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.

Phylogeography of microbial phototrophs in the dry valleys of the high Himalayas and Antarctica.

High-elevation valleys in dry areas of the Himalayas are among the most extreme, yet least explored environments on Earth. These barren, rocky valleys are subjected to year-round temperature fluctuations across the freezing point and very low availability of water and nutrients, causing previous workers to hypothesize that no photoautotrophic life (primary producers) exists in these locations. However, there has been no work using modern biogeochemical or culture-independent molecular methods to test the hypothesis that photoautotrophs are absent from high Himalayan soil systems. Here, we show that although microbial biomass levels are as low as those of the Dry Valleys of Antarctica, there are abundant microbial photoautotrophs, displaying unexpected phylogenetic diversity, in barren soils from just below the permanent ice line of the central Himalayas. Furthermore, we discovered that one of the dominant algal clades from the high Himalayas also contains the dominant algae in culture-independent surveys of both soil and ice samples from the Dry Valleys of Antarctica, revealing an unexpected link between these environmentally similar but geographically very distant systems. Phylogenetic and biogeographic analyses demonstrated that although this algal clade is globally distributed to other high-altitude and high-latitude soils, it shows significant genetic isolation by geographical distance patterns, indicating local adaptation and perhaps speciation in each region. Our results are the first to demonstrate the remarkable similarities of microbial life of arid soils of Antarctica and the high Himalayas. Our findings are a starting point for future comparative studies of the dry valleys of the Himalayas and Antarctica that will yield new insights into the cold and dry limits to life on Earth.

Microbial activity and diversity during extreme freeze-thaw cycles in periglacial soils, 5400 m elevation, Cordillera Vilcanota, Perú.

High-elevation periglacial soils are among the most extreme soil systems on Earth and may be good analogs for the polar regions of Mars where oligotrophic mineral soils abut with polar ice caps. Here we report on preliminary studies carried out during an expedition to an area where recent glacial retreat has exposed porous mineral soils to extreme, daily freeze-thaw cycles and high UV fluxes. We used in situ methods to show that inorganic nitrogen (NO(3) (-) and NH(4) (+)) was being actively cycled even during a period when diurnal soil temperatures (5 cm depth) ranged from -12 to 27 degrees C and when sub-zero, soil cooling rates reached 1.8 degrees C h(-1) (the most rapid soil cooling rates recorded to date). Furthermore, phylogenetic analyses of microbial phylotypes present at our highest sites (5410 m above sea level) showed the presence of nitrifying bacteria of the genus Nitrospira and newly discovered nitrite-oxidizing Betaproteobacteria. These soils were overwhelmingly dominated (>70% of phylotypes) by photosynthetic bacteria that were related to novel cyanobacteria previously found almost exclusively in other plant-free, high-elevation soils. We also demonstrated that soils from our highest sites had higher potential for mineralizing glutamate and higher microbial biomass than lower elevation soils that had been more recently covered by ice. Overall, our findings indicate that a diverse and robustly functioning microbial ecosystem is present in these previously unstudied high-elevation soils.

Direct evidence for extensive paternal mitochondrial DNA inheritance in the marine mussel Mytilus.

Inheritance of mitochondrial DNA in animals was thought to be strictly maternal. Recently, evidence for incidental paternal mtDNA leakage was obtained in hybrid crosses of Drosophila and mice. In mice, the frequency of paternal mtDNA contributions was estimated at 10(-4), compared with maternal contributions. The common occurrence in the marine mussel Mytilus of heteroplasmic individuals with two or more types of highly diverged mtDNA molecules was interpreted as strong evidence for biparental mtDNA inheritance by some, but not by others. We report here results from pair-matings involving two species of mussels, Mytilus edulis and Mytilus trossulus. Extensive contribution of paternal mtDNA, amounting to several orders of magnitude higher than that inferred for Drosophila or mice, was observed in both intra- and interspecific crosses.

An unusual type of mitochondrial DNA inheritance in the blue mussel Mytilus.

In animals, mitochondrial DNA (mtDNA) inheritance is predominantly maternal. In a few cases incidental transmission of paternal mtDNA was observed and estimated to account for only 10(-4)-10(-3) of an individual's mtDNA content. In contrast, biparental inheritance is common in mussels of the genus Mytilus. Here we present direct evidence that sex and mtDNA inheritance are coupled in Mytilus. Females inherit mtDNA only from their mother, but they transmit it to both daughters and sons. Males inherit mtDNA from both parents, but they transmit to sons only the mtDNA they inherited from their father. In pair matings, this mtDNA inheritance pattern is associated with a strong sex-ratio bias. These findings establish a newly discovered type of cytoplasmic DNA transmission. We also present evidence that the phenomenon breaks down in interspecific hybrids.