1

Bacteria: The High G + C Gram Positives

Chapter 24

2

Actinomycetes

• Source of most of currently used antibiotics

• Also produce metabolites that are anticancer, antihelminthic and immunosuppressive

• Complex life cycle

3

Life Cycle of Actinomycetes

• Filamentous cells (hyphae) and spores• Hyphae can form branching network

– can grow on surface of substrate or into it to produce a substrate mycelium

– some hyphae differentiate to form an aerial mycelium which extends above substratum

• form exospores which are called sporangiospores if they are located in a sporangium

– at this stage forms secondary metabolites some of which are medically useful

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4

substrate mycelium

aerial hyphae

Figure 24.2

5

Actinomycetes…..

• spores– most not heat resistant but withstand

desiccation

6

other characteristics used in actinomycete taxonomy

• morphology and color of the mycelium and sporangia

• surface features and arrangement of spores

• % GC in DNA

• cell membrane phospholipid composition

• heat resistance of spores

7

Ecological Significance of Actinomycetes

• Widely distributed in soil (e.g. genera Arthrobacter, Nocardia, Frankia, and Streptomyces)

• Play important role in mineralization of organic matter

• Source of many antibiotics e.g. Streptomycin, Rifamycins, Lincomycin

• A few are pathogens: e.g. Corynebacterium diphtheriae, Mycobacterium sp.(bovis, tuberculosis, leprae)

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Figure 24.3

99

Phylum Actinobacteria

• Actinomycetes and other high G + C gram-positive bacteria

1010

Table 24.3

1111

Genus Actinomyces• Straight or slightly curved rods and slender

filaments with true branching– may have swollen, clubbed, or clavate ends

• Facultative or obligate aerobes– require CO2 for best growth

• Normal flora of mucosal surfaces (especially oral cavity) of humans and other animals– e.g., A. bovis – lumpy jaw in cattle– e.g., A. israeli – most important human pathogen

• actinomycoses – ocular disease and periodontal disease in humans

1212

Figure 24.6

1313

Suborder Corynebacterineae

• Has seven families with many known genera such as– Corynebacterium

– Mycobacterium

– Nocardia

1414

Corynebacterium

• Some are harmless soil and water saprophytes

• Many are animal and human pathogens– e.g., C. diphtheriae - diphtheria

1515

Corynebacterium diphtheriae

• after snapping division bacteria often remain partially attached resulting in palisade arrangements of cells

Figure 24.9

1616

Genus Mycobacterium

• Straight or slightly curved rods, sometimes branch or form filaments

• Aerobic and catalase positive

1717

Figure 24.10

1818

Mycobacterial cell walls

• Contain waxes with 60 to 90 carbon mycolic acids

• Acid-fast– basic fuchsin dye cannot be removed

from cell by acid alcohol treatment

1919

Figure 24.11

2020

Important species of Mycobacterium

• M. bovis – tuberculosis in cattle and other ruminants

• M. tuberculosis – tuberculosis in humans

• M. leprae – leprosy

2121

Genus Nocardia

• Develop a substrate mycelium that readily breaks into rods and coccoid elements

• Some also form an aerial mycelium

2222

Nocardia

Figure 24.12

2323

Nocardia….

• Most are free-living saprophytes– can degrade many molecules

• e.g., petroleum hydrocarbons, detergents, benzene

• involved in biodegradation of rubber joints in water and sewage pipes

• Some are opportunistic pathogens causing nocardiosis– usually infect lungs; can infect central

nervous system

2424

Streptomycetes

• Are 1 to 20% of culturable soil microbiota– produce geosmin

• volatile substance that is source of moist earth odor

– important in mineralization process• aerobically degrade many resistant substances

(e.g., pectin lignin, and chitin)

• Produce vast array of antibiotics

• Most are nonpathogenic saprophytes

2525

Streptomyces

• Aerial hyphae that divide in single plane to form chains of 3-50 nonmotile spores

• G+C DNA content is 69-78%

2626

Figure 24.16

2727

Figure 24.17

2828

Pathogenic streptomycetes

• Streptomyces scabies– scab disease in potatoes and beets

• Streptomyces somaliensis– actinomycetoma

• infection of subcutaneous tissues in humans

• leads to swelling, abscesses, and bone destruction