Fundamentals of Microbiology

1.2.4 Other Prokaryotes

Other Prokaryotes

Actinomycetes (The Filamentous Bacteria)

The actinomycetes (sing. actinomycete) are a large group of aerobic, high G-C percentage Gram­-positive bacteria that form branching filaments or hyphae and asexual spores. These bacteria closely resemble fungi in overall morphology. When grown on agar-surface, the actinomycetes branch forming a network of hyphae growing both on the surface and under-surface of the agar. The on-the-surface hyphae are called aerial hyphae and the under-surface hyphae are called substrate hyphae. Septa normally divide the hyphae into long cells (20 mm and longer) possessing many bacterial chromosomes (nucleoids). These are the aerial hyphae that extend above the substratum and reproduce asexually. Most actinomycetes are non-motile. Actinomycetes are particularly useful because they break down hard organic materials like newspaper, tree bark and woody stems.

Actinomycete colony grown on agar surface

1. Chain of Conidiospores (Conidia)

2. Aerial Hyphae

3. Agar Surface

4. Substrate Hyphae

The composition of cell wall in actinomycetes varies greatly among different groups and is of considerable taxonomic significance. Four major cell wall types are distinguished in these filamentous bacteria on the basis of the features of peptidoglycan composition and structure.