Answer to Question #117779 in Microbiology for Prince Gyan

Question

Actinomycetes are usually classed within the same taxonomic family as bacteria but in many aspects of their morphology and growth patterns resemble fungi. Explain.

Answer 1

Actinomycetes are gram-positive bacteria that show branching, filamentous, or irregularly rod-shaped cell morphology. The term “actinomycetes” means “ray-fungus” in Greek, and suggests that these microorganisms were observed, cultured, and studied as fungi in the early periods of investigation. Now their taxonomic position is well established within the domain Bacteria. The essential features of the prokaryotic nature of actinomycetes are as follows: the lack of a membranous boundary which separates the nucleus and the cytoplasm as seen in fungi; the lack of unit membrane-bound cytoplasmic organelles; ribosomes of the 70S type in contrast to the 80S type found in fungi; and the presence of peptidoglycan as a component of actinomycetes cell wall. However, during growth on agar actinomycetes differentiate into two types of long and branching cells: substrate and aerial mycelia; the latter of which subsequently fragment and sporulate. This is similar to the growth and differentiation of fungi.