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In a lab-scale upflow anaerobic sludge blanket reactor inoculated with granular sludge from a full-scale wastewater treatment plant treating paper mill wastewater, methanethiol (MT) was degraded at 30°C to H 2 S, CO 2 , and CH 4 . At a hydraulic retention time of 9 h, a maximum influent concentration of 6 mM MT was applied, corresponding to a volumetric loading rate of 16.5 mmol liter −1 day −1 . The archaeal community within the reactor was characterized by anaerobic culturing and denaturing gradient gel electrophoresis analysis, cloning, and sequencing of 16S rRNA genes and quantitative PCR. Initially, MT-fermenting methanogenic archaea related to members of the genus Methanolobus were enriched in the reactor. Later, they were outcompeted by Methanomethylovorans hollandica , which was detected in aggregates but not inside the granules that originated from the inoculum, the microbial composition of which remained fairly unchanged. Possibly other species within the Methanosarcinacaea also contributed to the fermentation of MT, but they were not enriched by serial dilution in liquid media. The archaeal community within the granules, which was dominated by Methanobacterium beijingense , did not change substantially during the reactor operation. Some of the species related to Methanomethylovorans hollandica were enriched by serial dilutions, but their growth rates were very low. Interestingly, the enrichments could be sustained only in the presence of MT and did not utilize any of the other typical substrates for methylotrophic methanogens, such as methanol, methyl amine, or dimethylsulfide.

Many micro-organisms are known to produce efficient toxic substances against conspecifics and closely related species. The widespread coexistence of killer (toxin producer) and sensitive (non-producer) strains is a puzzle calling for a theoretical explanation. Based on stochastic cellular automaton simulations and the corresponding semi-analytical configuration-field approximation models, we suggest that metapopulation dynamics offers a plausible rationale for the maintenance of polymorphism in killer-sensitive systems. A slight trade-off between toxin production and population growth rate is sufficient to maintain the regional coexistence of toxic and sensitive strains, if toxic killing is a local phenomenon restricted to small habitat patches and local populations regularly go extinct and are renewed via recolonizations from neighbouring patches. Pattern formation on the regional scale does not play a decisive part in this mechanism, but the local manner of interactions is essential.