Biocontrol strains from the genera Bacillus and Pseudomonas and their bioactive secondary metabolites may be considered beneficial for plant health, since they act through several mechanisms, ...including direct antibiosis, plant growth promotion and the induction of systemic resistance in the plant hosts. These beneficial bacteria have been proven to be very active against bacterial and fungal phytopathogens, nematodes and different insects. Direct antibiosis, an induced immune system response (ISR) in the host plant and competition for nutrients and space are the most common biocontrol potential of these genera. Species belonging to the Bacillus genus are commonly considered ideal due to their rapid growth, ease of handling and excellent colonizing properties. These endospore‐forming Bacillus strains are capable of suppressing and inhibiting plant pathogens, both indirectly by competing with the pathogens for a niche or nutrient requirements, or directly by producing various lipopeptide compounds such as iturin, surfactin and fengycin, which are active on many plant pathogens. Furthermore, they are also capable of inducing systemic resistance in plants through the production of volatile substances including alcohols, aldehydes, aromatics, sulfides and ketones. Lipopeptides, polyketides and volatiles from Bacillus spp. can stimulate the expression of genes coding for pathogenesis-related (PR) proteins and other defense-related proteins in the plant hosts through the activation of jasmonic acid (JA), salicylic acid (SA) or ethylene (ET) signaling pathways. In addition, inhibition of quorum sensing in competitive bacteria and the capability to downregulate expression of genes involved in mycelial growth, penetration, sporulation and the virulence of a fungal pathogen is another property of Bacillus strains and their volatiles. The Pseudomonas genus is rich in species with the potential for biocontrol with positive effects on plant welfare, which actively participate in complex plant-pathogen-antagonist interaction. The most common molecules involved in this mechanism are, among others, 2,4‐diacetylphloroglucinol, phenazine‐1‐carboxylic acid, phenazine-1-carboxamide, pyoluteorin and pyrrolnitrin. Cyclic lipopeptides from Pseudomonas spp. such as nunamycin, nunapeptin, brasmycin and braspeptin were intensively studied as agents for plant biocontrol and biostimulation in agriculture. Nunamycin, nunapeptin, brasmycin and braspeptin were identified as essential in the antifungal role. Furthermore, phenazines, sessilins and orfamides were shown to have additive roles in the suppression of some fungal diseases. Additionally, Bacillus and Pseudomonas spp. produce chitinases, glucanases and proteases involved in the suppression of many fungal diseases. Their production is mainly induced by the presence of fungal pathogen biomass and their cell wall. This review provides an updated overview of the antimicrobial activity of plant-associated Bacillus and Pseudomonas involved in plant disease suppression via biological control mechanisms, including their molecular basis and direct activity, offering a better understanding in preventing different pests.
•Bacillus and Pseudomonas spp. produce wide array of secondary metabolites.•Secondary metabolites are involved in biocontrol and biofertilization mechanisms.•Numerous phytopathogens are controlled by Bacillus and Pseudomonas isolates.•Molecular mechanisms of biocontrol activity are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Curtobacterium sp. GD1 was isolated from leaves of conventionally grown soybean in Brazil. It was noteworthy that among all bacteria previously isolated from the same origin, only Curtobacterium sp. ...GD1 showed a strong chitinase activity. The enzyme was secreted and its production was induced by the presence of colloidal chitin in the medium. The chitinase was partially purified and characterized: molecular weight was approximately 37 kDa and specific activity 90.8 U/mg. Furthermore, Curtobacterium sp. GD1 genome was sequenced and analyzed. Our isolate formed a phylogenetic cluster with four other Curtobacterium spp. strains, with ANIb/ANIm ≥ 98%, representing a new, still non described Curtobacterium species. The circular genome visualization and comparison of genome sequences of strains forming new cluster indicated that most regions within their genomes were highly conserved. The gene associated with chitinase production was identified and the distribution pattern of glycosyl hydrolases genes was assessed. Also, genes associated with catabolism of structural carbohydrates such as oligosaccharides, mixed polysaccharides, plant and animal polysaccharides, as well as genes or gene clusters associated with resistance to antibiotics, toxic compounds and auxin biosynthesis subsystem products were identified. The abundance of putative glycosyl hydrolases in the genome of Curtobacterium sp. GD1 suggests that it has the tools for the hydrolysis of different polysaccharides. Therefore, Curtobacterium sp. GD1 isolated from soybean might be a bioremediator, biocontrol agent, an elicitor of the plant defense responses or simply degrader.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
New information has come to light about the biological activity of propolis and the quality of natural products which requires a rapid and reliable assessment method such as High Performance ...Thin-Layer Chromatography (HPTLC) fingerprinting. This study investigates chromatographic and chemometric approaches for determining the antimicrobial activity of propolis of Serbian origin against various bacterial species. A linear multivariate calibration technique, using Partial Least Squares, was used to extract the relevant information from the chromatographic fingerprints, i.e. to indicate peaks which represent phenolic compounds that are potentially responsible for the antimicrobial capacity of the samples. In addition, direct bioautography was performed to localize the antibacterial activity on chromatograms. The biological activity of the propolis samples against various bacterial species was determined by a minimum inhibitory concentration assay, confirming their affiliation with the European poplar type of propolis and revealing the existence of two types (blue and orange) according to botanical origin. The strongest antibacterial activity was exhibited by sample 26 against Staphylococcus aureus, with a MIC value of 0.5 mg/mL, and Listeria monocytogenes, with a MIC as low as 0.1 mg/mL, which was also the lowest effective concentration observed in our study. Generally, the orange type of propolis shows higher antimicrobial activity compared to the blue type. PLS modelling was performed on the HPTLC data set and the resulting models might qualitatively indicate compounds that play an important role in the activity exhibited by the propolis samples. The most relevant peaks influencing the antimicrobial activity of propolis against all bacterial strains were phenolic compounds at RF values of 0.37, 0.40, 0.45, 0.51, 0.60 and 0.70. The knowledge gained through this study could be important for attributing the antimicrobial activity of propolis to specific chemical compounds, as well as the verification of HPTLC fingerprinting as a reliable method for the identification of compounds that are potentially responsible for antimicrobial activity. This is the first report on the activity of Serbian propolis as determined by several combined methods, including the modelling of antimicrobial activity by HPTLC fingerprinting.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this study the efficacy of two different methods for extracting lipopeptides produced by five
strains-ethyl acetate extraction, and acid precipitation followed by methanol extraction-was ...investigated using mass spectrometry. High performance thin layer chromatography (HPTLC) was also used for the simultaneous separation of complex mixtures of lipopeptide extracts and for the determination of antimicrobial activity of their components. The mass spectra clearly showed well-resolved groups of peaks corresponding to different lipopeptide families (kurstakins, iturins, surfactins, and fengycins). The ethyl acetate extracts produced the most favorable results. The extracts of SS-12.6, SS-13.1, and SS-38.4 showed the highest inhibition zones. An iturin analog is responsible for the inhibition of
and
phytopathogenic strains. HPTLC bioautography effectively identified the active compounds from a mixture of lipopeptide extracts, proving
its potential for use in direct detection and determination of antimicrobials. In the test of potential synergism among individual extracts used in different mixtures, stronger antimicrobial effects were not observed. Biochemical and phylogenetic analysis clustered isolates SS-12.6, SS-13.1, SS-27.2, and SS-38.4 together with
, while SS-10.7 was more closely related to
.
The principal purpose of the study was to evaluate in vitro the potential ability of fungal isolates obtained from the painted layer of frescoes and surrounding air to induce symptoms of fresco ...deterioration, associated with their growth and metabolism, so that the risk of such deterioration can be precisely assessed and appropriate conservation treatments formulated. Biodegradative properties of the tested microfungi were qualitatively characterized through the use of a set of special agar plates: CaCO3 glucose agar (calcite dissolution), casein nutrient agar (casein hydrolysis), Czapek-Dox minimal medium (pigment secretion); and Czapek-Dox minimal broth (acid and alkali production). Most of the tested isolates (71.05%) demonstrated at least one of the degradative properties, with Penicillium bilaiae as the most potent, since it tested positive in all four. The remaining isolates (28.95%) showed no deterioration capabilities and were hence considered unlikely to partake in the complex process of fungal deterioration of murals via the tested mechanisms. The obtained results clearly indicate that utilization of fast and simple plate assays can provide insight into the biodegradative potential of deteriogenic fungi and allow for their separation from allochthonous transients, a prerequisite for precise assessment of the amount of risk posed by a thriving mycobiota to mural paintings.
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Cover crops play an important role in low-input cropping systems, increasing the use of agro-ecosystem services. Due to the lack of information about the impact of cover crops and bio-fertilizers on ...popcorn maize (
Sturt.) growth and yield quality, especially the popping volume and nutritive quality, such as concentrations of protein and mineral elements, this research aimed to provide essential information. The interrelation between popcorn maize productivity and quality with important groups of soil microorganisms presents additional novelty. The results demonstrated that field pea is a beneficial cover crop, especially when combined with a bio-fertilizer, supporting the accumulation of maize biomass, chlorophyll, yield potential, and the concentrations of protein, Ca, Mg, Fe, and Zn. In addition, field pea residues promoted N-fixing bacteria, and the number of total microorganisms, especially actinomycetes and decomposing bacteria, which could promote nutrient uptake and grain quality. Residues of cover crop mixtures, common vetch + winter oats and field pea + winter oats, promoted the total number of microorganisms in the soil, and up to the end of vegetation, a greater number of decomposition and ammonification microorganisms were found, especially when the bio-fertilizer was applied, which consequently could support greater maize biomass. Popping volume, as a main trait of popcorn maize, had the highest value in the common vetch + winter oats variant, supporting again the statement that quality traits could be enhanced in sustainable production. Unlike living cover crops, mulch mainly affected soil microbial communities and promoted the development of actinomycetes and cellulolytic microorganisms during the growing season. The results of this research could contribute to the development of sustainable popcorn maize production for improved grain quality. They could also serve as a basis for isolating beneficial soil microorganisms to develop new bio-fertilizers that could improve maize production in synergy with cover crops.
The principal aim of this study was to determine bacterial diversity within the Cave Church of Sts. Peter and Paul, via culturable and non-culturable approaches, and elucidate the antifungal ...potential of autochthonous antagonistic bacterial isolates against biodeteriogenic fungi. Furthermore, whole-genome sequencing of selected bacterial antagonists and the analysis of genes included in the synthesis of secondary metabolites were performed. With the highest RA values, determined in metabarcoding analysis, phyla
(12.08-54.00%) and
(25.34-44.97%) dominated most of the samples. A total of 44 different species, out of 96 obtained isolates, were determined as part of the culturable bacteriobiota, with the predominance of species from the genus
.
was the only isolated species simultaneously present in all investigated substrata within the church. The best antagonistic activity against 10 biodeteriogenic fungi was documented for
, followed by
,
, and
sp. with their highest PGI% values ranging of from 55.9% to 80.9%. These promising results indicate that characterized bacteria are excellent candidates for developing biocontrol strategies for suppressing deteriogenic fungi responsible for the deterioration of investigated fresco painting. Finally, isolate 11-11MM, characterized as
sp., represents a new species for science prompting the need for further study.
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European plum (
Prunus domestica
L.) is a significant commercial crop in Serbia in terms of total fruit production, and is traditionally processed into slivovitz brandy. The brown rot disease caused ...by
Monilinia laxa
drastically reduces plum yield almost every year. Fungal communities associated with leaves and fruits of four local Serbian plum cultivars (Požegača, Ranka, Čačanska Lepotica and Čačanska Rodna) were investigated in two phenological stages during early (May) and late (July) fruit maturation. Alpha diversity indices showed that fungal communities were heterogeneous and Beta diversity indicated that autochthonous fungal communities depended upon seasonal changes and the cultivars themselves. The phylum Ascomycota was the most abundant in all samples, with relative abundance (RA) between 46% in the Požegača cultivar (May) and 89% in the Lepotica cultivar (July). The most abundant genus for all plum cultivars in May was
Aureobasidium
, with RA from 19.27 to 33.69%, followed by
Cryptococcus
, with 4.8 to 48.80%. In July, besides
Cryptococcus
, different genera (
Metschnikowia
,
Fusarium
, and
Hanseniaspora
) were dominant on particular cultivars. Among all cultivable fungi, molecular identification of eleven
M. laxa
isolates from four plum cultivars was performed simultaneously. Bacterial isolates from the plum phyllosphere were tested for their potential antifungal activity against indigenous
M. laxa
isolates. The most potent antagonist P4/16_1, which significantly reduced mycelial growth of
M. laxa
, was identified as
Pseudomonas synxantha
. Further characterization of P4/16_1 revealed the production of volatile organic compounds and phenazine-1-carboxylic acid (PCA). Crude benzene extract of PCA exhibited 57–63% mycelial growth inhibition of
M. laxa
. LC/MS analysis of the crude extract confirmed the presence of phenazine derivatives amongst other compounds. Scanning electron microscopy revealed morpho-physiological changes in the hyphae of
M. laxa
isolates caused by the cell culture and the
P. synxantha
P4/16_1 crude benzene extract. This is the first report of antagonistic activity of
P. synxantha
against
M. laxa
induced by diffusible and volatile antifungal compounds, and it appears to be a promising candidate for further investigation for potential use as a biocontrol agent against brown rot-causing fungi.
•Bacillus group are well known as producers of a wide array of antimicrobials.•Most important molecules are non-ribosomally synthesized peptides and lipopeptides.•Very strong antimicrobial activity ...was confirmed through numerous studies.•Bacillus lipopeptides have strong impact through direct antibiosis on plant pathogens.
Bacteria from the Bacillus group are microorganisms that inhabit a large number of different habitats. They are well known as producers of a wide array of antagonistic compounds of different structures, having between 5 to 8% of the total genome devoted to biosynthesis of secondary metabolites. Most important bioactive molecules from the genus Bacillus are non-ribosomally synthesized peptides and lipopeptides, polyketide compounds, bacteriocins and siderophores. Lipopeptides from Bacillus have very complex mechanisms of biosynthesis catalyzed by non-ribosomal peptide synthetases (NRPSs), large enzyme complexes with modular structure, with each module being in charge for the incorporation of a particular amino acid. In general, they have a broad spectrum of antagonistic activity against plant pathogenic bacteria, fungi and viruses. Most important molecules from this group, circular lipopeptides from surfactin, iturin and fengycin families affect the target cells on the membrane level. Bacillus strains exhibit their biocontrol capacity predominantly through inhibitory activity on the growth of plant pathogens, as well as inducing systemic resistance in plants and competing for ecological niches with plant pathogens. Our previous studies showed the presence of multiple biosynthetic operons for synthesis of non-ribosomal lipopeptides in the collection of natural isolates of Bacillus, with many strains having more than one of them. Several strains of Bacillus sp. that we have recently characterized showed very strong antibacterial and antifungal activity against phytopathogens. The PCR analysis showed the presence of biosynthetic operons for iturin, bacillomycin, fengycin and surfactin in tested strains. Measurement of the kinetics of production of antimicrobial substances showed that, in most cases, synthesis started at the beginning of exponential phase of growth, reaching the maximum of antimicrobial activity at the beginning of the stationary growth phase and stayed at this level for the whole duration of observed period. Preparations of cell-free supernatants of tested strains were active against many fungal and bacterial pathogens, in vitro and in vivo. Mass spectrometry and HPTLC bioautography analysis of purified compounds confirmed the presence of lipopeptides of mentioned families, hence confirming the biocontrol capacity of Bacillus isolates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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