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

As actinobactérias são um grupo diversificado de bactérias Gram-positivas, incluindo corineformes, bactérias do ácido propiônico, micobactérias e actinomicetos, e se distinguem por seu alto teor de DNA G + C. As bactérias corineformes são bastonetes aeróbicos e imóveis com arranjos irregulares, em forma de taco ou em forma de V devido à divisão de encaixe. As principais espécies incluem Corynebacterium patogênico, diphtheriae, e Arthrobacter — um gênero de bactérias do solo capaz de alternar entre as formas de bastonetes e cocos. Bactérias do ácido propiônico, como Propionibacterium, são anaeróbios que fermentam ácido lático, produzindo dióxido de carbono e ácido propiônico. As micobactérias são comumente encontradas nos solos; a maioria é inofensiva, mas algumas, como Mycobacterium tuberculosis, são patógenos humanos significativos. Mycobacterium tuberculosis é uma espécie de crescimento lento, mas o gênero Mycobacterium também inclui espécies de crescimento rápido como Mycobacterium smegmatis. Suas características únicas incluem ácidos micólicos em suas paredes celulares e a capacidade de sofrer ramificações ou crescimento filamentoso. Os actinomicetos são bactérias filamentosas e aeróbicas, formando micélios e esporos resistentes à dessecação. Um gênero diverso, Streptomyces, é bem conhecido por sua produção de antibióticos.

filo bacteriano: actinobacteria

Bacterial Phylum Actinobacteria

As bact&#233;rias corineformes s&#227;o Gram-positivas, aer&#243;bias, im&#243;veis, em forma de bastonete, que possuem arranjos irregulares, em forma de clava, ou em V. Essa forma em V resulta da divis&#227;o por ruptura, na qual a camada interna da parede celular forma a parede cruzada, enquanto a camada externa permanece intacta at&#233; se romper de um lado, fazendo com que as c&#233;lulas-filhas se curvem para fora.
Os principais g&#234;neros s&#227;o Corynebacterium e Arthrobacter. Corynebacterium inclui esp&#233;cies diversas, variando de sapr&#243;fitas a pat&#243;genos como Corynebacterium diphtheriae. Em contraste, Arthrobacter, encontrado principalmente no solo, passa por um ciclo de desenvolvimento alternando entre formas de bastonete e coco. Embora algumas bact&#233;rias corineformes tamb&#233;m desenvolvam formas coc&#243;ides, Corynebacterium frequentemente possui estrutura em forma de clava, diferentemente de Arthrobacter, cuja morfologia &#233; menos distinta.
Esp&#233;cies de Arthrobacter s&#227;o altamente resistentes &#224; desseca&#231;&#227;o e &#224; fome, apesar de n&#227;o formarem esporos. Possuem adaptabilidade metab&#243;lica, degradando compostos como herbicidas, cafe&#237;na, nicotina e fen&#243;is, desempenhando um papel fundamental nos ecossistemas do solo.
As bact&#233;rias do &#225;cido propi&#244;nico (Propionibacterium) foram inicialmente identificadas no queijo su&#237;&#231;o, onde sua fermenta&#231;&#227;o produz CO_2, formando os orif&#237;cios caracter&#237;sticos, e &#225;cido propi&#244;nico, que contribui para o sabor distinto do queijo. Esses anaer&#243;bios Gram-positivos fermentam &#225;cido l&#225;tico, carboidratos e &#225;lcoois poli-hidroxilados, produzindo &#225;cido propi&#244;nico, &#225;cido ac&#233;tico e CO_2.
Na produ&#231;&#227;o de queijo su&#237;&#231;o, Propionibacterium participa da fermenta&#231;&#227;o secund&#225;ria, utilizando o lactato produzido por Streptococcus e Lactobacillus durante a forma&#231;&#227;o da coalhada. &#192; medida que a coalhada drena, as bact&#233;rias do &#225;cido propi&#244;nico se multiplicam, gerando CO_2 que se acumula em pontos fr&#225;geis, criando os furos do queijo.
Al&#233;m disso, Propionigenium, uma bact&#233;ria n&#227;o relacionada, produz propionato por fermenta&#231;&#227;o de succinato, demonstrando um processo metab&#243;lico diferente, mas energeticamente relevante.
As micobact&#233;rias s&#227;o comuns no solo, sendo em sua maioria inofensivas, mas algumas esp&#233;cies do g&#234;nero Mycobacterium s&#227;o pat&#243;genos humanos importantes, como Mycobacterium tuberculosis, causadora da tuberculose. Essas bact&#233;rias em forma de bastonete exibem acidorresist&#234;ncia devido &#224; presen&#231;a de &#225;cidos mic&#243;licos&#8212;lip&#237;dios complexos que conferem &#224; parede celular uma natureza cerosa e hidrof&#243;bica. Por isso, n&#227;o se coram bem com colora&#231;&#227;o de Gram e requerem a colora&#231;&#227;o acidorresistente de Ziehl&#8211;Neelsen, na qual ret&#234;m o corante vermelho enquanto as bact&#233;rias n&#227;o acidorresistentes se coram de azul.
As micobact&#233;rias podem apresentar pleomorfismo, por vezes formando estruturas ramificadas, mas, diferentemente dos actinomicetos, n&#227;o desenvolvem mic&#233;lio verdadeiro. S&#227;o classificadas em esp&#233;cies de crescimento lento (ex.: M. tuberculosis, M. avium, M. bovis) e esp&#233;cies de crescimento r&#225;pido (ex.: M. smegmatis, M. chelonae). As de crescimento lento, como M. tuberculosis, exigem incuba&#231;&#227;o prolongada para formar col&#244;nias, que s&#227;o densas, rugosas e hidrof&#243;bicas devido ao alto teor lip&#237;dico.
Nutricionalmente, as micobact&#233;rias crescem aerobicamente em meios minerais simples, usando am&#244;nio como fonte de nitrog&#234;nio e glicerol ou acetato como fonte de carbono. No entanto, M. tuberculosis cresce melhor na presen&#231;a de lip&#237;dios e &#225;cidos graxos. Sua virul&#234;ncia est&#225; associada &#224; forma&#231;&#227;o de agregados bacterianos em forma de corda, causados por um glicolip&#237;dio chamado fator corda.
Algumas micobact&#233;rias produzem pigmentos carotenoides, o que auxilia na identifica&#231;&#227;o. Podem ser n&#227;o pigmentadas (M. tuberculosis, M. bovis), foto-cromog&#234;nicas (produzem pigmento na presen&#231;a de luz, ex.: M. parafortuitum) ou escoto-cromog&#234;nicas (produzem pigmento mesmo no escuro, ex.: M. gordonae). Os carotenoides provavelmente protegem essas bact&#233;rias contra danos oxidativos causados por oxig&#234;nio singleto.
Os actinomicetos s&#227;o bact&#233;rias filamentosas, aer&#243;bias e Gram-positivas, comumente encontradas no solo. Muitas passam por um ciclo de desenvolvimento que inclui a forma&#231;&#227;o de esporos resistentes &#224; desseca&#231;&#227;o. Seu crescimento envolve elonga&#231;&#227;o e ramifica&#231;&#227;o dos filamentos, criando um mic&#233;lio semelhante ao de fungos. Quando os nutrientes se tornam escassos, hifas a&#233;reas se desenvolvem e se diferenciam em esporos para sobreviv&#234;ncia e dispers&#227;o.
O g&#234;nero Streptomyces, com mais de 500 esp&#233;cies, &#233; o mais importante desse grupo. Os filamentos de Streptomyces, geralmente com 0,5&#8211;1,0 &#956;m de di&#226;metro, crescem pelas extremidades e frequentemente se ramificam, formando um mic&#233;lio denso. &#192; medida que as col&#244;nias amadurecem, filamentos a&#233;reos chamados espor&#243;foros emergem, produzindo esporos conhecidos como con&#237;dios. Diferentemente dos end&#243;sporos de Bacillus e Clostridium, os con&#237;dios se formam por divis&#227;o transversal nos espor&#243;foros.
A classifica&#231;&#227;o das esp&#233;cies baseia-se em varia&#231;&#245;es nos filamentos a&#233;reos e nas estruturas dos esporos. Con&#237;dios e espor&#243;foros s&#227;o frequentemente pigmentados, conferindo cores distintas &#224;s col&#244;nias. As col&#244;nias maduras s&#227;o compactas, pigmentadas e apresentam apar&#234;ncia pulverulenta, tornando as col&#244;nias de Streptomyces facilmente identific&#225;veis em placas de &#225;gar.

Filo bacteriano: Actinobacteria

As bact&#233;rias corineformes s&#227;o Gram-positivas, aer&#243;bias, im&#243;veis, em forma de bastonete, que possuem arranjos irregulares, em forma de ...

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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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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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