09:30 〜 09:45
[BBG02-03] 鉱物試験片を用いた深海微生物の現場培養
キーワード：微生物、鉱物、硫黄酸化、鉄酸化、東青ヶ島海丘カルデラ熱水サイト
Microorganisms inhabit diverse environments across the Earth, performing energy metabolism adapted to their habitats. From a biogeochemical perspective, these metabolic processes play a crucial role in the cycling of inorganics. Our previous studies on microbiologically influenced corrosion of metal materials in freshwater and seawater environments have elucidated interactions between microbial metabolism and “solid” metallic materials. Analysis of microbial community structures on metal samples deployed in deep-sea environments revealed the prominent presence of sulfur-oxidizing bacteria alongside iron-oxidizing bacteria on corroded carbon steel. Furthermore, electrochemically active microorganisms were predominantly detected on corroded stainless steel and nickel alloys.
In recent years, the biological contributions to precipitation and dissolution reactions for deep-sea mineral formation have gained increasing attention. However, the relationships between microorganisms and different mineral types in these complex processes remain poorly understood. This study aimed to simplify the investigation of microbe-mineral interactions by conducting on-site cultivation experiments using characterized mineral specimens.
Chalcopyrite, pyrite, pyrrhotite, goethite, hematite, magnetite, and rhodonite were processed into specimens measuring 3–6 × 3–4 × 0.5–1.5 cm and mounted in PTFE jigs to construct as a ladder box system. These experimental setups were deployed at hydrothermal and cold-seep sites in the Higashi-Aogashima Knoll Caldera hydrothermal field during the cruise KM23-08_09C in June to July 2023 and were retrieved after approximately one year during the cruise KM24-09 in August to September 2024. Biofilms on one side of the recovered mineral specimens were swabbed for DNA extraction, and microbial community structures were analyzed using amplicon sequencing targeting 16S rRNA gene fragments.
All recovered mineral specimens exhibited black discoloration compared to their pre-immersion state, although the effect was minor for rhodonite, which does not contain iron and sulfur. In chalcopyrite, which contains copper, sedondary green copper oxides were visually observed. These findings suggest that chemical and/or biological processes influenced the mineral surfaces during the immersion period. Microbial community analysis detected multiple sulfur-oxidizing bacteria across all specimens. Given their low relative abundance in ambient seawater, these sulfur-oxidizing bacteria likely have any association with the minerals.
Comparing microbial communities between the hydrothermal and cold-seep sites for the same mineral types, significant differences were observed in pyrite and goethite, while variations in other minerals were minor. Pyrite and goethite are more susceptible to hydrothermal influences, which may have led to substantial microbial community shifts. Furthermore, mineral-specific differences in microbial community structures were evident. For example, chalcopyrite, which is the only copper-containing mineral, exhibited unique microbial taxa, while magnetite also harbored distinct microbial populations.
In natural mineral formation processes, precipitation and dissolution reactions progress in a complex manner, making it difficult to determine microbial associations solely from community analyses of naturally occurring mineral samples. However, the use of characterized mineral specimens for on-site cultivation, as demonstrated in this study, can provide insights into microbial affinities for specific minerals and their contributions to precipitation and dissolution reactions. Future research will focus on analyzing compositional changes in the reacted minerals to further elucidate the relationship between microbial activity and mineral transformation.
In recent years, the biological contributions to precipitation and dissolution reactions for deep-sea mineral formation have gained increasing attention. However, the relationships between microorganisms and different mineral types in these complex processes remain poorly understood. This study aimed to simplify the investigation of microbe-mineral interactions by conducting on-site cultivation experiments using characterized mineral specimens.
Chalcopyrite, pyrite, pyrrhotite, goethite, hematite, magnetite, and rhodonite were processed into specimens measuring 3–6 × 3–4 × 0.5–1.5 cm and mounted in PTFE jigs to construct as a ladder box system. These experimental setups were deployed at hydrothermal and cold-seep sites in the Higashi-Aogashima Knoll Caldera hydrothermal field during the cruise KM23-08_09C in June to July 2023 and were retrieved after approximately one year during the cruise KM24-09 in August to September 2024. Biofilms on one side of the recovered mineral specimens were swabbed for DNA extraction, and microbial community structures were analyzed using amplicon sequencing targeting 16S rRNA gene fragments.
All recovered mineral specimens exhibited black discoloration compared to their pre-immersion state, although the effect was minor for rhodonite, which does not contain iron and sulfur. In chalcopyrite, which contains copper, sedondary green copper oxides were visually observed. These findings suggest that chemical and/or biological processes influenced the mineral surfaces during the immersion period. Microbial community analysis detected multiple sulfur-oxidizing bacteria across all specimens. Given their low relative abundance in ambient seawater, these sulfur-oxidizing bacteria likely have any association with the minerals.
Comparing microbial communities between the hydrothermal and cold-seep sites for the same mineral types, significant differences were observed in pyrite and goethite, while variations in other minerals were minor. Pyrite and goethite are more susceptible to hydrothermal influences, which may have led to substantial microbial community shifts. Furthermore, mineral-specific differences in microbial community structures were evident. For example, chalcopyrite, which is the only copper-containing mineral, exhibited unique microbial taxa, while magnetite also harbored distinct microbial populations.
In natural mineral formation processes, precipitation and dissolution reactions progress in a complex manner, making it difficult to determine microbial associations solely from community analyses of naturally occurring mineral samples. However, the use of characterized mineral specimens for on-site cultivation, as demonstrated in this study, can provide insights into microbial affinities for specific minerals and their contributions to precipitation and dissolution reactions. Future research will focus on analyzing compositional changes in the reacted minerals to further elucidate the relationship between microbial activity and mineral transformation.