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.
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
.
Bats as flying mammals are potent vectors and natural reservoir hosts for many infectious viruses, bacteria, and fungi, also detected in their excreta such as guano. Accelerated deforestation, ...urbanization, and anthropization hastily lead to overpopulation of the bats in urban areas allowing easy interaction with other animals, expansion, and emergence of new zoonotic disease outbreaks potentially harmful to humans. Therefore, getting new insights in the microbiome of bat guano from different places represents an imperative for the future. Furthermore, the use of novel high-throughput sequencing technologies allows better insight in guano microbiome and potentially indicated that some species could be typical guano-dwelling members. Bats are well known as a natural reservoir of many zoonotic viruses such as Ebola, Nipah, Marburg, lyssaviruses, rabies, henipaviruses, and many coronaviruses which caused a high number of outbreaks including ongoing COVID-19 pandemic. Additionally, many bacterial and fungal pathogens were identified as common guano residents. Thus, the presence of multi-drug-resistant bacteria as environmental reservoirs of extended spectrum
β
-lactamases and carbapenemase-producing strains has been confirmed. Bat guano is the most suitable substrate for fungal reproduction and dissemination, including pathogenic yeasts and keratinophilic and dimorphic human pathogenic fungi known as notorious causative agents of severe endemic mycoses like histoplasmosis and fatal cryptococcosis, especially deadly in immunocompromised individuals. This review provides an overview of bat guano microbiota diversity and the significance of autochthonous and pathogenic taxa for humans and the environment, highlighting better understanding in preventing emerging diseases.
Key points
Bat guano as reservoir and source for spreading of autochthonous and pathogenic microbiota
Bat guano vs. novel zoonotic disease outbreaks
Destruction of bat natural habitats urgently demands increased human awareness
Bacteria active against multi-drug resistant pathogens, isolated by direct selection of colonies from clover silage samples, produce zones of inhibition against two Gram-negative (Klebsiella ...pneumoniae Ni9 and Pseudomonas aeruginosa MMA83) and two Gram-positive (Staphylococcus aureus ATCC25923 and Listeria monocytogenes ATCC19111) pathogens. Isolates BGSP7, BGSP9, BGSP11 and BGSP12 produced the largest zones of inhibition against all four pathogens when grown in LB broth with aeration at 37°C. Isolates BGSP7, BGSP9, BGSP11 and BGSP12 were identified as Brevibacillus laterosporus and pulsed field gel electrophoresis and extracellular protein profiles showed that three different strains (BGSP7, BGSP9 and BGSP11) were isolated. A semi-native SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) gel overlay assay showed that BGSP7 and BGSP9 produce small antimicrobial molecules of about 1.5 kDa, while BGSP11 produces antimicrobial molecules of 1.5 and 6 kDa active against S. aureus ATCC25923. Amino acid analysis of two antimicrobial molecules (1583.73 Da; from BGSP7 and 1556.31 Da; from BGSP11) revealed that they have a similar composition and differ only by virtue of the presence of a methionine which is present only in BGSP11 molecule. Genome sequencing of the three isolates revealed the presence of gene clusters associated with the production of non-ribosomally synthesized peptides (brevibacillin, bogorol, gramicidin S, plipastatin and tyrocin) and bacteriocins (laterosporulin, a lactococcin 972-like bacteriocin, as well as putative linocin M18, sactipeptide, UviB and lantipeptide-like molecules). Ultimately, the purification of a number of antimicrobial molecules from each isolate suggests that they can be considered as potent biocontrol strains that produce an arsenal of antimicrobial molecules active against Gram-positive and Gram-negative multi-resistant pathogens, fungi and insects.
Purpose
Flotation tailings represent an extremely unfriendly substrate for plant colonization due to toxic metal concentrations and marked macronutrient deficiencies. The perennial grass
Miscanthus
x
...giganteus
J.M.Greef & Deuter ex Hodk. & Renvoize was successfully cultivated in this infertile substrate for two years. Our aim was to identify composition of its rhizosphere bacterial community and to analyze the effects of the selected rhizobacteria on plant growth, root development, metal and P uptake.
Methods
Using the cultivation-dependent method, 75 isolates were collected from the rhizosphere and six rhizobacterial strains were selected for further characterization based on morphological and biochemical differences. The plant rhizomes were inoculated with the consortium of rhizobacteria and cultivated in the flotation tailings substrate.
Results
Detected bacterial strains were characterized as metal-resistant and plant growth-promoting rhizobacteria (PGPR) because of their metal tolerance (NiCl
2
, Pb(C
2
H
3
O
2
)
2
, CuSO
4
, NaAsO
2
, MnCl
2
) and some or all of the plant growth-promoting (PGP) properties (indole-3-acetic acid and siderophore production, 1-aminocyclopropane-1-carboxylic acid deaminase activity and phosphate solubilization). PGPR mitigated the negative effects of high metal concentrations and macronutrient deficiency as shown by stimulated lateral roots development, increased root hair length, plant below and above ground biomass yield, higher plant P uptake and metal accumulation rate.
Conclusions
The isolated PGPR strains could be used in PGP-bacteria assisted phytoremediation of flotation tailings and metal polluted soils by
M.
x
giganteus
. Their PGP effects on various metal-tolerant target plant species in the respective substrate remain to be verified.
Acinetobacter baumannii
is a leading cause of healthcare-associated infections worldwide. Its various intrinsic and acquired mechanisms of antibiotic resistance make the therapeutic challenge even ...more serious. One of the promising alternative treatments that is increasingly highlighted is phage therapy, the therapeutic use of bacteriophages to treat bacterial infections. Two phages active against nosocomial carbapenem-resistant
A. baumannii
strain 6077/12, vB_AbaM_ISTD, and vB_AbaM_NOVI, were isolated from Belgrade wastewaters, purified, and concentrated using CsCl gradient ultracentrifugation. The phages were screened against 103 clinical isolates of
A. baumannii
from a laboratory collection and characterized based on plaque and virion morphology, host range, adsorption rate, and one-step growth curve. Given that phage ISTD showed a broader host range, better adsorption rate, shorter latent period, and larger burst size, its ability to lyse planktonic and biofilm-embedded cells was tested in detail. Phage ISTD yielded a 3.5- and 2-log reduction in planktonic and biofilm-associated viable bacterial cell count, respectively, but the effect was time-dependent. Both phages produced growing turbid halos around plaques indicating the synthesis of depolymerases, enzymes capable of degrading bacterial exopolysaccharides. Halos tested positive for presence of phages in the proximity of the plaque, but not further from the plaque, which indicates that the observed halo enlargement is a consequence of enzyme diffusion through the agar, independently of the phages. This notion was also supported by the growing halos induced by phage preparations applied on pregrown bacterial lawns, indicating that depolymerizing effect was achieved also on non-dividing sensitive cells. Overall, good rates of growth, fast adsorption rate, broad host range, and high depolymerizing activity, as well as antibacterial effectiveness against planktonic and biofilm-associated bacteria, make these phages good candidates for potential application in combating
A. baumannii
infections.
In our previous study we demonstrated that proteinase PrtP is able to impair bacteriocin LcnB activity, despite being produced by the same organism and encoded by the same plasmid. However, precise ...mechanism of this action, i.e., the exact cleavage site within LcnB bacteriocin, as well as its effect on antimicrobial activity of the resulting peptide remained vague. Here we further explored the interplay between these two proteins and defined, using mass spectrometry, that this unusual hydrolysis indeed occurs
, between the sixth and seventh amino acid on the N terminus of LcnB. To address whether the cleaved form of LcnB retains any level of activity, both recombinant and chemically synthesized variant of truncated LcnB were engineered and produced, but demonstrated no antimicrobial activity. When LcnB was recombinantly overexpressed and subjected to PrtP digestion, the change in its antimicrobial activity was monitored and the degradation products analyzed with reverse-phase high-pressure liquid chromatography. The results confirmed the inactivity of the truncated LcnB and additionally corroborated the PrtP cleavage site in LcnB bacteriocin. In addition, it was demonstrated that, once truncated, LcnB is not able to bind its receptor and is susceptible to additional hydrolysis. This is the first report on proteolytic inactivation of bacteriocins inside the same bacterial host.
We examined the effect of drought-tolerant Bacillus safensis SS-2.7 and B. thuringiensis SS-29.2 strains on the response of four (133, 274, California Wonder—CalW, and Matica) sweet pepper genotypes ...to water deficiency conditions. Pepper seeds were sown in pots with (treated) and without (control) bacterial strain inoculation. After four weeks of growth under controlled conditions and regular watering, drought was imposed by completely withholding watering for seven days. Under conditions of normal watering, genotype 274 showed better seedling establishment than genotype 133 and CalW, while the slowest was genotype Matica. Antioxidant enzyme activity under drought conditions was genotype and bacterial treatment-dependent. The best response to bacterial treatment in order to cope with severe drought was found in the CalW genotype, while in genotype 133, we determined even faster plant decay during water deficiency in treated seeds. Inoculated seeds of the Matica genotype did not show different antioxidant enzyme activity under normal and drought conditions. According to the obtained results, we concluded that under drought conditions, the most susceptible was genotype 274, moderate susceptibility was detected in genotype 133, and CalW and Matica were the most tolerant genotypes. Our study demonstrates (1) that drought-tolerant Bacillus strains showed a plant growth-promoting effect on some selected pepper genotypes; (2) that there were genotype-dependent antioxidant enzyme activities under drought conditions in response to treatment with a particular bacterial strain; and (3) that we could expect a genotype-dependent response during biostimulant application, especially under stress conditions.
•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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