Regulation of metabolic flux in Lactobacillus casei for lactic acid production by overexpressed ldhL gene with two-stage oxygen supply strategy.

This study describes a novel strategy to regulate the metabolic flux for lactic acid production in Lactobacillus casei. The ldhL gene encoding L-lactate dehydrogenase (L-LDH) was overexpressed in L. casei, and a two-stage oxygen supply strategy (TOS) that maintained a medium oxygen supply level during the early fermentation phase, and a low oxygen supply level in the later phase was carried out. As a consequence, a maximum L-LDH activity of 95.6 U/ml was obtained in the recombinant strain, which was over 4-fold higher than that of the initial strain. Under the TOS for L. casei (pMG-ldhL), the maximum lactic acid concentration of 159.6 g/l was obtained in 36 h, corresponding to a 62.8% increase. The results presented here provide a novel way to regulate the metabolic flux of L. casei for lactic acid production in different fermentation stages, which is available to enhance organic acid production in other strains.

[Role of histone deacetylase in inhibiting invasion of human gastric carcinoma cell line SGC-7901 by PPARgamma-mediated pathway].

BACKGROUND AND OBJECTIVE: Histone deacetylase (HDAC) can attenuate the function of peroxisome proliferator-activated receptor gamma (PPARgamma) to drive adipocyte differentiation. PPARgamma activation is confirmed to inhibit the development and metastasis of a variety of malignant cells. This study was to investigate the role of HDAC in inhibiting the invasion of human gastric carcinoma SGC-7901 cells through PPARgamma-mediated pathway, and explore potential mechanism. METHODS: SGC-7901 cells were treated with different concentrations of Trichostatin A (TSA) and Rosiglitazone (ROZ) respectively to select the best combination through assessing cell proliferation by MTT assay. Then cells were randomly divided into control group, TSA group, ROZ group, and combination group. Cell proliferation was detected by MTT assay after 48 h; cell invasion was detected by Boyden chamber invasion test. The mRNA levels of PPARgamma and matrix metalloproteinase-2 (MMP-2) were assessed by reverse transcription-polymerase chain reaction (RT-PCR), and the protein level of MMP-2 was evaluated by Western blot. RESULTS: Both TSA and ROZ inhibited the proliferation of SGC-7901 cells in a dose-dependent manner. A combination of 20 nmol/L TSA and 5 mumol/L ROZ synergistically inhibited the invasion of SGC-7901 cells (q=1.41). ROZ down-regulated the mRNA and protein expression of MMP-2. TSA and ROZ in combination reduced MMP-2 expression more obviously than ROZ alone. TSA up-regulated the expression of PPARgamma mRNA. CONCLUSIONS: HDAC suppresses the activation of PPARgamma through a series of molecular mechanisms. The activity of ROZ in inhibiting invasion of human gastric carcinoma cells can be enhanced after the activity of HDAC is inhibited by TSA.