초록
<P><B>Background</B></P><P>Systems biology approaches to study metabolic switching in <I>Streptomyces coelicolor</I> A3(2) depend on cultivation conditions ensuring high reproducibility and distinct phases of culture growth and secondary metabolite production. In addition, biomass concentrations must be sufficiently high to allow for extensive time-series sampling before occurrence of a given nutrient depletion for transition triggering. The present study describes for the first time the development of a dedicated optimized submerged batch fermentation strategy as the basis for highly time-resolved systems biology studies of metabolic switching in <I>S. coelicolor</I> A3(2).</P><P><B>Results</B></P><P>By a step-wise approach, cultivation conditions and two fully defined cultivation media were developed and evaluated using strain M145 of <I>S. coelicolor</I> A3(2), providing a high degree of cultivation reproducibility and enabling reliable studies of the effect of phosphate depletion and L-glutamate depletion on the metabolic transition to antibiotic production phase. Interestingly, both of the two carbon sources provided, <SMALL>D-</SMALL>glucose and L-glutamate, were found to be necessary in order to maintain high growth rates and prevent secondary metabolite production before nutrient depletion. Comparative analysis of batch cultivations with (i) both L-glutamate and <SMALL>D-</SMALL>glucose in excess, (ii) L-glutamate depletion and <SMALL>D-</SMALL>glucose in excess, (iii) L-glutamate as the sole source of carbon and (iv) <SMALL>D-</SMALL>glucose as the sole source of carbon, reveal a complex interplay of the two carbon sources in the bacterium's central carbon metabolism.</P><P><B>Conclusions</B></P><P>The present study presents for the first time a dedicated cultivation strategy fulfilling the requirements for systems biology studies of metabolic switching in <I>S. coelicolor</I> A3(2). Key results from labelling and cultivation experiments on either or both of the two carbon sources provided indicate that in the presence of <SMALL>D-</SMALL>glucose, L-glutamate was the preferred carbon source, while <SMALL>D-</SMALL>glucose alone appeared incapable of maintaining culture growth, likely due to a metabolic bottleneck at the oxidation of pyruvate to acetyl-CoA.</P>