The Microbial Sulfur Cycle

pathways in sequenced Chlorobi are examined. Finally, the latest developments in microbial pathways for the degradation of DMSP, an extremely important component of the marine sulfur cycle are summarized. Three research articles focus on the regulation of sulfur oxidation genes in the purple sulfur bacterium Allochromatium vinosum, growth on tetrathionate vs. S(0) in Acidithiobacillus caldus and new Mycobacteria isolates from sandstone monuments that appear to grow as sulfur oxidizers. • Multi-organism interactions and symbiosis encompass the third category. Papers on exclusively prokaryotic symbioses and those that cross domain boundaries involving microbial eukaryotes and the symbionts of marine fauna provide a broad perspective in this arena grounded in the application of traditional (label tracing experiments to examine substrate exchange) and cutting edge (transcriptomic analysis of uncultured microbial symbionts) techniques. • Finally, this issue presents three papers on sulfur cycling at the level of ecosystems and communities. Two extreme environments are examined. Sorokin et al. (2011) summarize their long track record of work in soda lakes that combine high salinity with high pH. Both the reductive and oxidative arms of the sulfur cycle are discussed, and new insights into sulfidogenesis are presented for these fascinating systems. Yang et al. (2011) compare microbial communities and chemolithoautotrophic activity in relatively understudied freshwater hydrothermal vents in Yellowstone Lake. Finally, Luther et al. (2011) present a detailed analysis of the chemical parameters that influence abiotic oxidation of sulfide in natural environments. Sulfide oxidizing microbes must compete with this abiotic process and this report analyzes both literature and fresh experimental data to show that biotic sulfide oxidation will almost always occur at significantly faster rates due to kinetic restrictions on abiotic oxidation. Biology rules after all, as should be evident not just from this paper, but from the entire collection presented here.