Development of a System of High Ornithine and Citrulline Production by a Plant-Derived Lactic Acid Bacterium, Weissella confusa K-28

The metabolites of lactic acid bacteria: classification, biosynthesis and modulation of gut microbiota

Lactic acid bacteria (LAB) are ubiquitous microorganisms that can colonize the intestine and participate in the physiological metabolism of the host. LAB can produce a variety of metabolites, including organic acids, bacteriocin, amino acids, exopolysaccharides and vitamins. These metabolites are the basis of LAB function and have a profound impact on host health. The intestine is colonized by a large number of gut microorganisms with high species diversity. Metabolites of LAB can keep the balance and stability of gut microbiota through aiding in the maintenance of the intestinal epithelial barrier, resisting to pathogens and regulating immune responses, which further influence the nutrition, metabolism and behavior of the host. In this review, we summarize the metabolites of LAB and their influence on the intestine. We also discuss the underlying regulatory mechanisms and emphasize the link between LAB and the human gut from the perspective of health promotion.

Fermentation in Pineapple Juice Significantly Enhances Ornithine and Citrulline Production in Lactococcus lactis MSC-3G Isolated from Sugarcane

Lactic acid bacterial (LAB) fermentation of functional amino acids using fruit juices as a cultivation medium is not well-documented. In the present study, we successfully isolated a high ornithine- and citrulline-producing Lactococcus lactis strain, designated MSC-3G, from sugarcane and investigated the ornithine and citrulline production profile using various fruit juices as a cultivation medium. Among fruit juices, pineapple juice exhibited the highest potentiality to initiate ornithine production (56 mM), while the highest citrulline yield was obtained during lime juice cultivation (34.5 mM). Under the optimal cultivation condition, the highest yield of ornithine and citrulline in pineapple juice reached 98.9 ± 2.2 mM and 211.1 ± 35.7 mM, respectively, both of which were significantly higher than that in the well-known industrial strain of Corynebacterium (C.) glutamicum. Additionally, citrulline production was dependent on oxygen supplementation and increased twofold when grown aerobically. Whole genome sequencing showed that the MSC-3G genome possesses the arginine deiminase (ADI) gene cluster arcABD1C1C2TD2. The results of the ADI pathway enzyme activities of MSC-3G showed a significant increase in arginine deiminase activity, while ornithine carbamoyl transferase activity was decreased, which in turn indicates the high citrulline-accumulation ability of MSC-3G when cultivated in pineapple juice.

Metabolic engineering of Aureobasidium melanogenum for the overproduction of putrescine by improved L-ornithine biosynthesis

Aureobasidium melanogenum HN6.2 is a high siderophore-producing yeast-like fungal strain. After blocking siderophore biosynthesis and attenuating the expression of the ornithine carbamoyltransferase gene (the OTC gene), the obtained D-LCFAO-cre strain produced 2.1 ± 0.02 mg of intracellular L-ornithine per mg of the protein. The overexpression of the L-ornithine decarboxylase gene (the SPE1-S gene) from Saccharomyces cerevisiae in the mutant D-LCFAO-cre could make the transformant E-SPE1-S synthesize 3.6 ± 0.1 of intracellular ornithine per mg of protein and produce 10.5 g/L of putrescine. The further overexpression of the ArgB/C gene encoding bifunctional acetylglutamate kinase/N-acetyl-gamma-glutamyl-phosphate reductase in the transformant E-SPE1-S caused the transformant E-SPE1-S-ArgB/C to accumulate L-ornithine (4.2 mg/mg protein) and to produce 21.3 g/L of putrescine. During fed-batch fermentation, the transformant E-SPE1-S-ArgB/C could produce 33.4 g/L of putrescine, the yield was 0.96 g/g of glucose, and the productivity was 0.28 g/L/h. The putrescine titer was much higher than that produced by most engineered strains obtained thus far.

Characterization of High-Ornithine-Producing Weissella koreensis DB1 Isolated from Kimchi and Its Application in Rice Bran Fermentation as a Starter Culture

High-ornithine-producing Weissella koreensis DB1 were isolated from kimchi. Ornithine is produced from arginine via the intracellular arginine deiminase pathway in microorganisms; thus, high cell growth is important for producing ornithine in large quantities. In this study, excellent W. koreensis DB1 growth (A600: 5.15-5.39) was achieved in de Man, Rogosa, and Sharpe (MRS) medium supplemented with 1.0-3.0% arginine (pH 5.0) over 24-48 h at 30 °C, and the highest ornithine (15,059.65 mg/L) yield was obtained by culture in MRS containing 3.0% arginine for 48 h. W. koreensis DB1 was further investigated as a functional starter culture for rice bran fermentation. After 48 h of fermentation at 30 °C, the fermented rice bran was freeze-dried and ground. The prepared fermented rice bran contained 43,074.13 mg/kg of ornithine and 27,336.37 mg/kg of citrulline, which are used as healthcare supplements due to their beneficial effects. Furthermore, the organoleptic quality of the fermented rice bran was significantly improved, and the fermented product contained viable cells (8.65 log CFU/mL) and abundant dietary fiber. In addition, an investigation of its safety status showed that it has no harmful characteristics. These results indicate that the fermented rice bran product produced is a promising functional food candidate.

Characterization of Weissella koreensis SK Isolated from Kimchi Fermented at Low Temperature (around 0 °C) Based on Complete Genome Sequence and Corresponding Phenotype

This study identified lactic acid bacteria (LAB) that play a major role in kimchi fermented at low temperature, and investigated the safety and functionality of the LAB via biologic and genomic analyses for its potential use as a starter culture or probiotic. Fifty LAB were isolated from 45 kimchi samples fermented at -1.5~0 °C for 2~3 months. Weissella koreensis strains were determined as the dominant LAB in all kimchi samples. One strain, W. koreensis SK, was selected and its phenotypic and genomic features characterized. The complete genome of W. koreensis SK contains one circular chromosome and plasmid. W. koreensis SK grew well under mesophilic and psychrophilic conditions. W. koreensis SK was found to ferment several carbohydrates and utilize an alternative carbon source, the amino acid arginine, to obtain energy. Supplementation with arginine improved cell growth and resulted in high production of ornithine. The arginine deiminase pathway of W. koreensis SK was encoded in a cluster of four genes (arcA-arcB-arcD-arcC). No virulence traits were identified in the genomic and phenotypic analyses. The results indicate that W. koreensis SK may be a promising starter culture for fermented vegetables or fruits at low temperature as well as a probiotic candidate.

Microbial Engineering for Production of N-Functionalized Amino Acids and Amines

N-functionalized amines play important roles in nature and occur, for example, in the antibiotic vancomycin, the immunosuppressant cyclosporine, the cytostatic actinomycin, the siderophore aerobactin, the cyanogenic glucoside linamarin, and the polyamine spermidine. In the pharmaceutical and fine-chemical industries N-functionalized amines are used as building blocks for the preparation of bioactive molecules. Processes based on fermentation and on enzyme catalysis have been developed to provide sustainable manufacturing routes to N-alkylated, N-hydroxylated, N-acylated, or other N-functionalized amines including polyamines. Metabolic engineering for provision of precursor metabolites is combined with heterologous N-functionalizing enzymes such as imine or ketimine reductases, opine or amino acid dehydrogenases, N-hydroxylases, N-acyltransferase, or polyamine synthetases. Recent progress and applications of fermentative processes using metabolically engineered bacteria and yeasts along with the employed enzymes are reviewed and the perspectives on developing new fermentative processes based on insight from enzyme catalysis are discussed.