Abstract
Gram‐positive bacteria of the genus
Streptomyces
are major inhabitants of soil and grow as branching hyphae, strikingly like the filamentous fungi. Whereas their mycelium is multicellular, dispersal and long‐term survival are achieved by unicellular spores. Spore formation is part of a complex developmental cycle involving dedicated reproductive aerial hyphae. The long apical cells of the aerial hyphae are divided into chains of tens of prespore compartments, which in turn mature into thick‐walled spores with condensed nucleoids and low metabolic activity, primed for dispersal and survival. Aerial hyphae and spore surfaces are coated with a proteinaceous fibrous sheath. This highly hydrophobic sheath is required for aerial hyphal emergence, and may aid spore dispersal and interaction with various interfaces. When exposed to appropriate environmental conditions, spores rehydrate and swell. Cell polarisation is required for the emergence of a germ tube, which develops into a mycelium by apical growth and side‐branch formation.
Key Concepts:Streptomyces
spores are distinctly different from bacterial endospores.
Spores develop from dedicated reproductive structures called aerial hyphae.Streptomyces
spores are formed by division of long, multigenomic hyphal cells into unigenomic compartments.
A thick spore wall is assembled from within the maturing spore and contributes to quiescence and resilience.Spores are dehydrated, accumulate trehalose and have condensed nucleoids.An outer fibrous sheath confers surface hydrophobicity to aerial hyphae and spores.Germination involves rehydration, symmetrical swelling and establishment of polar growth leading to germ tube emergence.
