Zusammenfassung
In large-scale production processes, metabolic control is typically
achieved by limited supply of essential nutrients such as glucose or
ammonia. With increasing bioreactor dimensions, microbial producers such
as Escherichia coli are exposed to changing substrate availabilities due
to limited mixing. In turn, cells sense and respond to these dynamic
conditions leading to frequent activation of their regulatory
programmes. Previously, we characterized short- and long-term strategies
of cells to adapt to glucose fluctuations. Here, we focused on
fluctuating ammonia supply while studying a continuously running
two-compartment bioreactor system comprising a stirred tank reactor
(STR) and a plug-flow reactor (PFR). The alarmone ppGpp rapidly
accumulated in PFR, initiating considerable transcriptional responses
after 70s. About 400 genes were repeatedly switched on/off when E.coli
returned to the STR. E.coli revealed highly diverging long-term
transcriptional responses in ammonia compared to glucose fluctuations.
In contrast, the induction of stringent regulation was a common feature
of both short-term responses. Cellular ATP demands for coping with
fluctuating ammonia supply were found to increase maintenance by 15\%.
The identification of genes contributing to the increased ATP demand
together with the elucidation of regulatory mechanisms may help to
create robust cells and processes for large-scale application.
Nutzer
