We investigated the growth kinetics and transcriptional responses of
Corynebacterium glutamicum in environments with low (pCO(2) < 40 mbar)
and high (pCO(2) >= 300 mbar) CO2/HCO3 levels compared to standard
conditions. When cultivated at high CO2/HCO3--levels, C. glutamicum
showed increased (63\%) biomass to substrate yields during the initial
growth phase. Other kinetic parameters such as growth rate (mu),
specific glucose consumption rate (q(s)), and selected enzymatic
activities of anaplerotic reactions, the pentose phosphate pathway and
the tricarboxylic acid cycle were similar to standard conditions.
However, microarray hybridization disclosed a complex transcriptional
response involving 117 differentially expressed genes. Among those, 60
genes were assigned to the complete DtxR/RipA regulon controlling iron
homeostasis in C. glutamicum. Impaired growth of a Delta dtxR mutant at
high CO2/HCO3- levels validated the relevance of this master regulator
to cope with excessive CO2/HCO3- availability. At low CO2/HCO3- levels,
C. glutamicum grew in a bi-level manner with three distinct growth
phases. Differential analyses revealed approximately doubled activities
of glucose-6-phosphate dehydrogenase and 6-phosphogluconate
dehydrogenase accompanied by the formation of L-alanine and L-valine
during the lowest mu occurring in mid-phase of the cultivation. DNA
microarray analysis revealed more than 100 differentially expressed
genes in growth phase II compared to phase I including almost all
thiamin pyrophosphate (TPP) biosynthesis genes, which were significantly
up regulated. Concluding, we hypothesize that C. glutamicum counteracts
the lack of CO2/HCO3- by triggering TPP biosynthesis for increasing the
activities of TPP-dependent enzymes involved in CO2 formation. (C) 2013
Elsevier B.V. All rights reserved.
