Effects of Salt Stress on Plant Growth, Antioxidant Capacity, Glandular Trichome Density, and Volatile Exudates of Schizonepeta tenuifolia Briq.

Salinity is a major abiotic factor affecting plant growth and secondary metabolism. However, no information is available about its effects on Schizonepeta tenuifolia Briq., a traditional Chinese herb. Here, we investigated the changes of plant growth, antioxidant capacity, glandular trichome density, and volatile exudates of S. tenuifolia exposed to salt stress (0, 25, 50, 75, 100 mM NaCl). Results showed that its dry biomass was reduced by salt treatments except 25 mM NaCl. Contents of antioxidants, including phenolics and flavonoids, increased at low (25 mM) or moderate (50 mM) levels, but declined at severe (75 and 100 mM) levels. On leaf surfaces, big peltate and small capitate glandular trichomes (GTs) were found. Salt treatments, especially at moderate and severe concentrations, enhanced the density of total GTs on both leaf sides. The most abundant compound in GT volatile exudates was pulegone. Under salinity, relative contents of this component and other monoterpenes decreased significantly; biosynthesis and accumulation of esters were enhanced, particularly sulfurous acid,2-ethylhexyl hexyl ester, which became the second major compound as salinity increased. In conclusion, salt stress significantly influenced the growth and secondary metabolism of S. tenuifolia, enabling us to study the changes of its pharmacological activities.

[Changes of ion absorption, distribution and essential oil components of flowering Schizonepeta tenuifolia under salt stress].

In this paper, a pot experiment using quartz sands was conducted to study the effects of different concentrations of NaCl (0, 25, 50, 75, 100 mmol·L⁻¹) on the ion absorption, distribution and essential oil components of flowering Schizonepeta tenuifolia. The results showed that as NaCl concentration increased, Na⁺ content of root, stem, leaf and flower increased significantly, and that of the aerial parts was in a higher level than in the root. Regarding the K⁺ content, it decreased in the root but increased in stem, leaf and flower. Some changes were detected in the Ca²âº content, but not significant on the whole. The value of K⁺/Na⁺ and Ca²âº/Na⁺ reduced as a result of increasing NaCl concentrations. The content of essential oil increased under medium salt treatment (50 mmol·L⁻¹ NaCl). However, the synthesis and accumulation of essential oil was inhibited by the serious salt treatment (100 mmol·L⁻¹ NaCl). Over 98% of the essential oil components were terpenes, in which pulegone and menthone were the most two abundant compounds. Varieties of essential oil components did not change significantly under salt stress but their relative proportions did. The transformation of pulegone to menthone was enhanced and the value of pulegone/menthone based on their relative contents decreased with NaCl concentration increasing. Consequently, menthone ranked the most abundant compound by replacing pulegone. Relative content of D-limonene increased under medium and serious salt stress, and that of ß-caryophyllene only increased under mild treatments. So our research could provide references for the standard cultivation on saline soil of S. tenuifolia.

Yeast cell wall polysaccharides in Tibetan kefir grains are key substances promoting the formation of bacterial biofilm.

This study investigated the interaction among Kluyveromyces marxianus G-Y4 (G-Y4), Lacticaseibacillus paracasei GL1 (GL1) and Lactobacillus helveticus SNA12 (SNA12) that isolated from Tibetan kefir grains. Additionally, the effects of G-Y4 on the growth and biofilm formation of GL1 and SNA12 were determined. The results indicated that G-Y4 promoted the growth of GL1 and SNA12 and improved their biofilm-forming ability. Furthermore, the dead cells of G-Y4 were found that could enhance bacterial biofilm formation, and the cell wall polysaccharide (CWPS) produced by G-Y4 was performed to be key substances that promote the formation of bacterial biofilms. Moreover, the structure of soluble cell wall polysaccharides (SCWP) and insoluble cell wall polysaccharide (NCWP) of G-Y4 were studied to determine their contribution to biofilm formation. Results showed that G-Y4-SCWP was α-mannan with the main chain of a →6)-α-d-Manp-(1→ unit and the branch structure of →2)-α-d-Manp-(1. At the same time, G-Y4-NCWP was a glucan rich in ß-(1→3), ß-(1→2), or ß-(1→4) linkages.

In vitro simulated digestion and fecal fermentation of exopolysaccharides from Lacticaseibacillus paracasei GL1.

The prebiotic properties of two purified fractions (GL1-E1 and GL1-E2) of exopolysaccharides (EPSs) from Lacticaseibacillus paracasei GL1 were investigated through in vitro fermentation of pure and human fecal cultures. The results indicated that the simulated digestion under saliva, gastric, and small intestinal conditions had no effect on GL1-E1 and GL1-E2. Additionally, GL1-E1 and GL1-E2 can be used as substrates for Lactobacillus and Lactococcus growth. It was also found that both were gradually degraded and utilized by the gut microbiota. As fermentation proceeded, the pH continued to decrease. Additionally, the total short-chain fatty acid (SCFA) production significantly increased, especially the major SCFA of formic, lactic, and acetic acid. Furthermore, GL1-E1 and GL1-E2 could significantly regulate the composition of the gut microbiota, by increasing the relative abundances of Bacteroides and Phascolarctobacterium, and decreasing the pathogenic bacteria Escherichia-Shigella, Klebsiella, and Fusobacterium. These results suggest that GL1-E1 and GL1-E2 have the potential to be developed as a prebiotic.

Advanced structural characterization and in vitro fermentation prebiotic properties of cell wall polysaccharide from Kluyveromyces marxianus.

Through previous study, the three yeast α-mannans (MPS) from various sources of Kluyveromyces marxianus (LZ-MPS, MC-MPS, and G-MPS) were preliminarily characterized. In this study, the advanced structural characterization and the in vitro human fecal fermentation behavior of the three MPS were investigated. According to the results of this study, the polysaccharide molecules of the three MPS were aggregated in solution, supporting their branched chain structure. After in vitro fermentation, the molecular weight and pH of fermentation broth decreased significantly, indicating that the three MPS could be utilized by human gut microbiota. Meanwhile, the production of total short-chain fatty acids (SCFAs) of the three MPS was promoted, especially the production of propionic acid was 45.55, 38.23, and 38.87 mM, respectively. In particular, the three MPS have the ability to alter the composition of human gut microbiota, especially to promote the proliferation of Bacteroidetes, suggesting that the bioactivities of the three MPS can be significantly influenced by intestine Bacteroidetes. In terms of metabolism, all MPS can promote cofactors, vitamins, amino acid metabolism, and glycan biosynthesis and metabolism of bacteria. In consequence, the three MPS were confirmed to regulate the human gut microbiota, increase the level of SCFAs, promote the metabolisms of bacteria on amino acid and glycan, and improve the intestinal health.

Extraction, isolation, structural characterization and prebiotic activity of cell wall polysaccharide from Kluyveromyces marxianus.

In this study, three yeast α-mannans (LZ-MPS, MC-MPS, and G-MPS) were extracted from different sources of Kluyveromyces marxianus. The total sugar content of the three α-mannans ranged from 91.13-97.10%, whereas no proteins were detected. A structural arrangement was proposed using ultraviolet spectroscopy, Fourier-transform infrared spectroscopy, and one-dimensional and two-dimensional nuclear magnetic resonance. The main chain of the three yeast α-mannans was formed by a →6)-α-D-Manp-(1→ unit, which was slightly different from the repeating unit of the branch structure. The prebiotic potential of LZ-MPS, MC-MPS, and G-MPS was assessed using in vitro fermentation with pure and faecal cultures. The three yeast α-mannans could be utilised as substrates for the growth of Lactobacillus and Lactococcus strains. In addition, the three yeast α-mannans markedly regulated the intestinal microbiota composition by increasing the relative abundances of Bacteroides, Parabacteroides, and Phascolarctobacterium and decreasing the abundance of pathogenic bacteria.

Characterization and Immunological Activity of Exopolysaccharide from Lacticaseibacillus paracasei GL1 Isolated from Tibetan Kefir Grains.

Two exopolysaccharide fractions (GL1-E1 and GL1-E2) of Lacticaseibacillus paracasei GL1 were isolated with the molecular weights of 3.9 × 105 Da and 8.2 × 105 Da, respectively. Both fractions possessed mannose, glucose, and galactose in molar ratios of 1.16:1.00:0.1, and 3.81:1.00:0.12, respectively. A structural arrangement of two fractions was proposed by methylation, one-dimensional and two-dimensional nuclear magnetic resonance experiments. The backbone of GL1-E1 consisted of →4)-α-D-Glcp(1→, →3,4)-α-D-Manp(1→, →3,6)-α-D-Manp(1→, →6)-α-D-Manp(1→, and →6)-α-D-Galp(1→ with α-D-Glcp at branching point. The backbone of GL1-E2 consisted of →4)-α-D-Glcp(1→, →3,4)-α-D-Manp(1→, →3,6)-α-D-Manp(1→, →6)-α-D-Manp(1→, →6)-α-D-Galp(1→, and →4)-ß-D-Manp(1→, and the side chain also consisted of α-D-Manp residue. In addition, the differential scanning calorimetry (DSC) analysis indicated that both GL1-E1 and GL1-E2 had good thermal stability. Furthermore, the two fractions could promote the viability of RAW264.7 cells and exert an immunomodulatory role by enhancing phagocytosis, increasing nitric oxide (NO) release and promoting the expression of cytokines.

Biosynthesis of exopolysaccharide and structural characterization by Lacticaseibacillus paracasei ZY-1 isolated from Tibetan kefir.

Exopolysaccharide (EPS) was produced by Lacticaseibacillus paracasei ZY-1 isolated from Tibetan kefir grains, and the preliminary structure of two EPS fractions (EPS1 and EPS2) was investigated. NMR analysis revealed that the backbone of higher producing EPS1 was consisted of →6)-α-D-Manp-(1→, →2,6)-α-D-Glcp-(1→, α-D-Manp-(1→, →2)-α-D-Glcp-(1→, →3)-α-D-Manp-(1→, →6)-α-D-Glcp-(1→. Furthermore, an eps gene cluster that encodes the glycosyltransferase and relevant proteins for EPS biosynthesis was identified on the basis of bioinformation analysis of the complete genome. RT-qPCR results indicated that wzd (ZY-1_2260) and wze (ZY-1_2259) might be essential genes involved in EPS production. Meanwhile, the synthetic mechanism of EPS1 in L. paracasei ZY-1 was further proposed. Besides, the crude and purified EPS showed certain scavenging activities against DPPH, hydroxyl and ABTS radicals. Results provided a better understanding of EPS biosynthesis in L. paracasei ZY-1 at the gene level.