Fate of the subapical cell in Streptomyces granaticolor mycelia

Abstract

AbstractIn stained Streptomyces granaticolor mycelia the fate of the subapical cell (c2) formed periodically after each septation of the apical cell (c1) was analzyed. From the time of birth of c2, the intervals until the starts of first and second branching, the doubling of length by branch growth, and septation were determined. Since five cultures grown at different growth rates were used, the intervals were expressed in relation to the interseptation time of c1 (T) of the respective culture. With few exceptions, the determined values were rather independent of the growth rate. On average, the fate of c2 was: start of branching at 0.7 T, doubling in length at 1.4 T, and septation at 1.7 T, meaning that septation of c1 and c2 did not occur synchronously. A second branch was formed 1.7 T after the first, i.e. at the same interval between the first (in c1) and second (in c2) septation.The site of septation was either more or less median within the original c2‐length, or within the branch, adjacent to the branching site. The percentage of the former was higher in cultures showing delayed branching. Generally, the median position of septation prevailed. As a consequence, the branched c2 was divided into two differently sized and shaped daughter cells. On average, the branch‐receiving daughter was about 2.5 times larger than the branchless daughter.The increase of the frequency of septation within the original c2 cells was followed for five T‐times. Rate and degree of increase was dependent on the growth rate or on the original length of c2. As a result, within all cultures the interseptal distance within the main hyphae approached a length of about 5 μm.