MAIN CHARACTERISTIC FEATURES OF MAJOR GROUPS OF BACTERIA: ACTINOMYCETES AND MYCOPLASMA

ACTINOMYCETES (Ray fungus)

Actinomycetes are characterized by high G+C content in the cell. All the members are gram positive bacteria. They are aerobic bacteria having filamentous growth. They forms substrate mycelia made of hyphae, septa divides the mycelia into long cells, each containing several nucleoids. They may have aerial mycelia forming conidiospores at ends of filaments or sporangiospores within a sporangium. Formation of substrate and aerial mycelia by members of actinomycetes is one of the major characteristic features.

Some of the members are Non motile, some have flagella for motility. Their cell wall is diverse, has 60 varieties of murein with many di-amino acids and cross bridges and many polysaccharides or lipids. They may have chemoorganotrophic or non-photosynthetic nutrition. Their life cycle completes in two phases: stage of vegetative mycelial growth (primary and secondary) and stage of spore formation. They can grow on simple growth medium; 2-3 hours division cycle. Most of them are soil inhabitant and fermentative types present in body cavity of animals.

Classification:

Domain: Bacteria

Phylum: Actinobacteria

Class: Actinobacteira

Subclass: Actinobacteridae

Order: Actinomycetales

Suborders: Actinomyceneae

Micrococcineae

Catenulisporineae

Corynebacteineae

Micromonosporineae

Propionebacterineae

Actinopolysporineae

Pseudonocardineae

Streptomycineae

Streptosporandineae

Frankineae

Kineosporiineae

Glycomycineae

Actinomycetes have much importance for mankind. They have ecological role in the decomposition of organic matter of soil. They can degrade many organic compounds and are important in the mineralization process. They are known as producers of antibiotics: about 500 antibiotics are prepared from Streptomyces group (S. greceus: streptomycin; S.fradiae: neomycin; S.aureofaciens: tetracycline; S. erytheus: erythromycin).

They have more importance in Agriculture. They can be used as animal pathogen (Corynebacterium pyogens causes mastitis and pharyngitis in sheep and cow). Also used as plant pathogen (S. scabies causes potato scub). Some are important as agent of biological control. Some are enhancer of plant growth as some indirectly produces vitamin B in Pine rhizosphere. In silviculture: Frankia fixes atmospheric nitrogen in symbiosis with Angiosperms. They are also used as biodeteriogens and have important role as pollutants of aerial environment.

MYCOPLASMA (the Firmicutes)

These are very small prokaryotes; all are gram positive bacteria with low G+C content (23-41%).the members of this class are distinguished by lack of cell wall; surrounded by cytoplasmic membrane (a single triple layered unit membrane). The members are characteristically pleomorphic with varying shape from spherical or peer shaped with 0.3-0.8 µm in diameter to branched or helical filaments.

They can grow on artificial nutrient media (minute, colonies having characteristic “fried egg” appearance). They require fatty acids and sterol when grown in artificial culture medium. They are known to have the first completely artificial genome implanted into a functioning bacterial cell. They cannot synthesize peptidoglycan precursors hence, are penicillin resistant, pleomorphic and susceptible to lysis by osmotic shock and detergent treatment.

Some of the members are nonmotile and some glide over liquid surface. Most of them are facultative anaerobe and few are obligatory anaerobic.

They are known to be the smallest bacteria capable of reproduction. They can be saprophytic, commensals or parasites in nature. Some are pathogenic (Mycoplasma pneumonia causes pneumonia; Mycoplasma genitalium causes urogenital infections). Hence, can be isolated from plants, animals, soil and compost piles.

Classification:

Domain: Bacteria

Phylum: Tenericutes

Class: Mollicutes

Order: Mycoplasmatales

Family: Mycoplasmataceae