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

Abstract

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.

Environmental DNA signatures distinguish between tsunami and storm deposition in overwash sand

“…This result possibly suggests that microorganisms with the capacity to tolerate a broad range of environmental conditions increased in relative abundance after the pulse disturbance of the overwash as opposed to "habitat specialists" 55 , that would have found themselves at a competitive disadvantage. Our finding is in line with other tsunami microbial studies (Table 1) who report microbial community changed before and after a tsunami inundation event, and these community changes after the flooding disturbance remained up to 10 years after the event 21 .…”

“…However, each technique has inherent limitations. For example, grain size analysis can be inconclusive 9,16 ; microfossils such as diatoms, foraminifera, and ostracods may only be preserved for a relatively short time in tropical settings as compared to temperate locations [17][18][19] ; and chemical elemental signals present in the geological record might be misleading if they have been modified or removed by natural processes such as precipitation 20 and microbial activities 21 , or if the elemental sources are ambiguous 16 . In addition, compiling multiple proxies might not unequivocally show that deposits were laid down by overwash processes 22 .…”

“…There is a considerable amount of literature describing how microbial communities in different environmental settings respond to abrupt and intense "pulse" disturbances (i.e. relatively short-duration and discrete environmental alterations) 23 due to catastrophic events such as coastal flooding 21,[24][25][26][27][28][29] , wildfire 30,31 , earthquake 32,33 . The primary aim of such studies is commonly to investigate how microbes respond to a disturbance in nutrients 21,[28][29][30] , water resources 24,25 , substrate availability 25,[27][28][29][30][31][32] , or other physical environment changes 23,[31][32][33] .…”

“…However, the culturable fraction of the community is unlikely to contain a detailed signature of the type of overwash since only a few microorganisms (<5%) within natural microbial communities are culturable 34,35 . Somboonna et al 29 , and Asano et al 21,28 were pioneers in using metabarcoding to study tsunami deposits. They reported that microbial communities in the sediment samples on the coastal zone vary before and after tsunami events, implying that tsunami deposits may contain a distinctive microbial signature.…”

A potential microbiological approach to the evaluation of earthquake-induced soil liquefaction

“…After removing singletons (OTUs consisting of a maximum of one sequence read), 99.96% of the sequence reads in 18 soil samples were classified as bacteria and assigned to 44 phyla, 110 classes, 198 orders, 279 families, 646 genera, and 659 species. In general, the dominant phyla in the soil bacterial communities were Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia, Bacteroides, Chloroflexi, Planctomycetes, and Gemmatimonadetes ( Asano et al., 2020 ; Janssen, 2006 ). Table S1 showed the top 3 abundant bacterial phyla in our study, and the ranked order of the predominant phyla was Firmicutes (59.8%), followed by Proteobacteria (21.34%), Actinobacteria (6.27%), Bacteroidetes (4.21%), Chloroflexi (3.31%), Verrucomicrobia (1.12%), Spirochaetes (0.80%), Acidobacteria (0.67%), Planctomycetes (0.54%), Nitrospirae (0.47%), and Lentisphaerae (0.37%).…”