pH control in microwell fermentations of S-erythraea CA340:: influence on biomass growth kinetics and erythromycin biosynthesis

The creation of microscale fermentation procedures could have significant benefits at all stages of fermentation process development from discovery through to process optimisation. For both microbial and mammalian fermentations, pH is a vital process parameter as it has a marked affect on cell growth rate, viability and product synthesis. In this work, we describe the influence of various pH control strategies on growth and erythromycin synthesis by Saccharopolyspora erythraea CA340 at the 71 scale and show that the effects can be reproduced in pH-controlled microscale fermentations (thousandfold scale translation). At the 71 scale the implementation of base only or full pH control (NaOH and H(3)PO(4) additions) significantly increased both the maximum growth rate and biomass concentrations attained compared to fermentations without pH control. There was over a twofold increase in erythromycin biosynthesis and the ratio of erythromycin A (EA) to erythromycin C (EC) increased from 2:1 to 6:1 (base only pH control) to 11: 1 (full pH control). In order to measure pH during microscale fermentations, a specially designed microtitre plate was built that allowed the insertion of a micro-pH probe into each well (total well volume 7 ml). This, allowed manual base only pH control to be implemented in microwell fermentations which enhanced both the maximum specific growth rate and the maximum biomass concentration. Total erythromycin synthesis and the ratio of EA:EC were also significantly enhanced. This work has demonstrated the benefits of implementing pH control in microscale fermentations and now allows the specification of an automated pH control system. (C) 2003 Elsevier Science B.V.. All rights reserved.