Although of limited metabolic diversity, methanogenic archaea or methanogens possess great phylogenetic and ecological diversity. Only three types of methanogenic pathways are known: CO(2)-reduction, methyl-group reduction, and the aceticlastic reaction. Cultured methanogens are grouped into five orders based upon their phylogeny and phenotypic properties. In addition, uncultured methanogens that may represent new orders are present in many environments. The ecology of methanogens highlights their complex interactions with other anaerobes and the physical and chemical factors controlling their function.

Metabolic, phylogenetic, and ecological diversity of the methanogenic archaea.

Taxonomic, Phylogenetic, and Ecological Diversity of Methanogenic Archaea

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Treatment Wetlands, Second Edition

Trace compounds of biogas from different biogas production plants.

This review of anaerobic metabolism emphasizes aerobic oxidation, because the two processes cannot be separated in a complete treatment of the topic. It is process oriented and highlights the fascinating microorganisms that mediate anaerobic biogeochemistry. We begin this review with a brief discussion of CO 2 assimilation by autotrophs, the source of most of the reducing power on Earth, and then consider the biological processes that harness this potential energy. Energy liberation begins with the decomposition of organic macromolecules to relatively simple compounds, which are simplified further by fermentation. Methanogenesis is considered next because CH 4 is a product of acetate fermentation, and thus completes the catabolism of organic matter, particularly in the absence of inorganic electron acceptors. Finally, the organisms that use nitrogen, manganese, iron, and sulfur for terminal electron acceptors are considered in order of decreasing free-energy yield of the reactions.

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

Microbial cycling of volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS) and methanethiol (MT), is intensively studied because these compounds play an important role in the processes of global warming, acid precipitation, and the global sulfur cycle. VOSC concentrations in freshwater sediments are low due to the balance between the formation and degradation of these compounds. These reactions occur for the greater part at the oxic/anoxic interphase of sediment and water column. In contrast to marine ecosystems, where dimethylsulfoniopropionate is the main precursor of MT and DMS, in freshwater ecosystems, VOSCs are formed mainly by methylation of sulfide and to a lesser extent from the degradation of S-containing amino acids. One of the major routes for DMS and MT formation through sulfide methylation is anaerobic O-demethylation of methoxylated aromatic compounds. Inhibition studies have revealed that the major part of the endogenously produced MT and DMS is degraded anaerobically by methanogens. The major bacterial groups involved in formation and consumption of VOSCs are described.

Microbial cycling of volatile organic sulfur compounds.

Methanosarcina semesiae MD1T (T = type strain), a novel obligately methylotrophic methanogenic archaeon is described. Strain MD1T was isolated from an enrichment on dimethylsulfide inoculated with mangrove sediment. The cells were irregularly coccoid, non-motile, 1.4+/-0.2 microm in diameter and stained Gram-positive. The catabolic substrates used included dimethylsulfide, methanethiol, methanol and methylated amines, but not acetate, formate, H2/CO2 or a combination of these substrates. When cells grown on dimethylsulfide were transferred to trimethylamine or methanol and vice versa, a lag phase was observed. The same lag phase occurred when cells grown on trimethylamine were transferred to methanol and vice versa, indicating that for each substrate different enzymes were induced. Fastest growth occurred within a temperature range of 30-35 degrees C and a pH of 6.5-7.5. Both Na+ and Mg2+ were required for growth, with maximum growth rates at 200-600 mM Na+ and 20-100 mM Mg2+. The cells exhibited specific growth rates (h-1) of 0.07+/-0.02, 0.15+/-0.04 and 0.18-/+0.05 on dimethylsulfide, methanol and trimethylamine, respectively. Analysis of the 16S rRNA gene sequence showed that strain MD1T was phylogenetically closely related to members of the genus Methanosarcina, but clearly differed from all described species of this genus (94-97% sequence similarity).

Methanosarcina semesiae sp. nov., a dimethylsulfide-utilizing methanogen from mangrove sediment.

Microbial cycling of volatile organic sulfur compounds in anoxic environments

Mangrove forest sediments were investigated with respect to organic matter content, bacterial numbers, methane emission, sulphide concentration and redox potential profiles. The sediments had characteristically high organic matter content (varying from 8 to 30 % of dry weight) and high bacterial numbers (varying from 5 to 20 x 10 8 cells/g fw). Both values decreased with depth (0-30 cm). Methane emission, sulphide and redox profiles on the other hand, showed remarkable differences between and among sampling sites. In areas with a high abundance of leaf litter and few trees very high sulphide concentrations were encountered: increasing from about 1 mM at the surface to 25 mM at 30-40 cm depth. Redox values were consistently low; from -150 to -200 mV. Near trees, in between the roots, a remarkably lower sulphide concentration was observed in the top 5-30 cm of the sediment. Methane emission varied from 0 to 500 μmol/m 2 /h). In vitro measurements showed CH 4 production in the top layer occurring at a rate much higher than estimated from the emissions. The results clearly demonstrate the importance of the anaerobic microbial activity in mangrove sediments and indicate that aerial roots are responsible for a major input of oxygen into the sediment, which speeds up oxidation.

Methane Emission, Sulphide Concentration and Redox Potential Profiles in Mtoni Mangrove Sediment, Tanzania

A styrene-degrading bacterium isolated from soil showed the capability to respire styrene, styrene oxide, phenyl acetaldehyde, phenyl acetate, phenol, catechol, succinate, pyruvate, acetate and acetaldehyde. Succinate-grown cells respire styrene. The strain was used to inoculate a biofilter with lava stones as carrier material. After a short adaptation period the biofilter was able to remove over 98 % of the incoming styrene (1 mmol.m -3 ) at a space velocity of 160 h -1 .

A. Pol

Papers

Microbial cycling of volatile organic sulfur compounds.

Methanosarcina semesiae sp. nov., a dimethylsulfide-utilizing methanogen from mangrove sediment.

Microbial cycling of volatile organic sulfur compounds in anoxic environments

Methane Emission, Sulphide Concentration and Redox Potential Profiles in Mtoni Mangrove Sediment, Tanzania

Styrene Removal from Waste Gas with a Bacterial Biotrickling Filter