Maize Root Exudates Recruit Bacillus amyloliquefaciens OR2-30 to Inhibit Fusarium graminearum Infection

Bacillus spp. can exert plant growth-promoting effects and biocontrol effects after effective colonization, and bacterial chemotaxis toward plant root exudates is the initial step to colonize. Under biotic stress, plants are able to alter their root exudates to attract or avoid different types of microbes. Hence, Bacillus chemotaxis toward root exudates after pathogen infection is crucial for exerting their beneficial effects. In this study, the Bacillus amyloliquefaciens OR2-30 strain, which exhibited greater chemotaxis ability toward maize root exudates after Fusarium graminearum infection, was screened from 156 rhizosphere microorganisms. The infected maize root exudates were further confirmed to improve the swarming and biofilm formation ability of the OR2-30 strain. Chemotaxis, swarming, and biofilm formation ability were able to influence bacterial colonization. Indeed, the the OR2-30 strain displayed more effective colonization ability in the maize rhizosphere after F. graminearum inoculation. Moreover, lipopeptides produced by OR2-30 were identified as iturins and responsible for suppressing F. graminearum growth. Further study showed that lipopeptides suppressed the growth of F. graminearum by inhibiting conidia formation and germination, inducing reactive oxygen species production and causing cell death in mycelium. Eventually, the OR2-30 strain increased maize resistance against F. graminearum. These results suggested that maize root exudates could recruit B. amyloliquefacines OR2-30 after F. graminearum infection, and that OR2-30 then suppresses the F. graminearum by producing lipopeptides, such as iturins, to protect maize.

Detergent-assisted sample preparation for MALDI-MS: Investigation of octylglucoside and docecylmaltoside for matrix crystallization, on-plate digestion, and trypsin activity

We show an easy and fast method for improved detection of lipophilic peptides with MALDI-MS utilizing the nonionic detergents n-octylglucoside and n-dodecylmaltoside (laurylmaltoside). Investigations comprised on-plate digestion of proteins with trypsin, detergent effects on the protease trypsin, and the changes in MALDI matrix crystallization. Investigations also exhibited a higher tryptic activity in trypsin activity assay of 139% when using laurylmaltoside as supplement. Crystallization changed toward a more homogeneous crystal distribution and especially trypsinized insulin spectra recorded with MALDI-MS showed improved detectability of lipophilic peptides.

Qualitative analysis of biosurfactants from Bacillus species exhibiting antifungal activity

Bacillus spp. produce a broad spectrum of lipopeptide biosurfactants, among which surfactin, iturin and fengycin are widely studied families. The goals of this study were to characterize the biosurfactant activity of Bacillus spp. and to investigate their motility and biofilm formation capabilities. In addition, we extracted lipopeptides from these bacteria to assess their antifungal activities and analyzed these products by mass spectrometry (MS). B. amyloliquefaciens FZB42, Bacillus sp. NH 217 and B. subtilis NH-100 exhibited excellent biosurfactant and surface spreading activities, whereas B. atrophaeus 176s and Paenibacillus polymyxa C1225 showed moderate activity, and B. subtilis 168 showed no activity. Strains FZB42, NH-100, NH-217, 176s and CC125 exhibited excellent biofilm formation capabilities. Lipopeptide extracts displayed good antifungal activity against various phytopathogens and their associated diseases, such as Fusarium moniliforme (rice bakanae disease), Fusarium oxysporum (root rot), Fusarium solani (root rot) and Trichoderma atroviride (ear rot and root rot). Lipopeptide extracts of these strains also showed hemolytic activity, demonstrating their strong potential to produce surfactants. LCMS-ESI analyses identified the presence of surfactin, iturin and fengycin in the extracts of Bacillus strains. Thus, the strains assayed in this study show potential as biocontrol agents against various Fusarium and Trichoderma species.

Structural identification of lipopeptide biosurfactants produced by Bacillus subtilis strains grown on the media obtained from renewable natural resources

The aim of the study was to identify and characterize lipopeptide (LP) biosurfactants produced by two Bacillus subtilis strains (KP7 and I'-1a) grown on various media prepared from renewable natural resources: two different brewery wastewaters (BW#4 and BW#6), 2% beet molasses (M), apple peels extract (APE) supplemented with 0.25% of yeast extract (YE) or 0.25% peptone (P), and similarly supplemented carrot peels extract (CPE). In all used media both strains retained their individual LP production signature characterized by surfactin and iturin overproduction exhibited by KP7 and I'-1a strain, respectively. The production level and the structural diversity of synthesized LPs were dependent on the medium composition. In the CPE+YE medium it was higher than the yield obtained in Luria-Bertani (140.6 and 100.3 mg L^-1, respectively). Surfactins were produced by both strains as a mixture of four homologues (C13-C16) with the domination of variant C14. All other broths prepared from renewable resources strongly stimulated the iturin production by I'-1a strain with the exception of BW media. The highest iturin concentration (428.7 mg L^-1) obtained in the CPE+P culture of I'-1a strain was about seven-fold higher than in LB. In all cultures only iturin A was identified. Among four iturin homologues (C13-16) produced by I'-1a strain, the highest relative contents of C16 variant (70-80%) were calculated for samples obtained from APE+P and CPE+P media. The obtained data indicate that the waste composition has an influence on both the types and amounts of biosurfactants produced by studied B. subtilis strains.

Lipopeptides from a novel Bacillus methylotrophicus 39b strain suppress Agrobacterium crown gall tumours on tomato plants

BACKGROUND

This study aims to characterise the antibacterial activity of a novel Bacillus methylotrophicus strain named 39b against tumourigenic Agrobacterium tumefaciens C58 and B6 strains. It also aims to identify the compound that is responsible for its activity and to evaluate its efficiency to control crown gall disease in tomato plants.

RESULTS

B. methylotrophicus strain 39b was found to stop the growth of phytopathogenic A. tumefaciens strains in in vitro experiments. Lipopeptides - surfactins, iturins and fengycins - were detected under various isoforms by mass spectrometry analysis of the methanolic extract. The active principle acting against Agrobacterium strains was isolated from TLC plates and identified by mass spectrometry as surfactin. The strain was effective in reducing the weight and the number of galls induced by A. tumefaciens strains on tomato plants. Total inhibition of gall formation was observed using the antibacterial compounds.

CONCLUSION

B. methylotrophicus strain 39b exhibited antibacterial activity against phytopathogenic A. tumefaciens C58 and B6 both in vitro and in vivo. Lipopeptides are the main compounds that confer the biocontrol ability. This strain has the potential to be developed as a biological control agent for crown gall disease. © 2016 Society of Chemical Industry.

Fusaricidins from Paenibacillus polymyxa M-1, a family of lipohexapeptides of unusual complexity-a mass spectrometric study

Paenibacillus polymyxa are rhizobacteria with a high potential to produce natural compounds of biotechnological and medical interest. Main products of P. polymyxa are fusaricidins, a large family of antifungal lipopeptides with a 15-guanidino-3-hydroxypentadecanoic acid (GHPD) as fatty acid side chain. We use the P. polymyxa strain M-1 as a model organism for the exploration of the biosynthetic potential of these rhizobacteria. Using matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) about 40 new fusaricidins were detected which were fractionated by reversed-phase (rp) HPLC. Their structure was determined by MALDI-LIFT-TOF/TOF fragment analysis. The dominant fragment in the product ion spectra of fusaricidins appeared at m/z 256.3, 284.3 and 312.4, respectively, indicating variations in their fatty acid part. Two new subfamilies of fusaricidins were introduced which contain guanidino-3-hydroxyhepta- and nonadecanoic acid as fatty acid constituents. Apparently, the end-standing guanidine group is not modified as shown by direct infusion nano-electrospray ionization mass spectrometry (nano-ESI MS). The results of this study suggest that advanced mass spectrometry is the method of choice for investigating natural compounds of unusual diversity, like fusaricidins. Copyright © 2016 John Wiley & Sons, Ltd.

Inhibition of mycotoxin-producing fungi by Bacillus strains isolated from fish intestines

Bacillus strains isolated from the aquatic environment of the Brazilian Amazon region were tested for their activity against mycotoxigenic fungi. All tested bacteria showed antifungal activity, inhibiting at least 7 indicator fungi. Four Bacillus strains showing promising antifungal results were subsequently evaluated for their activity in reducing mycelial growth rate, sporulation, spore germination percentage, and mycotoxin production. Bacillus sp. P1 and Bacillus sp. P11 had a remarkable antifungal effect on toxigenic fungi. Washed bacterial cell suspension of strains P1 and P11 (10⁷CFU/ml) reduced by >70% the fungal colony diameters, including a complete inhibition of ochratoxin A (OTA) producing Aspergillus spp. Significant reduction of growth rate, sporulation and spore germination were also observed. The bacteria influenced the production of mycotoxins, causing a reduction around 99 and 97% in AFB1 and OTA concentration, respectively. Chromatographic analysis revealed the presence of lipopeptides (iturin A and surfactin isomers) in butanol extracts of cell-free supernatants and cell pellets of strains P1 and P11. Furthermore, antifungal activity of these extracts was confirmed against A. flavus A12 and A. carbonarius ITAL293, producers of AFB1 and OTA, respectively. These bacterial strains could be promising biocontrol agents against toxigenic fungi.

A liquid chromatography-mass spectrometric method for the detection of cyclic β-amino fatty acid lipopeptides

Bacterial lipopeptides, which contain β-amino fatty acids, are an abundant group of bacterial secondary metabolites exhibiting antifungal and/or cytotoxic properties. Here we have developed an LC-HRMS/MS method for the selective detection of β-amino fatty acid containing cyclic lipopeptides. The method was optimized using the lipopeptides iturin A and puwainaphycin F, which contain fatty acids of similar length but differ in the amino acid composition of the peptide cycle. Fragmentation energies of 10-55eV were used to obtain the amino acid composition of the peptide macrocycle. However, fragmentation energies of 90-130eV were used to obtain an intense fragment specific for the β-amino fatty acid (CnH2n+2N(+)). The method allowed the number of carbons and consequently the length of the β-amino fatty acid to be estimated. We identified 21 puwainaphycin variants differing in fatty acid chain in the crude extract of cyanobacterium Cylindrospermum alatosporum using this method. Analogously 11 iturin A variants were detected. The retention time of the lipopeptide variants showed a near perfect linear dependence (R(2)=0.9995) on the length of the fatty acid chain in linear separation gradient which simplified the detection of minor variants. We used the method to screen 240 cyanobacterial strains and identified lipopeptides from 8 strains. The HPLC-HRMS/MS method developed here provides a rapid and easy way to detecting novel variants of cyclic lipopeptides.

In Situ Analysis of Bacterial Lipopeptide Antibiotics by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is a technique developed in the late 1990s enabling the two-dimensional mapping of a broad variety of biomolecules present at the surface of a sample. In many applications including pharmaceutical studies or biomarker discovery, the distribution of proteins, lipids or drugs, and metabolites may be visualized within tissue sections. More recently, MALDI MSI has become increasingly applied in microbiology where the versatility of the technique is perfectly suited to monitor the metabolic dynamics of bacterial colonies. The work described here is focused on the application of MALDI MSI to map secondary metabolites produced by Bacilli, especially lipopeptides, produced by bacterial cells during their interaction with their environment (bacteria, fungi, plant roots, etc.). This chapter addresses the advantages and challenges that the implementation of MALDI MSI to microbiological samples entails, including detailed protocols on sample preparation (from both microbiologist and mass spectrometrist points of view), matrix deposition, and data acquisition and interpretation. Lipopeptide images recorded from confrontation plates are also presented.

Screening of endophytic bacteria against fungal plant pathogens

Bacterial endophytes were found from 6 plant leaves among 35 plant leaves screened. Two of the isolated bacteria showed antagonistic activity against fungal plant pathogens. An isolate named KL1 showed the clear inihibition against plant pathogens, Fusarium oxysporum and Rhizoctonia solani, on PDA as well as TSA plate. Supernatant of the bacterial culture also showed the clear inhibition against the fungal growth on the plate and the antibiotic substance was identified as iturin A by HPLC analysis. KL1 was identified as Bacillus sp. from the 16S rRNA gene analysis. Very thin hyphae of R. solani was miccroscopically observed when the fungus was co-cultivated with KL1.

Comparative study on the properties of lipopeptide products and expression of biosynthetic genes from Bacillus amyloliquefaciens XZ-173 in liquid fermentation and solid-state fermentation

This study compared the compositions and properties of lipopeptide products purified from liquid fermentation (LF) and solid-state fermentation (SSF) and transcription levels involved in lipopeptides under the two systems. Results of Fourier transform infrared spectroscopy and High performance liquid chromatography revealed no significant differences in the polarity and structure of the two lipopeptide products. A higher amino acid proportion was found for lipopeptide product in LF than in SSF. Lipopeptide product produced from LF had better emulsification and antagonistic activities than that from SSF. For SSF, the transcription accumulation levels of the lipopeptide synthetic genes srfAA and sfp were higher than for LF at the same stage. Transcripts for ituD and lpa-14 remained elevated for a longer period of time under SSF conditions, accounting for differences in the production and fermentation periods between SSF and LF. This is the first report that describes differences in lipopeptide product synthesis and molecular behaviors between LF and SSF systems.

Identification of orfamide A as an insecticidal metabolite produced by Pseudomonas protegens F6

The use of biosurfactants for agricultural crop protection has been gaining interest because they are generally biodegradable and environmentally friendly. In the present study, we identified an insecticidal biosurfactant produced by Pseudomonas protegens F6 (F6) and examined its use for aphid control. The growth of F6 was accompanied by increased aphid mortality and decreased water surface tension. Bioassay-guided chromatography coupled with instrumental analyses, nuclear magnetic resonance (NMR), and time-of-flight mass spectrometer (TOF MS) identified orfamide A as a major metabolite that showed insecticidal activity against green peach aphid ( Myzus persicae ). Orfamide A revealed a dose-dependent mortality against aphids, producing a LC50 value at 34.5 μg/mL, and caused a considerable decrease in the surface tension value of water, giving about 35.7 mN/m at 10 μg/mL. Laboratory and greenhouse mortality bioassays suggested that orfamide A may be applicable to control aphids in organic agriculture. This is the first report of orfamide A as an insecticidal metabolite against Myzus persicae .

Identification of orfamide A as an insecticidal metabolite produced by Pseudomonas protegens F6

The use of biosurfactants for agricultural crop protection has been gaining interest because they are generally biodegradable and environmentally friendly. In the present study, we identified an insecticidal biosurfactant produced by Pseudomonas protegens F6 (F6) and examined its use for aphid control. The growth of F6 was accompanied by increased aphid mortality and decreased water surface tension. Bioassay-guided chromatography coupled with instrumental analyses, nuclear magnetic resonance (NMR), and time-of-flight mass spectrometer (TOF MS) identified orfamide A as a major metabolite that showed insecticidal activity against green peach aphid ( Myzus persicae ). Orfamide A revealed a dose-dependent mortality against aphids, producing a LC50 value at 34.5 μg/mL, and caused a considerable decrease in the surface tension value of water, giving about 35.7 mN/m at 10 μg/mL. Laboratory and greenhouse mortality bioassays suggested that orfamide A may be applicable to control aphids in organic agriculture. This is the first report of orfamide A as an insecticidal metabolite against Myzus persicae .

Distinct lipopeptide production systems for WLIP (white line-inducing principle) in Pseudomonas fluorescens and Pseudomonas putida

The interaction of WLIP (white line-inducing principle), a member of the viscosin group of Pseudomonas lipopeptides, with tolaasin, a lipopeptide mycotoxin secreted by Pseudomonas tolaasii, enables identification of the mushroom pathogen relying on formation of a lipopeptide coprecipitate between confronted colonies of an indicator strain (designated Pseudomonas 'reactans') and P. tolaasii. The WLIP non-ribosomal lipopeptide synthesis system of the mushroom isolate P. 'reactans' LMG 5329 (Wip) was identified and shown to be most similar to the Pseudomonas fluorescens SBW25 viscosin system (Visc), but remarkably different from the WLIP-generating Wlp system previously identified in the rice rhizosphere isolate Pseudomonas putida RW10S2. The Wlp machinery is composed of modules most similar to those recruited for biosynthesis of the non-viscosin-type lipopeptides putisolvin and entolysin by strains from the P. putida clade. In line with the pronounced synteny between the wip and visc flanking regions, strain LMG 5329 was identified as an authentic P. fluorescens closely related to strain SBW25. In both P. putida and P. fluorescens, WLIP production confers similar phenotypes of microbial antagonism and surface colonization. Genotypes other than wlp or wip were not identified among WLIP producers isolated from mushroom, maize rhizosphere or water.

[Screening and identification of low temperature-adapted antagonistic Bacillus isolated from Kekexili region of West China and the analysis of the isolates lipopeptide compounds]

The research and exploitation of special microbial resources in extreme environment is of scientific significance and has broad applied prospect. In this paper, eight Bacillus strains isolated from the vegetation rhizospheres in Kekexili extreme region of Qinghai Province and presented good growth status at low temperature 4 and 10 degrees C were identified. Through physiological and biochemical analysis, rep-PCR fingerprinting, and 16S rDNA and gyrB partial sequence analyses, the eight strains were identified as Bacillus mojavensis (3 isolates), Bacillus amyloliquefaciens (1 isolate), and Bacillus simplex (4 isolates). The agar plate antagonistic test showed that four of the isolates presented distinct antagonistic activity to Sclerotinia sclerotiorum and Xanthomonas oryzae pv. oryzae. The MALDI-TOF-MS analysis showed that the strain KKD1 (B. mojavensis) produced fengycin and surfactin, whereas the strain KKD2 (B. amyloliquefaciens) produced iturin A, surfactin and fengycin, suggesting that the bio-control efficacy of the Bacillus strains could be related to the synthesis and excretion of the antifungal lipopeptide compounds. This study provided the bacterial resources for the research and exploitation of low temperature-adapted Bacillus bio-fertilizers and bio-pesticides.

Characterization of Bacillus subtilis HC8, a novel plant-beneficial endophytic strain from giant hogweed

Thirty endophytic bacteria were isolated from various plant species growing near Saint-Petersburg, Russia. Based on a screening for various traits, including plant-beneficial properties and DNA fragment patterns, potential siblings were removed. The remaining isolates were taxonomically identified using 16S rDNA sequences and potential human and plant pathogens were removed. The remaining strains were tested for their ability to promote radish root growth and to protect tomato plants against tomato foot and root rot. One strain, Bacillus subtilis HC8, isolated from the giant hogweed Heracleum sosnowskyi Manden, significantly promoted plant growth and protected tomato against tomato foot and root rot. Metabolites possibly responsible for these plant-beneficial properties were identified as the hormone gibberellin and (lipo)peptide antibiotics respectively. The antibiotic properties of strain HC8 are similar to those of the commercially available plant-beneficial strain Bacillus amyloliquefaciens FZB42. However, thin layer chromatography profiles of the two strains differ. It is speculated that endophytes such as B. subtilis HC8 contribute to the fast growth of giant hogweed.

Characterization and online detection of surfactin isomers based on HPLC-MS(n) analyses and their inhibitory effects on the overproduction of nitric oxide and the release of TNF-α and IL-6 in LPS-induced macrophages

A rapid method for characterization and online detection of surfactin isomers was developed based on HPLC-MS(n) (n = 1, 2, 3) analyses, and many surfactin isomers were detected and characterized from the bioactive fraction of the mangrove bacterium Bacillus sp. Inhibitory activities of surfactin isomers on the overproduction of nitric oxide and the release of TNF-α and IL-6 in LPS-induced macrophages were systematically investigated. It was revealed that the surfactin isomers showed strong inhibitory properties on the overproduction of nitric oxide and the release of IL-6 on LPS-induced murine macrophage cell RAW264.7 with IC(50) values ranging from 1.0 to 7.0 μM. Structure-activity relationship (SAR) studies revealed that the existence of the free carboxyl group in the structure of surfactin isomers was crucial. These findings will be very helpful for the development of this novel kind of natural product as new anti-inflammatory agents.

In situ detection of the intermediates in the biosynthesis of surfactin, a lipoheptapeptide from Bacillus subtilis OKB 105, by whole-cell cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in combination with mutant analysis

An innovative technique to investigate the intermediates involved in the biosynthesis of the lipoheptapeptide surfactin from Bacillus subtilis OKB105 combining whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) with targeted generation of knock-out mutants was demonstrated. This method allows efficient, sensitive detection of biosynthetic intermediates in a minimum of time directly at the outer surface of microbial cells picked from agar plates or in surface extracts prepared thereof. Biosynthesis of surfactin is encoded by the srf-operon which is organized into four open reading frames which have been attributed to three multifunctional NRPS enzymes (SrfA-C) and a thioesterase/acyltransferase enzyme SrfD. For the wild-type strain OKB 105 only the end product surfactin was found mass spectrometrically. For the detection of lipopeptide intermediates three plasmid- and transposon-insertion mutants were generated interrupting the surfactin assembly line at defined positions. Strain LAB 327 was mutated in the spacer region between enzymes SrfA and B. Here only SrfA was active with the lipotripeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu as the end product. Mutant OKB 120 bears a transposon mutation in SrfB between the first and second amino acid activating modules SrfB1 and SrfB2. It showed all intermediates from the lipodi- until to the lipotetrapeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu-L-Val. In LAB 223 SrfC was knocked out by a transposon mutation. It produced the lipohexapeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu. Our work highlights the applicability and the potential of whole-cell MALDI-TOFMS as an innovative efficient tool for the analysis of intermediate steps of biosynthetic pathways.

[Isolation and identification of lipopeptides produced by Bacillus subtilis using high performance liquid chromatography and electrospray ionization mass spectrometry]

Bacillus subtilis JA produces a broad spectrum of bioactive lipopeptides with great potential applications in agriculture and industry. Crude lipopeptides were extracted with 100% methanol from the precipitate which was obtained by adding 6 mol/L HCl to the cell-free culture broth. The crude extract was separated on a Diamonsil C18 column (5 microm, 250 mm x 4.6 mm) in reversed-phase high performance liquid chromatography (HPLC) system to separate the lipopeptide homologues. Five peaks were eluted from HPLC. Electrospray ionization mass spectrometry (ESI-MS) was used to analyze each HPLC fraction. The results showed three series of ion peaks. According to the values of m/z, the three series of ions were classified into surfactin, iturin and fengycin homologues, which were well-known biosurfactants produced by B. subtilis strains. The major ions were structurally characterized using tandem mass spectrometry. This study suggested a reasonable method for the isolation and identification of lipopeptides produced by B. subtilis strains.

[Isolation and identification of surfactin producing Bacillus subtilis strain and its effect of surfactin on crude oil]

Strains producing biological surfactants were isolated from formation water of Daqing oil field, Heilongjiang Province, China. From which a lipopeptide producing strain ZW-3 was screened out by PCR of the sfp gene. The morphology, cultural characteristics, physiological, biochemical properties and chemotaxonomy of strain ZW-3 were studied. The strain is rod shaped (0.7-0.8 microm x 2-3 microm), gram-positive, spore-forming and aerobic bacteria. Its (G+C) content was determined to be 42.2 mol%. Phylogenetic analysis based on 16S rRNA gene sequence demonstrated that it was closely related to the genus Bacillus subtilis, and the metabolites of strain ZW-3 was analyzed by thin layer chromatography and high performance liquid chromatography, the result indicated that the biosurfactant strain ZW-3 produced was surfactin. It could reduce surface tension of bacterial fermentation culture medium and water/oil- interfacial tension from 68.82 mN/m to 24.88 mN/m and from 23.53 mN/m to 4.57 mN/m, respectively, and its mixture with 1.8% NaOH could reduce water/oil- interfacial tension to an ultra low level (1.2 x 10(-3) mN/m), Its critical micelle concentration (CMC) was tested to be 33.3 mg/L (3.24 x 10(-5) mol/L)at 25 degrees C, and it had excellent emulsifying (2.89U) and foaming property. All these results showed that this biosurfactant had great potential in pharmaceutics, environmental protection, cosmetic, oil recovery and many other application fields.