Name: actinobacteria: soil bacteria and cheese
Uploaded: 2025-06-06T07:56:35.000Z
Duration: 1 min 30 s
Channel: JoVE

Gli actinobatteri sono un gruppo eterogeneo di batteri Gram-positivi, tra cui corineformi, batteri dell'acido propionico, micobatteri e actinomiceti, e si distinguono per il loro alto contenuto di DNA G+C.I batteri corineformi sono bastoncelli aerobici, non mobili, con disposizioni irregolari, a forma di clava o a forma di V dovute alla divisione a scatto.Le specie principali includono il Corynebacterium diphtheriae patogeno e l'Arthrobacter, un genere di batteri del suolo in grado di passare dalla forma a bastoncello a quella di cocco.I batteri dell'acido propionico, come il Propionibacterium, sono anaerobi che fermentano l'acido lattico, producendo anidride carbonica e acido propionico.I micobatteri si trovano comunemente nei suoli; la maggior parte sono innocui, ma alcuni, come il Mycobacterium tuberculosis, sono importanti agenti patogeni umani.Il Mycobacterium tuberculosis è una specie a crescita lenta, ma il genere Mycobacterium comprende anche specie a crescita rapida come il Mycobacterium smegmatis.Le loro caratteristiche uniche includono gli acidi micolici nelle pareti cellulari e la capacità di subire ramificazioni o crescita filamentosa.Gli actinomiceti sono batteri filamentosi e aerobi, che formano miceli e spore resistenti all'essiccamento.Un genere diversificato, Streptomyces, è noto per la sua produzione di antibiotici.

phylum batterico: actinobacteria

Bacterial Phylum Actinobacteria

I batteri corineformi sono bastoncelli Gram-positivi, aerobi e non mobili, che mostrano disposizioni irregolari, a forma di clava o a V. La forma a V deriva dalla divisione a scatto (snapping division), in cui lo strato interno della parete cellulare forma il setto, mentre lo strato esterno rimane intatto fino alla rottura su un lato, causando la flessione delle cellule figlie.
I generi principali sono Corinebatteri e gli Arthrobacter. I Corinebatteri comprendono specie molto diverse, dai saprofiti ai patogeni come Corynebacterium diphtheriae. Al contrario, gli Arthrobacter, presenti principalmente nel suolo, attraversano un ciclo di sviluppo che alterna forme a bastoncello e coccoidi. Sebbene alcuni batteri corineformi sviluppino anche cellule coccoidi, i Corinebatteri hanno spesso una struttura a clava, a differenza degli Arthrobacter, che sono meno distintamente definiti.
Le specie di Arthrobacter sono altamente resistenti alla disidratazione e alla carenza di nutrienti, nonostante non producano spore. Presentano adattabilit&#224; metabolica, degradando composti come erbicidi, caffeina, nicotina e fenoli, il che li rende attori chiave negli ecosistemi del suolo.
I batteri dell&#8217;acido propionico (Propionibacterium) furono identificati per la prima volta nel formaggio svizzero, dove la loro fermentazione produce CO_2, responsabile dei caratteristici fori, e acido propionico, che conferisce il sapore distintivo. Questi anaerobi Gram-positivi fermentano l&#8217;acido lattico, i carboidrati e gli alcoli poliidrossilati, producendo acido propionico, acido acetico e CO_2.
Nella produzione del formaggio svizzero, il Propionibacterium partecipa alla fermentazione secondaria, utilizzando il lattato prodotto da Streptococcus e Lactobacillus durante la formazione della cagliata. Man mano che la cagliata si asciuga, i batteri dell&#8217;acido propionico si moltiplicano, generando CO_2 che si accumula nei punti deboli, formando i fori nel formaggio.
Inoltre, il Propionigenium, un batterio non correlato, produce propionato attraverso la fermentazione del succinato, evidenziando un processo metabolico diverso ma energeticamente rilevante.
I micobatteri sono comuni nel suolo e sono per lo pi&#249; innocui, ma alcune specie del genere Mycobacterium sono patogeni umani di rilievo, tra cui il Mycobacterium tuberculosis, agente della tubercolosi. Questi batteri a forma di bastoncello sono acido-resistenti a causa della presenza di acidi micolici (lipidi complessi che conferiscono alla parete cellulare una natura cerosa e idrofoba). Per questo motivo, non si colorano bene con la colorazione di Gram e richiedono la colorazione acido-resistente di Ziehl&#8211;Neelsen, nella quale trattengono il colorante rosso, mentre i batteri non acido-resistenti risultano blu.
I micobatteri possono apparire pleomorfi, talvolta formando strutture ramificate, ma a differenza degli attinomiceti, non sviluppano veri miceli. Sono classificati in specie a crescita lenta (es. M. tuberculosis, M. avium, M. bovis) e a crescita rapida (es. M. smegmatis, M. chelonae). Le specie a crescita lenta come M. tuberculosis richiedono un&#8217;incubazione prolungata per formare colonie, che sono compatte, rugose e idrofobe a causa dell&#8217;alto contenuto lipidico.
Dal punto di vista nutrizionale, i micobatteri crescono aerobicamente in terreni minerali semplici, utilizzando l&#8217;ammonio come fonte di azoto e glicerolo o l&#8217;acetato come fonte di carbonio. Tuttavia, M. tuberculosis cresce meglio in presenza di lipidi e acidi grassi. La sua virulenza &#232; associata a un aggregato batterico simile a un cordone, causato da un glicolipide chiamato cord factor.
Alcuni micobatteri producono pigmenti carotenoidi, utili per l&#8217;identificazione. Possono essere non pigmentati (M. tuberculosis, M. bovis), fotocromogeni (producono pigmenti alla luce, es. M. parafortuitum), o scotocromogeni (producono pigmenti anche al buio, es. M. gordonae). I carotenoidi probabilmente proteggono questi batteri dal danno ossidativo causato dall&#8217;ossigeno singoletto.
Gli attinomiceti sono batteri filamentosi, aerobi, Gram-positivi, comuni nel suolo. Molti attraversano un ciclo di sviluppo che include la formazione di spore resistenti alla disidratazione. La loro crescita comporta l&#8217;allungamento e la ramificazione dei filamenti, creando un micelio simile a quello dei funghi. Quando i nutrienti scarseggiano, si sviluppano ife aeree che si differenziano in spore per la sopravvivenza e la dispersione.
Il genere Streptomyces, con oltre 500 specie, &#232; il pi&#249; rilevante di questo gruppo. I filamenti di Streptomyces, generalmente di 0,5&#8211;1,0 &#956;m di diametro, crescono alle estremit&#224; e si ramificano frequentemente, formando un micelio denso. Quando le colonie maturano, filamenti aerei chiamati sporofori emergono producendo spore denominate conidi. A differenza delle endospore di Bacillus e Clostridium, i conidi si formano mediante divisione con setti nei sporofori.
La classificazione delle specie si basa sulle variazioni nella morfologia dei filamenti aerei e delle strutture sporali. Conidi e sporofori sono spesso pigmentati, conferendo alle colonie colori distintivi. Le colonie mature sono compatte, pigmentate e hanno un aspetto polveroso, il che rende le colonie di Streptomyces facilmente riconoscibili sulle piastre di agar.

Phylum Batterico: Actinobacteria

I batteri corineformi sono bastoncelli Gram-positivi, aerobi e non mobili, che mostrano disposizioni irregolari, a forma di clava o a V. La forma a V ...

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actinobacteria: soil bacteria and cheese

Actinobacteria include several gram-positive bacteria that are common in soil and food production. This group includes coryneform bacteria, propionic acid bacteria, mycobacteria, and actinomycetes. Each group has a different shape, growth pattern, and role.

Coryneform bacteria are aerobic, nonmotile rods that often look irregular, club-shaped, or V-shaped. Their V-shape comes from snapping division. In this process, the inner cell wall forms the cross-wall first, while the outer wall stays intact until it breaks on one side, which bends the daughter cells apart.

The main coryneform genera are Corynebacterium and Arthrobacter. Corynebacterium includes species that range from harmless saprophytes to pathogens such as Corynebacterium diphtheriae. Arthrobacter is found mainly in soil and can switch between rod and coccus forms during its life cycle. It is also very resistant to drying and starvation, even though it does not form spores. Arthrobacter can break down herbicides, caffeine, nicotine, and phenols, so it plays an important role in soil ecosystems.

Propionic acid bacteria, or Propionibacterium, were first found in Swiss cheese. They carry out fermentation that produces carbon dioxide, which forms the holes, and propionic acid, which adds flavor. These gram-positive anaerobes can ferment lactic acid, carbohydrates, and polyhydroxy alcohols to make propionic acid, acetic acid, and CO2. During Swiss cheese making, they take part in secondary fermentation by using lactate made by Streptococcus and Lactobacillus as the curd forms. As the curd drains, the bacteria multiply and release CO2. The gas builds up at weak points and creates the cheese holes. Propionigenium is a different bacterium that also produces propionate, but it does so through succinate fermentation.

Mycobacteria are common soil bacteria, and most are harmless. Some species, however, are major human pathogens, including Mycobacterium tuberculosis, which causes tuberculosis. These rod-shaped bacteria are acid-fast because their cell walls contain mycolic acids, which are complex lipids that make the surface waxy and water repellent. They do not stain well with the Gram stain and instead are identified with the Ziehl-Neelsen acid-fast stain, where they keep the red dye while non-acid-fast cells stain blue.

Mycobacteria may look pleomorphic and can sometimes form branching shapes, but they do not make true mycelia like actinomycetes. They include slow-growing species such as M. tuberculosis, M. avium, and M. bovis, and fast-growing species such as M. smegmatis and M. chelonae. Slow growers need longer incubation and form tight, wrinkled, hydrophobic colonies because of their high lipid content. They grow aerobically in simple mineral salts media and can use ammonium as a nitrogen source and glycerol or acetate as a carbon source. M. tuberculosis grows better when lipids and fatty acids are present. Its virulence is linked to cord-like cell groups formed by cord factor, a glycolipid.

Some mycobacteria also make carotenoid pigments that help with identification. They may be nonpigmented, photochromogenic and pigment only in light, or scotochromogenic and pigment even in the dark. These carotenoids likely protect the cells from oxidative damage caused by singlet oxygen.

Actinomycetes are filamentous, aerobic, gram-positive bacteria that are commonly found in soil. Many form desiccation-resistant spores during their developmental cycle. Their growth starts with filament elongation and branching, which creates a mycelium that looks like fungal growth. When nutrients are low, aerial hyphae develop and form spores for survival and spread.

Streptomyces is the most important actinomycete genus and includes more than 500 species. Its filaments are usually 0.5 to 1.0 micrometers wide, grow at the tips, and branch often to form a dense mycelium. As colonies mature, aerial filaments called sporophores appear and make spores called conidia. Unlike Bacillus and Clostridium endospores, conidia form by cross-wall division in the sporophores. Species are classified by differences in aerial filaments and spore structures. Mature Streptomyces colonies are compact, pigmented, and dusty, which makes them easy to spot on agar plates.

Actinobacteria: Soil Bacteria and Cheese

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key terms and concepts

Learn how Actinobacteria include soil microbes, acid-fast mycobacteria, and Streptomyces, plus the bacteria that create Swiss cheese holes.

Actinobacteria: Soil Bacteria and Cheese | 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

Actinobacteria: Soil Bacteria and Cheese

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