Abundance, Distribution and Potential Activity of Methane Oxidising Bacteria in Permafrost Soils from the Lena Delta, Siberia

The methane oxidation potential of active layer profiles of permafrost soils from the Lena Delta, Siberia, was studied with regard to its respond to temperature, and abundance and distribution of type I and type II methanotrophs. Our results indicate vertical shifts within the optimal methane oxidation temperature and within the distribution of type I and type II methanotrophs. In the upper active layer, maximum methane oxidation potentials were detected at 21 °C. Deep active layer zones that are constantly exposed to temperatures below 2 °C showed a maximum potential to oxidise methane at 4 °C. Our results indicate a dominance of psychrophilic methanotrophs close to the permafrost table. Type I methanotrophs dominated throughout the active layer profiles but their number highly fluctuated with depth. In contrast, type II methanotrophs were constantly abundant through the whole active layer and displaced type I methanotrophs close to the permafrost table. No correlation between in-situ temperatures and the distribution of type I and type II methanotrophs was found. However, the distribution of type I and type II methanotrophs correlated significantly with in-situ methane concentrations. Beside vertical fluctuations, the abundance of methane oxidisers also fluctuated according to different geomorphic units. Similar methanotroph cell counts were detected in samples of a flood plain soil and a polygon rim soil, whereas cell counts in samples of a polygon centre soil were up to 100 times lower

The combined action of carvacrol and high hydrostatic pressure on Listeria monocytogenes Scott A

Aims: The aim of the study was to investigate the combined antimicrobial action of the plantderived volatile carvacrol and high hydrostatic pressure (HHP). Methods and Results: Combined treatments of carvacrol and HHP have been studied at different temperatures, using exponentially growing cells of Listeria monocytogenes, and showed a synergistic action. The antimicrobial effects were higher at 1°C than at 8 or 20°C. Furthermore, addition of carvacrol to cells exposed to sublethal HHP treatment caused similar reductions in viable numbers as simultaneous treatment with carvacrol and HHP. Synergism was also observed between carvacrol and HHP in semi-skimmed milk that was artifcially contaminated with L. monocytogenes. Conclusions: Carvacrol and HHP act synergistically and the antimicrobial effects of the combined treatment are greater at lower temperatures. Significance and Impact of the Study: The study demonstrates the synergistic antimicrobial effect of essential oils in combination with HHP and indicates the potential of these combined treatments in food processing