【光敏感微生物的全球丰度】Omri M Finkel Oded Béjà and Shimshon Belkin. Global abundance of microbial rhodopsins. The ISME Journal 2013 7 448–451
Abstract
Photochemical reaction centers and rhodopsins are the only phototrophic mechanisms known to have evolved on Earth. The minimal cost of bearing a rhodopsin-based phototrophic mechanism in comparison to maintaining a photochemical reaction center suggests that rhodopsin is the more abundant of the two. We tested this hypothesis by conducting a global abundance calculation of phototrophic mechanisms from 116 marine and terrestrial microbial metagenomes. On average 48% of the cells from which these metagenomes were generated harbored a rhodopsin gene exceeding the reaction center abundance by threefold. Evidence from metatranscriptomic data suggests that this genomic potential is realized to a substantial extent at least for the small-sized (>0.8 μm) of microbial fractions.
【N2O还原微生物群落】Christopher M Jones Daniel RH Graf David Bru Laurent Philippot and Sara Hallin. The unaccounted yet abundant nitrous oxide-reducing microbial community: a potential nitrous oxide sink. The ISME Journal 2013 7 417–426
Abstract
Nitrous oxide (N2O) is a major radiative forcing and stratospheric ozone-depleting gas emitted from terrestrial and aquatic ecosystems. It can be transformed to nitrogen gas (N2) by bacteria and archaea harboring the N2O reductase (N2OR) which is the only known N2O sink in the biosphere. Despite its crucial role in mitigating N2O emissions knowledge of the N2OR in the environment remains limited. Here we report a comprehensive phylogenetic analysis of the nosZ gene coding the N2OR in genomes retrieved from public databases. The resulting phylogeny revealed two distinct clades of nosZ with one unaccounted for in studies investigating N2O-reducing communities. Examination of N2OR structural elements not considered in the phylogeny revealed that the two clades differ in their signal peptides indicating differences in the translocation pathway of the N2OR across the membrane. Sequencing of environmental clones of the previously undetected nosZ lineage in various environments showed that it is widespread and diverse. Using quantitative PCR we demonstrate that this clade was most often at least as abundant as the other thereby more than doubling the known extent of the overall N2O-reducing community in the environment. Furthermore we observed that the relative abundance of nosZ from either clade varied among habitat types and environmental conditions. Our results indicate a physiological dichotomy in the diversity of N2O-reducing microorganisms which might be of importance for understanding the relationship between the diversity of N2O-reducing microorganisms and N2O reduction in different ecosystems.
【热带森林土壤的细菌群落结构】Nicholas J Bouskill Hsiao Chien Lim Sharon Borglin Rohit Salve Tana E Wood Whendee L Silver and Eoin L Brodie. Pre-exposure to drought increases the resistance of tropical forest soil bacterial communities to extended drought. The ISME Journal