Name: microbial parasites and host dependence
Uploaded: 2026-03-12T13:57:43.000Z
Duration: 1 min 22 s
Channel: JoVE

微生物寄生とは、寄生微生物が宿主を利用し、宿主に害を与える相互作用のことです。寄生微生物には3種類があります。表面に留まる外部寄生虫(外部寄生)と組織や内部構造に生息する内部寄生虫、そして宿主の細胞内に存在する細胞内寄生虫です。寄生虫は宿主と共存して繁殖、栄養分の獲得、免疫の回避を図ることがあります。寄生関係は宿主の継続的な利用を伴います。結果は宿主の防御機構、寄生虫負荷、環境条件に依存します。このバランスが崩れると、効果的な宿主防御や治療によって寄生虫を排除できますが、制御されない寄生虫の増殖は病気や死を引き起こす可能性があります。時には、寄生によって寄生虫のゲノムが減少し、宿主への依存により遺伝子が冗長化することもあります。例えば、アブラムシの Buchnera aphidicola や人間の Mycobacterium leprae は、必須栄養素の長期依存により多くの代謝遺伝子を失っています。

微生物間相互作用:寄生

Microbial Interactions: Parasitism

寄生とは、寄生微生物が宿主の栄養や隠れ場所を利用し、しばしば宿主の犠牲を前提に利用する微生物間の相互作用の一形態です。相利共生関係では両生物が利益を得るのに対し、寄生は寄生虫だけに利益をもたらし、宿主に害を与えます。寄生虫の分類微生物寄生虫は、宿主に対する位置に基づいて広く分類されます。<ul><li>外部寄生虫は 宿主の表面、例えば皮膚や外層組織に残り、外部から栄養を引き寄せます。</li><li>内寄生虫は 宿主の体内に存在し、組織や臓器に侵入します。</li><li>細胞内寄生虫はより専門的なカテゴリーで、宿主細胞の内部に生息し、内生虫の亜型と考えられています。</li></ul>これらの分類は、寄生虫が侵入し、持続し、病気を引き起こすために用いるさまざまなメカニズムを説明するのに役立ちます。ホストとの短い共存通常、寄生虫は宿主と限られた期間共存し、その間に繁殖して新しい宿主に広がります。この段階では、宿主の資源を栄養に利用し、宿主の免疫反応を回避または抑制するための戦略を講じることが多いです。これらの戦略には、抗原変異、免疫シグナル伝達の調節、宿主組織や細胞内での隠蔽などが含まれます。宿主と寄生虫の対立と疾患の結果このダイナミックな相互作用の結果は、どちらが優位に立つかによって決まります。宿主が効果的な免疫反応を示したり治療を受けた場合、寄生虫は排除されることがあります。しかし、寄生虫が免疫の検出や制御をうまく回避すると、持続的な感染や病気の進行、さらには死に至ることもあります。宿主依存性寄生虫におけるゲノム還元進化の過程で、一部の寄生微生物は ゲノム還元を経験します。これは宿主が提供する機能に依存しているため不要になる遺伝子を失う過程です。これにより、宿主内の生命に高度に特化した簡潔なゲノムが生まれます。その一例が、アブラムシの必須内共生体である ブフネラ・アフィディコラで、重要な代謝経路に関わる多くの遺伝子を失っています。同様に、ヒトのハンセン病を引き起こすマイ コバクテリウム・ハンセン病は、長期的に細胞内生活に適応したことを示す非常に低いゲノムを持っています。

Parasitism is a form of microbial interaction in which parasitic microbes exploit a host organism for nutrients and shelter, often at the host's expense. ...

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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

microbial parasites and host dependence

Microbial parasites depend on a host for nutrients and shelter, and this dependence often harms the host. In parasitism, only the parasite benefits. This is different from mutualism, where both organisms gain from the relationship.

Microbial parasites are classified by where they live in or on the host. Ectoparasites stay on the host’s surface, such as the skin or outer tissues, and take in nutrients from outside. Endoparasites live inside the host’s body and invade tissues or organs. Intracellular parasites are a more specialized type of endoparasite because they live inside host cells.

These parasites usually live with a host for only a limited time. During that period, they reproduce and spread to new hosts. Many also use ways to avoid or weaken the host immune response, such as antigenic variation, changes in immune signaling, or hiding in host tissues or cells.

The result of parasitism depends on which side has the advantage. If the host mounts an effective immune response or gets treatment, the parasite may be removed. If the parasite avoids immune detection and control, the infection can persist, disease can worsen, or the host may die.

Some host-dependent parasites also undergo genomic reduction over time. This means they lose genes that are no longer needed because the host supplies certain functions. Buchnera aphidicola, an obligate endosymbiont of aphids, has lost many genes for key metabolic pathways. Mycobacterium leprae, the bacterium that causes leprosy in humans, also has a highly reduced genome, reflecting its long-term intracellular lifestyle.

Microbial Parasites and Host Dependence

introduction to microbial ecology

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ecological niche

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methods to assess microbial communities

Measuring Microbial Diversity and Activity

Microbial communities include bacteria, archaea, and eukaryotic microorganisms. They live in many ecosystems and affect important environmental and biological processes. Scientists study these communities by looking at how many species are present, how many individuals each species has, and how evenly the species are spread out. Species richness is the number of different species in a sample. Species abundance is the relative amount of each species. Species evenness describes how uniformly the...

the winogradsky column

Microbial Layers Inside a Winogradsky Column

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microbial interactions: mutualism

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microbial interactions: cooperation

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microbial interactions: predation

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microbial interactions: competition

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microbial interactions: parasitism

Microbial parasites depend on a host for nutrients and shelter, and this dependence often harms the host. In parasitism, only the parasite benefits. This is different from mutualism, where both organisms gain from the relationship. Microbial parasites are classified by where they live in or on the host. Ectoparasites stay on the host’s surface, such as the skin or outer tissues, and take in nutrients from outside. Endoparasites live inside the host’s body and invade tissues or organs.

microbe-plant interactions

How Plant Microbes Affect Growth

Plant microbes can help, harm, or simply live alongside their hosts. These microbe-plant interactions shape plant growth, health, and ecosystem function. The plant microbiome includes bacteria, fungi, archaea, protists, and viruses, and these organisms may live on the plant surface, inside plant tissues, or in symbiosis throughout the plant. Some of the most important beneficial partnerships involve mycorrhizal fungi. These fungi form close connections with roots and are grouped as arbuscular...

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microbes and the nitrogen cycle

Microbial Steps in the Nitrogen Cycle

Microbes drive the nitrogen cycle by changing nitrogen into forms that plants and other organisms can use. This biogeochemical cycle keeps nitrogenous compounds balanced in ecosystems. It also supports plant growth and microbial growth. Nitrogen fixation begins the cycle by converting inert atmospheric nitrogen gas, N2, into ammonia, NH3. This step depends on nitrogenase enzymes. Free-living diazotrophs do this on their own. Aerobic bacteria such as Azotobacter spp. and anaerobic bacteria such...

microbes and the sulfur cycle

Sulfur Cycling Through Microbial Reactions

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microbes and other elemental cycles

Microbes Driving Iron and Manganese Cycles

Microbes drive iron and manganese cycling in aquatic environments by changing these metals between reduced and oxidized forms. These reactions are especially important along redox gradients, where oxygen levels shift across stratified water layers. The microbes use these metals for energy, growth, and structural needs. In oxygen-rich surface waters, iron is usually present as insoluble ferric iron, Fe(III). Some bacteria release siderophores, which are small organic molecules that bind ferric...

marine microbial ecology

Microbial Life in the Ocean

Marine microbial life is shaped by salinity, low nutrients, and changing oxygen levels. These physical and chemical limits influence which microbes can survive and how they function. They also affect how ocean microbes help drive nutrient and carbon cycling. Small cell size is common in these environments because it gives microbes a larger surface-to-volume ratio. That helps them take up nutrients more efficiently when nutrients are scarce. In estuaries, where salinity changes often,...

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soil microbial ecology

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key terms and concepts

Learn how microbial parasites live on or in hosts, evade immunity, cause disease, and evolve reduced genomes in host-dependent lifestyles.

Microbial Parasites and Host Dependence | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Microbial Parasites and Host Dependence

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