Changes in Bacterial Communities in Seawater-Flooded Soil in the Four Years After the 2011 Tohoku Tsunami in Japan

The 2011 Tohoku tsunami had a serious impact, such as an increase in harmful substances and salinity over a large area. Herein, we evaluated transitions in bacterial communities in agricultural fields in the four years after the 2011 Tohoku tsunami. Bacterial communities were compared across four different types of soil-unflooded field (UF) soil, soil flooded for a short term (ST), soil flooded for the long term (LT), soil flooded long term and cultivated fields (LTC), and marine environmental materials (bay sediment, sea sand and sea water), using a polymerase chain reaction (PCR) and pyrosequencing of 16S ribosomal RNA genes. In the soil bacterial communities that were flooded by the 2011 Tohoku tsunami, these effects were not seen after 2013. Although the difference in bacterial communities between LT and UF became smaller during the four years, the bacterial communities in LT were different from those in UF in several ways, such as a higher tendency frequency of sulfur-oxidizing bacteria (SOB) and the presence of halotolerant SOB. Therefore, it is thought that the Tohoku tsunami affected the microbial communities in the soil for more than four years. Especially genus Halothiobacillus, which is Halotolerant SOB in flooded soils, was detected neither in unflooded soil nor in the marine environment. Therefore, it is thought that inundation by a tsunami produces a unique environment with bacterial communities to form in soil. Further, SOB structure, especially halotolerant, might serve as a good indicators of the impacts of inundation on bacterial communities in agricultural fields over the long term.