Resolving environmental drivers of microbial community structure in Antarctic soils

Antarctic soils are extremely cold, dry, and oligotrophic, yet harbour surprisingly high bacterial diversity. The severity of environmental conditions has constrained the development of multi-trophic communities, and species richness and distribution is thought to be driven primarily by abiotic factors. Sites in northern and southern Victoria Land were sampled for bacterial community structure and soil physicochemical properties in conjunction with the US and New Zealand Latitudinal Gradient Project. Bacterial community structure was determined using a high-resolution molecular fingerprinting method for 80 soil samples from Taylor Valley and Cape Hallett sites which are separated by five degrees of latitude and have distinct soil chemistry. Taylor Valley is part of the McMurdo Dry Valleys, while Cape Hallett is the site of a penguin rookery and contains ornithogenic soils. The influence of soil moisture, pH, conductivity, ammonia, nitrate, total nitrogen and organic carbon on community structure was revealed using Spearman rank correlation, Mantel test, and principal components analysis. High spatial variability was detected in bacterial communities and community structure was correlated with soil moisture and pH. Both unique and shared bacterial community members were detected at Taylor Valley and Cape Hallett despite the considerable distance between the sites

Patterns of temperature adaptation in proteins from the bacteria Deinococcus radiodurans and Thermus thermophilus

It has long been known that amino acid substitutions in proteins of organisms living at moderate and high temperatures (mesophiles and thermophiles, respectively) are not all symmetrical; for example, more aligned sites have lysine in mesophiles and arginine in thermophiles than have the opposite pattern. This is generally taken to indicate that certain amino acids are favored over others by selection at different temperatures. Previous comparisons of protein sequences from mesophiles and thermophiles have used relatively small numbers of sequences from a diverse array of species, meaning that only the most common amino acid substitutions could be examined and any taxonspecific patterns would be obscured. Here, we compare a large number of proteins between mesophiles and thermophiles in the archaeal genus Methanococcus and the bacterial genus Bacillus. Each genus exhibits dramatically asymmetrical substitution patterns for many pairs of amino acids. There are several pairs of amino acids for which one amino acid is favored in thermophilic Bacillus and the other is favored in thermophilic Methanococcus; this appears to result from the higher GϩC content of the DNA of thermophilic Bacillus, a complication not seen in Methanococcus