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

Les actinobactéries sont un groupe diversifié de bactéries à Gram positif, y compris les corynéformes, les bactéries de l’acide propionique, les mycobactéries et les actinomycètes, et se distinguent par leur teneur élevée en ADN G+C. Les bactéries corynéformes sont des tiges aérobies non mobiles avec des arrangements irréguliers, en forme de massue ou en forme de V en raison de la division par claquement. Les espèces principales comprennent les pathogènes Corynebacterium, diphtheriae, et Arthrobacter - un genre de bactéries du sol capable de basculer entre les formes bâtonnet et coccus. Les bactéries de l’acide propionique, telles que Propionibacterium, sont des anaérobies qui fermentent l’acide lactique, produisant du dioxyde de carbone et de l’acide propionique. Les mycobactéries se trouvent couramment dans les sols ; la plupart sont inoffensifs, mais certains, comme Mycobacterium tuberculosis, sont des agents pathogènes humains importants. Mycobacterium tuberculosis est une espèce à croissance lente, mais le genre Mycobacterium comprend également des espèces à croissance rapide comme Mycobacterium smegmatis. Leurs caractéristiques uniques comprennent des acides mycoliques dans leurs parois cellulaires et la capacité de subir une croissance ramifiée ou filamenteuse. Les actinomycètes sont des bactéries filamenteuses et aérobies, formant des mycéliums et des spores résistantes à la dessiccation. Un genre diversifié, Streptomyces, est bien connu pour sa production d’antibiotiques.

phylum bactérien actinobactéries

Bacterial Phylum Actinobacteria

Les bact&#233;ries coryn&#233;formes sont des bact&#233;ries &#224; Gram positif, a&#233;robies, non mobiles, en forme de b&#226;tonnet, qui pr&#233;sentent des arrangements irr&#233;guliers, en forme de massue ou en V. Cette forme en V r&#233;sulte d&#8217;une division particuli&#232;re appel&#233;e division par claquement, o&#249; la couche interne de la paroi cellulaire forme la cloison transversale tandis que la couche externe reste intacte jusqu&#8217;&#224; ce qu&#8217;elle se rompe d&#8217;un c&#244;t&#233;, faisant plier les cellules filles en sens oppos&#233;.
Les genres principaux sont Corynebacterium et Arthrobacter. Le genre Corynebacterium comprend des esp&#232;ces vari&#233;es allant de saprophytes &#224; des pathog&#232;nes comme Corynebacterium diphtheriae. &#192; l&#8217;inverse, Arthrobacter, principalement pr&#233;sent dans le sol, suit un cycle de d&#233;veloppement passant d&#8217;une forme en b&#226;tonnet &#224; une forme cocco&#239;de. Bien que certaines bact&#233;ries coryn&#233;formes pr&#233;sentent &#233;galement des cellules cocco&#239;des, Corynebacterium poss&#232;de souvent une morphologie en massue, contrairement &#224; Arthrobacter, dont les formes sont moins distinctes.
Les esp&#232;ces d&#8217;Arthrobacter sont tr&#232;s r&#233;sistantes &#224; la dessiccation et &#224; la famine, malgr&#233; l&#8217;absence de spores. Elles pr&#233;sentent une grande adaptabilit&#233; m&#233;tabolique, capables de d&#233;grader des compos&#233;s tels que les herbicides, la caf&#233;ine, la nicotine et les ph&#233;nols, ce qui en fait des acteurs cl&#233;s dans les &#233;cosyst&#232;mes du sol.
Les bact&#233;ries de l&#8217;acide propionique (Propionibacterium) ont &#233;t&#233; initialement identifi&#233;es dans le fromage suisse, o&#249; leur fermentation produit du CO_2, formant les trous caract&#233;ristiques, ainsi que de l&#8217;acide propionique, contribuant &#224; l&#8217;ar&#244;me distinct du fromage. Ces bact&#233;ries ana&#233;robies &#224; Gram positif fermentent l&#8217;acide lactique, les glucides et les polyalcools, produisant de l&#8217;acide propionique, de l&#8217;acide ac&#233;tique et du CO_2.
Dans la fabrication du fromage suisse, Propionibacterium intervient dans la fermentation secondaire, en utilisant le lactate produit par Streptococcus et Lactobacillus durant la formation du caill&#233;. &#192; mesure que le caill&#233; s&#8217;&#233;goutte, les bact&#233;ries propioniques se multiplient, g&#233;n&#233;rant du CO_2 qui s&#8217;accumule dans les points faibles du fromage, cr&#233;ant ainsi ses cavit&#233;s.
De plus, Propionigenium, une bact&#233;rie non apparent&#233;e, produit du propionate par fermentation du succinate, illustrant un processus m&#233;tabolique distinct mais &#233;nerg&#233;tiquement significatif.
Les mycobact&#233;ries sont courantes dans le sol et majoritairement inoffensives, mais certaines esp&#232;ces du genre Mycobacterium sont des pathog&#232;nes humains notables, comme Mycobacterium tuberculosis, responsable de la tuberculose. Ces bacilles pr&#233;sentent une acidor&#233;sistance due &#224; la pr&#233;sence d&#8217;acides mycoliques &#8212; des lipides complexes qui conf&#232;rent &#224; leur paroi une nature cireuse et hydrophobe. Par cons&#233;quent, elles ne se colorent pas bien avec la coloration de Gram classique et n&#233;cessitent la coloration acidor&#233;sistante de Ziehl&#8211;Neelsen, o&#249; elles retiennent le colorant rouge tandis que les bact&#233;ries non acidor&#233;sistantes apparaissent bleues.
Les mycobact&#233;ries peuvent appara&#238;tre pl&#233;omorphes, formant parfois des structures ramifi&#233;es, mais contrairement aux actinomyc&#232;tes, elles ne d&#233;veloppent pas de myc&#233;lium v&#233;ritable. Elles sont class&#233;es en esp&#232;ces &#224; croissance lente (par exemple, M. tuberculosis, M. avium, M. bovis) et &#224; croissance rapide (par exemple, M. smegmatis, M. chelonae). Les esp&#232;ces &#224; croissance lente comme M. tuberculosis n&#233;cessitent une incubation prolong&#233;e pour former des colonies denses, rid&#233;es et hydrophobes en raison de leur forte teneur en lipides.
D&#8217;un point de vue nutritionnel, les mycobact&#233;ries croissent de mani&#232;re a&#233;robie sur des milieux simples &#224; base de sels min&#233;raux, utilisant l&#8217;ammonium comme source d&#8217;azote et le glyc&#233;rol ou l&#8217;ac&#233;tate comme source de carbone. Toutefois, M. tuberculosis cro&#238;t mieux en pr&#233;sence de lipides et d&#8217;acides gras. Sa virulence est associ&#233;e &#224; l&#8217;agr&#233;gation en cordons des bact&#233;ries, due &#224; un glycolipide appel&#233; facteur cordonal.
Certaines mycobact&#233;ries produisent des pigments carot&#233;no&#239;des, facilitant leur identification. Elles peuvent &#234;tre non pigment&#233;es (M. tuberculosis, M. bovis), photochromog&#232;nes (produisant des pigments &#224; la lumi&#232;re, par ex. M. parafortuitum), ou scotochromog&#232;nes (produisant des pigments m&#234;me dans l&#8217;obscurit&#233;, par ex. M. gordonae). Les carot&#233;no&#239;des prot&#232;gent probablement ces bact&#233;ries contre les dommages oxydatifs induits par l&#8217;oxyg&#232;ne singulet.
Les actinomyc&#232;tes sont des bact&#233;ries filamenteuses, a&#233;robies, &#224; Gram positif, fr&#233;quemment rencontr&#233;es dans les sols. Beaucoup suivent un cycle de d&#233;veloppement incluant la formation de spores r&#233;sistantes &#224; la dessiccation. Leur croissance implique l&#8217;&#233;longation et le ramification de filaments, formant un myc&#233;lium semblable &#224; celui des champignons. En cas de p&#233;nurie nutritive, des hyphes a&#233;riens se d&#233;veloppent et se diff&#233;rencient en spores pour assurer la survie et la dispersion.
Le genre Streptomyces, avec plus de 500 esp&#232;ces, est le plus important de ce groupe. Les filaments de Streptomyces, mesurant typiquement 0,5 &#224; 1,0 &#956;m de diam&#232;tre, croissent par leur extr&#233;mit&#233; et se ramifient fr&#233;quemment, formant un myc&#233;lium dense. &#192; mesure que les colonies m&#251;rissent, des filaments a&#233;riens appel&#233;s sporophores &#233;mergent, produisant des spores appel&#233;es conidies. Contrairement aux endospores de Bacillus et Clostridium, les conidies se forment par cloisonnement transversal dans les sporophores.
La classification des esp&#232;ces repose sur les variations dans les filaments a&#233;riens et les structures sporales. Les conidies et les sporophores sont souvent pigment&#233;s, conf&#233;rant aux colonies des couleurs distinctives. Les colonies matures sont compactes, pigment&#233;es et ont une apparence poudreuse, ce qui permet d&#8217;identifier facilement les colonies de Streptomyces sur des milieux solides.

Phylum bactérien Actinobactéries

Les bact&#233;ries coryn&#233;formes sont des bact&#233;ries &#224; Gram positif, a&#233;robies, non mobiles, en forme de b&#226;tonnet, qui ...

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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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Excavata Protists and Their Adaptations

Excavata protists show many different ways of living, from photosynthesis to parasitism. This group includes organisms that can use chemical energy, light, or both. Some also live in low-oxygen, or anaerobic, environments where they survive without normal oxygen-based metabolism. Among the main Excavata groups are diplomonads and parabasalids. These are flagellated protists, meaning they move with whip-like tails, and they lack mitochondria and chloroplasts. They often live in anoxic habitats,...

diversity of protists ii

Alveolates: Ciliates, Dinoflagellates, Apicomplexans

Alveolates are protists with tiny sacs called alveoli beneath the cell membrane. These sacs may help control water balance by limiting how much water moves in and out of the cell. In dinoflagellates, alveoli may also act like armor plates. The three main alveolate groups are ciliates, dinoflagellates, and apicomplexans. Ciliates move with cilia, which are short hair-like structures that can cover the whole cell or appear in rows or tufts. One well-known ciliate is Paramecium, which uses cilia...

diversity of protists iii

Rhizaria: Pseudopods, Tests, and Skeletons

Rhizaria are unicellular protists with threadlike pseudopodia, which are thin cytoplasmic extensions used for movement and feeding. Their amoeboid shape once caused taxonomic confusion, but molecular phylogenetics has since shown where they fit on the evolutionary tree. This group includes Chlorarachniophyta, Radiolaria, and Foraminifera, and each lineage has adapted to a different ecological niche and metabolic strategy. Chlorarachniophyta are unicellular phototrophic protists found in marine...

diversity of protists iv

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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