Antibacterial Mechanism of Rhamnolipids against Bacillus cereus and Its Application in Fresh Wet Noodles.

Bacillus cereus (B. cereus) is a common foodborne pathogen causing food poisoning incidents. This study aimed to evaluate the antibacterial activity and underlying mechanism of rhamnolipids (RLs) against B. cereus. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of RLs for B. cereus were determined to be 16.0 mg/L and 32.0 mg/L, respectively. Scanning electron microscopy and fluorescence microscope images, as well as data of membrane potential, relative electric conductivity, and leakage of intracellular components revealed that RLs disrupted the integrity of the cell membrane. Furthermore, the reactive oxygen species content, catalase (CAT) and superoxide dismutase (SOD) activity indicated that RLs activated the oxidative stress response of B. cereus in response to RLs. Fresh wet noodles (FWN) were used as a food model, and RLs showed a significant killing effect on B. cereus with a sustained inhibitory effect at the concentrations ranging from 128.0 to 1024.0 mg/kg. Additionally, RLs promoted the conversion of free water to bound water in FWN, which improved the storage of FWN and made the taste more resilient and chewy. These results suggest that RLs could be a potential alternative to antimicrobial agents and preservatives for applications in food processing.

Mannosylerythritol lipids: dual inhibitory modes against Staphylococcus aureus through membrane-mediated apoptosis and biofilm disruption.

Mannosylerythritol lipids (MELs) are novel biosurfactants performing excellent physical-chemical properties as well as bioactivities. This study is aimed to explore the antibacterial and antibiofilm activity of mannosylerythritol lipids against foodborne gram-positive Staphylococcus aureus. The results of growth curve and survival rate revealed the significant inhibitory effect of MELs against S. aureus. The visualized pictures by scanning electron microscope and transmission electron microscope exposed apparent morphological and ultrastructure changes of MEL-treated cells. Furthermore, flow cytometry confirmed that MELs have promoted cell apoptosis and damaged the cell membrane. Notably, MEL-A also exhibited outstanding antibiofilm activity against S. aureus biofilm on different material surfaces including polystyrene, glass, and stainless steel, verified by confocal laser scanning microscope. These findings suggest that the antimicrobial activity of MELs is related to inhibit planktonic cells and biofilm of S. aureus, indicating that it has potential to be an alternative to antibacterial agents and preservatives applied into food processing.Key Points • MELs have strong antibacterial activity against Staphylococcus aureus.• MELs mainly damage the cell membrane of Staphylococcus aureus.• Mannosylerythritol lipids inhibit the bacterial adhesion to remove biofilm.

Synthesis of gold nanoparticles derived from mannosylerythritol lipid and evaluation of their bioactivities.

In this study, we introduce a simple and green method for synthesis of gold nanoparticles (AuNPs) using microbial glycolipid mannosylerythritol lipid (MEL) produced from Ustilago maydis CGMCC 5.203 and to evaluate their biomedical activities. MEL was found 10.3 g/L using sunflower oil. The formation of MEL-AuNPs was verified using UV-visible spectrum, XRD, TEM, FTIR, SEM, and EDX. In the biomedical examinations, MEL-AuNPs demonstrated potential cytotoxicity against HepG2 cells, and IC50 values were found to be 100 and 75 µg/mL for 24 h and 48 h of exposure, respectively, which indicates its good performance against cancer cells. The IC50 value of MEL-AuNPs was found to be 115 and 124 µg/mL for DPPH and ABTS scavenging activities, respectively. The biosynthesized MEL-AuNPs significantly inhibited cell growth of pathogenic Gram-positive and Gram-negative bacteria. These findings indicated that MEL plays a crucial role in the rapid biofabrication method of metallic NPs possessed the potential of biomedical activities.

Production and characterization of a new glycolipid, mannosylerythritol lipid, from waste cooking oil biotransformation by Pseudozyma aphidis ZJUDM34.

Mannosylerythritol lipids (MELs) are glycolipids possessing unique biosurfactant properties. However, the prices of substrates currently used for MEL formation caused its unsustainable commercial development. Waste cooking oil poses significant ecological and economical problems. Thus, the production of MELs from used waste cooking oil using the biotransformation route is one of the better alternatives to utilize it efficiently and economically. This work aims at the production of MELs using waste cooking oil instead of soybean oil and evaluating the major characteristics and compositions of MELs. The titers reached 61.50 g/L by the optimization of culture medium, higher than the counterpart (10.25 ± 0.32 g/L) of the nonoptimized medium. MELs exhibited good surface activity and better performance in contrast to MELs grown on soybean oil. The water phase behavior of MEL-A was also evaluated. The process showed higher productivity of MELs with better surface activity and application stability than the conventional process using soybean oil. The findings of this study imply that the use of inexpensive fermentation substrates associated with straightforward downstream processing is expected to have a great impact on the economy of MEL production.

Comparative study of antidiabetic, bactericidal, and antitumor activities of MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA nanocomposites prepared by using MEL and gum arabic.

In this study, a variety of nanocomposites, namely, MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA were biosynthesized using MEL and gum arabic to serve in biomedical applications. The synthesized nanocomposites were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and FTIR spectroscopy. The physicochemical properties and biomedical activities of the synthesized nanocomposites were investigated. The Ag-ZnO/MEL/GA nanocomposites showed greater antidiabetic activity against α-amylase and α-glucosidase, and higher antibacterial activity compared to MEL@AgNPs and MEL@ZnONPs. Furthermore, HepG2 cells were exposed to MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA nanocomposites for 24 h and their IC50 values were 63.25, 26.91 and 28.97 µg mL-1 (P < 0.05), respectively. According to this comparative study, it is apparent that the Ag-ZnO/MEL/GA nanocomposites have a great potential to serve as antitumor agents against HepG2, and antidiabetic and antibacterial agents.

Fungal chitosan from Agaricus bisporus (Lange) Sing. Chaidam increased the stability and antioxidant activity of liposomes modified with biosurfactants and loading betulinic acid.

Agaricus bisporus (Lange) Sing. Chaidam, a special brown mushroom with thick body indigenous in Chaidam basin, was used for fungal chitosan extraction. FTIR, XRD and DSC spectra showed that fungal chitosan was similar to commercial chitosan from aquatic sources. Fungal chitosan and commercial chitosan were used to coat on betulinic acid-loaded liposomes modified with biosurfactants mannosylerythritol lipid A (MEL-A), respectively. After chitosan coating, the mean size, zeta potential and encapsulation efficiency of both liposomes increased. The liposomes coated with fungal chitosan were discovered to have smaller size and higher zeta potential. Furthermore, the wall material MEL-A and coating material chitosan endue liposomes with increased antioxidant capacity. Fungal chitosan coated liposomes also have stronger antioxidant effects than commercial chitosan. The findings implied that the fungal chitosan coated liposomes modified with MEL-A can be considered as a promising delivery system with enhanced antioxidant effects for bioactive compounds.

Preparation, Characterization, and Antibacterial Effects of Chitosan Nanoparticles Embedded with Essential Oils Synthesized in an Ionic Liquid Containing System.

Several chitosan sodium tripolyphosphate (TPP) nanoparticles embedded with Torreya grandis aril essential oils (TEOs) were synthesized using an emulsion-ionic gelation technique. Mannosylerythritol lipid A (MEL-A), a type of biosurfactant, was selected as the emulsifier. In order to replace acetic acid, an ionic liquid (IL) was employed to dissolve chitosan. The physical properties, diameters, morphology, embedding rate, and antibacterial effects of those essential oil loaded chitosan (CS) nanoparticles were characterized. The results demonstrated that chitosan nanoparticles can be successfully prepared in an ionic liquid containing system and the diameters for nanoparticles in acetic acid and ionic liquid solutions are 144.1 ± 1.457 and 219.0 ± 4.045 nm. After loading with essential oils, the size increased to 349.6 ± 10.55 and 542.9 ± 16.74 nm, respectively. Antibacterial properties were investigated by the observation of the inhibition zone against S. aureus. The results revealed that TEO loaded nanoparticles synthesized in acid and IL aqueous systems have stronger antibacterial activities than CS nanoparticles.

Cell-Free Production of Pentacyclic Triterpenoid Compound Betulinic Acid from Betulin by the Engineered Saccharomyces cerevisiae.

Betulinic acid is a product of plant secondary metabolism which has shown various bioactivities. Several CYP716A subfamily genes were recently characterized encoding multifunctional oxidases capable of C-28 oxidation. CYP716A12 was identified as betulin C-28 oxidase, capable of modifying betulin. This study aimed to induce the transformation of betulin to betulinic acid by co-expressing enzymes CYP716A12 from Medicago truncatula and ATR1 from Arabidopsis thaliana in Saccharomyces cerevisiae. The microsome protein extracted from the transgenic yeast successfully catalyzed the transformation of betulin to betulinic acid. We also characterized the optimization of cell fragmentation, protein extraction method, and the conversion conditions. Response surface methodology was implemented, and the optimal yield of betulinic acid reached 18.70%. After optimization, the yield and the conversion rate of betulin were increased by 83.97% and 136.39%, respectively. These results may present insights and strategies for the sustainable production of betulinic acid in multifarious transgenic microbes.

Characterization, enhancement and modelling of mannosylerythritol lipid production by fungal endophyte Ceriporia lacerate CHZJU.

The glycolipid biosurfactants mannosylerythritol lipids (MELs) attract great attention for their biodegradability, super emulsifying properties and versatile bioactivities. In this study, the MEL deriving from Ceriporia lacerate CHZJU was identified as MEL-A, and its critical micelle concentration and emulsifying activities were assessed. To examine the production of MELs from Ceriporia lacerate, a Plackett-Burman design and response surface methodology were used to optimize the culture nutrients. The optimal medium contains 1g/L yeast extract, 1.5g/L (NH4)2SO4, 0.5g/L KH2PO4, 0.04g/L CaCl2, 119.6mL/L soybean oil and 0.297g/L MnSO4. Subsequent verification revealed that the yield of MELs was 129.64±5.67g/L. Furthermore, an unstructured kinetic model was developed for mycelial growth, MEL production and substrate utilization. This work provides insight into Ceriporia lacerate CHZJU, a predominant fungus producing MEL-A. Optimization using response surface methodology enhanced the mannosylerythritol lipid recovery. Importantly, we developed fermentation kinetic modelling for mannosylerythritol lipid production.

Characterization and Inducing Melanoma Cell Apoptosis Activity of Mannosylerythritol Lipids-A Produced from Pseudozyma aphidis.

Mannosylerythritol lipids (MELs) are natural glycolipid biosurfactants which have potential applications in the fields of food, cosmetic and medicine. In this study, MELs were produced from vegetable oil by Pseudozyma aphidis. Their structural data through LC/MS, GC/MS and NMR analysis revealed that MEL-A with two acetyls was the major compound and the identified homologs of MEL-A contained a length of C8 to C14 fatty acid chains. This glycolipid exhibited a surface tension of 27.69 mN/m at a critical micelle concentration (CMC), self-assembling into particles in the water solution. It was observed to induce cell growth-inhibition and apoptosis of B16 melanoma cells in a dose-dependent manner, as well as cause cell cycle arrest at the S phase. Further quantitative RT-PCR analysis and western blotting revealed an increasing tendency of both mRNA and protein expressions of Caspase-12, CHOP, GRP78 and Caspase-3, and a down-regulation of protein Bcl-2. Combined with the up regulation of signaling IRE1 and ATF6, it can be speculated that MEL-A-induced B16 melanoma cell apoptosis was associated with the endoplasmic reticulum stress (ERS).