Showing papers by "Werner Liesack published in 2008"

Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2

Abstract: Methane-oxidizing bacteria (methanotrophs) attenuate methane emission from major sources, such as wetlands, rice paddies, and landfills, and constitute the only biological sink for atmospheric methane in upland soils. Their key enzyme is particulate methane monooxygenase (pMMO), which converts methane to methanol. It has long been believed that methane at the trace atmospheric mixing ratio of 1.75 parts per million by volume (ppmv) is not oxidized by the methanotrophs cultured to date, but rather only by some uncultured methanotrophs, and that type I and type II methanotrophs contain a single type of pMMO. Here, we show that the type II methanotroph Methylocystis sp. strain SC2 possesses two pMMO isozymes with different methane oxidation kinetics. The pmoCAB1 genes encoding the known type of pMMO (pMMO1) are expressed and pMMO1 oxidizes methane only at mixing ratios >600 ppmv. The pmoCAB2 genes encoding pMMO2, in contrast, are constitutively expressed, and pMMO2 oxidizes methane at lower mixing ratios, even at the trace level of atmospheric methane. Wild-type strain SC2 and mutants expressing pmoCAB2 but defective in pmoCAB1 consumed atmospheric methane for >3 months. Growth occurred at 10–100 ppmv methane. Most type II but no type I methanotrophs possess the pmoCAB2 genes. The apparent Km of pMMO2 (0.11 μM) in strain SC2 corresponds well with the Km(app) values for methane oxidation measured in soils that consume atmospheric methane, thereby explaining why these soils are dominated by type II methanotrophs, and some by Methylocystis spp., in particular. These findings change our concept of methanotroph ecology.

Substrate-induced growth and isolation of Acidobacteria from acidic Sphagnum peat.

Abstract: Fluorescence in situ hybridization (FISH) was applied to estimate the population size of the poorly characterized phylum Acidobacteria in acidic peat sampled from nine different Sphagnum-dominated wetlands of Northern Russia The cell numbers of these bacteria in oxic peat layers ranged from 04 x 10(6) to 13 x 10(7) cells per g of wet peat, comprising up to 4% of total bacterial cells Substrate-induced growth of acidobacteria was observed after amendment of peat samples with glucose, pectin, xylan, starch, ethanol and methanol, while weak or no response was obtained for acetate, pyruvate, mannitol and cellobiose Using low-nutrient media and FISH-mediated monitoring of the isolation procedure, we succeeded in obtaining nine strains of acidobacteria in pure cultures These strains belonged to subdivisions 1 and 3 of the Acidobacteria and represented strictly aerobic, heterotrophic organisms Except for methanol, the substrate utilization patterns of these isolates matched the results obtained in our substrate-amendment experiments with native peat All strains were also capable of utilizing galacturonic acid, a characteristic component of the cell wall in Sphagnum spp, which is released during moss decomposition Most isolates from subdivision 1 were truly acidophilic organisms with the growth optimum at pH 35-45, while the isolates from subdivision 3 grew optimally at pH 55-65 Another important phenotypic trait of novel strains was their capability of active growth at low temperatures Both acidophily and low-temperature growth are consistent with the occurrence of acidobacteria in cold and acidic northern wetlands