This chapter surveys the general characteristics of the actinomycetes and other organisms that are classified as high G + C gram-positives in the 2^nd edition of Bergey's Manual. The actnomycetes are filamentous bacteria that form branching hyphae and asexual spores.

After reading this chapter you should be able to:

• describe the filamentous actinomycetes
• describe the morphology and arrangement of spores, cell wall chemistry, and the types of sugars present in cell extracts within the actinomycetes
• discuss the roles of actinomycetes in the mineralization of organic compounds and in the production of antibiotics
• describe the important human pathogens contained in the genera Corynebacterium and Mycobacterium

1. General Properties of the Actinomycetes

1. Form substrate mycelia
2. Septa divide the mycelia into long cells (20 um and longer), each containing several nucleoids
3. Some form a tissue-like mass called a thallus
4. They may have aerial mycelia that for conidospores on the end of the filament, or that form sporangiospores within a sporangium
5. Spores are not heat resistant but withstand desiccation well
6. They generally are nonmotile, but the spores may be flagellated
7. Cell wall types vary
8. Cell wall type, sugars in extracts, morphology and color of mycelia and sporangia, G + C content, membrane phospholipid composition, and spore heat resistance are all important in classifying these organisms
9. Comparison of 16S rRNA sequences and pulse-field electrophoresis of large DNA fragments produced by restriction endonuclease digestion are also used for classification purposes
10. Widely distributed in soils; degrade a number of organic compounds; important in mineralization processes
11. They produce most of the medically important, naturally synthesized antibiotics
12. A few species are pathogenic in humans, other animals and plants

1. High G + C Gram-Positive Bacteria in Bergey's Manual

1. The 2^nd edition will reclassify the high G + C gram-positives using 16S rRNA sequences
2. Many genera will be grouped with the actinomycetes in the class Actinobacteria which will be divided into orders, suborders and families
3. This chapter will focus on the order Actinomycetales which is divided into 10 suborders
4. The order Bfidobacteriales also will be briefly described

1. Suborder Actinomycineae

1. Straight or slightly curved rods and slender filaments with true branching
2. Facultative or obligate anaerobes; require CO₂ for best growth
3. Cell walls contain lysine but not diaminopimelic acid
4. A. bovis causes lumpy jaw in cattle
5. Involved in ocular disease and periodontal disease in humans

1. Suborder Micrococcineae

1. Catalase-positive cocci that occur in pairs, tetrads or irregular clusters
2. Usually nonmotile
3. Often, yellow, red, or orange pigmented
4. Widespread in soil, water, and on mammalian skin
5. Not usually pathogenic

1. Arthrobacter

1. Aerobic, catalase-positive rods with respiratory metabolism and lysine in its

peptidoglycan

2. When growing in exponential phase they are rods that reproduce by a snapping

division

3. In stationary phase they change to coccoid form
4. Most important habitat is soil

1. Suborder Corynebacterineae

1. Contains five families with several important genera
2. Corynebacterium

1. Aerobic and facultative species; catalase-positive; straight to slightly curved rods,

often with tapered ends

2. Remain partially attached after snapping division resulting in angular arrangements
3. Form metachromatic granules
4. Cell walls contain meso-diaminopimelic acid
5. Some species are harmless soil and water saprophytes
6. Many are animal and human pathogens (e.g., C. diphtheriae - causative agent of diphtheria in humans

1. Straight or slightly curved rods
2. Aerobic and catalase-positive; grow slowly
3. Cell walls contain waxes with 60-90 carbon mycolic acids - makes them acid-fast (i.e., basic fuchsin dye cannot be removed with acid-alcohol treatment)
4. Some are free-living saprophytes
5. They are best known as human and animal pathogens

1. M. bovis - tuberculosis in cattle and other ruminants
2. M. tuberculosis - tuberculosis in humans
3. M. leprae - causes leprosy in humans

1. Develops a substrate mycelium that readily breaks into rods and coccoid elements
2. Some develop aerial mycelia
3. They are found in soil and aquatic habitats
4. Involved in biodegradation of rubber joints in water and sewage pipes
5. Some species (e.g., N. asteroides) are opportunistic pathogens causing

1. Suborder Micromonosporineae

1. Referred to as Actinoplantes
2. Extensive substrate mycelia; aerial mycelia are absent or rudimentary
3. Form conidiospores within a sporangium that extends above the surface of the substratum
4. Genera vary in arrangement and development of spores
5. Found in soil and freshwater habitats and occasionally in the ocean
6. Soil dwellers play an important role in plant and animal decomposition
7. Some produce antibiotics such as gentamicin

1. Suborder Propionibacterineae

1. The genus Propionibacterium contains pleiomorphic, nonmotile rods that are often club shaped; cells may also be coccoid or even branched; single cells, short chains, or in clumps
2. Facultatively anaerobic or aerotolerant; ferment sugars to produce propionic acid
3. Found on skin and in the digestive tract of animals; also in dairy products such as cheese
4. Contributes to the production of Swiss cheese
5. P. acne is involved in the development of body odor and acne vulgaris

1. Suborder Streptomycineae

1. Only one genus, Streptomyces
2. An enormous genus with around 500 species
3. Aerial mycelia divide in a single plane to form chains of nonmotile conidiospores
4. Ecologically and medically important
5. Natural habitat is soil where they represent from 1-20% of the organisms present
6. Impart the characteristic odor of moist earth by producing volatile substances such as geosmin
7. Metabolically flexible; major contributors to mineralization
8. Best known for the synthesis of a vast array of antibiotics useful in medicine and research
9. Only S. somaliensis is known to be pathogenic in humans; causes actinomycetoma, an infection of subcutaneous tissues that produces swelling, abscesses and even bone destruction

1. Suborder Streptosporangineae

1. Contains 3 families and 12 genera
2. Maduromycetes

1. They have the sugar madurose (3-O-methyl-D-galactose) in cell extracts
2. Aerial mycelia produces pairs or short chains of spores and the substrate mycelia are branched
3. Some genera form sporangia

1. Thermomonospora

1. Show considerable variation in morphology and lifestyle
2. Produce single spores on the aerial mycelium or on both the aerial and the substrate mycelium
3. Nocardiopsis has a substrate mycelium that fragments like the nocardioforms but it has a different cell wall chemistry

1. Suborder Frankineae

1. The genus Geodermatophilus has motile spores and is an aerobic soil organism
2. The genus Frankia:

1. Forms nonmotile sporangiospores in a sporogenous body
2. Grows in symbiotic relationship with at least 8 families of higher nonleguminous plants
3. Microaerophilic and able to fix atmospheric nitrogen

1. The genus Sporichthya lacks a substrate mycelium but use holdfasts to anchor to the

1. Order Bfidobacteriales

1. Contains one family and 3 genera
2. Falcivibrio and Gardnerella are found in the human genitourinary tract; Gardnerella may be a major cause of vaginitis
3. Bfidobacterium

1. Nonmotile, nonsporing, gram-positive rods of varied shapes that are slightly curved and clubbed; often they are branched
2. Rods can be single cells, in clusters or in V-shaped pairs
3. They are anaerobic and ferment lactose to produce acetic and lactic acids but no carbon dioxide
4. Found in the mouth and intestinal tract of warm-blooded animals, in sewage, and in insects
5. B. bfidus is a pioneer colonizer of the human intestinal tract, particularly when babies are breast fed
6. Some infections of humans have been reported but does not appear to be a major cause of disease