Anaerobic degradation of dimethylsulfoniopropionate to 3-S-methylmercaptopropionate by a marine Desulfobacterium strain

Dimethylsulfoniopropionate, an osmolyte of marine algae, is thought to be the major precursor of dimethyl sulfide, which plays a dominant role in biogenic sulfur emission. The marine sulfate-reducing bacterium Desulfobacterium strain PM4 was found to degrade dimethylsulfoniopropionate to 3-S-methylmercaptopropionate. The oxidation of one of the methyl groups of dimethylsulfoniopropionate was coupled to the reduction of sulfate; this process is similar to the degradation of betaine to dimethylglycine which was described earlier for the same strain. Desulfobacterium PM4 is the first example of an anaerobic marine bacterium that is able to demethylate dimethylsulfoniopropionate.

Degradation of 2-sec-butylphenol:3-sec-butylcatechol, 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid, and 2-methylbutyric acid as intermediates

Pseudomonas sp. strain HBP1 Prp, a mutant of strain HBP1 that was originally isolated on 2-hydroxybiphenyl, was able to grow on 2-sec-butylphenol as the sole carbon and energy source. During growth on 2-sec-butylphenol, 2-methylbutyric acid transiently accumulated in the culture medium. Its concentration reached a maximum after 20 hours and was below detection limit at the end of the growth experiment. The first three enzymes of the degradation pathway - a NADH-dependent monooxygenase, a metapyrocatechase, and a meta-fission product hydrolase - were partially purified. The product of the the monooxygenase reaction was identified as 3-sec-butylcatechol by mass spectrometry. This compound was a substrate for the metapyrocatechase and was converted to 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid which was identified by gas chromatography-mass spectrometry of its trimethylsilyl-derivative. The cofactor independent meta-cleavage product hydrolase used 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid as a substrate. All three enzymes showed highest activities for 2-hydroxybiphenyl and its metabolites, respectively, indicating that 2-sec-butylphenol is metabolized via the same pathway as 2-hydroxybiphenyl

Reliability factor for identification of amylolytic enzyme activity in the optimized starch-iodine assay

Amylolytic enzymes are a group of proteins degrading starch to its constitutional units. For high-throughput screening, simple yet accurate methods in addition to the reducing ends assays are required. In this article, the iodine assay, a photometric assay based on the intensely colored starch-iodine complex, was adapted to enable accurate and objective differentiation between enzyme and background activity using a newly introduced mathematical factor. The method was further improved by designing a simple setup for multiple time point detection and discussing the applicability of single wavelength measurements

METHANOGENIC CONVERSION OF 3-S-METHYLMERCAPTOPROPIONATE TO 3-MERCAPTOPROPIONATE

Anaerobic metabolism of dimethylsulfoniopropionate, an osmolyte of marine algae, in anoxic intertidal sediments involves either cleavage to dimethylsulfide or demethylation to 3-S-methylmercaptopropionate (MMPA) and subsequently to 3-mercaptopropionate. The methanogenic archaea Methanosarcina sp. strain MTP4 (DSM 6636), Methanosarcina acetivorans DSM 2834, and Methanosarcina (Methanolobus) siciliae DSM 3028 were found to use MMPA as a growth substrate and to convert it stoichiometrically to 3-mercaptopropionate. Approximately 0.75 mol of methane was formed per mol of MMPA degraded; methanethiol was not detected as an intermediate. Eight other methanogenic strains did not carry out this conversion. We also studied the conversion of MMPA in anoxic marine sediment slurries. Addition of MMPA (500 mu M) resulted in the production of methanethiol which was subsequently converted to methane (417 mu M). In the presence of the antibiotics ampicillin, vancomycin, and kanamycin (20 mu g/ml each), 275 mu M methane was formed from 380 mu M MMPA; no methanethiol was formed during these incubations. Only methanethiol was formed from MMPA when 2-bromoethanesulfonate (25 mM) was added to a sediment suspension. These results indicate that in natural environments MMPA could be directly or indirectly a substrate for methanogenic archaea.</p