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

Copyright © The McGraw-Hill companies, Inc. Permission required for reproduction or display. 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)

8 8 Figure 24.3

9 9 Phylum Actinobacteria Actinomycetes and other high G + C gram-positive bacteria

10 Table 24.3

11 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 CO 2 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

12 Figure 24.6

13 Suborder Corynebacterineae Has seven families with many known genera such as –Corynebacterium –Mycobacterium –Nocardia

14 Corynebacterium Some are harmless soil and water saprophytes Many are animal and human pathogens –e.g., C. diphtheriae - diphtheria

15 Corynebacterium diphtheriae after snapping division bacteria often remain partially attached resulting in palisade arrangements of cells Figure 24.9

16 Genus Mycobacterium Straight or slightly curved rods, sometimes branch or form filaments Aerobic and catalase positive

17 Figure 24.10

18 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

19 Figure 24.11

20 Important species of Mycobacterium M. bovis – tuberculosis in cattle and other ruminants M. tuberculosis – tuberculosis in humans M. leprae – leprosy

21 Genus Nocardia Develop a substrate mycelium that readily breaks into rods and coccoid elements Some also form an aerial mycelium

22 Nocardia Figure 24.12

23 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

24 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

25 Streptomyces Aerial hyphae that divide in single plane to form chains of 3-50 nonmotile spores G+C DNA content is 69-78%

26 Figure 24.16

27 Figure 24.17

28 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