Aerobic spore-forming bacteria associated with ropy bread: Identification, characterization and spoilage potential assessment

Aerobic spore-forming (ASF) bacteria have been reported to cause ropiness in bread. Sticky and stringy degradation, discoloration, and an odor reminiscent of rotting fruit are typical characteristics of ropy bread spoilage. In addition to economic losses, ropy bread spoilage may lead to health risks, as virulent strains of ASF bacteria are not uncommon. However, the lack of systematic approaches to quantify physicochemical spoilage characteristics makes it extremely difficult to assess rope formation in bread. To address this problem, the aim of this study was to identify, characterize and objectively assess the spoilage potential of ASF bacteria associated with ropy bread. Hence, a set of 82 ASF bacteria, including isolates from raw materials and bakery environments as well as strains from international culture collections, were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and their species identity confirmed by 16S rRNA and gyrA or panC gene sequencing. A standardized approach supported by objective colorimetric measurements was developed to assess the rope-inducing potential (RIP) of a strain by inoculating autoclaved bread slices with bacterial spores. In addition, the presence of potential virulence factors such as swarming motility or hemolysis was investigated. This study adds B. velezensis, B. inaquosorum and B. spizizenii to the species potentially implicated of causing ropy bread spoilage. Most importantly, this study introduces a standardized classification protocol for assessing the RIP of a bacterial strain. Colorimetric measurements are used to objectively quantify the degree of breadcrumb discoloration. Furthermore, our results indicate that strains capable of inducing rope spoilage in bread often exhibit swarming motility and virulence factors such as hemolysis, raising important food quality considerations.

Lipopeptide C17 Fengycin B Exhibits a Novel Antifungal Mechanism by Triggering Metacaspase-Dependent Apoptosis in Fusarium oxysporum

Fusarium wilt is a worldwide soil-borne fungal disease caused by Fusarium oxysporum that causes serious damage to agricultural products. Therefore, preventing and treating fusarium wilt is of great significance. In this study, we purified ten single lipopeptide fengycin components from Bacillus subtilis FAJT-4 and found that C17 fengycin B inhibited the growth of F. oxysporum FJAT-31362. We observed early apoptosis hallmarks, including reactive oxygen species accumulation, mitochondrial dysfunction, and phosphatidylserine externalization in C17 fengycin B-treated F. oxysporum cells. Further data showed that C17 fengycin B induces cell apoptosis in a metacaspase-dependent manner. Importantly, we found that the expression of autophagy-related genes in the TOR signaling pathway was significantly upregulated; simultaneously, the accumulation of acidic autophagy vacuoles in F. oxysporum cell indicated that the autophagy pathway was activated during apoptosis induced by C17 fengycin B. Therefore, this study provides new insights into the antifungal mechanism of fengycin.

A promising antifungal lipopeptide from Bacillus subtilis: its characterization and insight into the mode of action

Emerging resistance of fungal pathogens and challenges faced in drug development have prompted renewed investigations into novel antifungal lipopeptides. The antifungal lipopeptide AF3 reported here is a natural lipopeptide isolated and purified from Bacillus subtilis. The AF3 lipopeptide's secondary structure, functional groups, and the presence of amino acid residues typical of lipopeptides were determined by circular dichroism, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The lipopeptide's low minimum inhibitory concentrations (MICs) of 4-8 mg/L against several fungal strains demonstrate its strong antifungal activity. Biocompatibility assays showed that ~ 80% of mammalian cells remained viable at a 2 × MIC concentration of AF3. The treated Candida albicans cells examined by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy clearly showed ultrastructural alterations such as the loss of the cell shape and cell membrane integrity. The antifungal effect of AF3 resulted in membrane permeabilization facilitating the uptake of the fluorescent dyes-acridine orange (AO)/propidium iodide (PI) and FUN-1. Using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 4-(2-[6-(dioctylamino)-2-naphthalenyl] ethenyl)-1-(3-sulfopropyl) pyridinium inner salt (di-8-ANEPPS), we observed that the binding of AF3 to the membrane bilayer results in membrane disruption and depolarization. Flow cytometry analyses revealed a direct correlation between lipopeptide activity, membrane permeabilization (~ 75% PI uptake), and reduced cell viability. An increase in 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescence demonstrates endogenous reactive oxygen species production. Lipopeptide treatment appears to induce late-stage apoptosis and alterations to nuclear morphology, suggesting that AF3-induced membrane damage may lead to a cellular stress response. Taken together, this study illustrates antifungal lipopeptide's potential as an antifungal drug candidate. KEY POINTS: • The studied lipopeptide variant AF3 displayed potent antifungal activity against C. albicans • Its biological activity was stable to proteolysis • Analytical studies demonstrated that the lipopeptide is essentially membranotropic and able to cause membrane dysfunction, elevated ROS levels, apoptosis, and DNA damage.

The elucidation of the multimodal action of the investigational anti-Candida lipopeptide (AF4) lead from Bacillus subtilis

Background: Candida species are the main etiological agents for candidiasis, and Candida albicans are the most common infectious species. Candida species' growing resistance to conventional therapies necessitates more research into novel antifungal agents. Antifungal peptides isolated from microorganisms have potential applications as novel therapeutics. AF4 a Bacillus-derived lipopeptide demonstrating broad-spectrum antifungal activity has been investigated for its ability to cause cell death in Candida species via membrane damage and oxidative stress. Methods: Using biophysical techniques, the secondary structure of the AF4 lipopeptide was identified. Scanning electron microscopy and confocal microscopy with fluorescent dyes were performed to visualise the effect of the lipopeptide. The membrane disruption and permeabilization were assessed using the 1,6-diphenyl hexatriene (DPH) fluorescence assay and flow cytometric (FC) assessment of propidium iodide (PI) uptake, respectively. The reactive oxygen species levels were estimated using the FC assessment. The induction of apoptosis and DNA damage were studied using Annexin V-FITC/PI and DAPI. Results: Bacillus-derived antifungal variant AF4 was found to have structural features typical of lipopeptides. Microscopy imaging revealed that AF4 damages the surface of treated cells and results in membrane permeabilization, facilitating the uptake of the fluorescent dyes. A loss of membrane integrity was observed in cells treated with AF4 due to a decrease in DPH fluorescence and a dose-dependent increase in PI uptake. Cell damage was also determined from the log reduction of viable cells treated with AF4. AF4 treatment also caused elevated ROS levels, induced phosphatidylserine externalisation, late-stage apoptosis, and alterations to nuclear morphology revealed by DAPI fluorescence. Conclusion: Collectively, the mode of action studies revealed that AF4 acts primarily on the cell membrane of C. albicans and has the potential to act as an antifungal drug candidate.

Synergistic antifungal activity and potential mechanism of action of a glycolipid-like compound produced by Streptomyces blastmyceticus S108 against Candida clinical isolates

AIM

The present study aimed to investigate a novel antifungal compound produced by Streptomyces blastmyceticus S108 strain. Its effectiveness against clinical isolates of Candida species and its synergistic effect with conventional antifungal drugs were assessed, and its molecular mechanism of action was further studied against Candida albicans.

METHODS AND RESULTS

A newly isolated strain from Tunisian soil, S. blastmyceticus S108, showed significant antifungal activity against Candida species by well diffusion method. The butanolic extract of S108 strain supernatant exhibited the best anti-Candida activity with a minimal inhibitory concentration (MIC) value of 250 μg ml-1, determined by the microdilution method. The bio-guided purification steps of the butanolic extract were performed by chromatographic techniques. Among the fractions obtained, F13 demonstrated the highest level of activity, displaying a MIC of 31.25 μg ml-1. Gas chromatography-mass spectrometry and electrospray ionization mass spectrometry analyses of this fraction (F13) revealed the glycolipidic nature of the active molecule with a molecular weight of 685.6 m/z. This antifungal metabolite remained stable to physicochemical changes and did not show hemolytic activity even at 4MIC corresponding to 125 µg ml-1 toward human erythrocytes. Besides, the glycolipid compound was combined with 5-flucytosine and showed a high synergistic effect with a fractional inhibitory concentration index value 0.14 against C. albicans ATCC 10231. This combination resulted in a decrease of MIC values of 5-flucytosine and the glycolipid-like compound by 8- and 64-fold, respectively. The examination of gene expression in treated C. albicans cells by quantitative polymerase chain reaction (qPCR) revealed that the active compound tested alone or in combination with 5-flucytosine blocks the ergosterol biosynthesis pathway by downregulating the expression of ERG1, ERG3, ERG5, ERG11, and ERG25 genes.

CONCLUSION AND IMPACT OF THE STUDY

The new glycolipid-like compound, produced by Streptomyces S108 isolate, could be a promising drug for medical use against pathogenic Candida isolates.

The Secondary Metabolites of Bacillus subtilis Strain Z15 Induce Apoptosis in Hepatocellular Carcinoma Cells

The lipopeptides produced by Bacillus subtilis have anti-cancer potential. We had previously identified a secondary metabolite of B. subtilis strain Z15 (BS-Z15), which has an operon that regulates lipopeptide synthesis, and also demonstrated that the fermentation products of this strain exerted antioxidant and pro-immune effects. The purpose of this study was to investigate in vitro and in vivo the anticancer effects of BS-Z15 secondary metabolites (BS-Z15 SMs) on hepatocellular carcinoma (HCC) cells. BS-Z15 SMs significantly inhibited H22 cell-derived murine xenograft tumor growth without any systemic toxicity. In addition, BS-Z15 SMs decreased the viability of H22 cells and BEL-7404 cells in vitro with respective IC50 values of 33.83 and 27.26 µg/mL. Consistent with this, BS-Z15 SMs induced apoptosis and G0/G1 phase arrest in the BEL-7404 cells, and the mitochondrial membrane potential was also significantly reduced in a dose-dependent manner. Mechanistically, BS-Z15 SMs upregulated the pro-apoptotic p53, Bax, cytochrome C, and cleaved-caspase-3/9 proteins and downregulated the anti-apoptotic Bcl-2. These findings suggest that the induction of apoptosis in HCC cells by BS-Z15 SMs may be related to the mitochondrial pathway. Thus, the secondary metabolites of B. subtilis strain Z15 are promising to become new anti-cancer drugs for the clinical treatment of liver cancer.

Characterization ofantifungal properties of lipopeptide-producing Bacillus velezensis strains and their proteome-based response to the phytopathogens, Diaporthe spp

Introduction: B. velezensis strains are of interest in agricultural applications due to their beneficial interactions with plants, notable through their antimicrobial activity. The biocontrol ability of two new lipopeptides-producing B. velezensis strains ES1-02 and EFSO2-04, against fungal phytopathogens of Diaporthe spp., was evaluated and compared with reference strains QST713 and FZB42. All strains were found to be effective against the plant pathogens, with the new strains showing comparable antifungal activity to QST713 and slightly lower activity than FZB42. Methods: Lipopeptides and their isoforms were identified by high-performance thin-layer chromatography (HPTLC) and mass spectrometric measurements. The associated antifungal influences were determined in direct in vitro antagonistic dual culture assays, and the inhibitory growth effects on Diaporthe spp. as representatives of phytopathogenic fungi were determined. The effects on bacterial physiology of selected B. velezensis strains were analyzed by mass spectrometric proteomic analyses using nano-LC-MS/MS. Results and Discussion: Lipopeptide production analysis revealed that all strains produced surfactin, and one lipopeptide of the iturin family, including bacillomycin L by ES1-02 and EFSO2-04, while QST713 and FZB42 produced iturin A and bacillomycin D, respectively. Fengycin production was however only detected in the reference strains. As a result of co-incubation of strain ES1-02 with the antagonistic phytopathogen D. longicolla, an increase in surfactin production of up to 10-fold was observed, making stress induction due to competitors an attractive strategy for surfactin bioproduction. An associated global proteome analysis showed a more detailed overview about the adaptation and response mechanisms of B. velezensis, including an increased abundance of proteins associated with the biosynthesis of antimicrobial compounds. Furthermore, higher abundance was determined for proteins associated with oxidative, nitrosative, and general stress response. In contrast, proteins involved in phosphate uptake, amino acid transport, and translation were decreased in abundance. Altogether, this study provides new insights into the physiological adaptation of lipopeptide-producing B. velezensis strains, which show the potential for use as biocontrol agents with respect to phytopathogenic fungi.

Effect and regulation of fatty acids on bacillomycin D synthesis

Bacillomycin D is a cyclic antimicrobial lipopeptide that has excellent antifungal effects, but its application is limited due to its low yield. At present, it is not clear whether fatty acids regulate the synthesis of bacillomycin D. Therefore, the effects of nine fatty acids on the yield of bacillomycin D produced by Bacillus amyloliquefaciens fmbJ were studied. The results showed that sodium propionate, propionic acid, and butyric acid could increase the yield of bacillomycin D by 44, 40, and 10%, respectively. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression levels of bacillomycin D synthesis gene, signaling factors and genes related to fatty acid metabolism, so as to explore the mechanism of sodium propionate regulating bacillomycin D synthesis. In conclusion, sodium propionate could accelerate the tricarboxylic acid cycle and promoted spore formation, cell movement, the secretion of extracellular protease and the transcription of bacillomycin D synthesis gene by upregulating the expression of signal factors degU, degQ, sigH, sigM and spo0A and ultimately promoted the synthesis of bacillomycin D. In this study, the mechanism of sodium propionate increasing bacillomycin D production was explored from multiple perspectives, which provided theoretical support for the large-scale production of bacillomycin D and was expected to promote its wide application in food, agriculture and medicine fields.

Functional Characterization of a Bacillus-Derived Novel Broad-Spectrum Antifungal Lipopeptide Variant against Candida tropicalis and Candida auris and Unravelling Its Mode of Action

Limited treatment options, recalcitrance, and resistance to existing therapeutics encourage the discovery of novel antifungal leads for alternative therapeutics. Antifungal lipopeptides have emerged as potential candidates for developing new and alternative antifungal therapies. In our previous studies, we isolated and identified the lipopeptide variant AF4 and purified it to homogeneity via chromatography from the cell-free supernatant of Bacillus subtilis. AF4 was found to have broad-spectrum antifungal activity against more than 110 fungal isolates. In this study, we found that clinical isolates of Candida tropicalis and Candida auris exposed to AF4 exhibited low MICs of 4 to 8 mg/L. Time-kill assays indicated the in vitro pharmacodynamic potential of AF4. Biocompatibility assays demonstrated ~75% cell viability at 8 mg/L of AF4, indicating the lipopeptide's minimally cytotoxic nature. In lipopeptide-treated C. tropicalis and C. auris cells, scanning electron microscopy revealed damage to the cell surface, while confocal microscopy with acridine orange(AO)/propidium iodide (PI) and FUN-1 indicated permeabilization of the cell membrane, and DNA damage upon DAPI (4',6-diamidino-2-phenylindole) staining. These observations were corroborated using flow cytometry (FC) in which propidium iodide, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), and rhodamine 123 (Rh123) staining of cells treated with AF4 revealed loss of membrane integrity, increased reactive oxygen species (ROS) production, and mitochondrial membrane dysfunction, respectively. Membrane perturbation was also observed in the 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence study and the interaction with ergosterol was observed by an ergosterol binding assay. Decreased membrane dipole potential also indicated the probable binding of lipopeptide to the cell membrane. Collectively, these findings describe the mode of action of AF4 against fungal isolates by membrane disruption and ROS generation, demonstrating its antifungal potency. IMPORTANCE C. tropicalis is a major concern for candidiasis in India and C. auris has emerged as a resistant yeast causing difficult-to-treat infections. Currently, amphotericin B (AMB) and 5-flucytosine (5-FC) are the main therapeutics for systemic fungal infections; however, the nephrotoxicity of AMB and resistance to 5-FC is a serious concern. Antifungal lead molecules with low adverse effects are the need of the hour. In this study, we briefly describe the antifungal potential of the AF4 lipopeptide and its mode of action using microscopy, flow cytometry, and fluorescence-based assays. Our investigation reveals the basic mode of action of the investigated lipopeptide. This lipopeptide with broad-spectrum antifungal potency is apparently membrane-active, and there is a smaller chance that organisms exposed to such a compound will develop drug resistance. It could potentially act as a lead molecule for the development of an alternative antifungal agent to combat candidiasis.

Discovery of New Secondary Metabolites from Marine Bacteria Hahella Based on an Omics Strategy

Hahella is one characteristic genus under the Hahellaceae family and shows a good potential for synthesizing new natural products. In this study, we examined the distribution of the secondary metabolite biosynthetic gene cluster (SMBGC) under Hahella with anti-SMASH. The results derived from five genomes released 70 SMBGCs. On average, each strain contains 12 gene clusters, and the most abundant ones (45.7%) are from the family of non-ribosomal peptide synthetase (NRPS) and non-ribosomal peptide synthetase hybrid with polyketide synthase (NRPS/PKS), indicating a great potential to find bioactive compounds. The comparison of SMBGC between H. chejuensis and other species showed that H. chejuensis contained two times more gene clusters than H. ganghwensis. One strain, designed as NBU794, was isolated from the mangrove soil of Dongzhai Port in Haikou (China) by iChip. The 16S rRNA gene of NBU794 exhibited 99% identity to H. chejuensis KCTC 2396 and clustered with the H. chejuensis clade on the phylogenetic trees. Genome mining on strain NBU794 released 17 SMBGCs and two groups of bioactive compounds, which are chejuenolide A-C and nine prodiginines derivatives. The prodiginines derivatives include the well-known lead compound prodigiosin and two new compounds, 2-methyl-3-pentyl-4-O-methyl-prodiginine and 2-methyl-3-octyl-prodiginine, which were identified through fragmentation analysis based on LC-MS/MS. The anti-microbial activity assay showed prodigiosin and 2-methyl-3-heptyl-prodiginine exhibited the best performance in inhibiting Escherichia coli, Salmonella paratyphi B, MASA Staphylococcus aureus, Bacillus subtilis, and Candida albicans. Moreover, the yield of prodigiosin in H. chejuensis NBU794 was also evaluated, which could reach 1.40 g/L under the non-optimized condition and increase to 5.83 g/L in the modified ISP4 medium with macroporous adsorption beads added, indicating that NBU794 is a promising source of prodigiosin.

Identification of a Novel Biosurfactant with Antimicrobial Activity Produced by Rhodococcus opacus R7

Rhodococcus members excrete secondary metabolites, especially compounds which act as biosurfactants. In this work, we demonstrated the ability of Rhodococcus opacus R7 to produce a novel bioactive compound belonging to the class of biosurfactants with antimicrobial properties during the growth on naphthalene. Chemical and biochemical analyses of the isolated compound demonstrated that the biosurfactant could be classified as a hydrophobic peptide. The ESI-full mass spectrometry revealed that the isolated biosurfactant showed a molecular weight of 1292 Da and NMR spectra evidenced the composition of the following amino acid residues: Ala, Thr, Asp, Gly, Ser. Surfactant activity of the R. opacus R7 compound was quantified by the critical micelle dilution (CMD) method and the critical micelle concentration (CMC) was estimated around 20 mg L⁻¹ with a corresponding surface tension of 48 mN m⁻¹. Moreover, biological assays demonstrated that R. opacus R7 biosurfactant peptide exhibited antimicrobial activity against Escherichia coli ATCC 29522 and Staphylococcus aureus ATCC 6538 with the minimum inhibition growth concentration (MIC) values of 2.6 mg mL⁻¹ and 1.7 mg mL⁻¹, respectively. In this study for the first time, a hydrophobic peptide with both biosurfactant and antimicrobial activity was isolated from a bacterium belonging to Rhodococcus genus.

Antibacterial and antibiofilm activity of Peganum harmala seed extract against multidrug-resistant Pseudomonas aeruginosa pathogenic isolates and molecular mechanism of action

Biofilm formation of the opportunistic pathogen Pseudomonas (P). aeruginosa is one of the major global challenges to control nosocomial infections due to their high resistance to antimicrobials and host defense mechanisms. The present study aimed to assess the antibacterial and the antibiofilm activities of Peganum (P). harmala seed extract against multidrug-resistant P. aeruginosa isolates. Chemical identification of the active compound and determination of its molecular mechanism of action were also investigated. Results showed that P. harmala n-butanol "n-BuOH" extract exhibited antibacterial activity against multidrug-resistant P. aeruginosa isolates. This extract was even more active than conventional antibiotics cefazolin and vaamox when tested against three P. aeruginosa multidrug-resistant isolates. In addition, P. harmala n-BuOH extract exhibited potent bactericidal activity against PAO1 strain at MIC value corresponding to 500 µg/mL and attained 100% killing effect at 24 h of incubation. Furthermore, P. harmala n-BuOH extract showed an antibiofilm activity against P. aeruginosa PAO1 and exhibited 80.43% inhibition at sub-inhibitory concentration. The extract also eradicated 83.99% of the biofilm-forming bacteria. The active compound was identified by gas chromatography-mass spectrometry as an indole alkaloid harmaline. Transcriptomic analysis showed complete inhibition of the biofilm-related gene pilA when PAO1 cells were treated with harmaline. Our results revealed that P. harmala seed extract and its active compound harmaline could be considered as a candidate for a new treatment of multidrug-resistant P. aeruginosa pathogens-associated biofilm infections.

Characterization and Cytotoxicity of Pseudomonas Mediated Rhamnolipids Against Breast Cancer MDA-MB-231 Cell Line

A biosurfactant producing bacterium was identified as Pseudomonas aeruginosa DNM50 based on molecular characterization (NCBI accession no. MK351591). Structural characterization using MALDI-TOF revealed the presence of 12 different congeners of rhamnolipid such as Rha-C8-C8:1, Rha-C10-C8:1, Rha-C10-C10, Rha-C10-C12:1, Rha-C16:1, Rha-C16, Rha-C17:1, Rha-Rha-C10:1-C10:1, Rha-Rha-C10-C12, Rha-Rha-C10-C8, Rha-Rha-C10-C8:1, and Rha-Rha-C8-C8. The radical scavenging activity of rhamnolipid (DNM50RL) was determined by 2, 3-diphenyl-1-picrylhydrazyl (DPPH) assay which showed an IC₅₀ value of 101.8 μg/ ml. The cytotoxic activity was investigated against MDA-MB-231 breast cancer cell line by MTT (4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide) assay which showed a very low IC50 of 0.05 μg/ ml at 72 h of treatment. Further, its activity was confirmed by resazurin and trypan blue assay with IC₅₀ values of 0.01 μg/ml and 0.64 μg/ ml at 72 h of treatment, respectively. Thus, the DNM50RL would play a vital role in the treatment of breast cancer targeting inhibition of p38MAPK.

The Optimal Lipid Chain Length of a Membrane-Permeabilizing Lipopeptide Results From the Balance of Membrane Partitioning and Local Damage

Pseudodesmin A (PSD) is a cyclic lipodepsipeptide produced by Pseudomonas that kills certain bacteria at MIC_1/2 in the single micromolar range, probably by permeabilizing their cellular membranes. Synthetic PSD variants, where the native decanoic (C10) acyl chain is varied in length from C4 to C8 and C12 to C14 carbons, were described to be not or less active against a panel of gram-positive strains, as compared to native PSD-C10. Here, we test the membrane-permeabilizing activity of PSD-C4 through PSD-C14 in terms of calcein release from liposomes, which is characterized in detail by the fluorescence-lifetime based leakage assay. Antagonistic concentrations and their chain length dependence agree well for liposome leakage and antimicrobial activity. The optimal chain length is governed by a balance between membrane partitioning (favoring longer chains) and the local perturbation or “damage” inflicted by a membrane-bound molecule (weakening for longer chains). Local perturbation, in turn, may involve at least two modes of action. Asymmetry stress between outer and inner leaflet builds up as the lipopeptides enter the outer leaflet and when it reaches a system-specific stability threshold, it causes a transient membrane failure that allows for the flip of some molecules from the outer to the inner leaflet. This cracking-in may be accompanied by transient, incomplete leakage from the aqueous cores of the liposomes observed, typically, for some seconds or less. The mismatch of the lipopeptide with the lipid leaflet geometry, expressed for example in terms of a spontaneous curvature, has two effects. First, it affects the threshold for transient leakage as described. Second, it controls the rate of equilibrium leakage proceeding as the lipopeptide has reached sufficient local concentrations in both leaflets to form quasi-toroidal defects or pores. Both modes of action, transient and equilibrium leakage, synergize for intermediate chain lengths such as the native, i.e., for PSD-C10. These mechanisms may also account for the reported chain-length dependent specificities of antibiotic action against the target bacteria.

Isolation and Purification of a New Bacillus Subtilis Strain from Deer Dung with Anti-microbial and Anti-cancer Activities

OBJECTIVE

Bacillus strains are well known for their natural bioactive products that have antimicrobial and/or anti-cancer activities. Many of Bacillus' structurally unique metabolites can combat human diseases, including cancers. However, because Bacillus' metabolites are so abundant, few have been studied extensively enough to fully characterize their chemical constitutions and biological functions.

METHODS

In this study, we focused on the isolation and purification of a new Bacillus strain, and determined the effects of its metabolites on bacteria and cancer cells. Our study focused on a new strain of Bacillus isolated from deer dung. Based on BLAST results, this isolate belongs to Bacillus subtilis, and therefore we named the strain Bacillus subtilis NC16. Congo red assay was used to test the cellulase activity. The inhibition zone was measured to test the antimicrobial activity. CCK-8, wound healing and flow cytometry were used to test the anti-cancer activity.

RESULTS

Metabolites from Bacillus subtilis NC16 have both antimicrobial and anti-cancer activities. They can both suppress the growth of Trichoderma vride and Staphylococcus aureus, and inhibit the proliferation and promote the apoptosis of non-small cell lung cancer cell lines.

CONCLUSION

Our results suggest that Bacillus subtilis NC16 can not only degrade cellulose, but its metabolites may be sources of antibiotics and anti-cancer drugs.

Effect of Lipopeptide-Loaded Chitosan Nanoparticles on Candida albicans Adhesion and on the Growth of Leishmania major

Cyclic lipopeptides produced by Bacillus species exhibit interesting therapeutic potential. However, their clinical use remains limited due to their low stability, undesirable interactions with host macromolecules, and their potential toxicity to mammalian cells. The present work aims to develop suitable lipopeptide-loaded chitosan nanoparticles with improved biological properties and reduced toxicity. Surfactin and bacillomycin D lipopeptides produced by Bacillus amyloliquefaciens B84 strain were loaded onto chitosan nanoparticles by ionotropic gelation process. Nanoformulated lipopeptides exhibit an average size of 569 nm, a zeta potential range of 38.8 mV, and encapsulation efficiency (EE) of 85.58%. Treatment of Candida (C.) albicans cells with encapsulated lipopeptides induced anti-adhesive activity of 81.17% and decreased cell surface hydrophobicity (CSH) by 25.53% at 2000 µg/mL. Nanoformulated lipopeptides also induced antileishmanial activity against Leishmania (L.) major promastigote and amastigote forms at respective IC₅₀ values of 14.37 µg/mL and 22.45 µg/mL. Nanoencapsulated lipopeptides exerted low cytotoxicity towards human erythrocytes and Raw 264.7 macrophage cell line with respective HC₅₀ and LC₅₀ values of 770 µg/mL and 234.56 µg/mL. Nanoencapsulated lipopeptides could be used as a potential delivery system of lipopeptides to improve their anti-adhesive effect against C. albicans cells colonizing medical devices and their anti-infectious activity against leishmania.

Identification, characterization and evaluation of novel antifungal cyclic peptides from Neobacillus drentensis

Marine microbes secrete exopolymeric substances (EPS), which surrounds the biofilm and inhibits the fungal growth. Elucidation of the structure and function of the extracellular exopolymeric substances is of vital relevance therapeutically. The active compound responsible for bioactivity was purified and characterized using TLC, LC/MS/MS, GC/MS and FT-IR. Bioactivity of the characterized cyclic peptides (CLPs) against azole resistant and susceptible Candida strains were examined for growth and biofilm formation using scanning electron microscopy, flow cytometry, confocal microscopy. In the present study we identified bioactive cyclic peptides from marine isolated Neobacillus drentensis that exhibited promising tensio-active properties and antifungal efficacy against azole resistant and susceptible Candida albicans. The cluster is composed of five CLP isoforms which were sequenced and identified as new peptides with compositional and structural variations in the amino acid sequence and fatty acid chain. In vitro cytotoxic activity of CLPs was tested in human fibroblast normal cells. We have observed that the CLPs repressed the Candida albicans growth and multiplication by inhibiting the biofilm formation and disruption of branching filamentous hyphae. CLPs have been found to arrest the C. albicans cell cycle by a block at G1-S transition followed by apoptotic cell death. The current studies suggest these natural marine derived CLPs function as potential anti-biofilm agents against azole C. albicans resistant strains.

The ecological roles of microbial lipopeptides: Where are we going?

Lipopeptides (LPs) are secondary metabolites produced by a diversity of bacteria and fungi. Their unique chemical structure comprises both a peptide and a lipid moiety. LPs are of major biotechnological interest owing to their emulsification, antitumor, immunomodulatory, and antimicrobial activities. To date, these versatile compounds have been applied across multiple industries, from pharmaceuticals through to food processing, cosmetics, agriculture, heavy metal, and hydrocarbon bioremediation. The variety of LP structures and the diversity of the environments from which LP-producing microorganisms have been isolated suggest important functions in their natural environment. However, our understanding of the ecological role of LPs is limited. In this review, the mode of action and the role of LPs in motility, antimicrobial activity, heavy metals removal and biofilm formation are addressed. We include discussion on the need to characterise LPs from a diversity of microorganisms, with a focus on taxa inhabiting 'extreme' environments. We introduce the use of computational target fishing and molecular dynamics simulations as powerful tools to investigate the process of interaction between LPs and cell membranes. Together, these advances will provide new understanding of the mechanism of action of novel LPs, providing greater insights into the roles of LPs in the natural environment.

Anti-staphylococcal activity of a cyclic lipopeptide, C15 -bacillomycin D, produced by Bacillus velezensis NST6

AIM

The aim of this study was to assess antibacterial activity of a novel Bacillus velezensis strain NST6, and further identify its active compound against pathogenic Staphylococcus strains for clinical therapeutic applications.

METHODS AND RESULTS

In this study, a novel B. velezensis strain NST6 harbouring strong antimicrobial activity against human pathogenic bacteria was isolated from a soil sample. The solvent extract of the strain exhibited strong antibacterial activity against Gram-positive and Gram-negative bacteria in disc diffusion assay and measurement of minimal inhibitory concentration and bactericidal concentration, of which it showed notable efficacy to Staphylococcus species including Staphylococcus epidermidis, Staphylococcus aureus and methicillin-resistant S. aureus. Strong antibacterial effect against pathogenic S. aureus and low toxicity of the bacterial extract were further validated in Caenorhabditis elegans model. Moreover, by antibacterial activity-guided fractionation using RP-HPLC and LC-MS, we defined C₁₅ -bacillomycin D as the anti-staphylococcal compound produced by the strain.

CONCLUSION

The primary anti-staphylococcal compound from B. velezensis NST6 was identified as a cyclic lipopeptide, C₁₅ -bacillomycin D, which proved its potential to treat Staphylococcus strains in vitro and in vivo experiments with insignificant level of toxicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

We provide an alternative treatment option to Staphylococcus infections by investigating the specific anti-staphylococcal activity of C₁₅ -bacillomycin D produced by a B. velezensis strain.

Bacillomycin D-C16 triggers apoptosis of gastric cancer cells through the PI3K/Akt and FoxO3a signaling pathways

Bacillomycin D can inhibit the growth of Aspergillus ochraceus in food samples. In addition, it can induce apoptosis in and inhibit the proliferation of cancer cells, although the details of this mechanism are unknown. In this study, we separated bacillomycin D-C14, D-C15, D-C16 monomers from the Bacillus subtilis strain fmbJ. The bacillomycin D monomers containing longer fatty acid chains better induced apoptosis in Bgc-823, Sgc-7901, and Hgc-27 gastric cancer cells. The Bgc-823 cell line was the most sensitive. Acridine orange-ethidium bromide staining indicated that bacillomycin D-C16-induced Bgc-823 cell death by triggering apoptosis, characterized by membrane blebbing, cellular shrinkage, and DNA fragmentation. Flow cytometric analysis showed a bacillomycin D-C16 dose-dependent trigger of Bgc-823 apoptosis. Bacillomycin D-C16-induced the mitochondrial pathway, as indicated by a reduced Bcl-2/Bax expression ratio, enhanced cytochrome C release, and higher levels of cleaved caspase-3. Furthermore, bacillomycin D-C16 effectively repressed phosphorylation of the serine-threonine protein kinase Akt at Ser-473 and increased the levels of the FoxO3a protein. The combination of the PI3K/Akt-inhibitor BEZ235 with bacillomycin D-C16 enhanced the apoptosis of Bgc-823 cells. Together, these findings indicated that bacillomycin D-C16 induces apoptosis through the PI3K/Akt and FoxO3a signaling pathways.

Bacillomycin D effectively controls growth of Malassezia globosa by disrupting the cell membrane

Malassezia globosa is an opportunistic pathogen that causes various skin disorders, which disturbs people's life all the time, and conventional drugs are not completely satisfactory. Bacillomycin D (BD), an antifungal lipopeptide, could inhibit various fungi growth. However, the reports about its effect on M. globosa were not found yet. In this study, we showed that BD and BD-C16 (fatty acid chain had sixteen carbon atoms) completely inhibited growth of M. globosa at concentration of 64 μg/ml in 15 h, which was confirmed with the observation of irregular morphological change of M. globosa treated with BD. Significantly, the study on the working mechanism showed that BD induced cell death by changing cell membrane permeability and thus promoting the release of cellular contents, which may be mediated by the interaction between BD and ergosterol from membrane. Further study showed that BD reduced the overall content of cellular sterol, and interestingly, the expression of some genes involved in membrane and ergosterol synthesis were significantly upregulated, which was likely to be a feedback regulation. Besides, we found that BD had additive and synergistic effects with ketoconazole and amphotericin B, respectively, on inhibition of M. globosa, suggesting that combination use of BD with other commercial drugs could be a promising strategy to relieve skin disorders caused by M. globosa. KEY POINTS: • BD could efficiently inhibit the growth of M. globosa. • BD increases cell membrane permeability and thus promotes the release of cellular contents. • BD has additive or synergistic effect with other antifungal drugs.

Antifungal mechanism of bacillomycin D from Bacillus velezensis HN-2 against Colletotrichum gloeosporioides Penz

Anthracnose is a leaf spot, blossom blight, or fruit rot disease caused by Colletotrichum gloeosporioides (Penz.). It is the most prevalent disease in mango-growing countries worldwide. Lipopeptides, such as those in the iturin family, account for the majority of antifungal secondary metabolites in Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus velezensis, and includes bacillomycin D. Thus far, the mechanism of bacillomycin D's activity has not been clear. In this study, bacillomycin D was isolated from B. velezensis HN-2, which strongly inhibits C. gloeosporioides (Penz.). The median inhibitory concentration of bacillomycin D was 2.162 μg/mL, causing deformation and damage to C. gloeosporioides (Penz.). Bacillomycin D showed more potent activity against C. gloeosporioides (Penz.) than two common fungicides prochloraz and mancozeb. Scanning and transmission electron microscopy revealed that bacillomycin D could injure the cell wall and cell membrane of the hyphae and spores of C. gloeosporioides (Penz.), and the cytoplasm and organelles inside the cell were exuded and formed empty holes. This research clarifies the mechanism underlying bacillomycin D antifungal activity and reveals its high potential as a biopesticide to control phytopathogens.

In vitro efficacy of the lipopeptide biosurfactant surfactin-C15 and its complexes with divalent counterions to inhibit Candida albicans biofilm and hyphal formation

Surfactin is a type of cyclic lipopeptide biosurfactant implicated in a wide range of applications. Although its antimicrobial activity has been characterized, its effect on Candida albicans physiology remains to be elucidated. The present study evaluated the influence of surfactin-C₁₅ (SF) and its complexes with divalent counterions on C. albicans biofilm formation and preformed biofilms. The SF and metal(II)-SF complexes inhibited biofilm formation and reduced the metabolic activity of mature biofilms in a concentration-dependent manner. The same concentrations of the compounds studied dislodged preexisting biofilms grown on polystyrene plates. Moreover, SF and its metal(II) complexes reduced the mRNA expression of hypha-specific genes HWP1, ALS1, ALS3, ECE1 and SAP4 without exhibiting significant growth inhibition. Further research showed that the compounds tested reduced cellular surface hydrophobicity (CSH). These results suggest that SF and metal(II)-SF complexes could be used as anti-biofilm agents against C. albicans hypha-related infections in clinical practice.

Selected application of peptide molecules as pharmaceutical agents and in cosmeceuticals

Introduction: Peptide molecules are being vastly investigated as an emerging class of therapeutic molecules in recent years. Currently, 60 peptides have been approved by the US Food and Drug Administration (FDA), and more would enter the market in near future. Peptides have already opened their ways into cosmeceutical and food industries as well.Areas covered: Antibodies, vaccines, and antimicrobial agents are the major classes of therapeutic peptides. Additionally, peptides may be employed in drug development to support cell penetration or targeting. The interest in antimicrobial peptides is surging due to the increasing risk of antibiotic-resistant pathogens. Peptide vaccines with their significant advantages compared with traditional vaccines, are expected to find their place in coming years, especially for cancer, microbial and allergen-specific immunotherapy. The usage of peptides in cosmeceuticals is also growing rapidly.Expert opinion: Peptide synthesis has become accessible, and advances in peptide engineering, sequencing technologies, and structural bioinformatics have resulted in the rational designing of novel peptides. All these advancements would lead to the more prominent roles of peptides in the mentioned areas. In this review, we discuss applications of peptides in different fields including pharmaceuticals, cosmeceuticals, besides the critical factors in designing efficient peptide molecules.

Role of Lipid Composition, Physicochemical Interactions, and Membrane Mechanics in the Molecular Actions of Microbial Cyclic Lipopeptides

Several experimental and theoretical studies have extensively investigated the effects of a large diversity of antimicrobial peptides (AMPs) on model lipid bilayers and living cells. Many of these peptides disturb cells by forming pores in the plasma membrane that eventually lead to the cell death. The complexity of these peptide-lipid interactions is mainly related to electrostatic, hydrophobic and topological issues of these counterparts. Diverse studies have shed some light on how AMPs act on lipid bilayers composed by different phospholipids, and how mechanical properties of membranes could affect the antimicrobial effects of such compounds. On the other hand, cyclic lipopeptides (cLPs), an important class of microbial secondary metabolites, have received comparatively less attention. Due to their amphipathic structures, cLPs exhibit interesting biological activities including interactions with biofilms, anti-bacterial, anti-fungal, antiviral, and anti-tumoral properties, which deserve more investigation. Understanding how physicochemical properties of lipid bilayers contribute and determining the antagonistic activity of these secondary metabolites over a broad spectrum of microbial pathogens could establish a framework to design and select effective strategies of biological control. This implies unravelling-at the biophysical level-the complex interactions established between cLPs and lipid bilayers. This review presents, in a systematic manner, the diversity of lipidated antibiotics produced by different microorganisms, with a critical analysis of the perturbing actions that have been reported in the literature for this specific set of membrane-active lipopeptides during their interactions with model membranes and in vivo. With an overview on the mechanical properties of lipid bilayers that can be experimentally determined, we also discuss which parameters are relevant in the understanding of those perturbation effects. Finally, we expose in brief, how this knowledge can help to design novel strategies to use these biosurfactants in the agronomic and pharmaceutical industries.

Volatile organic compounds of Bacillus atrophaeus HAB-5 inhibit the growth of Colletotrichum gloeosporioides

The use of fungicides to control plant diseases creates a potential health risk. One alternative to this problem is the biological control, which has been succesfully applied to control plant diseases. Bacillus atrophaeus HAB-5 exhibits a high inhibitory acitivities against different fungal pathogens and suppresses them. The aim of current studies is to produce and identify the antifungal compounds produced by the strain HAB-5. We found that the submerge fermentation harvested from Luria-Bertani (LB) medium had the highest activity against Colletotrichum gloeosporioides. The petroleum ether crude extract was strongly bioactive and its activity was stable after heat treatment, pH treatment, illuminated light as well as ultra violet exposition. The antifungal compounds were purified using gel chromatography column. Based on Gas Chromatography-Mass Spectrometry (GC-MS) analysis, nineteen different volatile organic compounds (VOCs) were identified included the range of alkanes, alkenes, alcohols, and organics acid. Among these identified compounds, Chloroacetic acid, tetradecyl esters followed by Octadecane and Hexadecanoic acid, methyl ester showed antifungal activity against C. gloeosporioides. Our results clearly showed Chloroacetic acid, tetradecyl esters; Octadecane and Hexadecanoic acid, methyl ester are key inhibitory compounds produced by Bacillus atrophaeus HAB-5 against C. gloeosporioides.

Utilization of Grape Seed Flour for Antimicrobial Lipopeptide Production by Bacillus amyloliquefaciens C5 Strain

An endophytic Bacillus amyloliquefaciens strain called C5, able to produce biosurfactant lipopeptides with a broad antibacterial activity spectrum, has been isolated from the roots of olive tree. Optimization of antibacterial activity was undertaken using grape seed flour (GSF) substrate at 0.02, 0.2, and 2% (w/v) in M9 medium. Strain C5 exhibited optimal growth and antimicrobial activity (MIC value of 60 μg/ml) when incubated in the presence of 0.2% GSF while lipopeptide production culminated at 2% GSF. Thin layer chromatography analysis of lipopeptide extract revealed the presence of at least three active spots at Rf 0.35, 0.59, and 0.72 at 0.2% GSF. Data were similar to those obtained in LB-rich medium. MALDI-TOF/MS analysis of lipopeptide extract obtained from 0.2% GSF substrate revealed the presence of surfactin and bacillomycin D. These results show that GSF could be used as a low-cost culture medium supplement for optimizing the production of biosurfactants by strain C5.

Biological control of the soft rot bacterium Pectobacterium carotovorum by Bacillus amyloliquefaciens strain Ar10 producing glycolipid-like compounds

Four hundred and fifty bacteria were evaluated for antagonistic activity against bacterial soft rot of potato caused by Pectobacterium carotovorum sp strain II16. A strain Ar10 exhibiting potent antagonist activity has been identified as Bacillus amyloliquefaciens on the basis of biochemical and molecular characterization. Cell free supernatant showed a broad spectrum of antibacterial activity against human and phytopathogenic bacteria in the range of 10-60 AU/mL. Incubation of P. carotovorum cells with increasing concentrations of the antibacterial compound showed a killing rate of 94.8 and 96% at MIC and 2xMIC respectively. In addition, the antibacterial agent did not exert haemolytic activity at the active concentration and has been preliminary characterized by TLC and GC-MS as a glycolipid compound. Treatment of potato tubers with strain Ar10 for 72 h significantly reduced the severity of disease symptoms (100 and 85.05% reduction of necrosis deep / area and weight loss respectively). The same levels in disease symptoms severity was also recorded following treatment of potato tubers with cell free supernatant for 1 h. Data suggest that protection against potato soft rot disease may be related to glycolipid production by strain Ar10. The present study affords new alternatives for anti-Pectobacterium carotovorum bioactive compounds against the soft rot disease of potato.

Bioprospecting from marine coastal sediments of Colombian Caribbean: screening and study of antimicrobial activity

AIMS

To isolate micro-organisms associated with marine coastal sediments of Colombian Caribbean Sea and for evaluating its antimicrobial activity in order to identify the most active strains.

METHODS AND RESULTS

One hundred and four strains were isolated from sediment samples of the Colombian Caribbean Sea. First at all, an antimicrobial activity screening was made using agar well diffusion method against the pathogens: Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Candida albicans, Candida tropicalis and Pseudomonas aeruginosa. Seventeen strains showed strong antimicrobial activity and were identified as members of the Streptomyces, Micrococcus and Bacillus genera. Organic extracts were produced by liquid-liquid extraction and HPLC profiles of the most active extracts were obtained. Then, the antimicrobial activity of the extracts was evaluated with the broth microdilution test, finding antimicrobial activities superior to 90% against S. aureus MRSA and C. albicans. HPLC profiles indicated the presence of different antimicrobial compounds.

CONCLUSION

This study demonstrates that the microorganisms isolated from the Colombian Caribbean Sea are possible sources of antimicrobial compounds against pathogenic strains.

SIGNIFICANCE AND IMPACT OF STUDY

These results contribute to the knowledge of the biotechnological potential of the Colombian biodiversity for the development of pharmaceutical products that can counteract the increasing problem of pathogen resistance.

Hyporientalin A, an anti-Candida peptaibol from a marine Trichoderma orientale

A Trichoderma orientale strain LSBA1 was isolated from the Mediterranean marine sponge Cymbaxinella damicornis. The crude extract of T. orientale mycelium showed inhibitory activity against growth of Gram-positive and Gram-negative bacteria as well as clinical isolates of Candida albicans. Purification of the anti-Candida component was performed using a combination of open silica gel-60 column and reverse phase high performance liquid chromatography. The active compound called hyporientalin A has been identified as a peptaibol analogue of longibrachin-A-II using mass spectrometry. It exhibited fungicidal activity against clinical isolates of C. albicans with minimal inhibitory concentrations (MICs) ranging from 2.49 to 19.66 µM, comparable to that of the antifungal agent amphotericin B. Our data support the use of hyporientalin A as a promising new and efficient antifungal drug in the treatment of candidiasis while controlling toxicity.

Characterization of Milkisin, a Novel Lipopeptide With Antimicrobial Properties Produced By Pseudomonas sp. UCMA 17988 Isolated From Bovine Raw Milk

Biosurfactants such as lipopeptides are amphiphilic compounds produced by microorganisms such as bacteria of the genera of Pseudomonas and Bacillus. Some of these molecules proved to have interesting antimicrobial, antiviral, insecticide, and/or tensioactive properties that are potentially useful for the agricultural, chemical, food, and pharmaceutical industries. Raw milk provides a physicochemical environment that is favorable to the multiplication of a broad spectrum of microorganisms. Among them, psychrotrophic bacterial species, especially members of the genus Pseudomonas, are predominant and colonize milk during cold storage and/or processing. We isolated the strain Pseudomonas sp. UCMA 17988 from raw cow milk, with antagonistic activity against Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica Newport. Antimicrobial molecules involved in the antagonistic activity of this strain were characterized. A mass spectrometry analysis highlighted the presence of four lipopeptides isoforms. The major isoform (1409 m/z), composed of 10 carbons in the lipidic chain, was named milkisin C. The three other isoforms detected at 1381, 1395, and 1423 m/z, that are concomitantly produced, were named milkisin A, B, and D, respectively. The structure of milkisin, as confirmed by nuclear magnetic resonance analyses, is closely related to amphisin family. Indeed, the peptidic chain was composed of 11 amino acids, 6 of which are conserved among the family. In conclusion, Pseudomonas sp. UCMA 17988 produces new members of the amphisin family which are responsible for the antagonistic activity of this strain.

Calcium Alginate Bead-mediated Enhancement of the Selective Recovery of a Lead Novel Antifungal Bacillomycin Variant

In the pursuit of new antifungal compounds, five coproduced lipopeptide variants (AF₁ to AF₅) from wild-type Bacillus subtilis RLID 12.1 were identified in our previous study. Out of five, AF₄ was identified as a novel lead molecule belonging to the bacillomycin family showing less cytotoxicity at its respective minimum inhibitory concentrations (MIC) evaluated against 81 strains of Candida and Cryptococcus species (including clinical isolates); besides this, AF₄ purified in the present study exhibited encouraging MIC values against 10 clinical mycelial fungi. Aiming for a selective production augmentation of AF₄ lipopeptide variant, a new fermentation media comprising malt extract (1.01%), dextrose (0.55%), peptone (1.79%), MnSO₄ (2 mM), and NaCl (0.5%) was formulated. Maximum production of 954.8 ± 10.8 mg/L was achieved with 44% selectivity at 30 °C compared to unoptimized conditions (186.4 ± 6.1 mg/L). Use of calcium alginate beads in the formulated media during the onset of lipopeptide production resulted in an augmentation in the selectivity of the most efficacious AF₄ variant to about 72% presumably due to attenuation of other coproduced lipopeptide variants AF₁ and AF₂. Difference in yield of lipopeptides varied with bead size, bead preparation ratios, and sodium alginate concentrations. Use of Ca-alginate beads in the upstream production process of the lead AF₄ variant may be considered as a novel strategy to address the potential challenge that may arise during the scale-up and downstream processing steps. Another significant finding derived from the study is that the proportion of bacillomycin variants of B. subtilis RLID 12.1 could be controlled by temperature and metal ions under static and shaking conditions.

Environmental Microbiota Drives Microbial Succession and Metabolic Profiles during Chinese Liquor Fermentation

Many microorganisms in the environment participate in the fermentation process of Chinese liquor. However, it is unknown to what extent the environmental microbiota influences fermentation. In this study, high-throughput sequencing combined with multiphasic metabolite target analysis was applied to study the microbial succession and metabolism changes during Chinese liquor fermentation from two environments (old and new workshops). SourceTracker was applied to evaluate the contribution of environmental microbiota to fermentation. Results showed that Daqu contributed 9.10 to 27.39% of bacterial communities and 61.06 to 80.00% of fungal communities to fermentation, whereas environments (outdoor ground, indoor ground, tools, and other unknown environments) contributed 62.61 to 90.90% of bacterial communities and 20.00 to 38.94% of fungal communities to fermentation. In the old workshop, six bacterial genera (Lactobacillus [11.73% average relative abundance], Bacillus [20.78%], Pseudomonas [6.13%], Kroppenstedtia [10.99%], Weissella [16.64%], and Pantoea [3.40%]) and five fungal genera (Pichia [55.10%], Candida [1.47%], Aspergillus [10.66%], Saccharomycopsis [22.11%], and Wickerhamomyces [3.35%]) were abundant at the beginning of fermentation. However, in the new workshop, the change of environmental microbiota decreased the abundances of Bacillus (5.74%), Weissella (6.64%), Pichia (33.91%), Aspergillus (7.08%), and Wickerhamomyces (0.12%), and increased the abundances of Pseudomonas (17.04%), Kroppenstedtia (13.31%), Pantoea (11.41%), Acinetobacter (3.02%), Candida (16.47%), and Kazachstania (1.31%). Meanwhile, in the new workshop, the changes of microbial community resulted in the increase of acetic acid, lactic acid, malic acid, and ethyl acetate, and the decrease of ethyl lactate during fermentation. This study showed that the environmental microbiota was an important source of fermentation microbiota and could drive both microbial succession and metabolic profiles during liquor fermentation.IMPORTANCE Traditional solid-state fermentation of foods and beverages is mainly carried out by complex microbial communities from raw materials, starters, and the processing environments. However, it is still unclear how the environmental microbiota influences the quality of fermented foods and beverages, especially for Chinese liquors. In this study, we utilized high-throughput sequencing, microbial source tracking, and multiphasic metabolite target analysis to analyze the origins of microbiota and the metabolic profiles during liquor fermentation. This study contributes to a deeper understanding of the role of environmental microbiota during fermentation.

Evaluation of Antifungal Efficacy of Three New Cyclic Lipopeptides of the Class Bacillomycin from Bacillus subtilis RLID 12.1

New lipopeptide homologues (AF₃, AF₄, and AF₅) with antifungal activities against Candida and Cryptococcus spp. were purified from a cell-free supernatant of Bacillus subtilis RLID 12.1. The lipopeptides AF₃, AF₄, and AF₅ were identified with the same peptide sequence Asn-Pro-Tyr-Asn-Gln-Thr-Ser with variations in the fatty acid branching type and chain length (anteiso-C₁₇, iso-C₁₇, and iso-C₁₈, respectively). Upon comparing the three homologues for MICs against 81 Candida (n = 64) and Cryptococcus (n = 17) clinical isolates and their cytotoxicities, we found that AF₄ was the most promising antifungal lipopeptide, since it demonstrated 100% inhibition at geometric mean MICs of 3.31, 3.41, 3.48, and 2.83 μg/ml against Candida albicans, Candida tropicalis, Candida auris, and Cryptococcus neoformans, respectively, with low hemolysis values (<6%) and 50% inhibitory concentrations (13.31 μg/ml). The additive effects among the homologues AF₃, AF₄, and AF₅ were evaluated against three Candida species, along with the cytotoxicity studies. Five combinations exhibited good additive interaction effects: AF₃/AF₄ (at corresponding concentrations of 4 and 4 μg/ml [4/4 μg/ml]), AF₃/AF₅ (4/4 μg/ml), AF₃/AF₅ (2/4 μg/ml), AF₄/AF₅ (4/4 μg/ml), and AF₄/AF₅ (2/4 μg/ml) in planktonic cell inhibition and AF₃/AF₄ (4/4 μg/ml), AF₃/AF₅ (4/4 μg/ml), and AF₃/AF₅ (2/4 μg/ml) in the inhibition of biofilm formation. However, combinations AF₃/AF₄ and AF₃/AF₅, which showed >70% cell survival with low hemolysis (<5%), were found to be comparatively effective. We describe here the additive effects of lipopeptide homologues showing reduced cytotoxicity against mammalian cells; these combinations might serve as a potent antibiofilm-forming substitute.

Characterization of lpaH2 gene corresponding to lipopeptide synthesis in Bacillus amyloliquefaciens HAB-2

Background

Bacillus spp. have prominent ability to suppress plant pathogens and corresponding diseases. Previous analyses of Bacillus spp. revealed numerous gene clusters involved in nonribosomal synthesis of cyclic lipopeptides with distinct antimicrobial action. The 4′-phosphopantetheinyl transferase (PPTase) encoded by sfp gene is a key factor in lipopeptide synthesis in Bacillus spp. In previous study, B. amyloliquefaciens strain HAB-2 was found to inhibit a broad range of plant pathogens, which was attributed to its secondary metabolite lipopeptide.

Results

A sfp homologue lpaH2 which encoded phosphopantetheinyl transferase but shared 71% sequence similarity was detected in strain HAB-2. Disruption of lpaH2 gene resulted in losing the ability of strain HAB-2 to produce lipopeptide, as well as antifungal and hemolytic activities. When lpaH2 replaced sfp gene of B. subtilis strain 168, a non-lipopeptide producer, the genetically engineered strain 168 could produced lipopeptides and recovered antifungal activity. Quantitative PCR assays indicated that, the expression level of lpaH2 in B. subtilis 168 strain decrease to 0.27-fold compared that of the wild type B. amyloliquefaciens strain HAB-2.

Conclusion

Few studies have reported about lpa gene which can replace sfp gene in the different species. Taken together, our study showed for the first time that lpaH2 from B. amyloliquefaciens could replace sfp gene.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-1134-z) contains supplementary material, which is available to authorized users.

Identification of endophytic Bacillus mojavensis with highly specialized broad spectrum antibacterial activity

Biosynthetic adaptation of endophytic bacteria to chemically support host plant is very remarkable. Hence these organisms from medicinal plants are considered as highly valuable sources for natural products with diverse bioactivity. Their metabolite diversity and biosynthetic versatility have been increasingly explored for drug discovery. In this study, an endophytic Bacillus mojavensis with broad spectrum antibacterial properties has been analyzed for the chemical basis of its activity. By LC-MS/MS the organism was identified to have the biosynthetic ability to produce lipopeptides surfactin and fengycin. The impressive antibacterial activity of B. mojavensis as reported in the study indicates its broad antimicrobial applications.

Bacillomycin D and its combination with amphotericin B: promising antifungal compounds with powerful antibiofilm activity and wound-healing potency

AIMS

In this study, we evaluated the ability of the lipopeptide bacillomycin D and the antifungal drug amphotericin B as well as their combination, to inhibit Candida albicans biofilm formation and to accelerate keratinocyte cell migration.

METHODS AND RESULTS

The antibiofilm activity of bacillomycin D and its combination with amphotericin B was carried out by crystal violet colorimetric method. Our results have shown that, when combined together at low concentrations nontoxic to mammalian cells, corresponding to 1/32 MIC (0·39 μg ml(-1) ) and 1/4 MIC (0·06 μg ml(-1) ) for bacillomycin D and amphotericin B, respectively, a clear antibiofilm activity is manifested (95% inhibition of biofilm formation) along with a clear inhibition of germ tube formation. Moreover, the effect of both drugs on preformed biofilm of C. albicans strain was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. The combination of the two antifungal compounds at 0·39 and 1 μg ml(-1) for bacillomycin D and amphotericin B, respectively, resulted in a clear enhancement of biofilm eradication compared to the results obtained with each drug alone. Furthermore, this combination was found to promote the closure of a gap produced in a monolayer of human keratinocytes.

CONCLUSIONS

Bacillomycin D and its combination with amphotericin B display impressive anti-biofilm and wound-healing activities.

SIGNIFICANCE AND IMPACT OF THE STUDY

Application of the lipopeptide bacillomycin D and the antifungal drug amphotericin B in medical devices may offer a promising alternative for topical treatment of Candida-associated infections in the setting of a wound.

Characterization of antimicrobial lipopeptides produced by Bacillus sp. LM7 isolated from chungkookjang, a Korean traditional fermented soybean food

A wild-type microorganism exhibiting antimicrobial activities was isolated from the Korean traditional fermented soybean food Chungkookjang and identified as Bacillus sp. LM7. During its stationary growth phase, the microorganism secreted an antimicrobial substance, which we partially purified using a simple two-step procedure involving ammonium sulfate precipitation and heat treatment. The partially purified antimicrobial substance, Anti-LM7, was stable over a broad pH range (4.0-9.0) and at temperatures up to 80 °C for 30 min, and was resistant to most proteolytic enzymes and maintained its activity in 30% (v/v) organic solvents. Anti-LM7 inhibited the growth of a broad range of Gram-positive bacteria, including Bacillus cereus and Listeria monocytogenes, but it did not inhibit lactic acid bacteria such as Lactobacillus plantarum and Lactococcus lactis subsp. Lactis. Moreover, unlike commercially available nisin and polymyxin B, Anti-LM7 inhibited certain fungal strains. Lastly, liquid chromatography-mass spectrometry analysis of Anti-LM7 revealed that it contained eight lipopeptides belonging to two families: four bacillomycin D and four surfactin analogs. These Bacillus sp. LM7-produced heterogeneous lipopeptides exhibiting extremely high stability and a broad antimicrobial spectrum are likely to be closely related to the antimicrobial activity of Chungkookjang, and their identification presents an opportunity for application of the peptides in environmental bioremediation, pharmaceutical, cosmetic, and food industries.

Synergistic fungicidal activity of the lipopeptide bacillomycin D with amphotericin B against pathogenic Candida species

In the present study, the synergism of the lipopeptide bacillomycin D in combination with the polyene amphotericin B against pathogenic Candida species is described along with their potential cytotoxicity against mammalian cells. Bacillomycin D inhibited the growth of various Candida species at minimal concentrations from 12.5 to 25 μg ml(-1). Furthermore, it showed a synergistic effect with the antifungal drug amphotericin B in inhibiting the growth of Candida strains, with fractional inhibitory concentration indices ranging from 0.28 to 0.5. Time killing studies revealed a >2-log reduction in the viability of Candida albicans ATCC 10231 cells after 3 h incubation with the combination amphotericin B plus bacillomycin D, at their subinhibitory concentration. Interestingly, when the two drugs were used together at those dosages displaying a synergism in the anti-Candida activity, no cytotoxic effect was observed against mammalian cells. Therefore, the combination bacillomycin D/amphotericin B may represent a valid alternative to conventional antifungals for topical treatment of C. albicans infections. To the best of our knowledge, this is the first report describing the in vitro interaction between the antifungal drug amphotericin B and bacillomycin D against pathogenic Candida species.