Attendance on The 10th Asian Conference on Lactic Acid Bacteria
The Asian Conference on Lactic Acid Bacteria is the good platform for Asian researchers to know about the different fermented products in different Asian countries and to develop new probiotics with healthcare functions used in the fermented foods. The attendance to the conference was the great opportunity to know the human microbiota of Asian people which interestingly vary with the region to region and country to country for me. The satisfactory level of symbiotic bacteria, such as lactic acid bacteria and bifidobacteria, in the gut composition is necessary for healthy gut of human.
I presented my doctoral work theme, which was entitled “Establishment of an efficient method of ornithine and citrulline high-production by a plant-derived lactic acid bacterium, Weissella confusa K28”. In the study, I have isolated a plant-derived lactic acid bacterium, which is designated K-28, and identified as Weissella (W.) confusa. The K-28 strain has the proven efficacy to produce two amino acids ornithine and citrulline, from the precursor amino acid arginine. By using a commercial fed-batch jar fermenter high level ornithine (18 g/L) and citrulline (10 g/L) production was achieved by continuous feeding of arginine.
Although Coreynebacterium (C.) glutamicum is an industrially potencial strain for ornithine production, but some strains are bred by mutagenesis and genetic modification. The ornithine production by the wild-type of C. glutamicum is only 0.5 g/L, indicating that W. confusa K-28 (8.85 g/L) is superior to C. glutamicum in terms of ornithine production. K-28 also superior to W. koreensis MS1-3 (0.045 g/L) and W. koreensis MS1-14 (0.046 g/L) to produce ornithine under the same condition.
In the study, we determined an arginine deiminase gene cluster of K-28 strain which is 5.7 Kb in length and composed of five genes namely wkaA, wkaB, wkaD, wkaC, and wkaR. The RT-PCR analysis suggested that the expression of these genes decreases with cells growth. We also confirmed that the production of ornithine and the expression of the five genes are significantly decreased under the aerobic condition but not under the anaerobic one.In the presence or absence of arginine the expression of these genes did not differ, suggesting that in the K-28 strain the production of ornithine and citrulline was not induced by the exogenous arginine added to medium.