Evidence that chytrids dominate fungal communities in high-elevation soils.

Periglacial soils are one of the least studied ecosystems on Earth, yet they are widespread and are increasing in area due to retreat of glaciers worldwide. Soils in these environments are cold and during the brief summer are exposed to high levels of UV radiation and dramatic fluctuations in moisture and temperature. Recent research suggests that these environments harbor immense microbial diversity. Here we use sequencing of environmental DNA, culturing of isolates, and analysis of environmental variables to show that members of the Chytridiomycota (chytrids) dominate fungal biodiversity and perhaps decomposition processes in plant-free, high-elevation soils from the highest mountain ranges on Earth. The zoosporic reproduction of chytrids requires free water, yet we found that chytrids constituted over 70% of the ribosomal gene sequences of clone libraries from barren soils of the Himalayas and Rockies; by contrast, they are rare in other soil environments. Very few chytrids have been cultured, although we were successful at culturing chytrids from high-elevation sites throughout the world. In a more focused study of our sites in Colorado, we show that carbon sources that support chytrid growth (eolian deposited pollen and microbial phototrophs) are abundant and that soils are saturated with water for several months under the snow, thus creating ideal conditions for the development of a chytrid-dominated ecosystem. Our work broadens the known biodiversity of the Chytridomycota, and describes previously unsuspected links between aquatic and terrestrial ecosystems in alpine regions.

The earliest stages of ecosystem succession in high-elevation (5000 metres above sea level), recently deglaciated soils.

Global climate change has accelerated the pace of glacial retreat in high-latitude and high-elevation environments, exposing lands that remain devoid of vegetation for many years. The exposure of 'new' soil is particularly apparent at high elevations (5000 metres above sea level) in the Peruvian Andes, where extreme environmental conditions hinder plant colonization. Nonetheless, these seemingly barren soils contain a diverse microbial community; yet the biogeochemical role of micro-organisms at these extreme elevations remains unknown. Using biogeochemical and molecular techniques, we investigated the biological community structure and ecosystem functioning of the pre-plant stages of primary succession in soils along a high-Andean chronosequence. We found that recently glaciated soils were colonized by a diverse community of cyanobacteria during the first 4-5 years following glacial retreat. This significant increase in cyanobacterial diversity corresponded with equally dramatic increases in soil stability, heterotrophic microbial biomass, soil enzyme activity and the presence and abundance of photosynthetic and photoprotective pigments. Furthermore, we found that soil nitrogen-fixation rates increased almost two orders of magnitude during the first 4-5 years of succession, many years before the establishment of mosses, lichens or vascular plants. Carbon analyses (pyrolysis-gas chromatography/mass spectroscopy) of soil organic matter suggested that soil carbon along the chronosequence was of microbial origin. This indicates that inputs of nutrients and organic matter during early ecosystem development at these sites are dominated by microbial carbon and nitrogen fixation. Overall, our results indicate that photosynthetic and nitrogen-fixing bacteria play important roles in acquiring nutrients and facilitating ecological succession in soils near some of the highest elevation receding glaciers on the Earth.

Phylogeny and ecophysiology of opportunistic "snow molds" from a subalpine forest ecosystem.

Mats of coenocytic "snow molds" are commonly observed covering the soil and litter of alpine and subalpine areas immediately following snow melt. Here, we describe the phylogenetic placement, growth rates, and metabolic potential of cold-adapted fungi from under-snow mats in the subalpine forests of Colorado. SSU rDNA sequencing revealed that these fungi belong to the zygomycete orders Mucorales and Mortierellales. All of the isolates could grow at temperatures observed under the snow at our sites (0 degrees C and -2 degrees C) but were unable to grow at temperatures above 25 degrees C and were unable to grow anaerobically. Growth rates for these fungi were very high at -2 degrees C, approximately an order of magnitude faster than previously studied cold-tolerant fungi from Antarctic soils. Given the rapid aerobic growth of these fungi at low temperatures, we propose that they are uniquely adapted to take advantage of the flush of nutrient that occurs at the soil-snow interface beneath late winter snow packs. In addition, extracellular enzyme production was relatively high for the Mucorales, but quite low for the Mortierellales, perhaps indicating some niche separation between these fungi beneath the late winter snow pack.

Biogeochemical consequences of rapid microbial turnover and seasonal succession in soil.

Soil microbial communities have the metabolic and genetic capability to adapt to changing environmental conditions on very short time scales. In this paper we combine biogeochemical and molecular approaches to reveal this potential, showing that microbial biomass can turn over on time scales of days to months in soil, resulting in a succession of microbial communities over the course of a year. This new understanding of the year-round turnover and succession of microbial communities allows us for the first time to propose a temporally explicit N cycle that provides mechanistic hypotheses to explain both the loss and retention of dissolved organic N (DON) and inorganic N (DIN) throughout the year in terrestrial ecosystems. In addition, our results strongly support the hypothesis that turnover of the microbial community is the largest source of DON and DIN for plant uptake during the plant growing season. While this model of microbial biogeochemistry is derived from observed dynamics in the alpine, we present several examples from other ecosystems to indicate that the general ideas of biogeochemical fluxes being linked to turnover and succession of microbial communities are applicable to a wide range of terrestrial ecosystems.

Molecular and metabolic characterization of cold-tolerant alpine soil Pseudomonas sensu stricto.

Alpine soils undergo dramatic temporal changes in their microclimatic properties, suggesting that the bacteria there encounter uncommon shifting selection gradients. Pseudomonads constitute important members of the alpine soil community. In order to characterize the alpine Pseudomonas community and to assess the impact of shifting selection on this community, we examined the ability of cold-tolerant Pseudomonas isolates to grow on a variety of carbon sources, and we determined their phylogenetic relationships based on 16S ribosomal DNA sequencing. We found a high prevalence of Pseudomonas in our soil samples, and isolates from these soils exhibited extensive metabolic diversity. In addition, our data revealed that many of our isolates form a unique cold-adapted clade, representatives of which are also found in the Swedish tundra and Antarctica. Our data also show a lack of concordance between the metabolic properties and 16S phylogeny, indicating that the metabolic diversity of these organisms cannot be predicted by phylogeny.

Intraoperative management of penile erection with intracorporeal phenylephrine during endoscopic surgery.

Intraoperative penile tumescence during endoscopic surgery is a troublesome complication that often is refractory to recommended methods of management. We report a new approach of pharmacological management with intracorporeal penile injections of phenylephrine (total dose of 0.1 mg.), which was successful in 3 successive patients. This approach is prompt, safe and reproducible, and it provides sustained resolution of erection without systemic side effects. It is concluded that local intracorporeal penile administration of this sympathomimetic agent appears to be a potent new tool in the armamentarium of the endoscopic surgeon dealing with this frustrating clinical situation, which merits further clinical trial.