17:15 〜 18:45
[MIS22-P16] Discharge and dispersal of deep sub-seafloor microorganisms from mud volcanoes into ocean
キーワード：海底泥火山、微生物群集、堆積物
The microbial community structure in submarine mud volcanoes, which are known to be widespread off Tanegashima Island, and in water columns directly above mud volcanoes has been studied for 10 years. Through this study, we have reported for the first time the release of bacteria from deep below mud volcanoes into seawater along with fluids containing gases such as methane. Among the released bacteria, the phylum Atribacterota, which is not normally found in seawater but is ubiquitous in marine anaerobic sediments, was found, suggesting that a microbial circulation process is taking place as the bacteria, once dispersed in seawater, are deposited again. This presentation presents the results of microbiological analyses collected from KH-15-2 and KH-19-5 by the Hakuho Maru in 2015 and 2019, and from KS-21-27 by the Shinsei Maru in 2021.
Seven mud volcanoes, MV1, MV2, MV3, MV8, MV10, MV14 and MV15, were surveyed in the study. Several meters of sediment were cored from the summit and surrounding area of each volcano. Seawater samples directly above the mud volcanoes were collected continuously with Niskin water samplers from about 10 m above the mud volcanoes (at an altitude of 10 m) to about 1000 m altitude. DNA extracted from the sediment and seawater samples was used to obtain 16S rRNA gene sequences by amplicon sequencing to determine the microbial community composition in each sample. The abundance of Atribacterota, which we used as a marker species for microbial dispersal from sediment to seawater, varied significantly among mud volcanoes, with sediments such as MV15, MV8, and MV14 showing Atribacterota dominance of more than 50%, whereas MV3, MV1, and others had relatively low abundances. These observations correlate inversely with mud volcano activity, suggesting that the supply of material from seawater would recharge the Atribacterota in the sediments. Atribacterota in the water column above the mud volcanoes were detected at altitudes of 30-200 m at sampling sites where Atribacterota was abundant in the sediments, confirming the widespread distribution of the microorganism in the sediments, however the relationship with mud volcano activity remains unclear and further research is needed.
Seven mud volcanoes, MV1, MV2, MV3, MV8, MV10, MV14 and MV15, were surveyed in the study. Several meters of sediment were cored from the summit and surrounding area of each volcano. Seawater samples directly above the mud volcanoes were collected continuously with Niskin water samplers from about 10 m above the mud volcanoes (at an altitude of 10 m) to about 1000 m altitude. DNA extracted from the sediment and seawater samples was used to obtain 16S rRNA gene sequences by amplicon sequencing to determine the microbial community composition in each sample. The abundance of Atribacterota, which we used as a marker species for microbial dispersal from sediment to seawater, varied significantly among mud volcanoes, with sediments such as MV15, MV8, and MV14 showing Atribacterota dominance of more than 50%, whereas MV3, MV1, and others had relatively low abundances. These observations correlate inversely with mud volcano activity, suggesting that the supply of material from seawater would recharge the Atribacterota in the sediments. Atribacterota in the water column above the mud volcanoes were detected at altitudes of 30-200 m at sampling sites where Atribacterota was abundant in the sediments, confirming the widespread distribution of the microorganism in the sediments, however the relationship with mud volcano activity remains unclear and further research is needed.