Antibiotic production and biocontrol activity by Bacillus subtilis CL27 and Bacillus pumilus CL45

Use of green fluorescent protein as molecular marker for tagging Bacillus brevis in soil under the control of a novel constitutive promoter F1

A constitutive expression vector pHY300-Flgfp was constructed to test the function of promoter F1 subcloned from a rice epiphyte Bacillus brevis strain DX01. The DX01 cells harboring plasmid pHY300-F1gfp were detected to produce bright green fluorescence. Subsequently, the gfp-tagged B. brevis strain was released into the soil and its survival was investigated by PCR and the detection of green fluorescence. The spatial location of in situ gfp-tagged bacterial cells on the root surface of rice seedlings was visualized. All these results indicated that green fluorescent protein is an ideal molecular marker for the detection of the activities of promoter F1, and it is also a reliable probe to monitor specific B. brevis bacteria in the environment.

Inhibition of the growth of Paenibacillus larvae, the causal agent of American foulbrood of honeybees, by selected strains of aerobic spore-forming bacteria isolated from apiarian sources

The bacterium Paenibacillus larvae, the causative agent of American foulbrood disease of honeybee larvae, occurs throughout the world and is found in many beekeeping areas of Argentina. The potential as biocontrol agents of antagonic aerobic spore-forming bacteria isolated from honey samples and other apiarian sources were evaluated. Each isolate was screened against one strain of Paenibacillus larvae (ATCC 9545) by using a perpendicular streak technique. Ten randomly selected bacterial strains from the group that showed the best antagonistic effect to P. larvae ATCC 9545 were selected for further study. These were identified as Bacillus subtilis (m351), B. pumilus (m350), B. licheniformis (m347), B. cereus (mv33), B. cereus (m387), B. cereus (m6c), B. megaterium (m404), Brevibacillus laterosporus (BLAT169), B. laterosporus (BLAT170), and B. laterosporus (BLAT171). The antagonistic strains were tested against 17 P. larvae strains from different geographical origins by means of a spot test in wells. The analysis of variance and posterior comparison of means by Tukey method (P < 0.01) showed that the best antagonists were B. megaterium (m404), B. licheniformis (m347), B. cereus (m6c), B. cereus (mv33), and B. cereus (m387).

Identification and Characterization of Novel Genetic Markers Associated with Biological Control Activities in Bacillus subtilis

ABSTRACT Suppressive subtractive hybridization (SSH) was used to identify genetic markers associated with biological control of plant pathogens by Bacillus subtilis. The genomes of two commercialized strains, GB03 and QST713, were compared with that of strain 168, which has no defined biocontrol capacities, to obtain a pool of DNA fragments unique to the two biocontrol strains. The sequences of 149 subtracted fragments were determined and compared with those present in GenBank, but only 80 were found to correspond to known Bacillus genes. Of these, 65 were similar to genes with a wide range of metabolic functions, including the biosynthesis of cell wall components, sporulation, and antibiotic biosynthesis. Sixteen subtracted fragments shared a high degree of similarity to sequences found in multiple B. subtilis strains with proven biocontrol capacities. Oligonucleotide primers specific to nine of these genes were developed. The targeted genes included five genes involved in antibiotic synthesis (bmyB, fenD, ituC,srfAA, and srfAB) and four additional genes (yndJ, yngG, bioA, and a hypothetical open reading frame) not previously associated with biological control. All nine markers were amplified from the commercialized B. subtilis strains GB03, QST713, and MBI600, with the exception of ituC, which was not detected in GB03. The markers also were amplified from four other B. subtilis isolates, but they were not amplified from other related Bacillus strains, including the plant growth-promoting rhizobacteria IN937a and IN937b. Sequencing of the amplified markers revealed that all seven of the isolates that scored positive for multiple markers were genotypically distinct strains. Interestingly, strains scored positive for the amplifiable markers generally were more effective at inhibiting the growth of Rhizoctonia solani and Pythium ultimum than other Bacillus isolates that lacked the markers. The potential utility of the defined genetic markers to further define the diversity, ecology, and biocontrol activities of B. subtilis are discussed.

Mycosubtilin overproduction by Bacillus subtilis BBG100 enhances the organism's antagonistic and biocontrol activities

A Bacillus subtilis derivative was obtained from strain ATCC 6633 by replacement of the native promoter of the mycosubtilin operon by a constitutive promoter originating from the replication gene repU of the Staphylococcus aureus plasmid pUB110. The recombinant strain, designated BBG100, produced up to 15-fold more mycosubtilin than the wild type produced. The overproducing phenotype was related to enhancement of the antagonistic activities against several yeasts and pathogenic fungi. Hemolytic activities were also clearly increased in the modified strain. Mass spectrometry analyses of enriched mycosubtilin extracts showed similar patterns of lipopeptides for BBG100 and the wild type. Interestingly, these analyses also revealed a new form of mycosubtilin which was more easily detected in the BBG100 sample. When tested for its biocontrol potential, wild-type strain ATCC 6633 was almost ineffective for reducing a Pythium infection of tomato seedlings. However, treatment of seeds with the BBG100 overproducing strain resulted in a marked increase in the germination rate of seeds. This protective effect afforded by mycosubtilin overproduction was also visualized by the significantly greater fresh weight of emerging seedlings treated with BBG100 compared to controls or seedlings inoculated with the wild-type strain.

Biological control agent of common scab disease by antagonistic strain Bacillus sp. sunhua

AIMS

To identify an antagonistic strain against Streptomyces scabiei and to characterize the antibiotic agent. The efficacy of the isolated strain in controlling common scab disease was also evaluated.

METHODS AND RESULTS

A bacterial strain antagonistic against S. scabiei was isolated from the soil of a potato-cultivating area. This bacterium was identified as a Bacillus species by 16S rRNA gene sequence analysis and was designated Bacillus sp. sunhua. Antibiotics produced by this strain were proven to be stable within a broad pH range and at high temperatures. The culture broth was extracted with ethyl acetate, and then the crude extract was applied to HPLC. Two compounds were isolated and identified as iturin A and macrolactin A by 1H-NMR, 13C-NMR, HMBC, HMQC and mass spectrometer. The culture broth of Bacillus sp. sunhua had a suppressive effect on common scab disease in a pot assay, decreasing the infection rate from 75 to 35%. This strain also suppressed Fusarium oxysporum, the pathogen of potato dry rot disease.

CONCLUSIONS

Bacillus sp. sunhua was shown to inhibit S. scabiei effectively.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report demonstrating that macrolactin A and iturin A inhibit S. scabiei. This study demonstrated the possibility of controlling potato scab disease using Bacillus sp. sunhua.

Biological control of collar rot disease with broad-spectrum antifungal bacteria associated with groundnut

Bacteria associated with 6 habitats of groundnut were evaluated for their broad-spectrum antifungal activity and suppression of collar rot (Aspergillus niger) of groundnut. Three hundred and ninety-three strains were tested against 8 fungal pathogens of groundnut including 5 necrotrophic fungi, Aspergillus flavus, A. niger, Rhizoctonia bataticola, Rhizoctonia solani, and Sclerotium rolfsii, and 3 biotrophic fungi, Cercospora arachidicola, Phaeoisariopsis personata, and Puccinia arachidis. Pseudomonas sp. GRS 175, Pseudomonas aeruginosa GPS 21, GSE 18, GSE 19, and GSE 30, and their cell-free culture filtrates were highly antagonistic to all the test fungi. The cell-free culture filtrates of these bacteria were fungicidal and induced mycelial deformations including hyphal bulging and vacuolization in necrotrophic fungi. The cell-free culture filtrates at 10% (v/v) concentration significantly inhibited the spore germination of biotrophic fungi. In the greenhouse, P. aeruginosa GSE 18 emerged as an effective biocontrol agent of collar rot closely followed by P. aeruginosa GSE 19. The bacterium applied as a seed treatment reduced the pre-emergence rotting and postemergence wilting by > 60%. Pseudomonas aeruginosa GSE 18 effectively colonized the groundnut rhizosphere, both in native and in A. niger infested potting mixtures. Ninety-day-old peat formulation of P. aeruginosa GSE 18 had biocontrol ability comparable with the midlog-phase cells. Pseudomonas aeruginosa GSE 18, tolerant to thiram, in combination with the fungicide had an improved collar rot control. The present study was a successful attempt in selection of broad-spectrum and fungicide tolerant biocontrol agents that can be a useful component of integrated management of collar rot.

Production of antimicrobial substances by Bacillus subtilis LFE-1, B. firmus H2O-1 and B. licheniformis T6-5 isolated from an oil reservoir in Brazil

AIMS

Forty Bacillus strains isolated from a Brazilian oil reservoir were tested against each other to select strains producing antimicrobial substances (AMS). Three strains, Bacillus subtilis (LFE-1), Bacillus firmus (H2O-1) and Bacillus licheniformis (T6-5), were selected due to their ability to inhibit more than 65% of the Bacillus strains tested. These three strains were also investigated for their capability to inhibit sulphate-reducing bacteria (SRB). Furthermore, physiological and biochemical characteristics of the antimicrobial compounds produced by the selected strains were determined.

METHODS AND RESULTS

Among the forty strains tested, 36 (90%) strains were able to inhibit at least one Bacillus strain used as indicator in plate assays and three of them (LFE-1, T6-5 and H2O-1) were able to inhibit 65, 70 and 97.5% of the 40 strains studied here respectively. Clear zones of inhibition were observed when H2O-1 was tested against SRB-containing consortium T6-lab and Desulfovibrio alaskensis strain NCIMB 13491, while strain T6-5 was able to inhibit only the D. alaskensis strain. The three substances showed to be insensitive to different enzymes and chemicals, were heat stable and the substances produced by strains T6-5 and H2O-1 were active over a wide pH range.

CONCLUSIONS

Three different AMS produced by Bacillus strains from an oil reservoir, two of them with activity against SRB, are presented here.

SIGNIFICANCE AND IMPACT OF THE STUDY

The preliminary characterization of these AMS points to their potential use as biocides in the petroleum industry for controlling problems associated with SRB.

Bacillus subtilis M4 decreases plant susceptibility towards fungal pathogens by increasing host resistance associated with differential gene expression

Results presented in this paper describe the ability of Bacillus subtilis strain M4 to reduce disease incidence caused by Colletotrichum lagenarium and Pythium aphanidermatum on cucumber and tomato, respectively. Disease protection in both pathosystems was most probably due to induction of resistance in the host plant since experiments were designed in order to avoid any direct contact between the biocontrol agent and the pathogen. Pre-inoculation with strain M4 thus sensitised both plants to react more efficiently to subsequent pathogen infection. In cucumber, the use of endospores provided a disease control level similar to that obtained with vegetative cells. In contrast, a mixture of lipopeptides from the surfactin, iturin and fengycin families showed no resistance-inducing potential. Interestingly, treatment with strain M4 was also associated with significant changes in gene transcription in the host plant as revealed by cDNA-AFLP analyses. Several AFLP fragments corresponded to genes not expressed in control plants and specifically induced by the Bacillus treatment. In support to the macroscopic protective effect, this differential accumulation of mRNA also illustrates the plant reaction following perception of strain M4, and constitutes one of the very first examples of defence-associated modifications at the transcriptional level elicited by a non-pathogenic bacterium in a host plant.

Ecology of Bacillus and Paenibacillus spp. in Agricultural Systems

ABSTRACT Diverse populations of aerobic endospore-forming bacteria occur in agricultural fields and may directly and indirectly contribute to crop productivity. This paper describes recent advances in our understanding of the ecology of Bacillus and Paenibacillus spp. and how different subpopulations of these two genera can promote crop health. The abundance, diversity, and distribution of native populations and inoculant strains in agricultural fields have been characterized using a variety of methods. While native populations of these two genera occur abundantly in most agricultural soils, plant tissues are differentially colonized by distinct subpopulations. Multiple Bacillus and Paenibacillus spp. can promote crop health in a variety of ways. Some populations suppress plant pathogens and pests by producing antibiotic metabolites, while others may directly stimulate plant host defenses prior to infection. Some strains can also stimulate nutrient uptake by plants, either by promoting rhizobial and mycorrhizal symbioses or by fixing atmospheric nitrogen directly. Despite a wealth of new information on the genetics and physiology of Bacillus and related species, a better understanding of the microbial ecology of these two genera must be developed. To this end, several important, but unanswered, questions related to the ecological significance and potential for managing the beneficial activities of these bacteria are discussed.

Role of lipopeptides produced by Bacillus subtilis GA1 in the reduction of grey mould disease caused by Botrytis cinerea on apple

AIM

Test of Bacillus subtilis strain GA1 for its potential to control grey mould disease of apple caused by Botrytis cinerea.

METHODS AND RESULTS

GA1 was first tested for its ability to antagonize in vitro the growth of a wide variety of plant pathogenic fungi responsible for diseases of economical importance. The potential of strain GA1 to reduce post-harvest infection caused by B. cinerea was tested on apples by treating artificially wounded fruits with endospore suspensions. Strain GA1 was very effective at reducing disease incidence during the first 5 days following pathogen inoculation and a 80% protection level was maintained over the next 10 days. Treatment of fruits with an extract of GA1 culture supernatant also exerted a strong preventive effect on the development of grey mould. Further analysis of this extract revealed that strain GA1 produces a wide variety of antifungal lipopeptide isomers from the iturin, fengycin and surfactin families. A strong evidence for the involvement of such compounds in disease reduction arose from the recovery of fengycins from protected fruit sites colonized by bacterial cells.

CONCLUSIONS

The results presented here demonstrate that, despite unfavourable pH, B. subtilis endospores inoculated on apple pulp can readily germinate allowing significant cell populations to establish and efficient in vivo synthesis of lipopeptides which could be related to grey mould reduction.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work enables for the first time to correlate the strong protective effect of a particular B. subtilis strain against grey mould with in situ production of fengycins in infected sites of apple fruits.

Antifungal activity of Bacillus subtilis 355 against wood-surface contaminant fungi

A strain of Bacillus subtilis was examined for antifungal activity against phytopathogenic and wood-surface contaminant fungi. The bacterium was grown in five culture media with different incubation times in order to study cell development, sporulation, and the production of metabolites with antifungal activity. The anti-sapstain and anti-mould activity of the bacterium grown in yeast extract glucose broth (YGB) medium in wood was also evaluated. In YGB, the bacterium inhibited the growth of several fungi and displayed a broader spectrum of activity than in the other media tested. A relationship between bacterial spore production and the formation of metabolites with antifungal activity was detected. YGB medium displayed effective control in wood block tests. YGB medium was extracted with solvents of increasing polarity and the dry residues were applied to silicagel plates, resolved with the appropriate solvent and sprayed with different solutions, detecting the presence, of amines, and higher alcohols. The bioautographic method revealed the presence of at least two active compounds against the blue-stain fungus Cladosporium cucumerinum.

Expression of green fluorescent protein in Bacillus brevis under the control of a novel constitutive promoter F1 and insertion mutagenesis of F1 in Escherichia coli DH5alpha

The constitutive expression vector pHY300-F1gfp was constructed to test the function of a promoter, F1, cloned from the rice epiphyte Bacillus brevis strain DX01. The DX01 cells harboring the plasmid pHY300-F1gfp were shown to produce bright green fluorescence. The results were confirmed by Western blot analysis and fluorescence-activated cell sorting. Expression of the F1 promoter was constitutive. To improve the activity of F1, insertion mutagenesis of F1 based on in vitro transposition reaction was performed. Seven mutants with enhanced transcription activity in Escherichia coli DH5alpha were obtained. The enhanced promoters showed similar high activities in B. brevis strain DX01.

Antimicrobial activity of Paenibacillus peoriae strain NRRL BD-62 against a broad spectrum of phytopathogenic bacteria and fungi

AIMS

To investigate the potential antagonistic activity of Paenibacillus peoriae strain NRRL BD-62 against phytopathogenic micro-organisms and to determine the physiological and biochemical characteristics of the antimicrobial compound produced by this strain.

METHODS AND RESULTS

Strain NRRL BD-62 showed a broad inhibition spectrum with activity against various phytopathogenic bacteria and fungi. Physico-chemical characterization of the antimicrobial activity showed that it was stable during heat treatment and was retained even after autoclave at 121 degrees C for 10 min. The compound was also stable after the treatment with organic solvents, hydrolytic enzymes and its activity was preserved at a wide range of pH. The partial purification carried out by Sephadex G25 gel filtration showed two profiles of inhibition against the indicator strains tested, suggesting at least two different substances with distinct molecular weight.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the production of antimicrobial substances in P. peoriae. Besides the antimicrobial inhibition capability, the strain NRRL BD-62 is also able to effectively fix molecular nitrogen, and produce chitinases and proteases as well, suggesting that further studies should be addressed to use P. peoriae strain NRRL BD-62 as a plant growth promoter and/or as a biocontrol agent in field experiments.

Pathogen self-defense: mechanisms to counteract microbial antagonism,

Natural and agricultural ecosystems harbor a wide variety of microorganisms that play an integral role in plant health, crop productivity, and preservation of multiple ecosystem functions. Interactions within and among microbial communities are numerous and range from synergistic and mutualistic to antagonistic and parasitic. Antagonistic and parasitic interactions have been exploited in the area of biological control of plant pathogenic microorganisms. To date, biocontrol is typically viewed from the perspective of how antagonists affect pathogens. This review examines the other face of this interaction: how plant pathogens respond to antagonists and how this can affect the efficacy of biocontrol. Just as microbial antagonists utilize a diverse arsenal of mechanisms to dominate interactions with pathogens, pathogens have surprisingly diverse responses to counteract antagonism. These responses include detoxification, repression of biosynthetic genes involved in biocontrol, active efflux of antibiotics, and antibiotic resistance. Understanding pathogen self-defense mechanisms for coping with antagonist assault provides a novel approach to improving the durability of biologically based disease control strategies and has implications for the deployment of transgenes (microorganisms or plants).

Improving biological control by combining biocontrol agents each with several mechanisms of disease suppression

ABSTRACT Two biocontrol agents, a yeast (Pichia guilermondii) and a bacterium (Bacillus mycoides), were tested separately and together for suppression of Botrytis cinerea on strawberry leaves and plants. Scanning electron microscopy revealed significant inhibition of Botrytis cinerea conidial germination in the presence of Pichia guilermondii, whereas Bacillus mycoides caused breakage and destruction of conidia. When both biocontrol agents were applied in a mixture, conidial destruction was more severe. The modes of action of each of the biocontrol agents were elucidated and the relative quantitative contribution of each mechanism to suppression of Botrytis cinerea was estimated using multiple regression with dummy variables. The improvement in control efficacy achieved by introducing one or more mechanisms at a time was calculated. Pichia guilermondii competed with Botrytis cinerea for glucose, sucrose, adenine, histidine, and folic acid. Viability of the yeast cells played a crucial role in suppression of Botrytis cinerea and they secreted an inhibitory compound that had an acropetal effect and was not volatile. Bacillus mycoides did not compete for any of the sugars, amino acids, or vitamins examined at a level that would affect Botrytis cinerea development. Viable cells and the compounds secreted by them contributed similarly to Botrytis cinerea suppression. The bacteria secreted volatile and non-volatile inhibitory compounds and activated the defense systems of the host. The nonvolatile compounds had both acropetal and basipetal effects. Mixture of Pichia guilermondii and Bacillus mycoides resulted in additive activity compared with their separate application. The combined activity was due to the summation of biocontrol mechanisms of both agents. This work provides a theoretical explanation for our previous findings of reduced disease control variability with a mixture of Pichia guilermondii and Bacillus mycoides.

Bacillomycin D: an iturin with antifungal activity against Aspergillus flavus

AIMS

In a search for an antifungal peptide with a high activity against Aspergillus flavus, Bacillus subtilis AU195 was selected from a collection of isolates with antagonistic activity against A. flavus.

METHODS AND RESULTS

To identify the antifungal peptides, a protein purification scheme was developed based on the detection of the antifungal activity in purified fractions against A. flavus. Two lipopeptides were purified with anion exchange and gel filtration chromatography. Their masses were determined to be 1045 and 1059 m/z with mass spectrometry, and their peptide moiety was identical to bacillomycin D.

CONCLUSION

AU195 synthesized a mixture of two antifungal bacillomycin D analogues with masses of 1045 and 1059, the 14 mass unit difference representing the difference between a C15 and a C16 lipid chain.

SIGNIFICANCE AND IMPACT OF THE STUDY

Both bacillomycin D analogues were active at the same concentration against A. flavus, but the different lipid chain length apparently affected the activity of the lipopeptide against other fungi.

The natural functions of secondary metabolites

Secondary metabolites, including antibiotics, are produced in nature and serve survival functions for the organisms producing them. The antibiotics are a heterogeneous group, the functions of some being related to and others being unrelated to their antimicrobial activities. Secondary metabolites serve: (i) as competitive weapons used against other bacteria, fungi, amoebae, plants, insects, and large animals; (ii) as metal transporting agents; (iii) as agents of symbiosis between microbes and plants, nematodes, insects, and higher animals; (iv) as sexual hormones; and (v) as differentiation effectors. Although antibiotics are not obligatory for sporulation, some secondary metabolites (including antibiotics) stimulate spore formation and inhibit or stimulate germination. Formation of secondary metabolites and spores are regulated by similar factors. This similarity could insure secondary metabolite production during sporulation. Thus the secondary metabolite can: (i) slow down germination of spores until a less competitive environment and more favorable conditions for growth exist; (ii) protect the dormant or initiated spore from consumption by amoebae; or (iii) cleanse the immediate environment of competing microorganisms during germination.

Isolation of Bacillus strains from the rhizosphere of cereals and in vitro screening for antagonism against phytopathogenic, food-borne pathogenic and spoilage micro-organisms

Bacillus strains were isolated from the rhizosphere of cereals in order to be used as natural biocontrol agents (BCAs). They were screened for antagonism in vitro against various test micro-organisms. The isolates showing antagonism were identified to species level. A combination of techniques was employed for the isolation of Bacillus species. Using the direct method, only one of the 25 isolates screened showed antagonistic properties. This strain (IFS-01) was identified by means of API test strips and the ATB Plus computer programme. It proved to be Bacillus subtilis and consequently has been designated as Bacillus subtilis IFS-01. This strain produced either a broad spectrum antimicrobial compound or several compounds with different activities. The fungi and Gram-positive bacteria were more sensitive to the antagonistic isolate than the Gram-negative bacteria. A Bacillus strain producing BCAs which can be used as biopesticides or organic preservatives has been isolated and identified.

Inhibition of aflatoxin production of Aspergillus parasiticus NRRL 2999 by Bacillus pumilus

Six isolates of Bacillus pumilus were tested for their ability to inhibit aflatoxin production of Aspergillus parasiticus NRRL 2999 in yeast extract sucrose (YES) broth. Aflatoxin production was inhibited in both simultaneous and deferred antagonism assays, suggesting that the inhibitory activity was due to extracellular metabolites(s) produced in cell-free supernatant fluids of cultured broth. The inhibition was not due to organic acids or hydrogen peroxide produced by B. pumilus since the inhibitory activity was not lost after pH adjustment or treatment of supernatant fluids with catalase. A range of media tested for the production of inhibitory metabolite(s) in supernatant fluids showed that all media supported bacterial growth and production of the metabolite(s). The metabolite(s) were produced over a wide range of temperature (25 to 37 degrees C) and pH (4 to 9) of growth of B. pumilus. They were stable over a wide range of pH (4 to 10) and were not inactivated after autoclaving at 121 degrees C for 30 minutes.