Sporulation at minimum specific growth rate in Aspergillus nidulans chemostat culture predicted using protein synthesis efficiency estimations

Ribosomal efficiency (RE) estimates provide a quantitative descriptor of in trinsic growth rate of cell populations using readily-obtainable experiment al data. In Aspergillus nidulans chemostat cultures, RE increased linearly with growth rate over the range 25-60% of maximum growth rate (mu(max)) con sistent with increasing ribosomal usage with increased growth rate. Above 6 0%, RE did not in crease significantly, suggesting that all ribosomes were functional at 60% of mu(max), further increases in growth rate, presumably resulting from increased polypeptide chain elongation rate. Extrapolating t he linear part of the RE/growth rate curve predicted zero RE at a growth ra te of 0.04 h(-1). Chemostat steady state cultures at 0.04 h(-1) contained s pores (conidia), apparently undergoing a continuous sporulation/germination cycle. We propose that the RE estimates provide a means of predicting the value of minimum specific growth rate (mu(min)) below which net growth cann ot take place.