[Show abstract][Hide abstract] ABSTRACT: With the aim of elucidating the physiological characteristics of a low-pH tolerant strain Torulopsis glabrata RT-6.
The intracellular pH, ATP level, the membrane bound H(+)-ATPase activity, the membrane fatty acid composition and the intracellular polyphosphate content of the parent strain CCTCC M202019 and the mutant strain RT-6 were determined and compared under different pH conditions.
Compared to that of the parent strain, the cell growth and pyruvate concentration of the mutant strain RT-6 were increased by 60.6% and 85.4% (56 h), respectively. Similarly, the strain RT-6 had higher intracellular pH compared to the control strain at external pH5.0, 4.5, and 4.0. The ATP content, the membrane bound H(+)-ATPase activity and the intracellular polyphosphate content of the mutant strain RT-6 were increased by 11.7%, 13.6%, and 3.5% at external pH 5.5, while at external pH 4.0, increased by 61%, 38.6%, and 30.8%, respectively. Furthermore, the mutant strain RT-6 exhibited higher content of the unsaturated fatty acids and higher membrane fluidity.
Discharging more intracellular H+ and inhibiting the intracellular H+ production contributed to the strain RT-6's higher intracellular pH, and therefore the acid tolerance.
No preview · Article · Mar 2011 · ACTA MICROBIOLOGICA SINICA
[Show abstract][Hide abstract] ABSTRACT: We developed an engineered Sacchromyces cerevisiae strain to produce L-lactic acid efficiently by using glucose as carbon source.
For construction of the strain CEN. PK2-1C [LDH], we integrated an LDH gene coding L-lactic acid dehydrogenase from bovine into the genome of S. cerevisiae via homologous recombination and meanwhile knocked out a PDC1 gene coding pyruvate decarboxylase. The carbon fluxes were led into L-Lactic acid. We analyzed the Km value of these key enzymes to NADH and over-expressed an NADH oxidase (nox) from Streptococcus pneumoniae into the cytoplasm for the construction of S. cerevisiae CEN. PK2-1C [LDH] -nox.
Compared to the initial strain, the yield of L-lactic acid in CEN. PK2-1C [LDH] fermentation broth increased from 0 g/L to 15 g/L and the concentration of ethanol decreased from 27.3 g/L to 16.2 g/L. Compared to CEN. PK2-1C [LDH], the yield of L-lactic acid in CEN. PK2-1C [LDH] -nox fermentation broth increased from 15 g/L to 20 g/L and the concentration of ethanol decreased from 16.2 g/L to 8.2 g/L.
The carbon metabolic flux was redistributed to efficient accumulation of L-lactic acid through two-sided control that heterologous expression of the gene LDH and decreasing the ratio of NADH/NAD+.
No preview · Article · Jan 2011 · ACTA MICROBIOLOGICA SINICA