Morphogenetic behaviour of two Streptomyces strains analyzed by the use of chemostats.

Streptomyces granaticolor ETH 7347 and Streptomyces hygroscopicus IMET JA 6599 were cultivated in Casamino acids-limited chemostats. Amino acids served as sole source of energy, carbon and nitrogen, but their limitation affected primarily the catabolism of the mycelia. At different specific growth rates (mu) samples were withdrawn. After staining the cell walls of the mycelia the average length of the cells (mycelial length per cross wall: L/C) and of the hyphal growth units (mycelia-length per branch: L/N) were determined. L/C was only slightly influenced by mu. In S. granaticolor the cells were on average 11.5 microns and in S. hygroscopicus about 18.5 microns long. However, L/N was dependent on mu. Upon a shift from mu = 0.6 to mu = 0.1 L/N was reduced 1.2 fold in S. granaticolor and 1.8 fold in S. hygroscopicus. Especially growth rates below 0.2 stimulated branching. The opposite response of L/N to changes of mu was, however, observed in glucose-limited chemostat cultures (Riesenberg and Bergter 1979). Thus, the average length of the growth units is not determined by mu per se--even if in both cases the energy source was limited--but by specificities of the nutrient-dependent metabolism. Comparison of L/C and L/N showed that in all samples of S. granaticolor cells were smaller than the hyphal growth units, while they were larger in S. hygroscopicus. From a cellular point of view, thus there exist different mechanisms of branching--the single and the multiple branching--which were discussed.