bogs.

Fluxes of trichloroacetic acid between atmosphere, biota, soil, and groundwater.

Trichloroacetic acid (TCA), in former times used as a herbicide in agriculture, is now ubiquitous and almost evenly distributed in precipitations of the Northern and Southern Hemisphere, despite larger emissions of the possible precursors tetrachloroethene and 1,1,1-trichloroethane in the Northern Hemisphere. The permanent input of a herbicidal compound into most vulnerable ecosystems might lead to adverse effects to biota (plants, microorganisms, etc.). TCA soil levels of coniferous forests in mountainous regions of Central Europe are significantly elevated. Mass balance calculations show that precipitation as sole source of TCA in soil seems to be of minor importance and provide evidence for a natural formation of TCA within soil itself. In addition, the isolation of a chlorinating enzyme in soil and laboratory experiments with humic acid, iron and halide point to an omnipresent chlorinating capability of nature producing polyhalogenated organic compounds such as TCA. In this paper we present an overview of TCA levels in the environment and provide a new estimate about the extent of a natural TCA formation, especially in soil.

Formation of chloroacetic acids from soil, humic acid and phenolic moieties.

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe(2+), Fe(3+) and H(2)O(2) leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.

Abiotic Fe(III) induced mineralization of phenolic substances.

The redox process between iron(III) (in dissolved form and as the mineral phase ferrihydrite) and phenolic substances has been examined. We investigated the relationship between the structure and reactivity for the dihydrobenzene reductants catechol, hydroquinone and resorcine, and for the 2-methoxyphenol guaiacol with iron(III), by determining the rate of the Fe(III) reduction as well as the production of CO2. This work demonstrates that catechol and guaiacol will be effectively oxidized to CO2 by reducing iron(III). Hydroquinone shows a reduction of iron(III), but no accompanying mineralization could be determined. In contrast, resorcine showed no reaction with Fe(II). The deciding factor on whether or not mineralization occurs were controlled by the position of the hydroxy groups. It is shown that phenolic substances with two hydroxy groups in the orthoposition or at least one hydroxy group and a methoxy group can be oxidized to CO2 while iron(III) is reduced.

Halocarbons produced by natural oxidation processes during degradation of organic matter.

Volatile halogenated organic compounds (VHOC) play an important role in atmospheric chemical processes-contributing, for example, to stratospheric ozone depletion. For anthropogenic VHOC whose sources are well known, the global atmospheric input can be estimated from industrial production data. Halogenated compounds of natural origin can also contribute significantly to the levels of VHOC in the atmosphere. The oceans have been implicated as one of the main natural sources, where organisms such as macroalgae and microalgae can release large quantities of VHOC to the atmosphere. Some terrestrial sources have also been identified, such as wood-rotting fungi, biomass burning and volcanic emissions. Here we report the identification of a different terrestrial source of naturally occurring VHOC. We find that, in soils and sediments, halide ions can be alkylated during the oxidation of organic matter by an electron acceptor such as Fe(III): sunlight or microbial mediation are not required for these reactions. When the available halide ion is chloride, the reaction products are CH3Cl, C2H5Cl, C3H7Cl and C4H9Cl. (The corresponding alkyl bromides or alkyl iodides are produced when bromide or iodide are present.) Such abiotic processes could make a significant contribution to the budget of the important atmospheric compounds CH3Cl, CH3Br and CH3I.