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Naturally-occurring disease-suppressive soils provide control of plant pathogens via the activities of indigenous microbes. While all soils contain antagonistic microbes, there is little systematic understanding of the correlates of variation in indigenous antagonist populations and on their relationships with plant diseases. We characterized the population densities, inhibitory capacities, and phylogenetic composition of soil streptomycete communities in a potato field over time in relation to edaphic factors, antagonist inoculation, and potato common scab severities. Antagonistic Streptomyces populations were highly variable in time and space. Similarly, metagenomic analyses of streptomycete communities showed extensive spatial and temporal variation in composition. Soil characteristics (pH, potassium, organic matter, nitrate, and phosphorous) sometimes explained up to 50% of the spatial variation in Streptomyces population densities, proportion of inhibitory isolates, or pathogen suppressive capacity among locations in the field. Soil pH was positively correlated with common scab severity, and negatively correlated with the proportion of pathogen-inhibitory Streptomyces among locations in the field. This suggests that high pH may have direct beneficial effects on pathogen populations and disease development, and/or indirect effects on pathogen populations via reductions in pathogen-inhibitory Streptomyces populations. Mean pathogen suppressive capacity of antagonistic Streptomyces was negatively correlated with common scab disease. Streptomyces inoculants had no discernible effect on streptomycete community composition, antagonistic capacities, or potato common scab severities, likely reflecting poor colonization of inoculants. Further understanding of the relationships between indigenous antagonist populations and plant diseases will be important to harnessing the potential of indigenous communities to contribute to sustainable disease management.

Throughout the history of polar exploration and up to recent times, wood and other exotic materials have been brought to the Antarctic continent and left there. While the possible transportation of exotic fungal species on these materials is sometimes considered, the effects of these exotic substrates on indigenous fungal communities have not been previously evaluated. This study reports results from seven plots where organic materials were used in baiting studies to determine the fungal diversity present in soils. Four plots were on islands in the Palmer Archipelago on the Antarctic Peninsula and three at Ross Island, Antarctica. Samples of sterile wood and cellulose with and without nutrients added were buried in soil and left for either two or four years before being removed and evaluated for fungal colonization. There was a significant increase in fungal colony-forming units (CFU) from soil in direct contact with introduced, sterile wood and cellulose substrates compared to background soil levels. The type of substrate, 2 or 4 year incubation period in the field, or nutrient addition did not have a significant effect on culturable densities in soil. Fungal abundance on soil adhering to substrates was found to be similar to that found in non-polar soils indicating that lack of organic material may be the most significant limiting factor affecting densities of Antarctic fungal populations. Based on a high degree of colonization, these exotic substrates appear to have a significant effect on indigenous soil fungal abundance.

The historic expedition huts located in the Ross Sea Region of the Antarctic and the thousands of artifacts left behind by the early explorers represent important cultural heritage from the "Heroic Era" of Polar exploration. The hut at Cape Royds built by Ernest Shackleton and members of the 1907-1908 British Antarctic Expedition has survived the extreme Antarctic environment for over 100 years, but recent studies have shown many forms of deterioration are causing serious problems, and microbial degradation is evident in the historic wood. Conservation work to reduce moisture at the hut required removal of fodder, wood, and many different types of organic materials from the stables area on the north side of the structure allowing large numbers of samples to be obtained for these investigations. In addition, wood from historic food storage boxes exposed in a ravine adjacent to the hut were also sampled. Fungi were cultured on several different media, and pure cultures were obtained and identified by sequencing of the internal transcribed spacer region of rDNA. From the 69 cultures of filamentous fungi obtained, the most predominant genera were Cadophora (44%) followed by Thielavia (17%) and Geomyces (15%). Other fungi found included Cladosporium, Chaetomium, and isolates identified as being in Pezizomycotina, Onygenales, Nectriaceae, and others. No filamentous basidiomycetes were found. Phylogenetic analyses of the Cadophora species showed great species diversity present revealing Cadophora malorum, Cadophora luteo-olivacea, Cadophora fastigiata, as well as Cadophora sp. 4E71-1, a C. malorum-like species, and Cadophora sp. 7R16-1, a C. fastigiata-like species. Scanning electron microscopy showed extensive decay was present in the wood samples with type 1 and type 2 forms of soft rot evident in pine and birch wood, respectively. Fungi causing decay in the historic wooden structures and artifacts are of great concern, and this investigation provides insight into the identity and species diversity of fungi found at the site. The historic woods and other organic materials at this site represent a large input of carbon into the Antarctic environment. This as well as nutrient additions from the nearby Adélie penguin (Pygoscelis adeliae) colony and favorable conditions for fungal growth at Cape Royds appear responsible for the significant fungal diversity, and where extensive decay is taking place in wood in contact with the ground.

To survive in Antarctica, early explorers of Antarctica's Heroic Age erected wooden buildings and brought in large quantities of supplies. The introduction of wood and other organic materials may have provided new nutrient sources for fungi that were indigenous to Antarctica or were brought in with the materials. From 30 samples taken fromDiscoveryHut, 156 filamentous fungi were isolated on selective media. Of these, 108 were screened for hydrolytic activity on carboxymethyl cellulose, of which 29 demonstrated activities. Endo-1, 4-β-glucanase activity was confirmed in the extracellular supernatant from seven isolates when grown at 4°C, and also when they were grown at 15°C.Cladosporium oxysporumandGeomycessp. were shown to grow on a variety of synthetic cellulose substrates and to use cellulose as a nutrient source at temperate and cold temperatures. The research findings from the present study demonstrate that Antarctic filamentous fungi isolated from a variety of substrates (wood, straw, and food stuffs) are capable of cellulose degradation and can grow well at low temperatures.

Microorganisms play a dominant role in Antarctic ecosystems, yet little is known about how fungal diversity differs at sites with considerable human activity as compared to those that are remote and relatively pristine. Ross Island, Antarctica is the site of three historic expedition huts left by early explorers to the South Pole, Robert F. Scott and Ernest Shackleton. The fungal diversity of these wooden structures and surrounding soils was investigated with traditional culturing methods as well as with molecular methodology including denaturing gradient gel electrophoresis (DGGE) using the internal transcribed spacer (ITS) regions of ribosomal DNA for identification. From historic wood and artifact samples and soils adjacent to the huts as well as soil samples obtained from the Lake Fryxell Basin, a remote Dry Valley location, and remote sites at Mt. Fleming and the Allan Hills, 71 fungal taxa were identified. The historic huts and associated artifacts have been colonized and degraded by fungi to various extents. The most frequently isolated fungal genera from the historic woods sampled include Cadophora, Cladosporium and Geomyces. Similar genera were found in soil samples collected near the huts. Sampling of soils from locations in the Transantarctic Mountains and Lake Fryxell Basin at considerable distances from the huts and with different soil conditions revealed Cryptococcus spp., Epicoccum nigrum and Cladosporium cladosporioides as the most common fungi present and Cadophora species less commonly isolated. DGGE revealed 28 taxa not detected by culturing including four taxa which possibly have not been previously described since they have less than 50% ITS sequence identity to any GenBank accessions. Fungi capable of causing degradation in the wood and artifacts associated with the expedition huts appear to be similar to those present in Antarctic soils, both near and at more remote locations. These species of fungi are likely indigenous to Antarctica and were apparently greatly influenced by the introduction of organic matter brought by early explorers. Considerable degradation has occurred in the wood and other materials by these fungi.

Early explorers of Antarctica's Heroic Era erected wooden buildings and brought large quantities of supplies to survive in Antarctica. The introduction of wood and other organic materials provided nutrient sources for fungi that were indigenous to Antarctica or were brought in with the materials and adapted to the harsh conditions. Seventy-two isolates of filamentous fungi were cultured on selective media from interior structural wood of the Cape Evans historic hut and 27 of these screened positive for the ability to degrade carboxymethyl cellulose (CMC). Four non-CMC-degrading isolates were added to a group of 14 CMC-degrading isolates for further study, and endo-1, 4-beta-glucanase activity was demonstrated in the extracellular supernatant from all of these 18 isolates when grown at 4 degrees C, and also when they were grown at 15 degrees C. Isolates of Penicillium roquefortii and Cadophora malorum showed preference for growth at 15 degrees C rather than 25 degrees C or 4 degrees C indicating psychrotrophic characteristics. These results demonstrate that cellulolytic filamentous fungi found in Antarctica are capable of growth at cold temperatures and possess the ability to produce extracellular endo-1, 4-beta-glucanase when cultured at cold and temperate temperatures.