Enrichment of marine anammox bacteria in Hiroshima Bay sediments.

Anaerobic ammonium oxidation (anammox) involves the microbiological oxidation of ammonium with nitrite as the electron acceptor and dinitrogen gas as the main product. The Scalindua species, an anammox genus that dominates natural habitats, plays an important role in catalysing the loss of nitrogen from marine environments. Until now, a few Scalindua species have been reported to be enriched from sea sediments. The objective of this study is to enrich marine anammox bacteria with coastal sediments in Hiroshima Bay as the inocula. The enrichment was achieved using a continuous upflow column reactor with synthetic sea water containing ammonium and nitrite. After 48 days of incubation, a simultaneous decrease in ammonium and nitrite was observed. A total nitrogen removal rate of 1.16 kg-N m(-3) day(-1) was attained after 306 days of incubation when the nitrogen loading rate was 1.32 kg-N m(-3) day(-1). Phylogenetic analysis revealed that the sequence similarity between the marine anammox-like bacteria in this reactor and the unidentified Candidatus Scalindua sp. was 96-98%. We successfully enriched marine anammox bacteria in the sediments of Hiroshima Bay by using synthetic sea water. Further studies are needed to investigate the characteristics of marine anammox bacteria, including optimal pH, temperature, and nitrogen loading rate.

Estimation of the emission factors of PAHs by traffic with the model of atmospheric dispersion and deposition from heavy traffic road.

In order to consider the total atmospheric loadings of the PAHs (polycyclic aromatic hydrocarbons) from traffic activities, the emission factors of PAHs were estimated and from the obtained emission factors and vehicle transportation statistics, total atmospheric loadings were integrated and the loadings into the water body were estimated on a regional scale. The atmospheric concentration of PAHs was measured at the roadside of a road with heavy traffic in the Hiroshima area in Japan. The samplings were conducted in summer and winter. Atmospheric particulate matters (fine particle, 0.6-7 microm; coarse particle, over 7 microm) and their PAH concentration were measured. Also, four major emission sources (gasoline and diesel vehicle emissions, tire and asphalt debris) were assumed for vehicle transportation activities, the chemical mass balance method was applied and the source partitioning at the roadside was estimated. Furthermore, the dispersion of atmospheric particles from the vehicles was modelled and the emission factors of the sources were determined by the comparison to the chemical mass balance results. Based on emission factors derived from the modelling, an atmospheric dispersion model of nationwide scale (National Institute of Advanced Industrial Science and Technology - Atmospheric Dispersion Model for Exposure and Risk assessment) was applied, and the atmospheric concentration and loading to the ground were calculated for the Hiroshima Bay watershed area.

Effects of hydroxylamine on microbial community structure and function of autotrophic nitrifying biofilms determined by in situ hybridization and the use of microelectrodes.

Effects of hydroxylamine (NH2OH), an intermediate of NH4+ oxidation, on microbial community structure and function of two autotrophic nitrifying biofilms fed with and without NH2OH were analyzed by a 16S rRNA approach and the use of microelectrodes. In the NH2OH-added biofilm, partial oxidation of NH4+ to NO2- was observed, whereas complete oxidation of NH4+ to NO3- was achieved in the control biofilm. In situ hybridization results revealed that no nitrite-oxidizing bacteria (NOB) hybridized with any specific probes were detected in the NH2OH-added biofilm. Thus, the addition of low concentrations of NH2OH (250 microM) completely inhibited the growth of NOB. Phylogenetic analysis of 16S rDNA indicated that the ammonia-oxidizing bacteria (AOB) detected in both biofilms were closely related to Nitrosomonas europaea, and that the clone sequences from both biofilm libraries have more than 99% similarity to each other. However, in situ hybridization results revealed that the addition of NH2OH changed the form of growth pattern of the dominant Nitrosomonas spp. from dense clusters mode to single scattered cells mode. Microelectrode measurements revealed that the average NH4+ consumption rate calculated in the NH2OH-added biofilm was two times higher than that in the control biofilm. This clearly demonstrated that the oxidation of NH4+ was stimulated by NH2OH addition.