Agricultural ecosystems annually receive approximately 25% of the global nitrogen input, much of which is oxidized at least once by ammonia-oxidizing prokaryotes to complete the nitrogen cycle. Recent discoveries have expanded the known ammonia-oxidizing prokaryotes from the domain Bacteria to Archaea. However, in the complex soil environment it remains unclear whether ammonia oxidation is exclusively or predominantly linked to Archaea as implied by their exceptionally high abundance. Here we show that Bacteria rather than Archaea functionally dominate ammonia oxidation in an agricultural soil, despite the fact that archaeal versus bacterial amoA genes are numerically more dominant. In soil microcosms, in which ammonia oxidation was stimulated by ammonium and inhibited by acetylene, activity change was paralleled by abundance change of bacterial but not of archaeal amoA gene copy numbers. Molecular fingerprinting of amoA genes also coupled ammonia oxidation activity with bacterial but not archaeal amoA gene patterns. DNA-stable isotope probing demonstrated CO(2) assimilation by Bacteria rather than Archaea. Our results indicate that Archaea were not important for ammonia oxidation in the agricultural soil tested.

The as-grown CNTs and graphitized CNTs were used as adsorbents to remove 1,2-dichlorobenzene from water. The experiments demonstrate that it takes only 40 min for CNTs to attain equilibrium and the adsorption capacity of asgrown and graphitized CNTs is 30.8 and 28.7 mg/g, respectively, from a 20 mg/l solution. CNTs can be used as adsorbents in a wide pH range of 3-10. Thermodynamic calculations indicate that the adsorption reaction is spontaneous with a high affinity and the adsorption is an endothermic reaction.

The two-step nitrification process is an integral part of the global nitrogen cycle, and it is accomplished by distinctly different nitrifiers. By combining DNA-based stable isotope probing (SIP) and high-throughput pyrosequencing, we present the molecular evidence for autotrophic growth of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB) in agricultural soil upon ammonium fertilization. Time-course incubation of SIP microcosms indicated that the amoA genes of AOB was increasingly labeled by 13 CO 2 after incubation for 3, 7 and 28 days during active nitrification, whereas labeling of the AOA amoA gene was detected to a much lesser extent only after a 28-day incubation. Phylogenetic analysis of the 13 C-labeled amoA and 16S rRNA genes revealed that the Nitrosospira cluster 3-like sequences dominate the active AOB community and that active AOA is affiliated with the moderately thermophilic Nitrososphaera gargensis from a hot spring. The higher relative frequency of Nitrospira-like NOB in the 13 C-labeled DNA suggests that it may be more actively involved in nitrite oxidation than Nitrobacter-like NOB. Furthermore, the acetylene inhibition technique showed that 13 CO 2 assimilation by AOB, AOA and NOB occurs only when ammonia oxidation is not blocked, which provides strong hints for the chemolithoautotrophy of nitrifying community in complex soil environments. These results show that the microbial community of AOB and NOB dominates the nitrification process in the agricultural soil tested. The ISME Journal (2011) 5, 1226-1236; doi:10.1038/ismej.2011.5; published online 17 February 2011Subject Category: microbial ecology and functional diversity of natural habitats

Viruses play important roles in biogeochemical nutrient cycles and act as genomic reservoirs in marine and freshwater environments, the understanding of which brought about the so-called 'third age' of virus ecology in aquatic environments. Unfortunately, the third age is in oceanography and limnology and outside the soil world. The main reason why virus ecology in soils has shown less progress is that agronomical and epidemiological interests were the primary motivation of viral studies by soil microbiologists. In this review, past research on viruses in soils is summarized after the introduction of the ecological traits of viruses, which are the effects of viruses on beneficial bacteria and soil-borne plant pathogens, adsorption of viruses to soils, and soil factors affecting viral inactivation and survival in soils. Horizontal gene transfer (transduction) in soils is also reviewed. Second, the abundance of viruses and their roles in biogeochemical nutrient cycles are summarized in aquatic environments. Five to 25% of the carbon fixed by primary producers is estimated to enter into the microbial loop via virus-induced lysis at different trophic levels in aquatic environments. The diversity of virus communities in aquatic environments estimated from analyses of the frequency distribution of capsid sizes and the morphology of virus populations are reviewed, and recent findings on the genomic diversity of viruses and their roles as the greatest genomic reservoirs in aquatic environments follow in the subsequent section. Viral genomics is elucidating the viral diversity and phylogenetic relationships among viruses in different environments. As the soil environment is a more diverse habitat for viruses than aquatic environments, viruses in soils have great potential to play roles comparable in quantity, which are unique in quality, to those in aquatic environments. Therefore, the potentiality and characteristics of viruses in soils are discussed in the final section for future research on virus ecology in soils from the viewpoints of biogeochemistry and genomic diversity. Synecological approaches to viruses in soils may open up a new era of soil virus ecology.