Abstract
The substrate-carbon flow can be controlled in
continuous bioreactor cultures by the medium composition,
for example, by the C/N ratio. The carbon distribution
is optimal when a maximum fraction flows into the
desired product and the residual is just sufficient to
compensate for the dilution of the microbial catalyst.
Undershooting of the latter condition is reflected immediately
by changes in the Gibbs energy dissipation and
cellular states. Two calorimetric measurement principles
were applied to optimize the continuous synthesis of
polyhydroxybutyrate (PHB) by Variovorax paradoxus
DSM4065 during growth with constantly increasing
supply rates of fructose or toxic phenol. Firstly, the
changed slope of the heat production rate in a complete
heat balanced bioreactor (CHB) indicated optimum carbon
channeling into PHB. The extent of the alteration
depended directly on the toxic properties of the substrate.
Secondly, a flow through calorimeter was connected with
the bioreactor as a ‘‘measurement loop.’’ The optimum
substrate carbon distribution was indicated by a sudden
change in the heat production rate independent of
substrate toxicity. The sudden change was explained
mathematically and exploited for the long-term control of
phenol conversion into PHB. LASER flow cytometry
measurements distinguished between subpopulations
with completely different PHB-content. Populations
grown on fructose preserved a constant ratio of two
subpopulations with double and quadruple sets of DNA.
Cells grown on phenol comprised a third subpopulation
with a single DNA set. Rising phenol concentrations
caused this subpopulation to increase. It may thus be
considered as an indicator of chemostress.
Original language | English |
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Pages (from-to) | 541-552 |
Number of pages | 12 |
Journal | Biotechnology and Bioengineering |
Volume | 93 |
Issue number | 3 |
DOIs | |
Publication status | Published - 21 Oct 2005 |
Keywords
- chemostat
- calorimetry flow cytometry
- polyhydroxbutyrate (PHB)
- phenol
- Variovorax paradoxus DSM 4065