Introduction to Actinomycetes

Actinomycetes are a unique group of bacteria that are Gram-positive and filamentous in nature. They exhibit a branched growth pattern and form extensive colonies or mycelium. Despite being bacteria, their distinct characteristics make them a separate field of study.

Classification of Actinomycetes

Key Characteristics and Morphology

• Actinomycetes are prokaryotic organisms. Their size ranges from 1-2 µm in diameter.
• They are mostly aerobic organisms, although some can survive in anaerobic conditions as well.
• Actinomycetes are commonly found in soil but can also be seen in marine environments.
• Their mycelium occasionally breaks apart to form coccoid or rod-shaped colonies.
• Many actinomycetes form spores. The sporangia or spore case is usually found on the aerial hyphae.
• Actinomycetes are susceptible to infection by bacteriophages. The phages that infect actinomycetes are referred to as actinophages.
• Some actinomycetes have flagella, which provide them with motility.
• These organisms range from harmless bacteria to pathogenic species and even antibiotic producers.
• Actinomycetes can sometimes look like fungal hyphae. However, they are much smaller and can be distinguished based on size.
• They can act on different soil substrates such as less degradable insects and plant polymers including cellulose, chitin, and hemicellulose.

Examples of Actinomycetes

Actinomyces bovis

Streptomyces coelicolor

Nocardia brasiliensis

Streptomyces scabies

Actinomyces israelii

Reproduction in Actinomycetes

Actinomycetes reproduce through the fragmentation of hyphae or the formation of spores. During reproduction, they form conidiophores, oidiospores, or sporangiospores. The hyphae formed by actinomycetes during fragmentation are usually one-fifth to half the size of fungal hyphae.

Applications and Uses

• Actinomycetes produce geosmin, a compound responsible for the earthy smell of soil.
• They can degrade complex molecules such as cellulose and chitin.
• The genus Frankia is capable of biological nitrogen fixation.
• The genus Streptomyces is known for producing antimicrobial compounds such as streptomycin and actinomycin.
• Actinomycetes are an important source of antimicrobial compounds, contributing to approximately 61% of the total antibiotics production.