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J. Cell Biol.,
Volume 145, Number 3, May 3, 1999 515-525
Laboratorio de Microbiología, Facultad de Medicina, Universidad de Oviedo, 33006 Oviedo, Spain
During the life cycle of the streptomycetes,
large numbers of hyphae die; the surviving ones undergo cellular differentiation and appear as chains of
spores in the mature colony. Here we report that the
hyphae of Streptomyces antibioticus die through an orderly process of internal cell dismantling that permits
the doomed hyphae to be eliminated with minimum
disruption of the colony architecture. Morphological
and biochemical approaches revealed progressive disorganization of the nucleoid substructure, followed by
degradation of DNA and cytoplasmic constituents with
transient maintenance of plasma membrane integrity.
Then the hyphae collapsed and appeared empty of cellular contents but retained an apparently intact cell wall. In addition, hyphal death occurred at specific regions and times during colony development. Analysis of
DNA degradation carried out by gel electrophoresis
and studies on the presence of dying hyphae within the
mycelium carried out by electron microscopy revealed
two rounds of hyphal death: in the substrate mycelium during emergence of the aerial hyphae, and in the aerial
mycelium during formation of the spores. This suggests
that hyphal death in S. antibioticus is somehow included
in the developmental program of the organism.
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