Name: sulfur cycling through microbial reactions
Uploaded: 2026-03-12T13:57:43.000Z
Duration: 1 min 29 s
Channel: JoVE

無機硫黄は硫酸塩、元素硫黄、硫化物として環境中を循環します。火山や熱水噴出孔は硫化水素のような硫黄ガスを放出し、硫黄循環に重要な役割を果たしています。例えば、熱水噴出孔近くの無酸素で有機物が豊富な環境では、硫酸塩還元細菌が主に硫酸塩を硫化水素に変換します。このガスはほとんどの生命体にとって有毒ですが、さまざまな微生物によってより害の少ない硫酸塩や元素硫黄に変換されます。酸素豊富な環境では、硫黄酸化細菌( チオバチルス )が硫化水素を硫黄や硫酸塩に変換し、時に硫酸を形成して局所的なpHを下げます。一方、緑色および紫色の硫黄菌は硫化物を硫黄顆粒に変換し、 チオマルガリータ や類似の微生物はさらに酸化して硫酸塩に変換します。元素硫黄は、特殊な嫌気性細菌や古菌によって硫化物に還元されることがあります。無機変換に加え、海洋藻類は揮発性有機硫黄化合物であるジメチル硫化物を形成し、大気中でエアロゾルに変換されて雲の形成を促進し、地球の気候調節に寄与します。

微生物と硫黄循環

Microbes and the Sulfur Cycle

硫黄は地球の生物地球化学システムにおいて重要な元素です。硫酸塩(SO₄²⁻)、元素硫黄(S⁰)、硫化物(S²⁻)など、さまざまな無機状態を経由します。酸素および無酸素環境をまたぐ非生物的および生物学的メカニズムが、これらの変換を複雑に媒介しています。硫酸塩は硫黄の中で最も酸化された形態であり、主に岩石、海洋堆積物、海水中に蓄積され、地球規模の硫黄サイクルにおける長期的な貯留層として機能しています。酸化環境では、 チオバチルス 属などの化学的自律栄養細菌が還元硫黄化合物の酸化を触媒します。硫化物(H₂S)は、火山性の噴出ガスや熱水排出から得られ、生物的に酸化されて元素硫黄や硫酸塩に変換されます。逆に、無酸素条件下では、硫酸還元菌(SRB)である デスルフォビブリオ 属が同化性硫酸塩還元を行います。この嫌気性プロセスは、主要な中間体として硫酸塩(SO₃²⁻)を介して硫酸塩を硫化物に還元し、しばしば有機炭素酸化と結合します。緑色および紫色の硫黄菌を含む無酸素性光栄養生物は、硫化物を細胞内の硫黄顆粒に酸化します。これらの顆粒は、 ティオマルガリー タ属のような大型化学栄養細菌によってさらに硫酸塩に酸化され、酸化中に陽子を放出することで酸性化に寄与します。熱水噴出口生態系では、硫黄酸化性化学自律栄養生物が硫化物のエネルギーを利用して二酸化炭素を固定し、深海生息地における複雑な微生物・動物群集を支えています。海洋植物プランクトンは浸透圧を調節するためにジメチルスルホニオプロピオン酸(DMSP)を放出します。DMSPの細菌切断により、大気中に放出される揮発性化合物ジメチルスルフィド(DMS)が生成されます。DMSの光酸化は硫酸塩エアロゾルを生成し、これは雲の凝縮や陸上生態系への大気中の硫黄堆積に影響を与えます。最終的に、植物や微生物はこの硫酸塩を同化・還元しながら、システインやメチオニンなどの硫黄を含むアミノ酸を合成し、サイクルを完成させます。

Sulfur is a vital element in Earth's biogeochemical systems. It transitions through various inorganic states, including sulfate (SO&#8324;&#178;&#8315;), ...

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Education

JoVE Core

Microbiology

微生物学

Unit

ユニット

Microbial Ecology

微生物生態学

KEY TERMS AND CONCEPTS

主要用語と概念

sulfur cycling through microbial reactions

Sulfur cycling depends on microbial reactions that move sulfur through rocks, water, soil, and the air. In Earth systems, sulfur shifts among inorganic forms such as sulfate, elemental sulfur, and sulfide. These changes happen through both abiotic processes and biological activity in oxic and anoxic environments.

Sulfate is the most oxidized form of sulfur. It is stored mainly in rocks, marine sediments, and ocean water, where it acts as a long-term reservoir in the global sulfur cycle. In oxygen-rich settings, chemolithoautotrophic bacteria such as Thiobacillus spp. oxidize reduced sulfur compounds.

Sulfide, often present as H2S, can come from volcanic outgassing or hydrothermal emissions. Microbes can oxidize this sulfide into elemental sulfur and then into sulfate. In oxygen-free environments, sulfate-reducing bacteria such as Desulfovibrio spp. carry out dissimilatory sulfate reduction, which converts sulfate to sulfide through sulfite as an intermediate and is often linked to organic carbon oxidation.

Some microbes use sulfur in light-filled but low-oxygen habitats. Green and purple sulfur bacteria, which are anoxygenic phototrophs, oxidize sulfide and store the sulfur as intracellular granules. Large chemolithotrophic bacteria such as Thiomargarita spp. can then oxidize these granules further to sulfate. This process releases protons and can make the surrounding environment more acidic.

Sulfur cycling also powers life at hydrothermal vents. There, sulfur-oxidizing chemoautotrophs use energy from sulfide to fix carbon dioxide. Their activity supports complex microbial and animal communities in deep-sea ecosystems.

Sulfur also moves through the atmosphere. Marine phytoplankton release dimethylsulfoniopropionate, or DMSP, to help control osmotic pressure. Bacteria break DMSP down into dimethylsulfide, or DMS, a volatile gas that enters the atmosphere. Sunlight then photooxidizes DMS into sulfate aerosols, which affect cloud formation and sulfur deposition on land. Plants and microbes take up this sulfate and reduce it while making sulfur-containing amino acids such as cysteine and methionine, completing the cycle.

Sulfur Cycling Through Microbial Reactions

sulfur-cycling-through-microbial-reactions

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key terms and concepts

Explore how microbes move sulfur through sulfate, sulfide, and sulfur granules in oxic, anoxic, and marine environments across the sulfur cycle.

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microbiology

Sulfur Cycling Through Microbial Reactions

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