Biological activity of lipopeptides from Bacillus

Genomic characterization and production of antimicrobial lipopeptides by Bacillus velezensis P45 growing on feather by-products

AIMS

To investigate the potential of novel Bacillus velezensis P45 as an eco-friendly alternative for bioprocessing poultry by-products into valuable antimicrobial products.

METHODS AND RESULTS

The complete genome of B. velezensis P45 was sequenced using the Illumina MiSeq platform, showing 4455 protein and 98 RNA coding sequences according to the annotation on the RAST server. Moreover, the genome contains eight gene clusters for the production of antimicrobial secondary metabolites and 25 putative protease-related genes, which can be related to feather-degrading activity. Then, in vitro tests were performed to determine the production of antimicrobial compounds using feather, feather meal and brain-heart infusion (BHI) cultures. Antimicrobial activity was observed in feather meal and BHI media, reaching 800 and 3200 AU ml^-1 against Listeria monocytogenes respectively. Mass spectrometry analysis indicates the production of antimicrobial lipopeptides surfactin, fengycin and iturin.

CONCLUSIONS

The biotechnological potential of B. velezensis P45 was deciphered through genome analysis and in vitro studies. This strain produced antimicrobial lipopeptides growing on feather meal, a low-cost substrate.

SIGNIFICANCE AND IMPACT OF STUDY

The production of antimicrobial peptides by this keratinolytic strain may represent a sustainable alternative for recycling by-products from poultry industry. Furthermore, whole B. velezensis P45 genome sequence was obtained and deposited.

Modeling the time course of ComX: towards molecular process control for Bacillus wild-type cultivations

Wild-type cultivations are of invaluable relevance for industrial biotechnology when it comes to the agricultural or food sector. Here, genetic engineering is hardly applicable due to legal barriers and consumer’s demand for GMO-free products. An important pillar for wild-type cultivations displays the genus Bacillus. One of the challenges for Bacillus cultivations is the global ComX-dependent quorum sensing system. Here, molecular process control can serve as a tool to optimize the production process without genetic engineering. To realize this approach, quantitative knowledge of the mechanism is essential, which, however, is often available only to a limited extent. The presented work provides a case study based on the production of cyclic lipopeptide surfactin, whose expression is in dependence of ComX, using natural producer B. subtilis DSM 10 ^T. First, a surfactin reference process with 40 g/L of glucose was performed as batch fermentation in a pilot scale bioreactor system to gain novel insights into kinetic behavior of ComX in relation to surfactin production. Interestingly, the specific surfactin productivity did not increase linearly with ComX activity. The data were then used to derive a mathematic model for the time course of ComX in dependence of existing biomass, biomass growth as well as a putative ComX-specific protease. The newly adapted model was validated and transferred to other batch fermentations, employing 20 and 60 g/L glucose. The applied approach can serve as a model system for molecular process control strategies, which can thus be extended to other quorum sensing dependent wild-type cultivations.

The Role of Surfactin Production by Bacillus velezensis on Colonization, Biofilm Formation on Tomato Root and Leaf Surfaces and Subsequent Protection (ISR) against Botrytis cinerea

Many aspects regarding the role of lipopeptides (LPs) in bacterial interaction with plants are not clear yet. Of particular interest is the LP family of surfactin, immunogenic molecules involved in induced systemic resistance (ISR) and the bacterial colonization of plant surfaces. We hypothesize that the concentration of surfactin produced by a strain correlates directly with its ability to colonize and persist on different plant surfaces, which conditions its capacity to trigger ISR. We used two Bacillus velezensis strains (BBC023 and BBC047), whose antagonistic potential in vitro is practically identical, but not on plant surfaces. The surfactin production of BBC047 is 1/3 higher than that of BBC023. Population density and SEM images revealed stable biofilms of BBC047 on leaves and roots, activating ISR on both plant surfaces. Despite its lower surfactin production, strain BBC023 assembled stable biofilms on roots and activated ISR. However, on leaves only isolated, unstructured populations were observed, which could not activate ISR. Thus, the ability of a strain to effectively colonize a plant surface is not only determined through its production of surfactin. Multiple aspects, such as environmental stressors or compensation mechanisms may influence the process. Finally, the importance of surfactin lies in its impacts on biofilm formation and stable colonization, which finally enables its activity as an elicitor of ISR.

Genomic Features and Molecular Function of a Novel Stress-Tolerant Bacillus halotolerans Strain Isolated from an Extreme Environment

Simple Summary

The Qinghai–Tibet Plateau is known as the “third pole of the world”. Due to the extreme geographical location, Qinghai–Tibet Plateau has unique ecosystems characterized by oxygen deficiency, low temperature, high salinity and alkalinity. We carried out the current study to explore the excellent extremophilic Bacillus strains via potential stress resistance as well as biocontrol properties in the Qinghai–Tibet Plateau. We found a Bacillus halotolerans strain with a promising ability to withstand harsh environments and which also exhibits an optimistic biocontrol activity against plant pathogens. We revealed the whole genome sequencing and its taxonomic position and elucidated its molecular functions that were responsible for enhancing stress tolerance as well as suppressing plant pathogens at the genetic level. Lastly, we identified this strain harbored the specific genes associated with stresses resistance, biocontrol function, and can be used as a biological agent in the agriculture field.

Abstract

Due to its topographical position and climatic conditions, the Qinghai–Tibet Plateau possesses abundant microorganism resources. The extremophilic strain KKD1 isolated from Hoh Xil possesses strong stress tolerance, enabling it to propagate under high salinity (13%) and alkalinity (pH 10.0) conditions. In addition, KKD1 exhibits promising biocontrol activity against plant pathogens. To further explore these traits at the genomic level, we performed whole-genome sequencing and analysis. The taxonomic identification according to the average nucleotide identity based on BLAST revealed that KKD1 belongs to Bacillus halotolerans. Genetic screening of KKD1 revealed that its stress resistance mechanism depends on osmotic equilibrium, membrane transportation, and the regulation of ion balance under salt and alkaline stress. The expression of genes involved in these pathways was analyzed using real-time quantitative PCR. The presence of different gene clusters encoding antimicrobial secondary metabolites indicated the various pathways by which KKD1 suppresses phytopathogenic growth. Moreover, the lipopeptides surfactin and fengycin were identified as being significant antifungal components of KKD1. Through comparative genomics analysis, we noticed that KKD1 harbored specific genes involved in stress resistance and biocontrol, thus providing a new perspective on the genomic features of the extremophilic Bacillus species.

Expression of degQ gene and its effect on lipopeptide production as well as formation of secretory proteases in Bacillus subtilis strains

Bacillus subtilis is described as a promising production strain for lipopeptides. In the case of B. subtilis strains JABs24 and DSM10T , surfactin and plipastatin are produced. Lipopeptide formation is controlled, among others, by the DegU response regulator. The activating phospho-transfer by the DegS sensor kinase is stimulated by the pleiotropic regulator DegQ, resulting in enhanced DegU activation. In B. subtilis 168, a point mutation in the degQ promoter region leads to a reduction in gene expression. Corresponding reporter strains showed a 14-fold reduced expression. This effect on degQ expression and the associated impact on lipopeptide formation was examined for B. subtilis JABs24, a lipopeptide-producing derivative of strain 168, and B. subtilis wild-type strain DSM10T , which has a native degQ expression. Based on the stimulatory effects of the DegU regulator on secretory protease formation, the impact of degQ expression on extracellular protease activity was additionally investigated. To follow the impact of degQ, a deletion mutant was constructed for DSM10T , while a natively expressed degQ version was integrated into strain JABs24. This allowed strain-specific quantification of the stimulatory effect of degQ expression on plipastatin and the negative effect on surfactin production in strains JABs24 and DSM10T . While an unaffected degQ expression reduced surfactin production in JABs24 by about 25%, a sixfold increase in plipastatin was observed. In contrast, degQ deletion in DSM10T increased surfactin titer by threefold but decreased plipastatin production by fivefold. In addition, although significant differences in extracellular protease activity were detected, no decrease in plipastatin and surfactin produced during cultivation was observed.

Peptide-based system for sensing Pb2+ and molecular logic computing

Peptides with recognition, assembly, various activities exhibit strong power and application prospects in sensing, material science, biomedicine. However, peptide-based sensing and expanding application is still at an early stage. Herein, a peptide-based sensing and logic system was developed for highly sensitive and selective detection of Pb²⁺ and implementation of logic operations. Our Pb²⁺ assay method was ultra-rapid (less than 1 min), direct, simple with detection limit of 0.75 nM. Flexibility and scalability of peptide-based solution system facilitated the execution of sensing and logic operations from simple to complex. This research will not only inspire discovery and comprehensive applications (such as sensing and assembly) of more functional peptides, but also provide more opportunities for development and design of peptide-based systems and molecular information technologies.

Comprehensive genomic analysis of Bacillus velezensis AL7 reveals its biocontrol potential against Verticillium wilt of cotton

Verticilllium wilt of cotton is a devastating soil-borne disease, which is caused by Verticillium dahliae Kleb. Bacillus velezensis strain AL7 was isolated from cotton soil. This strain efficiently inhibited the growth of V. dahliae. But the mechanism of the biocontrol strain AL7 remains poorly understood. To understand the possible genetic determinants for biocontrol traits of this strain, we conducted phenotypic, phylogenetic and comparative genomics analysis. Phenotypic analysis showed that strain AL7 exhibited broad-spectrum antifungal activities. We determined that the whole genome sequence of B. velezensis AL7 is a single circular chromosome that is 3.89 Mb in size. The distribution of putative gene clusters that could benefit to biocontrol activities was found in the genome. Phylogenetic analysis of Bacillus strains by using single core-genome clearly placed strain AL7 into the B. velezensis. Meantime, we performed comparative analyses on four Bacillus strains and observed subtle differences in their genome sequences. In addition, comparative genomics analysis showed that the core genomes of B. velezensis are more abundant in genes relevant to secondary metabolism compared with B. subtilis strains. Single mutant in the biosynthetic genes of fengycin demonstrated the function of fengycin in the antagonistic activity of B. velezensis AL7. Here, we report a new biocontrol bacterium B. velezensis AL7 and fengycin contribute to the biocontrol efficacy of the strain. The results showed in the research further sustain the potential of B. velezensis AL7 for application in agriculture production and may be a worthy biocontrol strain for further studies.

Direct Antibiotic Activity of Bacillibactin Broadens the Biocontrol Range of Bacillus amyloliquefaciens MBI600

Bacillus amyloliquefaciens is considered the most successful biological control agent due to its ability to colonize the plant rhizosphere and phyllosphere where it outgrows plant pathogens by competition, antibiosis, and inducing plant defense. Its antimicrobial function is thought to depend on a diverse spectrum of secondary metabolites, including peptides, cyclic lipopeptides, and polyketides, which have been shown to target mostly fungal pathogens. In this study, we isolated and characterized the catecholate siderophore bacillibactin by B. amyloliquefaciens MBI600 under iron-limiting conditions and we further identified its potential antibiotic activity against plant pathogens. Our data show that bacillibactin production restrained in vitro and in planta growth of the nonsusceptible (to MBI600) pathogen Pseudomonas syringae pv. tomato. Notably, it was also related to increased antifungal activity of MBI600. In addition to bacillibactin biosynthesis, iron starvation led to upregulation of specific genes involved in microbial fitness and competition. IMPORTANCE Siderophores have mostly been studied concerning their contribution to the fitness and virulence of bacterial pathogens. In the present work, we isolated and characterized for the first time the siderophore bacillibactin from a commercial bacterial biocontrol agent. We proved that its presence in the culture broth has significant biocontrol activity against nonsusceptible bacterial and fungal phytopathogens. In addition, we suggest that its activity is due to a new mechanism of action, that of direct antibiosis, rather than by competition through iron scavenging. Furthermore, we showed that bacillibactin biosynthesis is coregulated with the transcription of antimicrobial metabolite synthases and fitness regulatory genes that maximize competition capability. Finally, this work highlights that the efficiency and range of existing bacterial biocontrol agents can be improved and broadened via the rational modification of the growth conditions of biocontrol organisms.

Review of antiviral peptides for use against zoonotic and selected non-zoonotic viruses

Viruses remain one of the leading causes of animal and human disease. Some animal viral infections spread sporadically to human populations, posing a serious health risk. Particularly the emerging viral zoonotic diseases such as the novel, zoonotic coronavirus represent an actual challenge for the scientific and medical community. Besides human health risks, some animal viral infections, although still not zoonotic, represent important economic loses to the livestock industry. Viral infections pose a genuine concern for which there has been an increasing interest for new antiviral molecules. Among these novel compounds, antiviral peptides have been proposed as promising therapeutic options, not only for the growing body of evidence showing hopeful results but also due to the many adverse effects of chemical-based drugs. Here we review the current progress, key targets and considerations for the development of antiviral peptides (AVPs). The review summarizes the state of the art of the AVPs tested in zoonotic (coronaviruses, Rift Valley fever viruses, Eastern Equine Encephalitis Virus, Dengue and Junín virus) and also non-zoonotic farm animal viruses (avian and cattle viruses). Their molecular target, amino acid sequence and mechanism of action are summarized and reviewed. Antiviral peptides are currently on the cutting edge since they have been reported to display anti-coronavirus activity. Particularly, the review will discuss the specific mode of action of AVPs that specifically inhibit the fusion of viral and host-cell membranes for SARS-CoV-2, showing in detail some important features of the fusion inhibiting peptides that target the spike protein of these risky viruses.

D-Amino Acid-Containing Lipopeptides Derived from the Lead Peptide BP100 with Activity against Plant Pathogens

From a previous collection of lipopeptides derived from BP100, we selected 18 sequences in order to improve their biological profile. In particular, analogues containing a D-amino acid at position 4 were designed, prepared, and tested against plant pathogenic bacteria and fungi. The biological activity of these sequences was compared with that of the corresponding parent lipopeptides with all L-amino acids. In addition, the influence of the length of the hydrophobic chain on the biological activity was evaluated. Interestingly, the incorporation of a D-amino acid into lipopeptides bearing a butanoyl or a hexanoyl chain led to less hemolytic sequences and, in general, that were as active or more active than the corresponding all L-lipopeptides. The best lipopeptides were BP475 and BP485, both incorporating a D-Phe at position 4 and a butanoyl group, with MIC values between 0.8 and 6.2 µM, low hemolysis (0 and 24% at 250 µM, respectively), and low phytotoxicity. Characterization by NMR of the secondary structure of BP475 revealed that the D-Phe at position 4 disrupts the α-helix and that residues 6 to 10 are able to fold in an α-helix. This secondary structure would be responsible for the high antimicrobial activity and low hemolysis of this lipopeptide.

Fengycin A Analogues with Enhanced Chemical Stability and Antifungal Properties

Fengycins are cyclic lipo-depsipeptides produced by Bacillus spp. that display potent antifungal properties but are chemically unstable. This instability has meant that no total synthesis of any fengycin has been published. Here we report the synthesis of fengycin A analogues that display enhanced antifungal properties and chemical stability under both basic and acidic conditions. The analogues prepared also demonstrate that the fengycin core structure can be modified and simplified without the loss of antifungal activity.

Discovery of Surfactins as Inhibitors of MicroRNA Processing Using Cat-ELCCA

MicroRNAs (miRNAs) are a family of small noncoding RNAs that regulate gene expression. Due to their important activity in the fine-tuning of protein translation, abnormal expression of miRNAs has been linked to many human diseases, making the targeting of miRNAs attractive as a novel therapeutic strategy. Accordingly, researchers have been heavily engaged in the discovery of small molecule modulators of miRNAs. With an interest in the identification of new chemical space for targeting miRNAs, we developed a high-throughput screening (HTS) technology, catalytic enzyme-linked click chemistry assay (cat-ELCCA), aimed at the discovery of small molecule ligands for pre-miR-21, a miRNA that is frequently overexpressed in human cancers. From our HTS campaign, we found that natural products, a source of many impactful human medicines, may be a promising source of potential pre-miR-21-selective maturation inhibitors. Herein we describe our first efforts in natural product inhibitor discovery leading to the identification of a depsipeptide class of natural products as RNA-binding inhibitors of Dicer-mediated miRNA processing.

Antifungal mechanism of Bacillus amyloliquefaciens strain GKT04 against Fusarium wilt revealed using genomic and transcriptomic analyses

The application of endophytic bacteria, particularly members of the genus Bacillus, offers a promising strategy for the biocontrol of plant fungal diseases, owing to their sustainability and ecological safety. Although multiple secondary metabolites that demonstrate antifungal capacity have been identified in diverse endophytic bacteria, the regulatory mechanisms of their biosynthesis remain largely unknown. To elucidate this, we sequenced the entire genome of Bacillus amyloliquefaciens GKT04, a strain isolated from banana root, which showed high inhibitory activity against Fusarium oxysporum f. sp. cubense race 4 (FOC4). The GKT04 genome consists of a circular chromosome and a circular plasmid, which harbors 4,087 protein‐coding genes and 113 RNA genes. Eight gene clusters that could potentially encode antifungal components were identified. We further applied RNA‐Seq analysis to survey genome‐wide changes in the gene expression of strain GKT04 during its inhibition of FOC4. In total, 575 upregulated and 242 downregulated genes enriched in several amino acid and carbohydrate metabolism pathways were identified. Specifically, gene clusters associated with difficidin, bacillibactin, and bacilysin were significantly upregulated, and their gene regulatory networks were constructed. Our work thereby provides insights into the genomic features and gene expression patterns of this B. amyloliquefaciens strain, which presents an excellent potential for the biocontrol of Fusarium wilt.

Characterization of Bacillus Species from Market Foods in Beijing, China

Foodborne diseases have been witnessing a constant rising trend worldwide, mainly caused by pathogenic microorganisms, such as Bacillus spp., posing a direct threat to public health. The purpose of this study was to evaluate the biological risk of foodborne and probiotic Bacillus spp. in Beijing markets. A total of 55 Bacillus isolates, including 29 B. cereus, 9 B. licheniformis and 7 B. subtilis, mostly found in dairy products (32.7%), were recovered from 106 samples and identified by matrix-assisted laser desorption/ionization mass spectrometry and polymerase chain reaction methods. The susceptibility towards 16 antibiotics was determined using a broth microdilution method. Bacillus showed a high level of resistance to florfenicol (100%), lincomycin (100%), tiamulin (78.2%) and ampicillin (67.3%), while they were all susceptible or intermediate to vancomycin and rifampin. Additionally, we obtained the whole genome of 19 Bacillus strains using high-throughput sequencing, and the rates of resistance genes van, fosB, erm and tet were 57.9%, 57.9%, 21.1% and 26.3%, respectively. Moreover, 100%, 9.1%, 45.5% and 100% of these isolates carried virulence genes nhe, hbl, cytK and entFM, respectively. Lastly, 60% Bacillus strains were positive in hemolysis tests, and 3 B. licheniformis strains displayed an inhibitory activity on the growth of S. aureus ATCC 29213 using agar overlay technique. Our study outlines the characteristics of foodborne Bacillus spp. and provides information for the monitoring of food safety.

Effects of Bacillus subtilis iturin A on HepG2 cells in vitro and vivo

Iturin A with cyclic peptide and fatty acid chain isolated from Bacillus subtilis fermentation shows a variety of biological activities. Among them, the anticancer activity attracted much attention. However, the molecular mechanism of its inhibitory effect on hepatocellular carcinoma was still unclear. Thus its effect on hepatocellular carcinoma was tested in this research. It was found that iturin A could enter HepG2 cells immediately and cause reactive oxygen species burst, disrupt cell cycle and induce apoptosis, paraptosis and autophagy in vitro. The iturin A without fatty acid chain showed no antitumor activity. Amphiphilic is critical to the activity of iturin A. The anticancer activity of iturin A to hepatocellular carcinoma was also verified in mice models carrying xenograft tumors constructed by HepG2 cells. At a dosage of 3 mg/kg/day, iturin A significantly inhibited the further increase of the tumor weight by 58.55%, and reduced the expression of Ki67 in tumor. In the tumor treated with iturin A, lymphocyte infiltration was found, and the expressions of TGF-β1and PD-L1 were decreased, which indicated that the tumor immune microenvironment was improved. Besides, iturin A showed no significant harm on the health of mice except slight disturbance of liver function. These results suggested that iturin A had significant antitumor effect in vitro and vivo, and provide a basis for the application of iturin A as anticancer agent.

Antifungal activity of silver nanoparticles synthesized by iturin against Candida albicans in vitro and in vivo

Candida albicans (C. albicans) is a fungal pathogen that is difficult to cure clinically due to lack of effective antifungal agents with low toxicity. In this study, iturin, a cyclic peptide having wide antifungal spectrum, was used to synthesize nanosilver particles (AgNPs), and a complex of iturin-AgNPs was formed. The antifungal activity of iturin-AgNPs against C. albicans and its mechanisms were tested in vitro. Iturin-AgNPs were also loaded in chitosan (CS) composite dressing and applied to skin wound healing in mice. As results, iturin-AgNPs showed excellent antifungal activity with the minimum inhibitory concentrations (MIC) of 1.25, 2.5, and 5 μg/mL at C. albicans concentrations of 1×10⁵, 1×10⁶, and 1×10⁷ CFU/mL, respectively. The MIC value still kept at 2.5 μg/mL against C. albicans (10⁵ CFU/mL) after 15 regeneration, showing less induction of drug resistance to the pathogenic fungus. The antifungal mechanisms of iturin-AgNPs against C. albicans were identified as the increase of membrane permeability, damage of cell membrane integrity, and leakage of cellular protein and nucleic acids. No toxicity was found for iturin-AgNPs to HaCaT cells at concentrations of lower than 10 μg/mL. In wound healing application, iturin-AgNP CS composite dressing significantly accelerated the healing of C. albicans infected skin wounds at the early 10 days. In conclusion, iturin-AgNPs were developed as an efficient antifungal agent against C. albicans in vitro and in vivo and showed potential application in wound healing promotion.

Recent Trends on Biosurfactants With Antimicrobial Activity Produced by Bacteria Associated With Human Health: Different Perspectives on Their Properties, Challenges, and Potential Applications

The attention towards the bacteria associated with human health is growing more and more, above all regarding the bacteria that inhabit the niches offered by the human body, i.e., the gastrointestinal tract, skin, vaginal environment, and lungs. Among the secondary metabolites released by microorganisms associated with human health, little consideration is given to the biosurfactants, molecules with both hydrophobic and hydrophilic nature. Their role in the complex human environment is not only the mere biosurfactant function, but they could also control the microbiota through the quorum sensing system and the antimicrobial activity. These functions protect them and, accordingly, the human body principally from microbial and fungal pathogens. Consequently, nowadays, biosurfactants are emerging as promising bioactive molecules due to their very different structures, biological functions, low toxicity, higher biodegradability, and versatility. Therefore, this review provides a comprehensive perspective of biosurfactants with antimicrobial activity produced by bacteria associated with the human body and related to everything human beings are in contact with, e.g., food, beverages, and food-waste dumping sites. For the first time, the role of an "-omic" approach is highlighted to predict gene products for biosurfactant production, and an overview of the available gene sequences is reported. Besides, antimicrobial biosurfactants' features, challenges, and potential applications in the biomedical, food, and nutraceutical industries are discussed.

Insights into the multitrophic interactions between the biocontrol agent Bacillus subtilis MBI 600, the pathogen Botrytis cinerea and their plant host

Botrytis cinerea is a plant pathogen causing the gray mold disease in a plethora of host plants. The control of the disease is based mostly on chemical pesticides, which are responsible for environmental pollution, while they also pose risks for human health. Furthermore, B. cinerea resistant isolates have been identified against many fungicide groups, making the control of this disease challenging. The application of biocontrol agents can be a possible solution, but requires deep understanding of the molecular mechanisms in order to be effective. In this study, we investigated the multitrophic interactions between the biocontrol agent Bacillus subtilis MBI 600, a new commercialized biopesticide, the pathogen B. cinerea and their plant host. Our analysis showed that this biocontrol agent reduced B. cinerea mycelial growth in vitro, and was able to suppress the disease incidence on cucumber plants. Moreover, treatment with B. subtilis led to induction of genes involved in plant immunity. RNA-seq analysis of B. cinerea transcriptome upon exposure to bacterial secretome, showed that genes coding for MFS and ABC transporters were highly induced. Deletion of the Bcmfs1 MFS transporter gene, using a CRISP/Cas9 editing method, affected its virulence and the tolerance of B. cinerea to bacterial secondary metabolites. These findings suggest that specific detoxification transporters are involved in these interactions, with crucial role in different aspects of B. cinerea physiology.

Recovery of Ag+ by cyclic lipopeptide iturin A and corresponding chain peptide: reaction mechanisms, kinetics, toxicity reduction, and applications

Iturin A, a cyclic lipopeptide produced by Bacillus subtilis, has great potential in removal of Ag⁺ from water, but the mechanisms and kinetic remain unclear. By comparison with the chain peptide (CP) that has the same amino acid sequence as iturin A, the mechanisms were found as iturin A reduced Ag⁺ to Ag⁰ and formed silver nanoparticles (AgNPs) via the groups of Ar-OH, CO, -NH-, O=C-O, and -C(CH).The cycle peptide fraction played an important role for the faster formation of AgNPs by iturin A than by CP. The overall Ag⁺ removal process by iturin A and CP could be well described by a Freundlich isotherm, with the equilibrium Ag⁺ removal capacity ranging from 58.41 to 61.03 mg/g within 293.15-333.15 K for iturin A. With the application of iturin A, the overall removal rate of Ag⁺ reached 91.8% in wastewater, the formed AgNPs could be easily recovered via charging the direct electric current, and the toxicity of Ag⁺ to paddy growth was greatly reduced.

Ligand screening assay for the enzyme kallikrein immobilized on NHS-activated Sepharose

Human tissue kallikreins (KLKs) are serine proteases involved in various physiological and pathological conditions, including cancer and neurological disorders. These enzymes constitute attractive drug targets, which has stimulated the search for new KLK inhibitors. In this study, we have covalently immobilized porcine pancreas KLK on an NHS-activated Sepharose matrix, to obtain KLK-Sepharose-NHS. The immobilized enzyme showed high recovered activity and maintained the ability of free KLK to recognize the synthetic substrate Z-Phe-Arg-AMC (K_Mapp = 10.3 ± 0.9 μM). As proof of concept, we used leupeptin as a reference inhibitor to perform inhibition studies for KLK-Sepharose-NHS and to determine the half-maximal inhibitory concentration (IC₅₀ = 0.13 ± 0.01 μM), the inhibition constant (K_i = 0.06 μM), and the leupeptin inhibition mechanism. We evaluated several complex matrixes (plant crude extract) by the same bioassay, to demonstrate their applicability. The species Solanum lycocarpum, Stryphnodendron adstringens, and Psychotria carthagenensis gave the best results. KLK-Sepharose-NHS was fully active after six consecutive reaction cycles and retained about 60 % of its initial activity after being used for at least five months, so the bioassay developed herein is a promising strategy to screen and to identify KLK ligands.

Evidence that protein corona reduces the release of antimicrobial peptides from polymeric nanocapsules in milk

The antimicrobial peptide produced by Bacillus velesensis P34 has a broad activity against Gram-positive bacteria, showing potential as natural food preservative. In this work, nanocapsules (NCs) containing the peptide P34 were produced using the polymers poly-ε-caprolactone (PCL) or Eudragit RS-100 (EUD), and their antimicrobial activities were assessed evaluating L. monocytogenes growth in synthetic media, milk and isolated milk proteins. As results, cationic and anionic nanocapsules were obtained, with zeta potential ranging from +15 to +28 mV for EUD and around -19 mV for PCL, and average diameter in the range of 104-130 nm and 224-245 nm, respectively. In the antimicrobial tests, only the P34-EUD NCs presented activity against L. monocytogenes in BHI broth, possibly due to the EUD high swelling and permeability properties, as compared with PCL. In whole and skimmed milk, the P34-EUD NCs caused no inhibition of L. monocytogenes growth, due to a possible interaction of casein proteins with the NCs surface resulting in protein corona formation, which interfered with the antimicrobial peptide release. Therefore, the application of polymeric NCs as antimicrobial delivery systems in foods could be limited by the polymer type, and the adhesion of specific matrix proteins that could form protein corona, reducing the bioactive compound release.

The Surfactin-Like Lipopeptides From Bacillus spp.: Natural Biodiversity and Synthetic Biology for a Broader Application Range

Surfactin is a lipoheptapeptide produced by several Bacillus species and identified for the first time in 1969. At first, the biosynthesis of this remarkable biosurfactant was described in this review. The peptide moiety of the surfactin is synthesized using huge multienzymatic proteins called NonRibosomal Peptide Synthetases. This mechanism is responsible for the peptide biodiversity of the members of the surfactin family. In addition, on the fatty acid side, fifteen different isoforms (from C12 to C17) can be incorporated so increasing the number of the surfactin-like biomolecules. The review also highlights the last development in metabolic modeling and engineering and in synthetic biology to direct surfactin biosynthesis but also to generate novel derivatives. This large set of different biomolecules leads to a broad spectrum of physico-chemical properties and biological activities. The last parts of the review summarized the numerous studies related to the production processes optimization as well as the approaches developed to increase the surfactin productivity of Bacillus cells taking into account the different steps of its biosynthesis from gene transcription to surfactin degradation in the culture medium.

Transcriptomic and Functional Analyses Indicate Novel Anti-viral Mode of Actions on Tobacco Mosaic Virus of a Microbial Natural Product ε-Poly-l-lysine

Novel anti-viral natural product ε-poly-l-lysine (ε-PL) produced by Streptomyces is a homopolymer of l-lysine, of which the underlying molecular mode of action remains to be further elucidated. In this study, ε-PL induced significant fragmentation of tobacco mosaic virus (TMV) virions and delayed the systemic infection of TMV-GFP as well as wild-type TMV in plants. ε-PL treatment also markedly inhibited RNA accumulation of TMV in tobacco BY-2 protoplasts. The results of RNA-seq indicated that the agent induced significantly differential expression of genes that are associated with defense response, stress response, autophagy, and ubiquitination. Among them, 15 critical differential expressed genes were selected for real-time quantitative PCR validation. We further demonstrated that ε-PL can induce host defense responses by assessing the activity of several defense-related enzymes in plants. Our results provided valuable insights into molecular anti-viral mode of action for ε-PL, which is expected to be applied as a novel microbial natural product against plant virus diseases.

The Influence of Obesity and Associated Fatty Acids on Placental Inflammation

PURPOSE

Maternal obesity, affecting nearly 1 in 4 pregnancies, is associated with increased circulating saturated fatty acids, such as palmitate. These fatty acids are implicated in placental inflammation, which may in turn exacerbate both maternal-fetal tolerance and responses to pathogens, such as group B Streptococcus. In this review, we address the question, "How do obesity and associated fatty acids influence placental inflammation?"

METHODS

In this narrative review, we searched PubMed and Google Scholar using combinations of the key words placental inflammation or pregnancy and lipids, fatty acids, obesity, palmitate, or other closely related search terms. We also used references found within these articles that may have been absent from our original search queries. We analyzed methods and key results of these articles to compare and contrast their findings, which were occasionally at odds with each other.

FINDINGS

Although obesity can be studied as a whole, complex phenomena with in vivo mouse models and human samples from patients with obesity, in vitro modeling often relies on the treatment of cells or tissues with ≥1 fatty acids and occasionally other compounds (eg, glucose and insulin). We found that palmitate, most commonly used in vitro to recreate hallmarks of obesity, induces apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation in many placental cell types. We compare this to in vivo models of obesity wherever possible. We found that obesity as a whole may have more complex regulation of these phenomena (apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation) compared with in vitro models of fatty acid treatment (primarily palmitate) because of the presence of unsaturated fatty acids (ie, oleate), which may have anti-inflammatory effects.

IMPLICATIONS

The interaction of unsaturated fatty acids with saturated fatty acids may ameliorate many inflammatory effects of saturated fatty acids alone, which complicates interpretation of in vitro studies that focus on a particular fatty acid in isolation. This complication may explain why certain studies of obesity in vivo have differing outcomes from studies of specific fatty acids in vitro.

Photo-induced radical thiol-ene chemistry: a versatile toolbox for peptide-based drug design

While the global market for peptide/protein-based therapeutics is witnessing significant growth, the development of peptide drugs remains challenging due to their low oral bioavailability, poor membrane permeability, and reduced metabolic stability. However, a toolbox of chemical approaches has been explored for peptide modification to overcome these obstacles. In recent years, there has been a revival of interest in photoinduced radical thiol-ene chemistry as a powerful tool for the construction of therapeutic peptides.

Engineering of a genome-reduced strain Bacillus amyloliquefaciens for enhancing surfactin production

Background

Genome reduction and metabolic engineering have emerged as intensive research hotspots for constructing the promising functional chassis and various microbial cell factories. Surfactin, a lipopeptide-type biosurfactant with broad spectrum antibiotic activity, has wide application prospects in anticancer therapy, biocontrol and bioremediation. Bacillus amyloliquefaciens LL3, previously isolated by our lab, contains an intact srfA operon in the genome for surfactin biosynthesis.

Results

In this study, a genome-reduced strain GR167 lacking ~ 4.18% of the B. amyloliquefaciens LL3 genome was constructed by deleting some unnecessary genomic regions. Compared with the strain NK-1 (LL3 derivative, ΔuppΔpMC1), GR167 exhibited faster growth rate, higher transformation efficiency, increased intracellular reducing power level and higher heterologous protein expression capacity. Furthermore, the chassis strain GR167 was engineered for enhanced surfactin production. Firstly, the iturin and fengycin biosynthetic gene clusters were deleted from GR167 to generate GR167ID. Subsequently, two promoters PR_suc and PR_tpxi from LL3 were obtained by RNA-seq and promoter strength characterization, and then they were individually substituted for the native srfA promoter in GR167ID to generate GR167IDS and GR167IDT. The best mutant GR167IDS showed a 678-fold improvement in the transcriptional level of the srfA operon relative to GR167ID, and it produced 311.35 mg/L surfactin, with a 10.4-fold increase relative to GR167.

Conclusions

The genome-reduced strain GR167 was advantageous over the parental strain in several industrially relevant physiological traits assessed and it was highlighted as a chassis strain for further genetic modification. In future studies, further reduction of the LL3 genome can be expected to create high-performance chassis for synthetic biology applications.

Structural and Functional Insights into Iturin W, a Novel Lipopeptide Produced by the Deep-Sea Bacterium Bacillus sp. Strain wsm-1

Plant disease caused by pathogenic fungi is one of the most devastating diseases, which affects the food safety of the whole world to a great extent. Biological control of plant diseases by microbial natural products is more desirable than traditional chemical control. In this study, we discovered a novel lipopeptide, iturin W, with promising prospects in biological control of plant diseases. Moreover, the effects of different carbon and nitrogen sources and amino acids on production of C₁₄ iturin W and C₁₅ iturin W would provide a reasonable basis for the optimization of the fermentation process of lipopeptides. Notably, the structure of iturin W was different from that of any previously reported lipopeptide, suggesting that deep-sea microorganisms might produce many novel natural products and have significant potential in the development of biological products in the future.

In the present study, a deep-sea bacterial strain designated Bacillus sp. strain wsm-1 was screened and found to exhibit strong antifungal activity against many plant-pathogenic fungi, and corresponding antifungal agents were thereby purified and determined by tandem mass spectrometry to be two cyclic lipopeptide homologs. These homologs, which were different from any previously reported lipopeptides, were identified to possess identical amino acid sequences of β-amino fatty acid-Asn-Ser-Asn-Pro-Tyr-Asn-Gln and deduced as two novel lipopeptides designated C₁₄ iturin W and C₁₅ iturin W. Electron microscopy observation indicated that both iturin W homologs caused obvious morphological changes and serious disruption of plasma membrane toward fungal cells, while C₁₅ iturin W exhibited more serious cell damages than C₁₄ iturin W did, which was well consistent with the results of the antifungal activity assays. To improve the yield and antifungal activity of iturin W, the effects of different carbon and nitrogen sources and amino acids on production of C₁₄ iturin W and C₁₅ iturin W were investigated. The results indicated that supplements of most of the detected carbon and nitrogen sources could increase the yield of C₁₄ iturin W, but inhibit the yield of C₁₅ iturin W, while supplements of tryptone and most of the detected amino acids could increase the yield of both C₁₄ iturin W and C₁₅ iturin W.

IMPORTANCE Plant disease caused by pathogenic fungi is one of the most devastating diseases, which affects the food safety of the whole world to a great extent. Biological control of plant diseases by microbial natural products is more desirable than traditional chemical control. In this study, we discovered a novel lipopeptide, iturin W, with promising prospects in biological control of plant diseases. Moreover, the effects of different carbon and nitrogen sources and amino acids on production of C₁₄ iturin W and C₁₅ iturin W would provide a reasonable basis for the optimization of the fermentation process of lipopeptides. Notably, the structure of iturin W was different from that of any previously reported lipopeptide, suggesting that deep-sea microorganisms might produce many novel natural products and have significant potential in the development of biological products in the future.

Biosurfactants as a Novel Additive in Pharmaceutical Formulations: Current Trends and Future Implications

BACKGROUND

Surfactants are an important category of additives that are used widely in most of the formulations as solubilizers, stabilizers, and emulsifiers. Current drug delivery systems comprise of numerous synthetic surfactants (such as Cremophor EL, polysorbate 80, Transcutol-P), which are associated with several side effects though used in many formulations. Therefore, to attenuate the problems associated with conventional surfactants, a new generation of surface-active agents is obtained from the metabolites of fungi, yeast, and bacteria, which are termed as biosurfactants.

OBJECTIVES

In this article, we critically analyze the different types of biosurfactants, their origin along with their chemical and physical properties, advantages, drawbacks, regulatory status, and detailed pharmaceutical applications.

METHODS

243 papers were reviewed and included in this review.

RESULTS

Briefly, Biosurfactants are classified as glycolipids, rhamnolipids, sophorolipids, trehalolipids, surfactin, lipopeptides & lipoproteins, lichenysin, fatty acids, phospholipids, and polymeric biosurfactants. These are amphiphilic biomolecules with lipophilic and hydrophilic ends and are used as drug delivery vehicles (foaming, solubilizer, detergent, and emulsifier) in the pharmaceutical industry. Despite additives, they have some biological activity as well (anti-cancer, anti-viral, anti-microbial, P-gp inhibition, etc.). These biomolecules possess better safety profiles and are biocompatible, biodegradable, and specific at different temperatures.

CONCLUSION

Biosurfactants exhibit good biomedicine and additive properties that can be used in developing novel drug delivery systems. However, more research should be driven due to the lack of comprehensive toxicity testing and high production cost which limits their use.

Bacterial Natural Compounds with Anti-Inflammatory and Immunomodulatory Properties (Mini Review)

Inflammation is part of the body's complex biological response to harmful stimuli such as damaged cells, pathogens, or irritants. It is a protective response involving blood cells, immune cells, and molecular mediators. The inflammation not only can eliminate the primary cause of cell injury but also clears out necrotic cells, tissue damaged from the original insults and inflammatory process. Furthermore, it can initiate tissue repair. Pro-inflammatory cytokines are produced predominantly by activated macrophages and are involved in the up-regulation of inflammatory reactions. They are involved in further regulating inflammatory reactions. There is ample evidence that some pro-inflammatory cytokines, such as interleukin 1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), are involved in the pathological pain process. Some of the natural compounds promote cytokines production and inhibit inflammatory responses. The natural compounds which are produced from microorganisms such as omega-3 fatty acid, cyclic peptide, antimicrobial peptide, oligosaccharides, and polysaccharides can reduce inflammation and could be easily incorporated into the diet without any adverse effects. For example, SCFA (short-chain fatty acids), peptide bacteriocin, and polycyclic peptide bacteriocin (nisin) could be used in the treatment of atherosclerosis, orthopedic postoperative infections, and mycobacterium tuberculosis infection, respectively. Also, fatty acids (saturated and unsaturated fatty acids) can be introduced as anti-inflammatory drugs. This review article summarizes bacterial natural compounds with modulating effects on cytokines that are surveyed which may have potential anti-inflammatory drug-like activity.

Kinetic study and characterization of surfactin production by Bacillus subtilis UFPEDA 438 using sugarcane molasses as carbon source

The present study evaluated the surfactin production by Bacillus subtilis UFPEDA 438 using sugarcane molasses as a substrate. The effects of the cultivation conditions (temperature, agitation and aeration ratio) on the biosurfactant production and kinetic parameters were investigated. Characteristics of the biosurfactant were obtained after analyses of the emulsification index (EI) and critical micellar concentration (CMC) of the fermentation broth. The results showed that in relation to the product its formation kinetics is strongly affected by operational conditions. It was also observed that surfactin production can be partially dependent or fully independent on microbial growth. The maximum values of surfactin concentration (199.45 ± 0.13 mg/L) and productivity (8,187 mg/L.h) were obtained in the culture under cultivation time of 24 h, temperature of 36 °C, agitation of 100 rpm and aeration ratio of 0.4. Under optimal conditions, the fermentation broth achieved good emulsification capacity (EI >40%) and CMC value of 20.73 mg/L. The results revealed that Bacillus subtilis UFPEDA 438 is a good producer of biosurfactant and that sugarcane molasses is a viable substrate for the production of surfactin.

Endophytic Strain Bacillus subtilis 26DCryChS Producing Cry1Ia Toxin from Bacillus thuringiensis Promotes Multifaceted Potato Defense against Phytophthora infestans (Mont.) de Bary and Pest Leptinotarsa decemlineata Say

Novel properties of a previously obtained Bacillus subtilis 26DCryChS strain are described. The B. subtilis 26DCryChS strain is able to produce Cry1Ia δ-endotoxin from B. thuringiensis B-5351 and to exist in internal plant tissues of potato plants in the same manner as the endophytic B. subtilis 26D source strain (487 ± 53 and 420 ± 63 CFU*10³/g, respectively). B. subtilis 26DCryChS, as much as the original B. subtilis 26D strain, inhibited mycelium growth of oomycete Phytophthora infestans (Mont.) de Bary and reduced late blight symptoms development on plants by 35% compared with non-treated ones, as well as showed insecticidal activity against Leptinotarsa decemlineata. Production of the fluorescent GFP protein in the B. subtilis 26D genome allowed visualizing the endophytes around damaged sites on beetle intestines. Bacillus strains under investigation induced systemic resistance to P. infestans and L. decemlineata through the activation of the transcription of PR genes in potato plants. Thus, the B. subtilis 26DCryChS strain was able to induce transcription of jasmonate-dependent genes and acquired the ability to promote transcription of a salicylate-dependent gene (PR1) in plants infected with the late blight agent and damaged by Colorado potato beetle larvae. The B. subtilis 26DCryChS strain could be put forward as a modern approach for biocontrol agents design.

Biliary Tract Carcinogenesis Model Based on Bile Metaproteomics

Purpose: To analyze human and bacteria proteomic profiles in bile, exposed to a tumor vs. non-tumor microenvironment, in order to identify differences between these conditions, which may contribute to a better understanding of pancreatic carcinogenesis.

Patients and Methods: Using liquid chromatography and mass spectrometry, human and bacterial proteomic profiles of a total of 20 bile samples (7 from gallstone (GS) patients, and 13 from pancreatic head ductal adenocarcinoma (PDAC) patients) that were collected during surgery and taken directly from the gallbladder, were compared. g:Profiler and KEGG (Kyoto Encyclopedia of Genes and Genomes) Mapper Reconstruct Pathway were used as the main comparative platform focusing on over-represented biological pathways among human proteins and interaction pathways among bacterial proteins.

Results: Three bacterial infection pathways were over-represented in the human PDAC group of proteins. IL-8 is the only human protein that coincides in the three pathways and this protein is only present in the PDAC group. Quantitative and qualitative differences in bacterial proteins suggest a dysbiotic microenvironment in the PDAC group, supported by significant participation of antibiotic biosynthesis enzymes. Prokaryotes interaction signaling pathways highlight the presence of zeatin in the GS group and surfactin in the PDAC group, the former in the metabolism of terpenoids and polyketides, and the latter in both metabolisms of terpenoids, polyketides and quorum sensing. Based on our findings, we propose a bacterial-induced carcinogenesis model for the biliary tract.

Conclusion: To the best of our knowledge this is the first study with the aim of comparing human and bacterial bile proteins in a tumor vs. non-tumor microenvironment. We proposed a new carcinogenesis model for the biliary tract based on bile metaproteomic findings. Our results suggest that bacteria may be key players in biliary tract carcinogenesis, in a long-lasting dysbiotic and epithelially harmful microenvironment, in which specific bacterial species' biofilm formation is of utmost importance. Our finding should be further explored in future using in vitro and in vivo investigations.

Novel Biomedical Functions of Surfactin A from Bacillus subtilis in Wound Healing Promotion and Scar Inhibition

Surfactin produced by Bacillus subtilis is a powerful biosurfactant in food, cosmetics, and pesticide industries. However, its suitability in wound healing applications is uncertain. In this article, we determined the effects of surfactin A from B. subtilis on wound healing, angiogenesis, cell migration, inflammatory response, and scar formation. The results indicated that 80.65 ± 2.03% of surfactin A-treated wounds were closed, whereas 44.30 ± 4.26% of the vehicle-treated wound areas remained open on day 7 (P < 0.05). In mechanisms, it upregulated the expression of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF), accelerated keratinocyte migration through mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signaling pathways, and regulated the secretion of proinflammatory cytokines and macrophage phenotypic switch. More attractive, surfactin A showed a seductive capability to inhibit scar tissue formation by affecting the expression of α-smooth muscle actin (α-SMA) and transforming growth factor (TGF-β). Overall, the study revealed a new function and potential of surfactin A as an affordable and efficient wound healing drug.

Lipopeptide(s) associated with human microbiome as potent cancer drug

Human microbiota comprises of trillions of microbes which have evolved with and continued to live on/ within their human hosts. Different environmental factors and diet have a large impact upon human microbiota population. These microorganisms live in synergy with their hosts and are beneficial to the host in many different ways. Many microorganisms help to fight against human diseases. Cancer is one such diseases which effects a large human population often leading to death. Cancer is also one of the most fatal human diseases killing millions of people world-wide every year. Though many treatment procedures are available but none is 100 % effective in curing cancer. In this review, we seek to understand the role of human microbiota in cancer treatment. Lipopeptide(s) (LPs) produced by different microorganisms can act as efficient drug(s) against cancer. LPs are low molecular weight lipo-proteins that are also known for their anti-cancer activities. As human microbiota belongs to an environment within the host body, a drug prepared using these microorganisms will be easily accepted by the body. This novel approach of using LPs produced by human microbiota can be considered for the much needed change in cancer treatment. Therefore, it is proposed that research should focus on the host-microbe interaction which could pave the way in understanding role played by these microorganisms in cancer treatment.

Chain-End Modifications and Sequence Arrangements of Antimicrobial Peptoids for Mediating Activity and Nano-Assembly

Poly(N-substituted glycine) "peptoids" are an interesting class of peptidomimics that can resist proteolysis and mimic naturally found antimicrobial peptides (AMPs), which exhibit wide spectrum activity against bacteria. This work investigates the possibility of modifying peptoid AMP mimics (AMPMs) with aliphatic lipid "tails" to generate "lipopeptoids" that can assemble into micellar nanostructures, and evaluates their antimicrobial activities. Two families of AMPMs with different distributions of hydrophobic and cationic residues were employed-one with a uniform repeating amphiphilicity, the other with a surfactant-like head-to-tail amphiphilicity. To further evaluate the interplay between self-assembly and activity, the lipopeptoids were variously modified at the AMPM chain ends with a diethylene glycol (EG2) and/or a cationic group (Nlys-Nlys dipeptoid) to adjust amphiphilicity and chain flexibility. Self-assembly was investigated by critical aggregation concentration (CAC) fluorescence assays and dynamic light scattering (DLS). The structure of a key species was also verified by small-angle X-ray scattering (SAXS) and cryo-electron microscopy (cryo-EM). To screen for antibacterial properties, we measured the minimum inhibitory concentrations (MIC) against S. aureus, E. coli, and P. aeruginosa. We found that certain combinations of lipid tail and AMPM sequences exhibit increased antibacterial activity (i.e., decreased MICs). Perhaps counter-intuitively, we were particularly interested in increased MICs in combination with low CACs. Concealing antimicrobial interactions due to packing of AMPMs in nano-assemblies could pave the way to AMPMs that may be "inert" even if unintentionally released and prevent microbes from gaining resistance to the lipopeptoids. Overall, incorporation of EG2 significantly improved lipopeptoids packing while the hydrophobic tail length was found to have a major influence over the MIC. One particular sequence, which we named C15-EG2-(kss)4, exhibited a very low CAC of 34 μM (0.0075 wt.%) and a significantly increased MIC above values for the unmodified AMPM. With the sequence design trends uncovered from this study, future work will focus on discovering more species such as C15-EG2-(kss)4 and on investigating release mechanisms and the potency of the released lipopeptoids.

Anaerobiosis: A Surfactant Helps Bacteria Breathe a Sigh of Relief

Oxygen is essential for many organisms who have therefore evolved mechanisms to enable survival during hypoxia. A new study describes how a well-known bacterial surfactant, called surfactin, facilitates bacterial viability when oxygen becomes limiting by reducing oxygen consumption.

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.

Isolation and Characterization of Biosurfactant-Producing Bacteria From Oil Well Batteries With Antimicrobial Activities Against Food-Borne and Plant Pathogens

Microbial biosurfactants, produced by fungi, yeast, and bacteria, are surface-active compounds with emulsifying properties that have a number of known activities, including the solubilization of microbial biofilms. In an on-going survey to uncover new or enhanced antimicrobial metabolite-producing microbes from harsh environments, such as oil-rich niches, 123 bacterial strains were isolated from three oil batteries in the region of Chauvin, Alberta, and characterized by 16S rRNA gene sequencing. Based on their nucleotide sequences, the strains are associated with 3 phyla (Actinobacteria, Proteobacteria and Firmicutes), as well as 17 other discrete genera that shared high homology with known sequences, with the majority of these strains identified to the species level. The most prevalent strains associated with the three oil wells belonged to the Bacillus genus. Thirty-four of the 123 strains were identified as biosurfactant-producers, among which Bacillus methylotrophicus strain OB9 exhibited the highest biosurfactant activity based on multiple screening methods and a comparative analysis with the commercially available biosurfactant, Tween 20. B. methylotrophicus OB9 was selected for further antimicrobial analysis and addition of live cultures of B. methylotrophicus OB9 (or partially purified biosurfactant fractions thereof) were highly effective on biofilm disruption in agar diffusion assays against several Gram-negative food-borne bacteria and plant pathogens. Upon co-culturing with B. methylotrophicus OB9, the number of either Salmonella enterica subsp. enterica Newport SL1 or Xanthomonas campestris B07.007 cells significantly decreased after 6 h and were not retrieved from co-cultures following 12 h exposure. These results also translated to studies on plants, where bacterized tomato seedlings with OB9 significantly protected the tomato leaves from Salmonella enterica Newport SL1 contamination, as evidenced by a 40% reduction of log10 CFU of Salmonella/mg leaf tissue compared to non-bacterized tomato leaves. When B. methylotrophicus 0B9 was used for bacterized lettuce, the growth of X. campestris B07.007, the causal agent of bacterial leaf spot of lettuce, was completely inhibited. While limited, these studies are noteworthy as they demonstrate the inhibition spectrum of B. methylotrophicus 0B9 against both human and plant pathogens; thereby making this bacterium attractive for agricultural and food safety applications in a climate where microbial-biofilm persistence is an increasing problem.

An endophytic strain of the genus Bacillus isolated from the seeds of maize (Zea mays L.) has antagonistic activity against maize pathogenic strains

Plant endophytes are microbes that colonize plant internal tissues and are ubiquitously associated with plants. In this study, seven endophytic bacterial strains, 665L2, 725L2, 725R2, 92R2, 728R3, 728R4 and 2416T3, were isolated from seeds of five healthy maize varieties (Zea mays L.) and all identified as Bacillus velezensis by polyphasic taxonomy based on 16S rRNA and gyrA gene phylogenetic analysis. In addition, according to the genotyping results from random amplified polymorphic DNA (RAPD), 665L2, 725L2, 725R2 and 92R2 belonged to the same strain, while 728R3 and 2416T3 belonged to another strain. Pathogenic fungal strains 4, 5 and 6 were isolated from three diseased maize varieties (Zea mays L.), and they were identified as Talaromyces funiculosus, Penicillium oxalicum and Fusarium verticillioides, respectively, by polyphasic taxonomy based on morphological identification, ITS rDNA and bio-control gene phylogenetic analyses. Seven endophytic bacterial Bacillus velezensis strains had favourable antagonistic activity, and antagonistic testing was carried out against the three pathogenic strains, Talaromyces funiculosus 4, Penicillium oxalicum 5 and Fusarium verticillioides 6. Biological control lipopeptide antibiotic genes (bioA, bmyB, ituC, fenD, srfAA, srfAB, yngG and yndJ) were amplified using specific primers, and they were found in the seven endophytic bacterial Bacillus velezensis strains. This study provides a scientific basis for future research on the use of resistant endophytic bacterial resources to enhance crop production.

Fengycins From Bacillus amyloliquefaciens MEP218 Exhibit Antibacterial Activity by Producing Alterations on the Cell Surface of the Pathogens Xanthomonas axonopodis pv. vesicatoria and Pseudomonas aeruginosa PA01

Bacillus amyloliquefaciens MEP₂18 is an autochthonous bacterial isolate with antibacterial and antifungal activities against a wide range of phytopathogenic microorganisms. Cyclic lipopeptides (CLP), particularly fengycins, produced by this bacterium; are the main antimicrobial compounds responsible for the growth inhibition of phytopathogens. In this work, the CLP fraction containing fengycins with antibacterial activity was characterized by LC-ESI-MS/MS. In addition, the antibacterial activity of these fengycins was evaluated on the pathogens Xanthomonas axonopodis pv. vesicatoria (Xav), a plant pathogen causing the bacterial spot disease, and Pseudomonas aeruginosa PA01, an opportunistic human pathogen. In vitro inhibition assays showed bactericidal effects on Xav and PA01. Atomic force microscopy images revealed dramatic alterations in the bacterial surface topography in response to fengycins exposure. Cell damage was evidenced by a decrease in bacterial cell heights and the loss of intracellular content measured by potassium efflux assays. Furthermore, the viability of MRC-5 human normal lung fibroblasts was not affected by the treatment with fengycins. This study shows in vivo evidence on the less-known properties of fengycins as antibacterial molecules and leaves open the possibility of using this CLP as a novel antibiotic.