[Chromosome segregation and cell division during the growth and differentiation of Streptomyces].
Streptomyces, soil-dwelling actinomycetales, grow by forming a mycelium. During the development of Streptomyces colonies, vegetative hyphae undergo morphological differentiation which involves the formation of aerial hyphae and spore chains. Differentiation is controlled by a regulatory cascade of bld and whi genes products. Long, multigenomic compartments of vegetative hyphae are delimited by infrequent crosswalls and remain adjacent to each other. Chromosome replication in vegetative hyphae is asynchronous. The chromosomes are uncondensed and do not undergo active segregation. On the other hand, in multigenomic aerial hyphae that undergo synchronized septation, the chromosomes are condensed and segregated into unigenomic compartments. Efficient chromosomal segregation depends on ParA and ParB proteins. ParB binds DNA, forming a large nucleoprotein complex, a segregosome. ParA assembles into a filament extending along the hyphae. The ParA filament enables the regular distribution of the segregosomes, ensuring that each of the spore compartments receives one copy of the chromosome. A unique feature of Streptomyces discussed in this review is the spatial and temporal regulation of chromosomal segregation and septation.