Name: microbes driving iron and manganese cycles
Uploaded: 2026-03-12T13:57:36.000Z
Duration: 1 min 24 s
Channel: JoVE

I microbi guidano il ciclo di ferro e manganese spostando questi elementi tra la loro forma ossidata e quella ridotta.In habitat neutri ricchi di ossigeno, il ferro ferrico predomina in forma insolubile e precipitata.Alcuni batteri secernono piccole molecole chiamate siderofori, che si legano e solubilizzano il ferro ferrico.Le cellule quindi raccolgono questo ferro solubile e lo riducono alla forma ferrosa per uso metabolico.All'interfaccia ossico-anossica, dove i livelli di ossigeno sono bassi, batteri magnetotattici come Magnetospirillum usano il ferro per formare cristalli di magnetite, allineandosi con il campo magnetico terrestre per raggiungere strati anosici.Nella stessa zona, batteri filamentosi come Leptothrix ossidano ferro ferroso, producendo guaine rivestite da ossidi di ferro.Ossidano anche il manganese(II) in anidride di manganese insolubile, che può affondare in strati anosici più profondi, dove batteri riduttori di metalli come Geobacter lo riconvertono in manganese (II).Nelle zone anossiche, batteri come Shewanella esegueno una riduzione dissimilativa del ferro, dove il ferro ferrico è l'accettatore terminale degli elettroni.

microbes and other elemental cycles

Microbes and Other Elemental Cycles

L&#x27;attivit&#xE0; microbica svolge un ruolo fondamentale nel ciclo biogeochimico del ferro e del manganese, soprattutto in corrispondenza dei gradienti redox caratteristici degli ambienti acquatici stratificati. Questi cicli sono guidati dalle trasformazioni microbiche tra le forme ossidate e ridotte dei metalli, consentendo agli organismi di sfruttarli per ricavare energia metabolica e per scopi strutturali.
Ciclo del ferro attraverso i gradienti redox
Nelle acque superficiali neutre e ricche di ossigeno, il ferro si trova prevalentemente nella sua forma ferrica [Fe(III)] ossidata e insolubile. Per accedere a questo nutriente essenziale, alcuni batteri sintetizzano e secernono siderofori, composti organici a basso peso molecolare con un&#x27;elevata affinit&#xE0; per il ferro ferrico. Queste molecole legano il ferro ferrico, rendendolo solubile e disponibile per l&#x27;assorbimento. Una volta internalizzato, il ferro ferrico viene ridotto enzimaticamente alla forma ferrosa [Fe(II)], che &#xE8; pi&#xF9; biodisponibile e supporta diverse funzioni cellulari.
All&#x27;interfaccia ossica-anossica, dove le condizioni redox fluttuano, batteri come Leptothrix ossidano il ferro ferroso solubile a ferro ferrico, formando guaine extracellulari di ossido di ferro. Queste guaine svolgono una duplice funzione: prevengono l&#x27;incrostazione cellulare e possono offrire supporto strutturale. I batteri magnetotattici, anch&#x27;essi presenti in questa zona, internalizzano il ferro per biomineralizzare cristalli di magnetite (Fe&#x2083;O&#x2084;). Questi cristalli agiscono come bussole intracellulari, allineandosi con il campo magnetico terrestre per guidare le cellule verso ambienti a basso contenuto di ossigeno, ottimali per il loro metabolismo.
I batteri acidofili come Acidithiobacillus facilitano il ciclo del ferro in ambienti acidi e ricchi di ossigeno. Questi organismi prosperano a basso pH e contribuiscono al ricambio del ferro ossidando Fe&#xB2;&#x207A;, o ferro ferroso, a Fe&#xB3;&#x207A;, o ferro ferrico. Questo processo di ossidazione &#xE8; fondamentale in ambienti come i sistemi di drenaggio acido di miniera.
Ciclo del manganese nelle nicchie microbiche
Le specie di Leptothrix contribuiscono anche al ciclo del manganese ossidando gli ioni manganosi solubili [Mn(II)] in diossido di manganese insolubile [MnO&#x2082;], che si deposita nei sedimenti anossici sottostanti. In questi strati, batteri riduttori di metalli come Geobacter riducono enzimaticamente il diossido di manganese riconvertendolo in Mn(II), completando il ciclo. Analogamente, i batteri fototrofi in condizioni anossiche utilizzano Fe(II) come donatore di elettroni nella fotosintesi anossigenica, mentre gli anaerobi facoltativi come Shewanella riducono il ferro ferrico attraverso vie dissimilatorie per ricavare energia.
Questi processi microbici, nel loro insieme, mantengono l&#x27;omeostasi del ferro e del manganese negli ecosistemi acquatici, regolandone la disponibilit&#xE0; e la distribuzione attraverso le interfacce redox.

Microbial activity plays a pivotal role in the biogeochemical cycling of iron and manganese, especially at the redox gradients characteristic of ...

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Microbial Ecology

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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 iron and make it soluble for uptake. After the iron enters the cell, enzymes reduce it to ferrous iron, Fe(II), which is easier for the cell to use.

At the oxic-anoxic interface, bacteria such as Leptothrix oxidize soluble Fe(II) back to Fe(III). This creates extracellular iron oxide sheaths around the cells. The sheaths help keep the cells from becoming encrusted and may also provide support. Magnetotactic bacteria live in this zone too. They build magnetite, Fe3O4, crystals inside the cell. These crystals act like tiny compasses and align with Earth’s magnetic field, helping the bacteria move toward low-oxygen conditions.

Acidophilic bacteria such as Acidithiobacillus also take part in iron cycling. They live in acidic, oxygen-rich environments and oxidize Fe(II) to Fe(III). This activity is important in places such as acid mine drainage systems. In manganese cycling, Leptothrix species oxidize soluble Mn(II) to insoluble manganese dioxide, MnO2. The MnO2 then sinks into anoxic sediments below.

In those sediments, metal-reducing bacteria such as Geobacter reduce manganese dioxide back to Mn(II). That closes the manganese cycle. Other microbes also use iron in special ways. Phototrophic bacteria under anoxic conditions use Fe(II) as an electron donor during anoxygenic photosynthesis. Facultative anaerobes such as Shewanella reduce ferric iron through dissimilatory pathways to gain energy. Together, these microbial processes control where iron and manganese are found in aquatic ecosystems and help maintain their cycling across redox interfaces.

Microbes Driving Iron and Manganese Cycles

microbes-driving-iron-and-manganese-cycles

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key terms and concepts

Learn how microbes move iron and manganese through aquatic environments, from siderophores and magnetite to metal reduction in redox zones.

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microbiology

Microbes Driving Iron and Manganese Cycles

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