Assessment of antifungal effects of a novel compound from Burkholderia cepacia against Fusarium solani by fluorescent staining

Insight into the adaptation mechanisms of high hydrostatic pressure in physiology and metabolism of hadal fungi from the deepest ocean sediment

High hydrostatic pressure (HHP) influences the life processes of organisms living at depth in the oceans. While filamentous fungi are one of the essential members of deep-sea microorganisms, few works have explored their piezotolerance to HHP. Here, we obtained three homogeneous Aspergillus sydowii from terrestrial, shallow, and hadal areas, respectively, to compare their pressure resistance. A set of all-around evaluation methods including determination of growth rate, metabolic activity, and microscopic staining observation was established and indicated that A. sydowii DM1 from the hadal area displayed significant piezotolerance. Global analysis of transcriptome data under elevated HHP revealed that A. sydowii DM1 proactively modulated cell membrane permeability, hyphae morphology, and septal quantities for seeking a better livelihood under mild pressure. Besides, differentially expressed genes were mainly enriched in the biosynthesis of amino acids, carbohydrate metabolism, cell process, etc., implying how the filamentous fungi respond to elevated pressure at the molecular level. We speculated that A. sydowii DM1 could acclimatize itself to HHP by adopting several strategies, including environmental response pathway HOG-MAPK, stress proteins, and cellular metabolisms.IMPORTANCEFungi play an ecological and biological function in marine environments, while the physiology of filamentous fungi under high hydrostatic pressure (HHP) is an unknown territory due to current technologies. As filamentous fungi are found in various niches, Aspergillus sp. from deep-sea inspire us to the physiological trait of eukaryotes under HHP, which can be considered as a prospective research model. Here, the evaluation methods we constructed would be universal for most filamentous fungi to assess their pressure resistance, and we found that Aspergillus sydowii DM1 from the hadal area owned better piezotolerance and the active metabolisms under HHP indicated the existence of undiscovered metabolic strategies for hadal fungi. Since pressure-related research of marine fungi has been unexpectedly neglected, our study provided an enlightening strategy for them under HHP; we believed that understanding their adaptation and ecological function in original niches will be accelerated in the perceivable future.

The Concentration-Dependent Effects of Essential Oils on the Growth of Fusarium graminearum and Mycotoxins Biosynthesis in Wheat and Maize Grain

The presence of Fusarium fungi and their toxic metabolites in agricultural crops contributes to significant quantitative and qualitative losses of crops, causing a direct threat to human and animal health and life. Modern strategies for reducing the level of fungi and mycotoxins in the food chain tend to rely on natural methods, including plant substances. Essential oils (EOs), due to their complex chemical composition, show high biological activity, including fungistatic properties, which means that they exhibit high potential as a biological plant protection factor. The aim of this study was to determine the fungistatic activity of three EOs against F. graminearum, and the reduction of mycotoxin biosynthesis in corn and wheat grain. All tested EOs effectively suppressed the growth of F. graminearum in concentrations of 5% and 10%. Cinnamon and verbena EOs also effectively reduced the ergosterol (ERG) content in both grains at the concentration of 1%, while at the 0.1% EO concentration, the reduction in the ERG amount depended on the EO type as well as on the grain. The degree of zearalenone (ZEA) reduction was consistent with the inhibition of ERG biosynthesis, while the reduction in deoxynivalenol (DON) was not consistent with this parameter.

Microorganisms from corn stigma with biocontrol potential of Fusarium verticillioides

Abstract The mycotoxigenic fungus Fusarium verticillioides is the primary maize pathogen and causes the maize stalk and ear rot diseases with significant economic losses. Furthermore, the excessive use of fungicides to control F. verticillioides constitutes threats to the environment and human health. Thus, sustainable alternatives such as biological control are needed to minimize the hazards associated with the current method. Although much is known about the vulnerability of the maize silks as a gateway for several fungal pathogens invading the developing grains, studies on the chemical properties of silk extracts and their resident microbiota are scarce. This study isolated and characterized bacteria and fungi that colonize the maize stigma to assess new potential biocontrol agents. The samples were collected from maize fields in the Brazilian localities of Sete Lagoas-MG, Sidrolândia-MS, Sertaneja-PR, and Goiânia-GO. One hundred sixty-seven microorganisms were isolated, 46% endophytic and 54% epiphytic. First, the antagonist activity was evaluated by the agar disc diffusion method performed in triplicate, and 83% of the isolates showed antagonist activity against F. verticillioides. Then, the 42 most efficient isolates were identified based on the partial sequencing of the bacterial 16S rRNA gene and fungi ITS region. The bacteria belong to the genera Bacillus (57.1%), Burkholderia (23.8%), Achromobacter (7.1%), Pseudomonas (2.4%), and Serratia (2.4%), while the fungi are Penicillium (2.4%), Candida (2.4), and Aspergillus (2.4%). The results showed that microorganisms from maize stigma might represent new promising agents for F. verticillioides control.

Burkholderia in the genomic era: from taxonomy to the discovery of new antimicrobial secondary metabolites

Species of Burkholderia are highly versatile being found not only abundantly in soil, but also as plants and animals' commensals or pathogens. Their complex multireplicon genomes harbour an impressive number of polyketide synthase (PKS) and nonribosomal peptide-synthetase (NRPS) genes coding for the production of antimicrobial secondary metabolites (SMs), which have been successfully deciphered by genome-guided tools. Moreover, genome metrics supported the split of this genus into Burkholderia sensu stricto (s.s.) and five new other genera. Here, we show that the successful antimicrobial SMs producers belong to Burkholderia s.s. Additionally, we reviewed the occurrence, bioactivities, modes of action, structural, and biosynthetic information of thirty-eight Burkholderia antimicrobial SMs shedding light on their diversity, complexity, and uniqueness as well as the importance of genome-guided strategies to facilitate their discovery. Several Burkholderia NRPS and PKS display unusual features, which are reflected in their structural diversity, important bioactivities, and varied modes of action. Up to now, it is possible to observe a general tendency of Burkholderia SMs being more active against fungi. Although the modes of action and biosynthetic gene clusters of many SMs remain unknown, we highlight the potential of Burkholderia SMs as alternatives to fight against new diseases and antibiotic resistance.

Effects of Selected Functional Bacteria on Maize Growth and Nutrient Use Efficiency

Plant growth-promoting rhizobacteria (PGPR), which include isolates from genera Paraburkholderia, Burkholderia and Serratia, have received attention due to their numerous plant growth-promoting mechanisms such as their ability to solubilize insoluble phosphates and nitrogen-fixation. However, there is a dearth of information on the potential plant growth-promoting effects of these three groups of bacteria on non-legumes such as maize. This study determined the influences of the aforementioned strains on soil properties, maize growth, nutrient uptake and nutrient use efficiency. A pot trial using maize as a test crop was done using a randomized complete block design with 7 treatments each replicated 7 times. The treatments used in this study were: Control (no fertilizer), chemical fertilizer (CF), organic-chemical fertilizers combination without inoculum (OCF) and with inocula consisting of single strains [cellulolytic bacteria (TC), organic fertilizer and chemical fertilizer with N-fixing bacteria (TN), organic fertilizer and chemical fertilizer with P-solubilizing bacteria (TP)) and three-strain inocula (TCNP), respectively. The variables measured included plant growth and nutrient content, soil nutrient content and functional rhizospheric bacterial populations. Paraburkholderia nodosa NB1 and Burkholderia cepacia PB3 showed comparable effects on maize biomass and also improved N and P use efficiencies when compared to full chemical fertilization. Nitrogen-fixing rhizobacteria had a positive effect on above-ground biomass of maize. Paraburkholderia nodosa NB1 improved soil total C and organic matter contents, besides being the only bacterial treatment that improved K use efficiency compared to OCF. The results suggest that P. nodosa NB1 and B. cepacia PB3 have potential usage in bio-fertilizers. In contrast, treatments with Serratia nematodiphila C46d and consortium strains showed poorer maize nutrient uptake and use efficiency than the other single strain treatments. Bacterial treatments generally showed comparable or higher overall N and P use efficiencies than full chemical fertilization. These findings suggest that at least half the amounts of N and P fertilizers could be reduced through the use of combined fertilization together with beneficial bacteria.

The antifungal action mode of the rice endophyte Streptomyces hygroscopicus OsiSh-2 as a potential biocontrol agent against the rice blast pathogen

Microbial antagonists and their bioactive metabolites provide one of the best alternatives to chemical pesticides to control crop disease for sustainable agriculture and global food security. The rice endophyte Streptomyces hygroscopicus OsiSh-2, with remarkable antagonistic activity towards the rice blast fungus Magnaporthe oryzae, was reported in our previous study. The present study deciphered the possible direct interaction mode of OsiSh-2 against M. oryzae. An in vitro antibiotic assay for OsiSh-2 culture filtrate revealed strong suppression of mycelial growth, conidial germination and appressorial formation of M. oryzae. Meanwhile, severe morphological and internal abnormalities in M. oryzae hyphae were observed under a scanning electron microscope and transmission electron microscope. Foliar treatment of rice seedlings by OsiSh-2 culture filtrate in the greenhouse and in the field showed 23.5% and 28.3% disease reduction, respectively. Correspondingly, OsiSh-2 culture filtrate could induce disorganized chitin deposition in the cell wall and lowered ergosterol content in the cell membrane of M. oryzae. Additionally, cell wall integrity pathway activation, large cell electrolytes release, reactive oxygen species accumulation and tricarboxylic acid cycle-related enzyme activity changes were found in M. oryzae. All these results suggested that the direct antagonistic activity of OsiSh-2 against M. oryzae may be attributed to damaging the integrity of the cell wall and membrane and disrupting mitochondrial function in the pathogen.

Bacillus amyloliquefaciens Q-426 as a potential biocontrol agent against Fusarium oxysporum f. sp. spinaciae

In recent years, Bacillus species have received considerable attention for the biological control of many fungal diseases. In this study, Bacillus amyloliquefaciens Q-426 was tested for its potential use against a variety of plant pathogens. Our screen for genes involved in the biosynthesis of antifungal agents revealed that the fen and bmy gene clusters are present in the Q-426 genome. Lipopeptides such as bacillomycin D, fengycin A, and fengycin B were purified from the bacterial culture broth and subsequently identified by ESI-mass spectrometry. The minimal inhibitory concentration of fengycin A against Fusarium oxysporum f. sp. spinaciae W.C. Snyder & H.N. Hansen O-27 was determined to be 31.25 μg ml(-1) . However, exposure of fungal cells to 50 μg ml(-1) of fengycin A did not allow permeation of fluorescein diacetate into the cytoplasm through the cell membrane. Moreover, leakage of intracellular inorganic cations, nucleic acid and protein were also not detected, indicating that the fungal cell membrane is not the primary target of action for fengycin A. Profound morphological changes were observed in the F. oxysporum strain and spore germination was completely inhibited, suggesting that 50 μg ml(-1) of fengycin A acts, at least, as a fungistatic agent.

Diazotrophic Burkholderia species isolated from the Amazon region exhibit phenotypical, functional and genetic diversity

Forty-eight Burkholderia isolates from different land use systems in the Amazon region were compared to type strains of Burkholderia species for phenotypic and functional characteristics that can be used to promote plant growth. Most of these isolates (n=46) were obtained by using siratro (Macroptilium atropurpureum - 44) and common bean (Phaseolus vulgaris - 2) as the trap plant species; two isolates were obtained from nodules collected in the field from Indigofera suffruticosa and Pithecellobium sp. The evaluated characteristics were the following: colony characterisation on "79" medium, assimilation of different carbon sources, enzymatic activities, solubilisation of phosphates, nitrogenase activity and antifungal activity against Fusarium oxysporium f. sp. phaseoli. Whole cell protein profiles, 16S rRNA, gyrB, and recA gene sequencing and multilocus sequence typing were used to identify the isolates. The isolates showed different cultural and biochemical characteristics depending on the legume species from which they were obtained. Except for one isolate from I. suffruticosa, all isolates were able to solubilise calcium phosphate and present nitrogenase activity under free-living conditions. Only one isolate from common beans, showed antifungal activity. The forty four isolates from siratro nodules were identified as B. fungorum; isolates UFLA02-27 and UFLA02-28, obtained from common bean plants, were identified as B. contaminans; isolate INPA89A, isolated from Indigofera suffruticosa, was a close relative of B. caribensis but could not be assigned to an established species; isolate INPA42B, isolated from Pithecellobium sp., was identified as B. lata. This is the first report of nitrogenase activity in B. fungorum, B. lata and B. contaminans.