Molecular and Phenotypic Investigation on Antibacterial Activities of Limonene Isomers and Its Oxidation Derivative against Xanthomonas oryzae pv. oryzae.

Xanthomonas oryzae pv. oryzae (Xoo) causes a devastating bacterial leaf blight in rice. Here, the antimicrobial effects of D-limonene, L-limonene, and its oxidative derivative carveol against Xoo were investigated. We revealed that carveol treatment at ≥ 0.1 mM in liquid culture resulted in significant decrease in Xoo growth rate (> 40%) in a concentration-dependent manner, and over 1 mM, no growth was observed. The treatment with D-limonene and L-limonene also inhibited the Xoo growth but to a lesser extent compared to carveol. These results were further elaborated with the assays of motility, biofilm formation and xanthomonadin production. The carveol treatment over 1 mM caused no motilities, basal level of biofilm formation (< 10%), and significantly reduced xanthomonadin production. The biofilm formation after the treatment with two limonene isomers was decreased in a concentration-dependent manner, but the degree of the effect was not comparable to carveol. In addition, there was negligible effect on the xanthomonadin production mediated by the treatment of two limonene isomers. Field emission-scanning electron microscope (FE-SEM) unveiled that all three compounds used in this study cause severe ultrastructural morphological changes in Xoo cells, showing shrinking, shriveling, and holes on their surface. Moreover, quantitative real-time PCR revealed that carveol and D-limonene treatment significantly down-regulated the expression levels of genes involved in virulence and biofilm formation of Xoo, but not with L-limonene. Together, we suggest that limonenes and carveol will be the candidates of interest in the development of biological pesticides.

Isolation of Lactiplantibacillus sp. from Korean salted and fermented seafoods for effective fermentation of strawberry leaf extract: enhanced anti-inflammatory activity.

Berries are rich in bioactive phytochemicals and phenolic compounds. In the present study, strawberry leaves obtained from Nangsan-myeon, Jeollabuk-do, Korea in 2019 were fermented using Lactiplantibacillus plantarum B1-4 and studied for antioxidant and anti-inflammatory properties. Comparative testing of active ingredients in the raw and fermented extract showed an increase in total polyphenol content and total flavonoid content from 92.0 mg GAE/g and 40.4 mg QE/g, respectively, to 116.1 mg GAE/g and 49.5 mg QE/g, respectively, in fermented extracts. Similarly, catechin content in fermented extract was increased by 26.5% and epicatechin content was decreased by 9.3%. Total and reducing sugar contents in the fermented extract were decreased by 58.4% and 50.4%. DPPH radical scavenging activity of the extracts before and after fermentation increased by about 10.7% from 35.6 to 46.3% at 250 µg/mL and ABTS by about 6.0% from 48.6 to 54.6% at 500 µg/mL. Cytotoxicity assay confirmed that fermented extract caused no harm to chromatid structure of RAW 264.7 cells up to 500 µg/mL concentration. Fermented extracts (400 µg/mL) reduced nitric oxide production (9.7%) and the levels of TNF-α (18.1%) and IL-6 (11.8%), making them ideal for integration into skin care products. The significant functional groups present in raw and fermented extracts were identified using FTIR. Thus, this study adds to the notion of using fermented extracts in functional foods due to their anti-inflammatory properties.