Explore the vast range of titles available.

Archaeal populations are abundant in cold and temperate environments, but little is known about their potential response to climate change-induced temperature changes. The effects of temperature on archaeal communities in unamended slurries of weakly acidic peat from Spitsbergen were studied using a combination of fluorescent in situ hybridization (FISH), 16S rRNA gene clone libraries and denaturing gradient gel electrophoresis (DGGE). A high relative abundance of active archaeal cells (11–12% of total count) was seen at low temperatures (1 and 5 °C), and this community was dominated by Group 1.3b Crenarchaeota and the euryarchaeal clusters rice cluster V (RC-V), and Lake Dagow sediment (LDS). Increasing temperature reduced the diversity and relative abundance of these clusters. The methanogenic community in the slurries was diverse and included representatives of Methanomicrobiales , Methanobacterium , Methanosarcina and Methanosaeta . The overall relative abundance and diversity of the methanogenic archaea increased with increasing temperature, in accordance with a strong stimulation of methane production rates. However, DGGE profiling showed that the structure of this community changed with temperature and time. While the relative abundance of some populations was affected directly by temperature, the relative abundance of other populations was controlled by indirect effects or did not respond to temperature.

Emissions of the greenhouse gas methane from Arctic wetlands have been studied extensively, though little is known about the ecology and community structure of methanogenic archaea that catalyze the methane production. As part of a project addressing microbial transformations of methane in Arctic wetlands, we studied archaeal communities in two wetlands (Solvatnet and Stuphallet) at Spitsbergen, Norway (78°N) during two summer seasons. Directly extracted peat community DNA and enrichment cultures of methanogenic archaea were analyzed by nested PCR combined with denaturing gradient gel electrophoresis and subsequent sequencing of 16S rRNA gene fragments. Sequences affiliated with Methanomicrobiales, Methanobacteriaceae, Methanosaeta and Group I.3b of the uncultured crenarchaeota were detected at both sites. Sequences affiliated with Methanosarcina were recovered only from the site Solvatnet, while sequences affiliated with the euryarchaeotal clusters Rice Cluster II and Sediment 1 were detected only at the site Stuphallet. The phylogenetic affiliation of the recovered sequences suggested a potential of both hydrogenotrophic and acetoclastic methanogenesis at both sites. At Solvatnet, there were clear temporal trends in the archaeal community structure over the Arctic summer season. The archaeal community composition was significantly affected by factors influencing the activity of the overall bacterial community, as measured by in situ emissions of CO 2. Methane emissions at both sites were influenced more by peat temperatures and thaw depth than by the archaeal community structure. Enrichment cultures for methanogenic archaea determined that most of the methanogens detected directly in peat could grow in culture at 10 °C. Culture based biases were indicated in later enrichment steps by the abundant growth of a Methanosarcina strain that was not detected directly in peat samples.

Viable counts of heterotropic soil bacteria were 3-5 times higher on low-nutrient agar media compared with a series of conventional agar media. Substantial amounts of monosaccharides and amino acids were present in solid media made from distilled water and agar powder, and a salt-solution agar medium (without organic substrates added) gave practically the same colony counts as the low nutrient soil extract agar medium. MPN values were comparable to or lower than plate counts. A search for slow-growing cells in the negative MPN tubes by fluorescence microscopical examination after 3 months incubation was negative. The viable counts were 2-4% of the total microscopical counts in different soils. Assuming that the colony-forming cells did not derive from the numerous \"dwarf\" cells present in soil, a calculated percent viability of the larger cells was about 10%. The ecological significance of the plate-counting technique is discussed.

The course of nitrogen fixation by moss-associated cyanobacteria in Svalbard (78°N, 16°E), Norway, was studied using the acetylene reduction assay. In situ field measurements of nitrogen fixation activity were conducted in six different types of moss-dominated arctic vegetation from the beginning of the snowmelt in early June to the end of July 1998. Concurrently, the water content of the soil/vegetation layer was determined and correlated with the nitrogen fixation rates. At all sites with diminishing water content during the summer season, nitrogen fixation activity was positively correlated with the amount of available water in the vegetation. At two sites, where water content of the vegetation was constantly higher than 80% (w/w) throughout the season, nitrogen fixation activity was correlated with temperature. Depending on the type of vegetation, nitrogen fixation became limited when the water status fell below a minimum threshold level. The most desiccation-tolerant vegetation for nitrogen fixation activity was the cryptobiotic crust, where nitrogen fixation decreased only after the water content of the soil/vegetation was less than 50% of the its fresh weight, while in the other types of vegetation nitrogen fixation stopped when water content was around 60%. The results from the present study confirm that, in arctic regions with low precipitation during the growing season, nitrogen fixation in different types of vegetation is mostly limited either to the period of snowmelt when water is sufficiently available, or to habitats that stay wet during summer.

Possible effects on the physiological activity and culturability of soil microorganisms by different soil dispersion procedures, and effects on activity caused by extracting bacteria from soil, were investigated. There was no apparent difference in cfu's with dispersion of a silty loam soil and a loamy sand soil with pyrophosphate as compared to dispersion in NaCl. Substrate-induced respiration was reduced in the silty loam soil, and methanol oxidation was reduced in the loamy sand soil with dispersion in pyrophosphate, and the soil pH was irreversibly increased by the treatment. Extracted bacterial fractions had lower numbers of culturable cells as percentage of the total number of bacteria in each fraction, lower respiration rates and no methanol oxidation activity as compared to the soil slurry both before and after extraction. The physiological activity was apparently not affected by the number of cells extracted. This indicates that the increased extraction rate of indigenous soil bacteria obtained by effective disruption of aggregates and detachment of cells from surfaces, only results in increased extraction of cells that have been physiologically changed as a result of the extraction process.

Possible effects on the physiological activity and culturability of soil microorganisms by different soil dispersion procedures, and effects on activity caused by extracting bacteria from soil, were investigated. There was no apparent difference in cfu's with dispersion of a silty loam soil and a loamy sand soil with pyrophosphate as compared to dispersion in NaCl. Substrate-induced respiration was reduced in the silty loam soil, and methanol oxidation was reduced in the loamy sand soil with dispersion in pyrophosphate, and the soil pH was irreversibly increased by the treatment. Extracted bacterial fractions had lower numbers of culturable cells as percentage of the total number of bacteria in each fraction, lower respiration rates and no methanol oxidation activity as compared to the soil slurry both before and after extraction. The physiological activity was apparently not affected by the number of cells extracted. This indicates that the increased extraction rate of indigenous soil bacteria obtained by effective disruption of aggregates and detachment of cells from surfaces, only results in increased extraction of cells that have been physiologically changed as a result of the extraction process.

The influence of environmental factors on the nitrogen fixation activity in soil and vegetation samples from different types of plant communities from the Sassen Valley (78°N, 16°E), Svalbard, Norway, was measured under controlled laboratory conditions using the acetylene reduction assay throughout the summers of 1997 and 2000. Samples for study were chosen from six sites along a 2-km-long transect representing different types of arctic vegetation. The influence of temperature, soil water content, and light intensity on acetylene reduction rates was studied. Samples from all sites showed low and almost constant acetylene reduction rates between 0 and 10°C. Above 10°C the activity of all samples increased rapidly and reached its maximum at about 25 and 32°C for the samples with free-living cyanobacteria and moss-associated cyanobacteria, respectively. There was a significant water-dependent increase of acetylene reduction activity for all types of vegetation. The samples showed a clear response to varying light conditions, i.e. a rapid decrease in acetylene reduction rates when light intensity decreased from 140 to 80 μmol m-2 s-1 depending on the type of vegetation.

The number of bacterial cells in soil that form colonies on nutrient agar represent a small fraction of the direct microscopic counts (DMC). The colony-forming cells have larger cell dimensions than the very small (\"dwarf\") cells which represent the majority of the DMC. This may indicate that the dwarf cells are species unable to form visible colonies on agar, or that they swell to normal dimensions when growing. Indigenous bacterial cells were separated from soil by density gradient centrifugation and fractionated according to diameter by filtration through polycarbonate filters. Each filtrate was studied with respect to DMC, cell dimensions, colony-forming cells (visible colonies and microcolonies), and cell dimensions during growth on the agar. The calculated average percent viability was only 0.2% for cells with diameters below 0.4 μm, about 10% for cells with diameters between 0.4 and 0.6 μm, and 30-40% for cells with diameters above 0.6 μm. Only 10-20% of the viable cells with diameters <0.4 μm increased their diameter to >0.4 μm prior to growth. Thus, size change during starvation and growth cycles did not explain the high numbers of dwarf cells observed by microscopy. The results show that despite the relatively low number of colony-forming bacteria in soil, the species that form colonies may be fairly representative for the medium size and large cells, which constitute a major part of the bacterial biovolume. Thus plate counting could be a useful method to count and isolate the bacteria accounting for much of the biovolume in soil. The origin of the dwarf cells is still unclear, but the low number of small cells that increased in size seems to indicate that the majority of these bacterial cells are not small forms of ordinary sized bacteria.

The FWPCA issued a grant to evaluate an automatic water monitoring unit with 12 channels. The parameters were: Nitrate, Nitrite, Alkalinity-pH 8.3, Alkalinity-pH 4.6, Phenol, Free Ammonia, Sulfate, Phosphate, Iron (Fe), COD, Methylene Blue Active Substance, and Fluoride. The monitor site was on the Hudson River, 3 miles south of Albany, New York. Operational problems of the unit are discussed. Modifications to the unit in attempts to overcome some problems are discussed and factors which must be taken into consideration in the design of an automatic system are reported.