Effect of salt stress on structure and function of the methanogenic archaeal community in rice field soil

초록

Soil salinity of recently reclaimed rice field soil from the saltmarsh is typically higher than that of upland one. The changes of relationship between funcion and structure of the methanogenic archaeal community under the salt stress were investigated in rice field soil. To investigate how salt stress affects the function of methanogenic archaeal community, soil physiochemical properties and methanogenic metabolites were measured at the soil slurries treated with different concentration of 100, 300, 500, 1000mM NaCl during the anaerobic incubation. Under the salt stress, the soil slurry was slightly more acidic and less reduced. Addition of salt above 100mM to soil slurries resulted in longer lag phase of CH4 production, decrease of H2 accumulation, and a transient accumulation of acetate. Therefore, relative contribution of hydrogen as an immediate substrate on methane production might be increased under the salt stress. To investigate how salt stress affects the structure of methanogenic archaeal community, total DNA was extracted from four soil slurries with the different sampling time and salt concentration. Archaeal small subunit rRNA gene(SSU rDNA) of the DNA samples was PCR amplified and used for the generation of clone libraries. Representative rDNA clones (n=120) were characterized by comparative sequence analysis and phylogenetic affiliation. At the initial stage of methanogenesis, archaeal community was dominated by Methanosarcinaceae, archaea of rice cluster I, and Methanosaetaceae. After 45 days of anaerobic incubation, Methanomicrobiaceae was not detected in the control slurry and archaea of three unclutured groups, rice cluster IV, rice cluster V, and deep-sea hydrothermal vent euryarchaeotic group 6 (DHVE6) were appeared. abundance of Methanosarcinaceae was increased in the archaeal community under the salt stress of 300 mM NaCl, and archaea of rice cluster I were abundant under the salt stress of 500 mM NaCl. Beacuse these two groups use H2/CO2 as