This 1974 study examined the micromorphology and sclerotial development in four Chainia species (barodensis, poonensis, ochracea, and 33br), actinomycetes known for producing sclerotia—discrete, resistant vegetative structures. Using light microscopy, microtomy, and scanning electron microscopy, researchers observed that Chainia species rapidly transform normal hyphae into thick sclerotial hyphae (1–3 μm wide) through extensive septation. Sclerotial initials develop through well-defined stages and form discrete bodies with pseudoparenchymatous internal structure lacking zone differentiation. Different species showed varying developmental patterns: C. barodensis and C. poonensis produced intercalary sclerotia within hyphae, while C. ochracea produced lateral buds on multihyphal strands, and C. 33br exhibited both patterns. Some species formed stromal crusts embedding sclerotia. Scanning electron microscopy revealed characteristic surface architecture with ridges and craters. The authors conclude actinomycete sclerotia are definitive morphological entities distinct from simple hyphal aggregations, differing from fungal sclerotia by exhibiting cross-septation in multiple planes and being physically dissociable into individual units.

Key findings

• Chainia species undergo rapid sclerotization, forming broad, closely-septate sclerotial hyphae (1–3 μm wide) distinct from normal hyphae
• Sclerotial development occurs through well-defined stages: intercalary formation in C. barodensis and C. poonensis versus lateral origin on multihyphal strands in C. ochracea
• Sclerotia possess pseudoparenchymatous structure composed of large polygonal cells without internal zone differentiation, distinguishing them from simple hyphal aggregations
• Cross-septation in different planes during sclerotium development is a unique feature not observed in fungal sclerotia or typical Streptomyces
• Actinomycete sclerotia are physically dissociable into individual units and display characteristic surface topography with ridges and craters under scanning electron microscopy