[Ala4]surfactin, a novel isoform from Bacillus subtilis studied by mass and NMR spectroscopies

Lipopeptides development in cosmetics and pharmaceutical applications: A comprehensive review

Lipopeptides are surface active, natural products of bacteria, fungi and green-blue algae origin, having diverse structures and functionalities. In analogy, a number of chemical synthesis techniques generated new designer lipopeptides with desirable features and functions. Lipopetides are self-assembly guided, supramolecular compounds which have the capacity of high-density presentation of the functional epitopes at the surface of the nanostructures. This feature contributes to their successful application in several industry sectors, including food, feed, personal care, and pharmaceutics. In this comprehensive review, the novel class of ribosomally synthesized lipopeptides is introduced alongside the more commonly occuring non-ribosomal lipopeptides. We highlight key representatives of the most researched as well as recently described lipopeptide families, with emphasis on structural features, self-assembly and associated functions. The common biological, chemical and hybrid production routes of lipopeptides, including prominent analogues and derivatives are also discussed. Furthermore, genetic engineering strategies aimed at increasing lipopeptide yields, diversity and biological activity are summarized and exemplified. With respect to application, this work mainly details the potential of lipopeptides in personal care and cosmetics industry as cleansing agents, moisturizer, anti-aging/anti-wrinkling, skin whitening and preservative agents as well as the pharmaceutical industry as anitimicrobial agents, vaccines, immunotherapy, and cancer drugs. Given that this review addresses human applications, we conclude on the topic of safety of lipopeptide formulations and their sustainable production.

Pseudophomins A-D Produced from Pseudomonas sp. HN8-3 Using an OSMAC Approach and Their Roles in Biocontrol of Phytophthora capsici in Cucumbers

In this study, two new cyclic lipopeptides (CLPs) pseudophomins C (3) and D (4) and two known CLPs pseudophomins A (1) and B (2) were produced and characterized from the bacterial supernatant of Pseudomonas sp. HN8-3 by an OSMAC (one strain-many compounds) approach. OSMAC is a strategy that involves feeding of a single microorganism with divergent substrates to stimulate the production of new secondary metabolites. These pseudophomins were purified and identified via chromatographic methods, droplet collapse assay, genome mining, spectroscopic and spectrometric analyses, and single-crystal X-ray diffraction (XRD). Moreover, bioactivity tests showed that pseudophomins could lyse the zoospores of Phytophthora capsici in vitro, and coapplication of pseudophomins with zoospores of P. capsici further reduced the incidence of P. capsici on cucumber leaves. Collectively, these results indicated that pseudophomins have the potential to be developed as biopesticides for controlling P. capsici in cucumber.

Surfactin isoforms isolated from a mushroom derived Bacillus halotolerans DMG-7-2

A new iso-C₁₄ [Val², Val⁷] surfactin isoform (1) together with eight known ones (2-9), was isolated from the culture of a mushroom derived bacterium, Bacillus halotolerans DMG-7-2. The structures of them were mainly elucidated by NMR and MS data, and the NMR data of 5 also was reported for the first time. The absolute configuration of 1 was determined by Marfey's analysis (for amino acid residues) and the ¹³C NMR calculation of the two plausible epimers of 1 (for fatty acid). Compounds 1-9 showed moderate cytotoxicity against two human cancer cell lines (A549, MCF-7) and mice microglial BV2 cells, the IC₅₀ values ranged from 8.91 to 33.00 µM, and the IC₅₀ values of the positive control 5-FU were 99.94, 71.49 and 0.12 µM, respectively.

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.

Surfactants: physicochemical interactions with biological macromolecules

Macromolecules are essential cellular components in biological systems responsible for performing a large number of functions that are necessary for growth and perseverance of living organisms. Proteins, lipids and carbohydrates are three major classes of biological macromolecules. To predict the structure, function, and behaviour of any cluster of macromolecules, it is necessary to understand the interaction between them and other components through basic principles of chemistry and physics. An important number of macromolecules are present in mixtures with surfactants, where a combination of hydrophobic and electrostatic interactions is responsible for the specific properties of any solution. It has been demonstrated that surfactants can help the formation of helices in some proteins thereby promoting protein structure formation. On the other hand, there is extensive research towards the use of surfactants to solubilize drugs and pharmaceuticals; therefore, it is evident that the interaction between surfactants with macromolecules is important for many applications which includes environmental processes and the pharmaceutical industry. In this review, we describe the properties of different types of surfactants that are relevant for their physicochemical interactions with biological macromolecules, from macromolecules–surfactant complexes to hydrophobic and electrostatic interactions.

Construction of a hydrocarbon-degrading consortium and characterization of two new lipopeptides biosurfactants

Apparent solubility and bioavailability of hydrophobic compounds are the major problems in the bioremediation process, which could be overcome by the bacteria capable of biosurfactant production and concurrent hydrocarbon degradation. In this work, we constructed an artificial bacterial consortium containing Lysinibacillus, Paenibacillus, Gordonia and Cupriavidus spp. from glyceryl tributyrate enriched bacteria collected from the non-contaminated site. The consortium was capable of using common raw materials (olive oil, paraffin oil, and glycerol) and polyaromatic hydrocarbons pollutants (naphthalene and anthracene) as the sole carbon source with simultaneous biosurfactant production. Two new lipopeptide isoforms, containing heptapeptide and lipid moieties, were structurally elucidated by LC-MS/MS, FTIR, NMR and molecular networking analysis. Our findings indicate that hydrocarbons degradation and biosurfactant production is an intrinsic property of non-contaminated soil community. Interestingly, we observed the hyper chemotactic activity of Lysinibacillus strains towards glyceryl tributyrate, which has not been reported before. The study may deepen our understanding of microbial strains and consortium with the potential to be used for bioremediation of hydrocarbons contaminated environments.

Genomics and LC-MS Reveal Diverse Active Secondary Metabolites in Bacillus amyloliquefaciens WS-8

Bacillus amyloliquefaciens is an important plant disease-preventing and growth-promoting microorganism. B. amyloliquefaciens WS-8 can stimulate plant growth and has strong antifungal properties. In this study, we sequenced the complete genome of B. amyloliquefaciens WS-8 by Pacific Biosciences RSII (PacBio) Single Molecule Real-Time (SMRT) sequencing. The genome consists of one chromosome (3,929,787 bp) and no additional plasmids. The main bacteriostatic substances were determined by genome, transcriptome, and mass spectrometry data. We thereby laid a theoretical foundation for the utilization of the strain. By genomic analysis, we identified 19 putative biosynthetic gene clusters for secondary metabolites, most of which are potentially involved in the biosynthesis of numerous bioactive metabolites, including difficidin, fengycin, and surfactin. Furthermore, a potential class II lanthipeptide biosynthetic gene cluster and genes that are involved in auxin biosynthesis were found. Through the analysis of transcriptome data, we found that the key bacteriostatic genes, as predicted in the genome, exhibited different levels of mRNA expression. Through metabolite isolation, purification, and exposure experiments, we found that a variety of metabolites of WS-8 exert an inhibitory effect on the necrotrophic fungus Botrytis cinerea, which causes gray mold; by mass spectrometry, we found that the main substances are mainly iturins and fengycins. Therefore, this strain has the potential to be utilized as an antifungal agent in agriculture.

The Mode of Action of Bacillus Species against Fusarium graminearum, Tools for Investigation, and Future Prospects

Fusarium graminearum is a pervasive plant pathogenic fungal species. Biological control agents employ various strategies to weaken their targets, as shown by Bacillus species, which adopt various mechanisms, including the production of bioactive compounds, to inhibit the growth of F. graminearum. Various efforts to uncover the antagonistic mechanisms of Bacillus against F. graminearum have been undertaken and have yielded a plethora of data available in the current literature. This perspective article attempts to provide a unified record of these interesting findings. The authors provide background knowledge on the use of Bacillus as a biocontrol agent as well as details on techniques and tools for studying the antagonistic mechanism of Bacillus against F. graminearum. Emphasizing its potential as a future biological control agent with extensive use, the authors encourage future studies on Bacillus as a useful antagonist of F. graminearum and other plant pathogens. It is also recommended to take advantage of the newly invented analytical platforms for studying biochemical processes to understand the mechanism of action of Bacillus against plant pathogens in general.

Bioactive Secondary Metabolites from Bacillus subtilis: A Comprehensive Review

Bacillus subtilis is widely underappreciated for its inherent biosynthetic potential. This report comprehensively summarizes the known bioactive secondary metabolites from B. subtilis and highlights potential applications as plant pathogen control agents, drugs, and biosurfactants. B. subtilis is well known for the production of cyclic lipopeptides exhibiting strong surfactant and antimicrobial activities, such as surfactins, iturins, and fengycins. Several polyketide-derived macrolides as well as nonribosomal peptides, dihydroisocoumarins, and linear lipopeptides with antimicrobial properties have been reported, demonstrating the biosynthetic arsenal of this bacterium. Promising efforts toward the application of B. subtilis strains and their natural products in areas of agriculture and medicine are underway. However, industrial-scale availability of these compounds is currently limited by low fermentation yields and challenging accessibility via synthesis, necessitating the development of genetically engineered strains and optimized cultivation processes. We hope that this review will attract renewed interest in this often-overlooked bacterium and its impressive biosynthetic skill set.

Characterization and Synergistic Antimicrobial Evaluation of Lipopeptides from Bacillus amyloliquefaciens Isolated from Oil-Contaminated Soil

Lipopeptides show great potential for biomedical application. Several lipopeptides exhibit narrow and broad-spectrum inhibition activities. The aim of the study is to characterize the lipopeptides produced by B. amyloliquefaciens strain MD4-12 and evaluate the synergistic antimicrobial activity in combination with a conventional antibiotic against Gram-negative bacteria. B. amyloliquefaciens strain MD4-12 was isolated from oil-contaminated soil. The isolate was cultivated in McKeen medium, and the lipopeptides were isolated by precipitation and extraction with methanol. Characterization of the lipopeptides by ESI-MS gave nine mass ion peaks with m/z 994–1072, resulted from protonating of the main ions in [M + H]⁺ and [M + Na]⁺ ion form. These mass ion peaks attributed to surfactin homologs. By tandem mass spectrometry, five variants of surfactin with the same amino acid sequence in peptide moiety could be revealed. The peptide moiety contains seven amino acids identified as Glu-Leu/Ile-Leu-Val-Asp-Leu-Leu/Ile while the fatty acid moiety comprises a different length of chain from C₁₂ to C₁₆. Surfactin showed antibacterial activity against various Gram-positive and Gram-negative bacteria. Combination surfactin with ampicillin showed a synergistic effect against P. aeruginosa ATCC 27853.

Toxicity and applications of surfactin for health and environmental biotechnology

Characterized as one of the most potent biosurfactants, surfactin is a cyclic lipopeptide synthesized by several strains of Bacillus genus. The aim of this review was to present the physicochemical and structural properties of surfactin and to demonstrate advances and applications of this biosurfactant for health and environmental biotechnology. Further, this review also focused on toxicological effects of surfactin on in vivo and in in vitro systems. The hydrophobic nature of surfactin enables interaction with membrane-bound phospholipids and indicates the ability of the molecule to act as a new weapon with respect to therapeutic and environmental properties. Seeking to avoid environmental contamination produced by widespread use of synthetic surfactants, surfactin emerges as a biological control agent against pathogen species owing to its antibacterial and antiviral properties. In addition, the mosquitocidal activity of surfactin was suggested as new strategy to control disease vectors. The current findings warrant future research to assess the toxicity of surfactin to enable an optimizing anticancer therapy and to seek refined methodologies, including nanotechnology techniques, to allow for an improved delivery of the biogenic molecule on target cells.

Effects of Different Cultivation Parameters on the Production of Surfactin Variants by a Bacillus subtilis Strain

Surfactins are lipopeptide-type biosurfactants produced mainly by Bacillus species, consisting of a peptide loop of seven amino acids and a hydrophobic fatty acid chain (C₁₂–C₁₆). These molecules have been proven to exhibit various biological activities; thus, their therapeutic and environmental applications are considered. Within the surfactin lipopeptide family, there is a wide spectrum of different homologues and isomers; to date, more than 30 variants have been described. Since the newest members of these lipopeptides were described recently, there is no information that is available on their characteristic features, e.g., the dependence of their production from different cultivation parameters. This study examined the effects of both the different carbon sources and various metal ions on the surfactin production of a selected B. subtilis strain. Among the applied carbon sources, fructose and xylose had the highest impacts on the ratio of the different variants, regarding both the peptide sequences and the lengths of the fatty acids. Furthermore, the application of metal ions Mn²⁺, Cu²⁺ and Ni²⁺ in the media completely changed the surfactin variant compositions of the fermenting broths leading to the appearance of methyl esterified surfactin forms, and resulted in the appearance of novel surfactin variants with fatty acid chains containing no more than 11 carbon atoms.

High-Frequency Occurrence of Surfactin Monomethyl Isoforms in the Ferment Broth of a Bacillus subtilis Strain Revealed by Ion Trap Mass Spectrometry

Surfactins are cyclic lipopeptides consisting of a β-hydroxy fatty acid of various chain length and a peptide ring of seven amino acids linked together by a lactone bridge, forming the cyclic structure of the peptide chain. These compounds are produced mainly by Bacillus species and possess numerous biological effects such as antimicrobial (antiviral, antibacterial, and antifungal) activities. A mixture of surfactins extracted from Bacillus subtilis strain SZMC 6179J was examined by HPLC-ESI-IT-MS technique, enhancing their separation to reveal novel lipopeptide varieties with higher masses and to characterize their structures. During the MS² spectra analyses of their sodiated molecular ions [M + Na]⁺, a previously rarely encountered group of surfactins was detected and two novel types of the group were discovered containing methyl esterified aspartic acid residue in their fifth amino acid position. The relative amounts of these monomethyl isoforms exceeded 35% of the produced surfactin in total. In the m/z value of 1114, all the detected isoforms possessed aspartic acid 4-methyl ester residue in their fifth amino acid position (C17-[Lxx4, AME5], C18-[AME5]), offering an opportunity to separate a pure fraction of the compound and to study its biological activities in the future.

Identification and ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry characterization of biosurfactants, including a new surfactin, isolated from oil-contaminated environments

Biosurfactant-producing bacteria were isolated from samples collected in areas contaminated with crude oil. The isolates were screened for biosurfactant production using qualitative drop-collapse test, oil-spreading and emulsification assays, and measurement of their tensoactive properties. Five isolates tested positive for in the screening experiments and displayed decrease in the surface tension below 30 mN m^-1 . The biosurfactants produced by these isolates were further investigated and their molecular identification revealed that they are bacteria related to the Bacillus genus. Additionally, the biosurfactants produced were chemically characterized via UHPLC-HRMS experiments, indicating the production of surfactin homologues, including a new class of these molecules.

Characterization of lipopeptides produced by Bacillus licheniformis using liquid chromatography with accurate tandem mass spectrometry

RATIONALE

The plant endophyte Bacillus licheniformis, isolated from leaves of Vitis vinifera, was studied to individuate and characterize the presence of bioactive lipopeptides having amino acidic structures.

METHODS

Crude extracts of liquid cultures were analyzed by ultra-high-performance liquid chromatography (UHPLC) coupled to a quadrupole time-of-flight (QTOF) mass analyzer. Chromatographic conditions were optimized in order to obtain an efficient separation of the different isobaric lipopeptides, avoiding merged fragmentations of co-eluted isomeric compounds and reducing possible cross-talk phenomena. Composition of the amino acids was outlined through the interpretation of the fragmentation behavior in tandem high-resolution mass spectrometry (HRMS/MS) mode, which showed both common-class and peculiar fragment ions. Both [M + H](+) and [M + Na](+) precursor ions were fragmented in order to differentiate some isobaric amino acids, i.e. Leu/Ile. Neutral losses characteristic of the iso acyl chain were also evidenced.

RESULTS

More than 90 compounds belonging to the classes of surfactins and lichenysins, known as biosurfactant molecules, were detected. Sequential LC/HRMS/MS analysis was used to identify linear and cyclic lipopeptides, and to single out the presence of a large number of isomers not previously reported. Some critical issues related to the simultaneous selection of different compounds by the quadrupole filter were highlighted and partially solved, leading to tentative assignments of several structures. Linear lichenysins are described here for the first time.

CONCLUSIONS

The approach was proved to be useful for the characterization of non-target lipopeptides, and proposes a rationale MS experimental scheme aimed to investigate the difference in amino acid sequence and/or in the acyl chain of the various congeners, when standards are not available. Results expanded the knowledge about production of linear and cyclic bioactive compounds from Bacillus licheniformis, clarifying the structures of isomeric forms, and enabling the use of selected endophytes to produce fungicides for eco-friendly biocontrol. Copyright © 2016 John Wiley & Sons, Ltd.

Ion trap mass spectrometry of surfactins produced by Bacillus subtilis SZMC 6179J reveals novel fragmentation features of cyclic lipopeptides

RATIONALE

Surfactins are mixtures of cyclic lipopeptides consisting of variants of a heptapeptide and a linked β-hydroxy fatty acid with various chain lengths of 13-15 carbon atoms. A lactone bridge between the β-hydroxy functional group of the fatty acid and the carboxy terminal functional component of the peptide chain form their cyclic structures. Such lipopeptides, produced mainly by Bacillus species, possess several remarkable biological effects such as antitumor and antimicrobial activities, some of which are highly promising for utilization in plant disease biocontrol. The strain Bacillus subtilis SZMC 6179J was previously shown to exert significant antifungal properties against various phytopathogenic filamentous fungi; therefore, we characterized the structural features of the surfactins produced by this strain in order to explore the origin of the observed antagonistic effects of this potential biocontrol organism.

METHODS

Bacillus subtilis SZMC 6179J was used to produce surfactins, which were characterized by high-performance liquid chromatography/electrospray ionisation ion trap mass spectrometry (HPLC/ESI-ITMS) techniques after precipitation and extraction steps.

RESULTS

The 26 isoforms separated and identified represent three types of known surfactin variants and a fourth, previously unknown group characterised by the replacement of the leucine residue by valine in position 2. The relative amounts of this newly identified surfactin group were below 1%, and their cyclic structures were closed by C13-C15 hydroxy fatty acids. The structural assessment of the isoforms by MS(2) measurements led to the characterisation and description of a new fragmentation mechanism of surfactins.

CONCLUSIONS

The detected new natural lipoheptapeptide compounds with modified structures have significant potential for biotechnological and biocontrol applications. The complementary ITMS(2) data as well as the described internal fragmentation mechanism obtained from the sodiated surfactin molecules may further facilitate the structural elucidation of cyclic lipopeptides in the future. Copyright © 2016 John Wiley & Sons, Ltd.

Purification and characterization of biosurfactant produced by Bacillus licheniformis Y-1 and its application in remediation of petroleum contaminated soil

In our previous research, a petroleum degrading bacteria strain Bacillus licheniformis Y-1 was obtained in Dagang Oilfield which had the capability of producing biosurfactant. This biosurfactant was isolated and purified in this work. The biosurfactant produced by strain Y-1 had the capability to decrease the surface tension of water from 74.66 to 27.26mN/m, with the critical micelle concentration (CMC) of 40mg/L. The biosurfactant performed not only excellent stabilities against pH, temperature and salinity, but also great emulsifying activities to different kinds of oil, especially the crude oil. According to the results of FT-IR spectrum and (1)H NMR spectrum detection, the surfactant was determined to be a cyclic lipopeptide. Furthermore, through the addition of surfactant, the effect of petroleum contaminated soil remediation by fungi got a significant improvement.

Synergistic Effects of [Ile⁷]Surfactin Homologues with Bacillomycin D in Suppression of Gray Mold Disease by Bacillus amyloliquefaciens Biocontrol Strain SD-32

We previously reported that Bacillus amyloliquefaciens biocontrol strain SD-32 produces powerful antifungal lipopeptides, C17 bacillomycin D homologues. In the course of the investigation we found that the antifungal activity of the culture supernatant of this bacterium was not ascribed exclusively to bacillomycin D. We attempted to identify metabolites other than bacillomycin D to gain insight into the mechanism for the biocontrol by this bacterium. After purifying the fractions of the culture supernatant exhibiting synergistic activity with bacillomycin D, we isolated two new cyclic lipodepsipeptides, anteiso-C13 and iso-C13 [Ile(7)]surfactins, together with three known [Ile(7)]surfactins. Interestingly, [Ile(7)]surfactins showed synergistic activities with bacillomycin D to gray mold disease on cucumber leaves but not to Botrytis cinerea itself in vitro, suggesting that the synergistic effects might be on infection processes of the fungus. Actually, we observed that they did not show synergistic actions on conidial germination or mycelial growth of B. cinerea on the leaves.

Chemical structure, property and potential applications of biosurfactants produced by Bacillus subtilis in petroleum recovery and spill mitigation

Lipopeptides produced by microorganisms are one of the five major classes of biosurfactants known and they have received much attention from scientific and industrial communities due to their powerful interfacial and biological activities as well as environmentally friendly characteristics. Microbially produced lipopeptides are a series of chemical structural analogues of different families and, among them, 26 families covering about 90 lipopeptide compounds have been reported in the last two decades. This paper reviews the chemical structural characteristics and molecular behaviors of surfactin, one of the representative lipopeptides of the 26 families. In particular, two novel surfactin molecules isolated from cell-free cultures of Bacillus subtilis HSO121 are presented. Surfactins exhibit strong self-assembly ability to form sphere-like micelles and larger aggregates at very low concentrations. The amphipathic and surface properties of surfactins are related to the existence of the minor polar and major hydrophobic domains in the three 3-D conformations. In addition, the application potential of surfactin in bioremediation of oil spills and oil contaminants, and microbial enhanced oil recovery are discussed.

Structural diversity of the microbial surfactin derivatives from selective esterification approach

Surfactin originated from genus Bacillus is composed of a heptapeptide moiety bonded to the carboxyl and hydroxyl groups of a β-hydroxy fatty acid and it can be chemically modified to prepare the derivatives with different structures, owing to the existence of two free carboxyl groups in its peptide loop. This article presents the chemical modification of surfactin esterified with three different alcohols, and nine novel surfactin derivatives have been separated from products by the high performance liquid chromatography (HPLC). The novel derivatives, identified with Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS), are the mono-hexyl-surfactin C14 ester, mono-hexyl-surfactin C15 ester, mono-2-methoxy-ethyl-surfactin C14 ester, di-hexyl-surfactin C14 ester, di-hexyl-surfactin ester C15, di-2-methoxy-ethyl-surfactin ester C14, di-2-methoxy-ethyl-surfactin ester C15, di-6-hydoxyl-hexyl-surfactin C14 ester and, di-6-hydoxyl-hexyl-surfactin C15 ester. The reaction conditions for esterification were optimized and the dependence of yields on different alcohols and catalysts were discussed. This study shows that esterification is one of the most efficient ways of chemical modification for surfactin and it can be used to prepare more derivatives to meet the needs of study in biological and interfacial activities.

Surfactin from Bacillus subtilis displays an unexpected anti-Legionella activity

A contaminant bacterial strain was found to exhibit an antagonistic activity against Legionella pneumophila, the causative agent of Legionnaires' disease. The bacterial strain was identified as a Bacillus subtilis and named B. subtilis AM1. PCR analysis revealed the presence of the sfp gene, involved in the biosynthesis of surfactin, a lipopeptide with versatile bioactive properties. The bioactive substances were extracted from AM1 cell-free supernatant with ethyl acetate and purified using reversed phase HPLC (RP-HPLC). Subsequent ESI-MS analyses indicated the presence of two active substances with protonated molecular ions at m/z 1008 and 1036 Da, corresponding to surfactin isoforms. Structures of lipopeptides were further determined by tandem mass spectrometry and compared to the spectra of a commercially available surfactin mixture. Surfactin displays an antibacterial spectrum almost restricted to the Legionella genus (MICs range 1-4 μg/mL) and also exhibits a weak activity toward the amoeba Acanthamoeba castellanii, known to be the natural reservoir of L. pneumophila. Anti-biofilm assays demonstrated that 66 μg/mL of surfactin successfully eliminated 90 % of a 6-day-old biofilm. In conclusion, this study reveals for the first time the potent activity of surfactin against Legionella sp. and preformed biofilms thus providing new directions toward the use and the development of lipopeptides for the control of Legionella spread in the environment.

Identification of surfactins and iturins produced by potent fungal antagonist, Bacillus subtilis K1 isolated from aerial roots of banyan (Ficus benghalensis) tree using mass spectrometry

The banyan endophyte, Bacillus subtilis K1, produces a complex mixture of lipopeptides exhibiting potent antifungal activity. These lipopeptides were purified by high-performance liquid chromatography and analyzed using MALDI-TOF-MS as well as liquid chromatography coupled with ESI-MS. A heterogenous mixture of lipopeptides belonging to three different families of cyclic lipopeptides, viz., fengycins, iturins and surfactins, was detected in the cell-free extracellular extract of B. subtilis K1. The detailed mass spectrometric characterization revealed the presence of four variants of iturin A and three variants of iturin C varying in the β-amino fatty acid chain length from C₁₃ to C₁₇. The MS/MS of monovalent alkali metal ion adducts (Na and K) of iturin suggested the Glu⁴ as a binding site for metal ion. The LC-ESI-MS/MS analysis of surfactins enabled the identification of seven surfactin variants with the variations in Val/Ile/Leu at position 4 and C₁₃–C₁₇ β-hydroxy fatty acids. This study demonstrates the application of tandem mass spectrometry in identification of closely related lipopeptides from a heterogenous mixture obtained from a natural source. Furthermore, this is the first report of an endophytic bacillus strain co-producing so many variants of surfactins and iturins.

Identification and characterization of novel surfactins produced by fungal antagonist Bacillus amyloliquefaciens 6B

The broad-spectrum fungal antagonist, Bacillus amyloliquefaciens 6B (BA6B), isolated from the Jakhao coast of Kutch, India, was investigated for its antifungal metabolites using mass spectrometry. The cyclic lipopeptides harvested from the cell-free fermentation broth of BA6B by acid precipitation and subsequently dissolved in methanol were subjected to liquid chromatography coupled with electrospray ionization mass spectrometry (LC-ESI-MS/MS) for their identification and sequence determination. The 26 types of surfactin variants were identified from the methanolic extract by LC-ESI-MS/MS analysis. Among 26 surfactin species, several new cyclic as well as acyclic surfactin variants based on the variation in the β-hydroxy fatty acid (β-OH FA) chain length and/or in amino acid positions 4, 5, 6, and 7 were identified. The mass spectrometric analysis of crude extract also enabled the identification of 11 unique molecular mass ions with minimum two or maximum four types of isobaric peptide variants.

Control efficacy of an endophytic Bacillus amyloliquefaciens strain BZ6-1 against peanut bacterial Wilt, Ralstonia solanacearum

We aimed to isolate and identify endophytic bacteria that might have efficacy against peanut bacterial wilt (BW) caused by Ralstonia solanacearum. Thirty-seven endophytic strains were isolated from healthy peanut plants in R. solanacearum-infested fields and eight showed antagonistic effects against R. solanacearum. Strain BZ6-1 with the highest antimicrobial activity was identified as Bacillus amyloliquefaciens based on morphology, biochemistry, and 16S rRNA analysis. Culture conditions of BZ6-1 were optimized using orthogonal test method and inhibitory zone diameter in dual culture plate assay reached 34.2 mm. Furthermore, main antimicrobial substances of surfactin and fengycin A homologues produced by BZ6-1 were analyzed by high performance liquid chromatography electrospray ionization tandem mass spectrometry. Finally, pot experiments were adopted to test the control efficiency of BZ6-1 against peanut BW. Disease incidence decreased significantly from 84.5% in the control to 12.1% with addition of 15 mL (10(8) cfu mL(-1)) culture broth for each seedling, suggesting the feasibility of strain BZ6-1 in the biological control of peanut plants BW.

Cyclic lipopeptide profile of the plant-beneficial endophytic bacterium Bacillus subtilis HC8

In a previous study (Malfanova et al. in Microbial Biotech 4:523-532, 2011), we described the isolation and partial characterization of the biocontrol endophytic bacterium B. subtilis HC8. Using thin-layer chromatography, we have detected several bioactive antifungal compounds in the methanolic extract from the acid-precipitated supernatant of HC8. In the present study, we have further analyzed this methanolic extract using liquid chromatography-mass spectrometry. Based on the comparison of retention times and molecular masses with those of known antifungal compounds, we identified three families of lipopeptide antibiotics. These include four iturins A having fatty acyl chain lengths of C14 to C17, eight fengycins A (from C14 to C18 and from C15 to C17 containing a double bond in the acyl chain), four fengycins B (C15 to C18), and five surfactins (C12 to C16). Evaluation of the antifungal activity of the isolated lipopeptides showed that fengycins are the most active ones. To our knowledge, this is the first report of an endophytic Bacillus subtilis producing all three major families of lipopeptide antibiotics containing a very heterogeneous mixture of homologues. The questions remain open which of these lipopeptides (1) are being produced during interaction with the plant and (2) are contributing to the biocontrol activity of HC8.

Importance of the long-chain fatty acid beta-hydroxylating cytochrome P450 enzyme YbdT for lipopeptide biosynthesis in Bacillus subtilis strain OKB105

Bacillus species produce extracellular, surface-active lipopeptides such as surfactin that have wide applications in industry and medicine. The steps involved in the synthesis of 3-hydroxyacyl-coenzyme A (CoA) substrates needed for surfactin biosynthesis are not understood. Cell-free extracts of Bacillus subtilis strain OKB105 synthesized lipopeptide biosurfactants in presence of l-amino acids, myristic acid, coenzyme A, ATP, and H₂O₂, which suggested that 3-hydroxylation occurs prior to CoA ligation of the long chain fatty acids (LCFAs). We hypothesized that YbdT, a cytochrome P450 enzyme known to beta-hydroxylate LCFAs, functions to form 3-hydroxy fatty acids for lipopeptide biosynthesis. An in-frame mutation of ybdT was constructed and the resulting mutant strain (NHY1) produced predominantly non-hydroxylated lipopeptide with diminished biosurfactant and beta-hemolytic activities. Mass spectrometry showed that 95.6% of the fatty acids in the NHY1 biosurfactant were non-hydroxylated compared to only ∼61% in the OKB105 biosurfactant. Cell-free extracts of the NHY1 synthesized surfactin containing 3-hydroxymyristic acid from 3-hydroxymyristoyl-CoA at a specific activity similar to that of the wild type (17 ± 2 versus 17.4 ± 6 ng biosurfactant min⁻¹·ng·protein⁻¹, respectively). These results showed that the mutation did not affect any function needed to synthesize surfactin once the 3-hydroxyacyl-CoA substrate was formed and that YbdT functions to supply 3-hydroxy fatty acid for surfactin biosynthesis. The fact that YbdT is a peroxidase could explain why biosurfactant production is rarely observed in anaerobically grown Bacillus species. Manipulation of LCFA specificity of YbdT could provide a new route to produce biosurfactants with activities tailored to specific functions.

Isolation and characterization of two new lipopeptide biosurfactants produced by Pseudomonas fluorescens BD5 isolated from water from the Arctic Archipelago of Svalbard

The arctic freshwater bacterium Pseudomonas fluorescens BD5 produces biosurfactants when grown on 2% glucose. Crude biosurfactants were extracted from a cell-free culture supernatant with ethyl acetate and purified by preparative reversed phase high performance liquid chromatography (RP-HPLC). The chemical structure of the purified biosurfactants, pseudofactin I and II, was analyzed by matrix assisted laser desorption/ionization time of flight (MALDI TOF) mass spectrometry and tandem mass spectrometry (MS/MS). Both compounds are novel cyclic lipopeptides with a palmitic acid connected to the terminal amino group of eighth amino acid in peptide moiety. The C-terminal carboxylic group of the last amino acid (Val or Leu) forms a lactone with the hydroxyl of Thr3. Pseudofactin II reduced the surface tension of water from 72 mN/m to 31.5 mN/m at a concentration of 72 mg/l. Its emulsification activity and stability was greater than that of the synthetic surfactants Tween 20 and Triton X-100; pseudofactins thus have a great potential for application in industrial fields such as bioremediation or biomedicine.

LC/ESI-MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti-adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI-MS) and ESI-MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI-MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI-MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI-MS/MS analysis of fraction I showed the presence of C(13), C(14) and C(15) surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na](+) at m/z 1030, 1044 and 1058. LC/ESI-MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H](+) at m/z 1478 and 1506 corresponding to C(17) fengycin A and C(17) fengycin B, respectively. Other homologues (C(14) to C(16)) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed.

Structural and molecular characteristics of lichenysin and its relationship with surface activity

Lichenysins are most potent anionic cyclic lipoheptapeptide biosurfactants produced by Bacillus licheniformis on hydrocarbonless medium with mainly glucose as carbon source. They have the capacity to lower the surface tension of water from 72 to 27 mN/m. Based on species specific variations they are named lichenysin A, B, C, D, G and surfactant BL86. The lowest ever interfacial tension against decane of 0.006 mN/m is obtained with acid precipitated lichenysin B. Surfactant BL86 and lichenysin B have recorded lowest ever CMC of 10 mg/L by any surfactant under optimal conditions. Surface and interfacial tension lowering ability bears significance in the context of oil recovery from oil reservoir. Similarity exists between structure and biosynthesis of surfactin and lichenysin. Surfactin being the most studied of the two, understanding its structure and biosynthesis gives an insight into the structure and biosynthesis of lichenysin. Lichenysin is synthesized by a multienzyme complex, lichenysin synthetase (LchA/Lic) encoded by 32.4 (26.6 kb) lichenysin operon lchA (lic). The structure of lichenysin and its operon indicate the nonribosomal biosynthesis with the same multifunctional modular arrangement as seen in surfactin synthetase SrfA. The lchA operon consists of lchAA-AC (lic A-C) and lchA TE (licTE) genes encoding the proteins LchAA, LchAB, LchAC and thioesterase LchA-TE. The licA (lchAA) gene is 10,746 bp and codes for a 3,582 amino acids protein, licB (lchAB) gene is 10,764 bp and codes for a similar sized protein, while licC (lchAC) gene is 3,864 bp and codes for protein containing 1,288 amino acid. The biotechnological potential of lichenysin in MEOR has triggered research on structure-activity relationship. Both the nature of peptide and fatty acid dictate the activity of the biosurfactant. Tailormade biosurfactant with desired attributes can be obtained from engineered synthetases. Basic studies are lacking on mechanism of biosynthesis by lichenysin synthetase however, studies on various aspects of lichenysin including regulation are expected to swell in coming years.

Isolation and characterization of a C12-lipopeptide produced by Bacillus subtilis HSO 121

A new lipopeptide with C12 fatty acid has been isolated from the cell broth of Bacillus subtilis HSO121 by chromatographic methods, which is believed to be the homologue of lipopeptides. The fatty acid portion was methylated and analyzed by GC/MS, ESI Q-TOF MS and 1H-NMR. The peptide portion, of which the amino acid composition was obtained by HPLC combined with a phenyl isothiocyanate (PITC) derivatization methods, was analyzed by ESI Q-TOF MS. Comparing the obtained results with surfactin C13 showed that the new lipopeptide has a peptide moiety similar to that of surfactin and the difference exists in the fatty acid portion, which is an iso-C12 beta-hydroxy fatty acid. The critical micelle concentration (CMC) of this new homologue is estimated to be 6.27 x 10(-5) mol/l in 10 mmol/l phosphate buffer solution (PBS, pH 8.0) at 30 degrees C, and the surface tension at CMC (gamma CMC) achieved is as little as 27.71 mN/m. The hemolytic activities of the C12-lipopeptide on 2% human erythrocytes showed a HC50 of 26.5 micromol/l.

Determination of the structure of the fatty acid chain in a cyclic lipopeptide using GC-MS

A GC-EIMS method to determine the structure of the fatty acid chains in cyclic lipopeptides is described. The structure of the fatty acid chains can be determined by the characteristic peaks of the MS spectrogram according to the fact that the alpha cleavage predominates the MS of a fatty acid with amino and hydroxy groups, while the McLafferty rearrangement predominates the MS of one without amino or hydroxy group. The characteristics of the strongest peaks of 103 and 102 in MS spectrograms due to alpha cleavage represent the beta-hydroxy-fatty acid and the beta-amino fatty acid, respectively; the strongest peak of 117 due to alpha cleavage and the relatively weak peak of 88 due to McLafferty rearrangement indicate the beta-hydroxy-fatty acid with a branched methyl group at its alpha position. The strongest peak of 74 due to McLafferty suggests the fatty acid without hydroxy or amino group. The ratio of relative intensity (I(43)/I(57)) characterizes the branches of alkyl chains. The greater I(43)/I(57) corresponds to an iso alkyl, and the smaller I(43)/I(57) corresponds to an anteiso alkyl. This method can be used to determine the full structure of the fatty acid chains in lipopeptides.

Determination of the amino acid sequence in a cyclic lipopeptide using MS with DHT mechanism

A TOF MS/MS method to directly determine the amino acid sequence in a cyclic lipopeptide without its hydrolysis is described. The fragments of the peptide and the hydrocarbon chains were identified through comparing the MS of two analogues of the lipopeptide; the connecting relationship of amino acid residues in the lipopeptide was determined based on the difference of mass to charge ratio between peaks in the MS spectra and the amino acid analysis; and finally, according to the mechanism of double hydrogen transfer(DHT) the C-terminal of peptide and hydroxy aliphatic acid in the lipopeptide was directly determined without the hydrolysis. The determined sequence of amino acid residues in the cyclic lipopeptide is also supported by the rest peaks in the MS spectra grounded on simple fragmenting mechanism. This method can be used to determine the amino acid sequence in any aliphatic acid loop-inlaying cyclic lipopeptides.

Importance of 3-hydroxy fatty acid composition of lipopeptides for biosurfactant activity

Biosurfactant production may be an economic approach to improving oil recovery. To obtain candidates most suitable for oil recovery, 207 strains, mostly belonging to the genus Bacillus, were tested for growth and biosurfactant production in medium with 5% NaCl under aerobic and anaerobic conditions. All strains grew aerobically with 5% NaCl, and 147 strains produced a biosurfactant. Thirty-five strains grew anaerobically with 5% NaCl, and two produced a biosurfactant. In order to relate structural differences to activity, eight lipopeptide biosurfactants with different specific activities produced by various Bacillus species were purified by a new protocol. The amino acid compositions of the eight lipopeptides were the same (Glu/Gln:Asp/Asn:Val:Leu, 1:1:1:4), but the fatty acid compositions differed. Multiple regression analysis showed that the specific biosurfactant activity depended on the ratios of both iso to normal even-numbered fatty acids and anteiso to iso odd-numbered fatty acids. A multiple regression model accurately predicted the specific biosurfactant activities of four newly purified biosurfactants (r2= 0.91). The fatty acid composition of the biosurfactant produced by Bacillus subtilis subsp. subtilis strain T89-42 was altered by the addition of branched-chain amino acids to the growth medium. The specific activities of biosurfactants produced in cultures with different amino acid additions were accurately predicted by the multiple regression model derived from the fatty acid compositions (r2= 0.95). Our work shows that many strains of Bacillus mojavensis and Bacillus subtilis produce biosurfactants and that the fatty acid composition is important for biosurfactant activity.

Structural and functional characterization of gene clusters directing nonribosomal synthesis of bioactive cyclic lipopeptides in Bacillus amyloliquefaciens strain FZB42

The environmental strain Bacillus amyloliquefaciens FZB42 promotes plant growth and suppresses plant pathogenic organisms present in the rhizosphere. We sampled sequenced the genome of FZB42 and identified 2,947 genes with >50% identity on the amino acid level to the corresponding genes of Bacillus subtilis 168. Six large gene clusters encoding nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) occupied 7.5% of the whole genome. Two of the PKS and one of the NRPS encoding gene clusters were unique insertions in the FZB42 genome and are not present in B. subtilis 168. Matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis revealed expression of the antibiotic lipopeptide products surfactin, fengycin, and bacillomycin D. The fengycin (fen) and the surfactin (srf) operons were organized and located as in B. subtilis 168. A large 37.2-kb antibiotic DNA island containing the bmy gene cluster was attributed to the biosynthesis of bacillomycin D. The bmy island was found inserted close to the fen operon. The responsibility of the bmy, fen, and srf gene clusters for the production of the corresponding secondary metabolites was demonstrated by cassette mutagenesis, which led to the loss of the ability to produce these peptides. Although these single mutants still largely retained their ability to control fungal spread, a double mutant lacking both bacillomycin D and fengycin was heavily impaired in its ability to inhibit growth of phytopathogenic fungi, suggesting that both lipopeptides act in a synergistic manner.

A novel lipopeptide, an inhibitor of bacterial adhesion, from the thermophilic and halotolerant subsurface Bacillus licheniformis strain 603

A new Bacillus licheniformis strain, 603, isolated from a mixture of drilling fluid and subsurface thermal water, has been found to produce a cyclic lipopeptide which is released into cultural medium as well as present in cells as the major lipid constituent (57% of the total cell lipids extractable with 2:1 chloroform-methanol). The quantitative ratio of the extracellular and intracellular lipopeptide has been estimated as 23:10. The metabolite represents a heptapeptide, L-Asp-->L-Leu-->L-Leu-->L-Val-->L-Val-->L-Glu-->L-Leu, N-acylated to the N-terminal amino acid, L-Asp, by a 3-hydroxy fatty acid (from 13:0 to 17:0 with n-, iso-, and anteiso-chains), the 3-OH group of which is esterified by the C-terminal amino acid, L-Leu. The chemical structure of the lipopeptide has been established by means of infrared (IR), 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionisation (ESI) mass spectrometry (MS), including secondary ion mass spectrometry, along with chemical and enzymatic degradation. Although a diversity of similar metabolites synthesised by various B. licheniformis strains are presently known, such a structure has not been reported thus far. Added to the growth medium of strain 603 at the concentration of 1.6 microg/ml, the lipopeptide prevents adhesion of cells to a glass surface. Also, it exhibits a considerable growth-inhibiting activity against Corynebacterium variabilis and a much lower activity against Acinetobacter sp.