Physiological Roles of Short-Chain and Long-Chain Menaquinones (Vitamin K2) in Lactococcus cremoris

Development of optimized functional clove fortified probiotic yoghurt

We focused on assessing the antimicrobial effects of functional yoghurts supplemented with clove and probiotics. The formulation of aqueous clove extract (ACE) incorporated with probiotic yoghurt (Streptococcus thermophilus, Lactobacillus bulgaricus, and Lactococcus lactis) was optimised in terms of aqueous clove extract concentrations (2.5-7.5% v/v), fermentation temperature (32-42 °C), and total culture concentration (1.5-4.5% v/v). pH, titratable acidity, syneresis, water holding capacity, viscosity, springiness, color difference, lactic acid bacteria viability, and the antibacterial property of 17 runs were determined as responses using Box-Behnken design. The results indicate that elevated ACE concentration leads to a significant (p < 0.05) increase in titratable acidity, antibacterial effectiveness (against K. pneumoniae and P. aeruginosa), springiness, and color profile. Conversely, an elevated fermentation temperature significantly (p < 0.05) reduces pH and L. bulgaricus viability (log CFU/mL). Additionally, there is a significant (p < 0.05) decline in S. thermophilus and L. lactis viability (log CFU/mL) as well as springiness with an increased culture concentration. The optimal conditions identified are 7.5% (v/v) ACE concentration, a fermentation temperature of 36.6 °C (37 °C), and a total culture concentration of 4.5% (v/v), resulting in a 79% desirability score. The spectra of components were mainly obtained at wavelength of 3258 cm-1, 1636 cm-1 and 1075 cm-1 in Fourier transform infrared (FTIR) spectroscopy of optimized functional yoghurt. Where, 3258 cm-1 corresponds to the stretching vibration of O-H (hydroxyl) groups, 1636 cm-1 corresponds to the C=O (carbonyl) stretching vibration, and 1075 cm-1 corresponds to the C-O (ether or alcohol) stretching vibration.

Construction of white-rot fungal-bacterial consortia with improved ligninolytic properties and stable bacterial community structure

It is believed that wood-rot fungi change their wood decay activities due to influences from co-existing bacterial communities; however, it is difficult to elucidate experimentally the interaction mechanisms in fungal-bacterial consortia because the bacterial community structure is quite unstable and readily changes. Indeed, the wood decay properties of fungal-bacterial consortia consisting of a white-rot fungus Phanerochaete sordida YK-624 and a natural bacterial community changed dramatically during several sub-cultivations on wood. Therefore, development of a sub-cultivation method that imparts stability to the bacterial community structure and fungal phenotype was attempted. The adopted method using agar medium enabled maintenance of fungal phenotypes relating to wood decay and the bacterial community even through dozens of repetitive sub-cultures. Some bacterial metabolic pathways identified based on gene predictions were screened as candidates involved in P. sordida-bacterial interactions. In particular, pathways related to prenyl naphthoquinone biosynthesis appeared to be involved in an interaction that promotes higher lignin degradation selectivity by the consortia, as naphthoquinone derivatives induced phenol-oxidizing activity. Based on these results, it is expected that detailed analyses of the relationship between the wood-degrading properties of white-rot fungal-bacterial consortia and bacterial community structures will be feasible using the sub-cultivation method developed in this study.

The Extracellular Electron Transport Pathway Reduces Copper for Sensing by the CopRS Two-Component System under Anaerobic Conditions in Listeria monocytogenes

The renowned antimicrobial activity of copper stems in part from its ability to undergo redox cycling between Cu^1+/2+ oxidation states. Bacteria counter copper toxicity with a network of sensors that often include two-component signaling systems to direct transcriptional responses. As in typical two-component systems, ligand binding by the extracellular domain of the membrane bound copper sensor component leads to phosphorylation and activation of the cognate response regulator transcription factor. In Listeria monocytogenes, the plasmid-borne CopRS two-component system upregulates both copper resistance and lipoprotein remodeling genes upon copper challenge, but the oxidation state of copper bound by CopS is unknown. Herein, we show CopS utilizes a triad of key residues (His-His-Phe) that are predicted to be at the dimerization interface and that are analogous with the Escherichia coli CusS copper sensor to specifically bind Cu¹⁺/Ag¹⁺ and activate CopR transcription. We demonstrate Cu²⁺ only induces CopRS if first reduced by electron transport systems, as strains lacking menaquinone carriers were unable to respond to Cu²⁺. The flavin-dependent extracellular electron transport system (EET) was the main mechanism for metal reduction, capable of either generating inducing ligand (Cu²⁺ to Cu¹⁺) or removing it by precipitation (Ag¹⁺ to Ag⁰). We show that EET flux is directly proportional to the rate of Cu²⁺ reduction and that since EET activity is low under oxygenated conditions when a competing respiratory chain is operating, CopRS signaling in turn is activated only under anaerobic conditions. EET metal reduction thus sensitizes cells to copper while providing resistance to silver under anaerobic growth. IMPORTANCE Two-component extracellular copper sensing from the periplasm of Gram-negative bacteria has been well studied, but copper detection at the cell surface of the Gram-positive L. monocytogenes is less understood. Collectively, our results show that EET is most active under anaerobic conditions and reduces Cu²⁺ and Ag¹⁺ to, respectively, generate or remove the monovalent ligands that directly bind to CopS and lead to the induction of lipoprotein remodeling genes. This reducing activity regulates CopRS signaling and links the upregulation of copper resistance genes with increasing EET flux. Our studies provide insight into how a two-component copper sensing system is integrated into a model monoderm Firmicute to take cues from the electron transport chain activity.

Lactococcus lactis‑fermented spinach juice suppresses LPS‑induced expression of adhesion molecules and inflammatory cytokines through the NF‑κB pathway in HUVECs

Spinach (Spinacia oleracea L.), a green leafy vegetable, is widely regarded as a functional food due to its biological activities; however, to the best of our knowledge, there are no previous studies that have investigated the protective effects of fermented spinach against endothelial dysfunction and its underlying mechanisms. Therefore, this study investigated the effects and possible mechanisms of action of fresh spinach juice (S.juice) and fermented S.juice on lipopolysaccharide (LPS)-induced inflammatory responses in human umbilical vein endothelial cells (HUVECs). The HUVECs were treated with S.juice and fermented S.juice for 18 h before LPS exposure, and the levels of cytokines and chemokines, such as monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6), were detected using enzyme-linked immunosorbent assays (ELISA). Furthermore, to examine the changes in inflammatory responses to the two treatments, immunofluorescence analysis was used to visualize the nuclear translocation of nuclear factor-κB (NF-κB). Western blot analysis was also performed to detect the differences in the expression of endothelial cell adhesion molecules, specifically vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). Both S.juice and fermented S.juice inhibited the LPS-induced expression of MCP-1 and IL-6, and suppressed VCAM-1 and ICAM-1. Additionally, fermented S.juice inhibited the LPS-induced activation of NF-κB and degradation of the inhibitor of NF-κB (IκBα) in an LPS dose-dependent manner. These results suggest that the anti-inflammatory effect of vitamin K₂-enriched fermented S.juice is mediated by the suppression of the NF-κB pathway, suggesting its potential as a novel therapeutic candidate for inflammatory cardiovascular disease.