Streptomycete Spores

Abstract

The Gram‐positive Streptomyces bacteria are major inhabitants of soil, and, unusually for bacteria, they have a complex, multicellular life cycle that looks remarkably fungal‐like. Vegetative growth involves the extension of multicellular, branching hyphae, while reproductive growth involves the emergence of nonbranching hyphae into the air, away from the branching vegetative hyphal mass. These aerial hyphae are converted into chains of prespore compartments by coordinated cell division and chromosome segregation. Prespores then mature into thick‐walled spores that have condensed nucleoids, low metabolic activity and are primed for dispersal and survival. Aerial hyphae and spore surfaces are coated with a hydrophobic, proteinaceous fibrous sheath that aids in aerial growth and may help to promote subsequent spore dispersal and interaction with various interfaces. When exposed to appropriate environmental conditions, spores re‐establish metabolic activity, initiate germination and begin the vegetative phase of their life cycle anew. Key Concepts Streptomyces spores are distinctly different from bacterial endospores and may be regarded as a type of exospore. Spores develop from dedicated reproductive structures called aerial hyphae. Streptomyces spores are formed by partitioning long, multigenomic hyphal cells into unigenomic prespore compartments, through developmentally regulated cell division and chromosome segregation events. An outer fibrous sheath, containing the lanthionine peptide SapB, the chaplins and the rodlins, confers surface hydrophobicity to aerial hyphae and spores. A dedicated ‘ Streptomyces spore wall synthesis complex’ directs the development of a thick spore wall that contributes to mature spore quiescence and resilience. Spores have reduced metabolic activity, accumulate trehalose and have condensed nucleoids. Germination involves rehydration, symmetrical swelling and establishment of polar growth, leading to germ tube emergence and vegetative hyphal outgrowth.

Influence of core divisome proteins on cell division in Streptomyces venezuelae ATCC 10712

“…The apical parts of such aerial hyphae are partitioned into chains of prespores via synchronous formation of several tens of cell division septa in each hypha, and thereafter prespores mature to form pigmented and thick-walled spores with condensed nucleoids and a hydrophobic outer surface layer, before being released into the environment (reviewed in e.g. [3][4][5]). When conditions are favourable, spores germinate and grow to form a new mycelium.…”

“…When conditions are favourable, spores germinate and grow to form a new mycelium. The formation of aerial mycelia and spores is governed by a regulatory cascade of transcription factors that has mainly been studied in S. coelicolor, but more recently much progress has been made in mapping the developmental regulatory networks in the new model organism Streptomyces venezuelae [3][4][5].…”