Exploring the contributions of two glutamate decarboxylase isozymes in Lactobacillus brevis to acid resistance and γ-aminobutyric acid production.

BACKGROUND: The glutamate decarboxylase (GAD) system of Lactobacillus brevis involves two isoforms of GAD, GadA and GadB, which catalyze the conversion of L-glutamate to γ-aminobutyric acid (GABA) in a proton-consuming reaction contributing to intracellular pH homeostasis. However, direct experimental evidence for detailed contributions of gad genes to acid tolerance and GABA production is lacking. RESULTS: Molecular analysis revealed that gadB is cotranscribed in tandem with upstream gadC, and that expression of gadCB is greatly upregulated in response to low ambient pH when cells enter the late exponential growth phase. In contrast, gadA is located away from the other gad genes, and its expression was consistently lower and not induced by mild acid treatment. Analysis of deletion mutations in the gad genes of L. brevis demonstrated a decrease in the level of GAD activity and a concomitant decrease in acid resistance in the order of wild-type> ΔgadA> ΔgadB> ΔgadC> ΔgadAB, indicating that the GAD activity mainly endowed by GadB rather than GadA is an indispensable step in the GadCB mediated acid resistance of this organism. Moreover, engineered strains with higher GAD activities were constructed by overexpressing key GAD system genes. With the proposed two-stage pH and temperature control fed-batch fermentation strategy, GABA production by the engineered strain L. brevis 9530: pNZ8148-gadBC continuously increased reaching a high level of 104.38 ± 3.47 g/L at 72 h. CONCLUSIONS: This is the first report of the detailed contribution of gad genes to acid tolerance and GABA production in L. brevis. Enhanced production of GABA by engineered L. brevis was achieved, and the resulting GABA level was one of the highest among lactic acid bacterial species grown in batch or fed-batch culture.

[Exclusion of the association of five known mutations with congenital stationary nyctalopia in a large Chinese family].

OBJECTIVE: To detect gene mutations associated with autosomal dominant congenital stationary night blindness(ADCSNB) in a large Chinese family. METHODS: Genomic DNAs were extracted from peripheral blood samples of 16 affected and 14 unaffected family members. According to 5 missense mutations in 3 genes reported previously, 4 pairs of primers were designed and corresponding exons containing the five mutation sites were amplified by polymerase chain reaction. Amplified products were purified and sequenced by MegaBACE1000 capillary array electrophoresis DNA sequencer. Full field electroretinogram (ERG, ISCEV) of patients was recorded and analyzed by Roland Consult System. RESULTS: Dark-adapted ERG showed a-wave was normal, but b-wave of the patients was markedly decreased. None of the five missense mutations were detected in 16 affected and 14 unaffected family members. CONCLUSION: The molecular pathogenesis of ADCSNB in this family does not involve point mutations or deletions of these five sites, which indicates the heterogeneity of ADCSNB.

[Detection of a novel mutation in COL4A5 gene from a Chinese family with X-linked alport syndrome].

By means of PCR and direct sequencing, all 51 exons and their neighbouring intronic sequences of the COL4A5 gene were analyzed to detect mutations in 17 members from a Chinese family with X-linked Alport syndrome(XLAS). At the position 2240 in exon 26, a single-base deletion(2240deIC) is found in all male patients, and a heterozygous deletion is found in all female patients, whereas no mutation is found in normal and 80 control individuals. Meanwhile, the corresponding PCR products of female patients are cloned and sequenced to confirm the results. It is concluded that the 2240deIC mutation is the underlying cause of XLAS in this family,not a polymorphism. Furthermore,this single-base deletion mutation in COL4A5 gene is first reported in X-linked Alport syndrome.