F.A.M. de Bok

Pathway of Propionate Oxidation by a Syntrophic Culture of Smithella propionica and Methanospirillum hungatei

ABSTRACT The pathway of propionate conversion in a syntrophic coculture ofSmithella propionica and Methanospirillum hungatei JF1 was investigated by 13C-NMR spectroscopy. Cocultures produced acetate and butyrate from propionate. [3-13C]propionate was converted to [2-13C]acetate, with no [1-13C]acetate formed. Butyrate from [3-13C]propionate was labeled at the C2 and C4 positions in a ratio of about 1:1.5. Double-labeled propionate (2,3-13C) yielded not only double-labeled acetate but also single-labeled acetate at the C1 or C2 position. Most butyrate formed from [2,3-13C]propionate was also double labeled in either the C1 and C2 atoms or the C3 and C4 atoms in a ratio of about 1:1.5. Smaller amounts of single-labeled butyrate and other combinations were also produced. 1-13C-labeled propionate yielded both [1-13C]acetate and [2-13C]acetate. When 13C-labeled bicarbonate was present, label was not incorporated into acetate, propionate, or butyrate. In each of the incubations described above, 13C was never recovered in bicarbonate or methane. These results indicate that S. propionica does not degrade propionate via the methyl-malonyl-coenzyme A (CoA) pathway or any other of the known pathways, such as the acryloyl-CoA pathway or the reductive carboxylation pathway. Our results strongly suggest that propionate is dismutated to acetate and butyrate via a six-carbon intermediate.

A simple and fast method for determining colony forming units

Aims:  To develop a flexible and fast colony forming unit quantification method that can be operated in a standard microbiology laboratory.

Degradation of Methanethiol by Methylotrophic Methanogenic Archaea in a Lab-Scale Upflow Anaerobic Sludge Blanket Reactor

ABSTRACT 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 H2S, CO2, and CH4. 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.

Hydrogenases and formate dehydrogenases of Syntrophobacter fumaroxidans

The syntrophic propionate-oxidizing bacterium Syntrophobacter fumaroxidans possesses two distinct formate dehydrogenases and at least three distinct hydrogenases. All of these reductases are either loosely membrane-associated or soluble proteins and at least one of the hydrogenases is located in the periplasm. These enzymes were expressed on all growth substrates tested, though the levels of each enzyme showed large variations. These findings suggest that both H2 and formate are involved in the central metabolism of the organism, and that both these compounds may serve as interspecies electron carriers during syntrophic growth on propionate.