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

Las actinobacterias son un grupo diverso de bacterias grampositivas, que incluyen corineforme, bacterias del ácido propiónico, micobacterias y actinomicetos, y se distinguen por su alto contenido de ADN G + C.Las bacterias corineformes son bacilos aeróbicos, inmóviles, con disposiciones irregulares, en forma de maza o en forma de V debido a la división por chasquido.Las principales especies incluyen la patógena Corynebacterium diphtheriae y Arthrobacter, un género de bacterias del suelo capaz de cambiar entre las formas de bastón y coco.Las bacterias del ácido propiónico, como el Propionibacterium, son anaerobios que fermentan el ácido láctico, produciendo dióxido de carbono y ácido propiónico.Las micobacterias se encuentran comúnmente en los suelos; la mayoría son inofensivas, pero algunas, como Mycobacterium tuberculosis, son patógenos humanos importantes.Mycobacterium tuberculosis es una especie de crecimiento lento, pero el género Mycobacterium también incluye especies de crecimiento rápido como Mycobacterium smegmatis.Sus características únicas incluyen ácidos micólicos en sus paredes celulares y la capacidad de experimentar ramificación o crecimiento filamentoso.Los actinomicetos son bacterias filamentosas y aeróbicas, que forman micelios y esporas resistentes a la desecación.Un género diverso, Streptomyces, es bien conocido por su producción de antibióticos.

filo bacteriano: actinobacteria

Bacterial Phylum Actinobacteria

Las bacterias corineformes son bacilos Gram positivos, aer&#243;bicos y no m&#243;viles que presentan disposiciones irregulares, en forma de maza o en forma de V. Esta &#250;ltima se origina por una divisi&#243;n en bisagra, en la que la capa interna de la pared celular forma el tabique, mientras que la capa externa permanece intacta hasta que se rompe, por un lado, provocando que las c&#233;lulas hijas se separen en &#225;ngulo.
Los g&#233;neros principales son Corynebacterium y Arthrobacter. Corynebacterium incluye especies diversas, que van desde sapr&#243;fitos hasta pat&#243;genos como Corynebacterium diphtheriae. En cambio, Arthrobacter, que se encuentra principalmente en el suelo, presenta un ciclo de desarrollo que alterna entre formas de bacilo y de coco. Aunque algunas bacterias corineformes tambi&#233;n desarrollan formas cocoides, Corynebacterium suele presentar una estructura en forma de maza, a diferencia de Arthrobacter, cuya morfolog&#237;a es menos definida.
Las especies de Arthrobacter son altamente resistentes a la desecaci&#243;n y la inanici&#243;n, a pesar de no formar esporas. Exhiben una notable adaptabilidad metab&#243;lica, degradando compuestos como herbicidas, cafe&#237;na, nicotina y fenoles, lo que las convierte en elementos clave en los ecosistemas ed&#225;ficos.
Las bacterias del &#225;cido propi&#243;nico (Propionibacterium) se identificaron por primera vez en el queso suizo, donde su fermentaci&#243;n produce CO_2, formando los caracter&#237;sticos agujeros, y &#225;cido propi&#243;nico, que contribuye al sabor distintivo del queso. Estos anaerobios grampositivos fermentan &#225;cido l&#225;ctico, carbohidratos y alcoholes polihidroxilados, produciendo &#225;cido propi&#243;nico, &#225;cido ac&#233;tico y CO_2.
En la producci&#243;n de queso suizo, Propionibacterium participa en la fermentaci&#243;n secundaria, utilizando el lactato generado por Streptococcus y Lactobacillus durante la formaci&#243;n de la cuajada. A medida que se escurre la cuajada, las bacterias propi&#243;nicas se multiplican, generando CO_2 que se acumula en puntos d&#233;biles, formando as&#237; los agujeros del queso.
Adem&#225;s, Propionigenium, una bacteria no relacionada, produce propionato mediante fermentaci&#243;n de succinato, lo que destaca un proceso metab&#243;licamente relevante, aunque distinto.
Las micobacterias son bacterias comunes del suelo, en su mayor&#237;a inofensivas, pero algunas especies del g&#233;nero Mycobacterium son pat&#243;genos humanos importantes, como Mycobacterium tuberculosis, causante de la tuberculosis. Estos bacilos presentan acidorresistencia debido a la presencia de &#225;cidos mic&#243;licos (l&#237;pidos complejos que confieren a la pared celular una naturaleza cerosa e hidrof&#243;bica). Por ello, no se ti&#241;en bien con la tinci&#243;n de Gram y requieren la tinci&#243;n acidorresistente de Ziehl&#8211;Neelsen, en la que retienen el colorante rojo mientras que las bacterias no acidorresistentes se ti&#241;en de azul.
Las micobacterias pueden presentar pleomorfismo, con estructuras a veces ramificadas, pero a diferencia de los actinomicetos, no desarrollan micelios verdaderos. Se clasifican en especies de crecimiento lento (por ejemplo, M. tuberculosis, M. avium, M. bovis) y de crecimiento r&#225;pido (por ejemplo, M. smegmatis, M. chelonae). Las especies de crecimiento lento como M. tuberculosis requieren una incubaci&#243;n prolongada para formar colonias, que son compactas, arrugadas e hidrof&#243;bicas debido a su alto contenido lip&#237;dico.
Desde el punto de vista nutricional, las micobacterias crecen aer&#243;bicamente en medios minerales simples, utilizando amonio como fuente de nitr&#243;geno y glicerol o acetato como fuente de carbono. Sin embargo, M. tuberculosis prospera mejor en presencia de l&#237;pidos y &#225;cidos grasos. Su virulencia se asocia a agregados bacterianos en forma de cord&#243;n, causados por un glicol&#237;pido llamado factor cord&#243;n.
Algunas micobacterias producen pigmentos carotenoides, lo que facilita su identificaci&#243;n. Pueden ser no pigmentadas (M. tuberculosis, M. bovis), fotocrom&#243;genas (producen pigmento en presencia de luz, como M. parafortuitum) o escotocrom&#243;genas (producen pigmento incluso en la oscuridad, como M. gordonae). Los carotenoides probablemente protegen a estas bacterias del da&#241;o oxidativo causado por el ox&#237;geno singlete.
Los actinomicetos son bacterias filamentosas, aer&#243;bicas y Gram positivas, com&#250;nmente encontradas en el suelo. Muchas de ellas presentan un ciclo de desarrollo que incluye la formaci&#243;n de esporas resistentes a la desecaci&#243;n. Su crecimiento implica el alargamiento y la ramificaci&#243;n de filamentos, formando un micelio similar al de los hongos. Ante la escasez de nutrientes, desarrollan hifas a&#233;reas que se diferencian en esporas para la supervivencia y dispersi&#243;n.
El g&#233;nero Streptomyces, con m&#225;s de 500 especies, es el m&#225;s destacado de este grupo. Los filamentos de Streptomyces, t&#237;picamente de entre 0,5&#8211;1,0 &#956;m de di&#225;metro, crecen en sus extremos y se ramifican con frecuencia, formando un micelio denso. A medida que las colonias maduran, emergen filamentos a&#233;reos llamados espor&#243;foros que producen esporas denominadas conidios. A diferencia de las endosporas de Bacillus y Clostridium, los conidios se forman mediante divisi&#243;n por tabiques en los espor&#243;foros.
La clasificaci&#243;n de especies se basa en variaciones en los filamentos a&#233;reos y estructuras de las esporas. Los conidios y espor&#243;foros suelen estar pigmentados, confiriendo a las colonias colores distintivos. Las colonias maduras son compactas, pigmentadas y de apariencia pulverulenta, lo que facilita la identificaci&#243;n de Streptomyces en placas de agar.

Filo bacteriano: Actinobacteria

Las bacterias corineformes son bacilos Gram positivos, aer&#243;bicos y no m&#243;viles que presentan disposiciones irregulares, en forma de maza o en ...

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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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Amoebozoa: Movement and Life Cycles

Amoebozoa are a diverse group of terrestrial and aquatic protists. They move and feed with lobe-shaped pseudopodia. This feature sets them apart from Rhizaria, which have threadlike pseudopodia. The group includes gymnamoebas, entamoebas, and the plasmodial and cellular slime molds. Phylogenetic evidence also shows that Amoebozoa split from a lineage that later gave rise to fungi and animals. Gymnamoebas are free-living protists that live in water and soil. They move by amoeboid movement,...

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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