GROWTH-RATE CONTROL OF PROTEIN AND NUCLEIC-ACID CONTENT IN STREPTOMYCES-COELICOLOR A3(2) AND ESCHERICHIA-COLI B R/

Escherichia coli possesses regulatory mechanisms that coordinate cell growth with the synthesis of essential macromolecules (protein, RNA an d DNA). While fundamental differences have been identified in the grow th habit and chromosome structure of E. coli and Streptomyces, little is known about these regulatory mechanisms in filamentous bacteria. Th is paper reports on the relationship between the macromolecule content of S. coelicolor A3(2) and its specific growth rate. The protein, RNA and DNA contents (g per 100 g biomass) of S. coelicolor A3(2) grown i n steady-state continuous culture over a range of specific growth rate s (0.025-0.3 h(-1)) were 31-45, 10-22 and 3.5-4.5 % (w/w), respectivel y. This composition is qualitatively similar to that of other microorg anisms. Changes in the macromolecular content of S. coelicolor A3(2) a nd S. coli B/r with specific growth rate appear to be essentially simi lar. However, the data indicate that the RNA content of S. coelicolor A3(2), grown under the conditions used, exceeds that of S. coli grown at the same specific growth rate. The data also suggest that overlappi ng rounds of replication are not a feature of DNA synthesis in S. coel icolor A3(2). This may be a function of the organism's low maximum spe cific growth rate. Alternatively, it may be a consequence of regulator y mechanisms which act to inhibit the initiation of DNA synthesis in a linear chromosome which is already undergoing replication.