Degradation of aromatic compounds through the β-ketoadipate pathway is required for pathogenicity of the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici

The Ubiquitous Wilt-Inducing Pathogen Fusarium oxysporum-A Review of Genes Studied with Mutant Analysis

Fusarium oxysporum is one of the most economically important plant fungal pathogens, causing devastating Fusarium wilt diseases on a diverse range of hosts, including many key crop plants. Consequently, F. oxysporum has been the subject of extensive research to help develop and improve crop protection strategies. The sequencing of the F. oxysporum genome 14 years ago has greatly accelerated the discovery and characterization of key genes contributing to F. oxysporum biology and virulence. In this review, we summarize important findings on the molecular mechanisms of F. oxysporum growth, reproduction, and virulence. In particular, we focus on genes studied through mutant analysis, covering genes involved in diverse processes such as metabolism, stress tolerance, sporulation, and pathogenicity, as well as the signaling pathways that regulate them. In doing so, we hope to present a comprehensive review of the molecular understanding of F. oxysporum that will aid the future study of this and related species.

Comparison of Bacterial Communities in Five Ectomycorrhizal Fungi Mycosphere Soil

Ectomycorrhizal fungi have huge potential value, both nutritionally and economically, but most of them cannot be cultivated artificially. To better understand the influence of abiotic and biotic factors upon the growth of ectomycorrhizal fungi, mycosphere soil and bulk soil of five ectomycorrhizal fungi (Calvatia candida, Russula brevipes, Leucopaxillus laterarius, Leucopaxillus giganteus, and Lepista panaeola) were used as research objects for this study. Illumina MiSeq sequencing technology was used to analyze the community structure of the mycosphere and bulk soil bacteria of the five ectomycorrhizal fungi, and a comprehensive analysis was conducted based on soil physicochemical properties. Our results show that the mycosphere soil bacteria of the five ectomycorrhizal fungi are slightly different. Escherichia, Usitatibacter, and Bradyrhizobium are potential mycorrhizal-helper bacteria of distinct ectomycorrhizal fungi. Soil water content, soil pH, and available potassium are the main factors shaping the soil bacterial community of the studied ectomycorrhizal fungi. Moreover, from the KEGG functional prediction and LEfSe analysis, there are significant functional differences not only between the mycosphere soil and bulk soil. 'Biosynthesis of terpenoidsand steroids', 'alpha-Linolenic acid metabolism', 'Longevity regulating pathway-multiple species', 'D-Arginine and D-ornithine metabolism', 'Nitrotoluene degradation' and other functions were significantly different in mycosphere soil. These findings have pivotal implications for the sustainable utilization of ectomycorrhizal fungi, the expansion of edible fungus cultivation in forest environments, and the enhancement of derived economic benefits.

Allelopathic effect of phenolic acids in various extracts of wheat against Fusarium wilt in faba bean

Allelopathy is the main reason for disease control in intercropping systems. The effects of different extracts, root secretions and phenolic acids of wheat and faba bean on Fusarium oxysporum f. fabae (FOF) growth were studied to explore the allelopathy mechanism of wheat in disease control of faba bean. Various extracts and root exudate of faba bean were promoted but those of wheat inhibited the growth and reproduction of FOF. High-performance liquid chromatography revealed significant differences in the contents of phenolic acids in the various extracts and root exudate of wheat and faba bean. The total content of syringic acid (SA) was much higher, but that of other five phenolic acids were lower in wheat than in faba bean. The in vitro addition of these phenolic acids revealed that cinnamic acid (CA), p-hydroxybenzoic acid (PHBA), benzoic acid (BA), vanillic acid (VA) and ferulic acid (FA) exhibited significant promoting effects and SA exhibited strong inhibitory effects on the growth of FOF. These results suggest that the inhibitory effect of various extracts and root exudates from wheat on FOF growth may be due to differences in phenolic acid content and high levels of SA.

Metabolic regulation mechanism of Trametes gibbosa CB_1 on lignin

White rot fungi can degrade lignin and play a significant role in the recycling of carbon resources for environmental protection. Trametes gibbosa is the main white rot fungus in Northeast China. The main acids produced by T. gibbosa degradation, include long-chain fatty acids, lactic acid, succinic acid, and some small molecular compounds for example benzaldehyde. A variety of proteins respond to lignin stress and play an important role in xenobiotics metabolism, metal ion transport, and redox. Coordinated regulation and detoxification activation of H₂O₂ produced in oxidative stress by peroxidase coenzyme system and Fenton reaction. The Dioxygenase cleavage pathway and β-ketoadipic acid pathway are the main oxidation pathways of lignin degradation, which mediate the entry of "COA" into the TCA cycle. In the joint action of hydrolase and coenzyme, cellulose, hemicellulose, and other polysaccharides are degraded and finally converted to glucose to participate in energy metabolism. The expression of the laccase (Lcc_1) protein was verified by E. coli. Also, the Lcc_1 overexpression mutant was established. The morphology of mycelium was dense and the lignin degradation rate was improved. We completed the first non-directional mutation of in T. gibbosa. It also improved the mechanism of T. gibbosa in response to lignin stress.

Application of vermicompost and biochar suppresses Fusarium root rot of replanted American ginseng

Soil sterilization integrated with agronomic measures is an effective method to reduce soilborne replant diseases. However, the effect of vermicompost or biochar application after soil sterilization on soilborne diseases is poorly understood. A pot experiment was conducted in American ginseng to investigate the effects of vermicompost (VF), biochar (BF), and a combination of vermicompost and biochar (VBF) applied after soil sterilization on the incidence of Fusarium root rot using natural recovery (F) as control. After one growing season, the disease index of root rot, the phenolic acids, and the microbial communities of American ginseng rhizosphere soil were analyzed. The disease index of VF, BF, and VBF decreased by 33.32%, 19.03%, and 80.96%, respectively, compared with F. The highest bacterial richness and diversity were observed in the rhizosphere soil of VBF. Besides, VF and VBF significantly increased the relative abundance of beneficial bacteria (Pseudomonas, Lysobacter, and Chryseolinea) in the rhizosphere soil. Higher concentrations of vanillin, one of the phenolic acids in the roots exudates, were recorded in the rhizosphere soils of BF and VBF. The vanillin concentration showed a significant negative correlation with the disease index. To conclude, vermicompost improved the beneficial bacteria of the rhizosphere soil, while biochar regulated the allelopathic effect of the phenolic acids. The study proposes a combined application of biochar and vermicompost to the rhizosphere soil to control Fusarium root rot of replanted American ginseng effectively. KEY POINTS: Vermicompost improves the relative abundance of rhizosphere beneficial bacteria. Biochar inhibits the degradation of phenolic acids by adsorption. The combination of vermicompost and biochar enhances the disease control effect.

Lower Funneling Pathways in Scedosporium Species

Lignin, a natural polyaromatic macromolecule, represents an essential component of the lignocellulose biomass. Due to its complexity, the natural degradation of this molecule by microorganisms still remains largely misunderstood. Extracellular oxidative degradation is followed by intracellular metabolic degradation of conserved aromatic intermediate compounds (protocatechuate, catechol, hydroxyquinol, and gentisic acid) that are used as carbon and energy sources. The lower funneling pathways are characterized by the opening of the aromatic ring of these molecules through dioxygenases, leading to degradation products that finally enter into the tricarboxylic acid (TCA) cycle. In order to better understand the adaptation mechanisms of Scedosporium species to their environment, these specific catabolism pathways were studied. Genes encoding ring-cleaving dioxygenases were identified in Scedosporium genomes by sequence homology, and a bioinformatic analysis of the organization of the corresponding gene clusters was performed. In addition, these predictions were confirmed by evaluation of the expression level of the genes of the gentisic acid cluster. When the fungus was cultivated in the presence of lignin or gentisic acid as sole carbon source, experiments revealed that the genes of the gentisic acid cluster were markedly overexpressed in the two Scedosporium species analyzed (Scedosporium apiospermum and Scedosporium aurantiacum). Only the gene encoding a membrane transporter was not overexpressed in the gentisic acid-containing medium. Together, these data suggest the involvement of the lower funneling pathways in Scedosporium adaptation to their environment.

Bacterial Community Selection of Russula griseocarnosa Mycosphere Soil

Russula griseocarnosa is a wild, ectomycorrhizal, edible, and medicinal fungus with high economic value in southern China. R. griseocarnosa fruiting bodies cannot be artificially cultivated. To better understand the effects of abiotic and biotic factors on R. griseocarnosa growth, the physicochemical properties of R. griseocarnosa and its associated bacterial communities were investigated in two soil types (mycosphere and bulk soil) from Fujian, Guangdong, and Guangxi Provinces. The results revealed that the diversity, community structure, and functional characteristics of the dominant mycosphere bacteria in all geographical locations were similar. Soil pH and available nitrogen (AN) are the major factors influencing the mycosphere-soil bacterial communities' structure. The diversity of soil bacteria is decreased in R. griseocarnosa mycosphere when compared with the bulk soil. Burkholderia-Paraburkholderia, Mycobacterium, Roseiarcus, Sorangium, Acidobacterium, and Singulisphaera may also be mycorrhiza helper bacteria (MHB) of R. griseocarnosa. The functional traits related to the two-component system, bacterial secretion system, tyrosine metabolism, biosynthesis of unsaturated fatty acids, and metabolism of cofactors and vitamins were more abundant in R. griseocarnosa mycosphere soil. The mycosphere soil bacteria of R. griseocarnosa play a key role in R. griseocarnosa growth. Application of management strategies, such as N fertilizer and microbial fertilizer containing MHB, may promote the conservation, propagation promotion, and sustainable utilization of R. griseocarnosa.

The Plant Pathogenic Bacterium Streptomyces scabies Degrades the Aromatic Components of Potato Periderm via the β-Ketoadipate Pathway

The outer potato periderm layer consists of dead suberized cells. Suberin, a protective biopolymer, is made of a polyaliphatic portion covalently linked to polyaromatic moieties. Evidence accumulates that Streptomyces scabies, the main causal agent of potato common scab, can degrade the suberin aliphatic part but its ability to degrade the aromatic portion has not been documented. This polyaromatic portion is mainly composed of cinnamic acids. In this study, two cinnamates (trans-ferulic or p-coumaric acids) were added to the culture medium of S. scabies strains EF-35 and 87.22. HPLC quantification revealed that both strains efficiently utilized these compounds. A proteomic study coupled with gene expression analysis led to the identification of putative catabolic pathways for cinnamates. Catabolism of both compounds appeared to occur via the β-ketoadipate pathway. Gene SCAB_15301, encoding for a putative vanillate monooxygenase, was partly deleted from S. scabies strain 87.22 genome. The mutant retained its ability to catabolize trans-ferulic acid into vanillate but lost its ability to further degrade the latter compound. When the wild-type mutant and complemented strains were grown in the presence of suberin-enriched potato periderm, accumulation of vanillic acid was observed only in the mutant culture medium. This work presents evidence that S. scabies can degrade not only the aliphatic part of suberin but also the constituents of suberin aromatic portion. This may provide ecological and pathological advantages to S. scabies as a saprophyte and pathogen.

Mapping the diversity of microbial lignin catabolism: experiences from the eLignin database

Lignin is a heterogeneous aromatic biopolymer and a major constituent of lignocellulosic biomass, such as wood and agricultural residues. Despite the high amount of aromatic carbon present, the severe recalcitrance of the lignin macromolecule makes it difficult to convert into value-added products. In nature, lignin and lignin-derived aromatic compounds are catabolized by a consortia of microbes specialized at breaking down the natural lignin and its constituents. In an attempt to bridge the gap between the fundamental knowledge on microbial lignin catabolism, and the recently emerging field of applied biotechnology for lignin biovalorization, we have developed the eLignin Microbial Database ( www.elignindatabase.com ), an openly available database that indexes data from the lignin bibliome, such as microorganisms, aromatic substrates, and metabolic pathways. In the present contribution, we introduce the eLignin database, use its dataset to map the reported ecological and biochemical diversity of the lignin microbial niches, and discuss the findings.

Co-option of microbial associates by insects and their impact on plant-folivore interactions

Plants possess a suite of traits that make them challenging to consume by insect herbivores. Plant tissues are recalcitrant, have low levels of protein, and may be well defended by chemicals. Insects use diverse strategies for overcoming these barriers, including co-opting metabolic activities from microbial associates. In this review, we discuss the co-option of bacteria and fungi in the herbivore gut. We particularly focus upon chewing, folivorous insects (Coleoptera and Lepidoptera) and discuss the impacts of microbial co-option on herbivore performance and plant responses. We suggest that there are two components to microbial co-option: fixed and plastic relationships. Fixed relationships are involved in integral dietary functions and can be performed by microbial enzymes co-opted into the genome or by stably transferred associates. In contrast, the majority of gut symbionts appear to be looser and perform more facultative, context-dependent functions. This more plastic, variable co-option of bacteria likely produces a greater number of insect phenotypes, which interact differently with plant hosts. By altering plant detection of herbivory or mediating insect interactions with plant defensive compounds, microbes can effectively improve herbivore performance in real time within and between generations.

Degradation of salicylic acid by Fusarium graminearum

Fusarium head blight (FHB) is a major cereal crop disease, caused most frequently by the fungus Fusarium graminearum. We have previously demonstrated that F. graminearum can utilize SA as sole source of carbon to grow. In this current study, we further characterized selected four fungal SA-responsive genes that are predicted to encode salicylic acid (SA)-degrading enzymes and we used a gene replacement approach to characterize them further. These included two genes predicted to encode a salicylate 1-monooxygenase, FGSG_03657 and FGSG_09063, a catechol 1, 2-dioxygenase gene, FGSG_03667, and a 2, 3-dihydroxybenzoic acid decarboxylase gene, FGSG_09061. For each gene, three independent gene replacement strains were assayed for their ability to degrade salicylic acid in liquid culture. Salicylate 1-monooxygenase FGSG_03657 and catechol 1, 2-dioxygenase FGSG_03667 were shown to be essential for SA degradation, while a loss of 2, 3-dihydroxybenzoic acid decarboxylase FGSG_09061 caused only a partial reduction of SA degradation and a loss of salicylate 1-monooxygenase FGSG_09063 had no effect when compared to wild type culture. Salicylate 1-monooxygenase FGSG_03657 and catechol 1, 2-dioxygenase FGSG_03667 were identified as the first two key enzyme steps of SA degradation via catechol in the β-ketoadipate pathway. Expression profiles for all four genes were also determined in liquid culture and in planta. Salicylate 1-monooxygenase FGSG_03657 and catechol 1, 2-dioxygenase FGSG_03667 were co-expressed and their expression was substrate dependent in liquid culture; however their expression was uncoupled in planta. Disruption of the gene for catechol 1, 2-dioxygenase FGSG_03667 was shown to have no effect on fungal virulence on wheat. Our results with 2, 3-dihydroxybenzoic acid decarboxylase FGSG_09061 raise the possibility of an alternate non-oxidative decarboxylation pathway for the conversion of SA to catechol via 2, 3-dihydrozybenzoic acid and for a connection between the oxidative and the non-oxidative decarboxylation pathways for SA conversion.

Microbial Biotreatment of Actual Textile Wastewater in a Continuous Sequential Rice Husk Biofilter and the Microbial Community Involved

Textile dying processes often pollute wastewater with recalcitrant azo and anthraquinone dyes. Yet, there is little development of effective and affordable degradation systems for textile wastewater applicable in countries where water technologies remain poor. We determined biodegradation of actual textile wastewater in biofilters containing rice husks by spectrophotometry and liquid chromatography mass spectrometry. The indigenous microflora from the rice husks consistently performed >90% decolorization at a hydraulic retention time of 67 h. Analysis of microbial community composition of bacterial 16S rRNA genes and fungal internal transcribed spacer (ITS) gene fragments in the biofilters revealed a bacterial consortium known to carry azoreductase genes, such as Dysgonomonas, and Pseudomonas and the presence of fungal phylotypes such as Gibberella and Fusarium. Our findings emphasize that rice husk biofilters support a microbial community of both bacteria and fungi with key features for biodegradation of actual textile wastewater. These results suggest that microbial processes can substantially contribute to efficient and reliable degradation of actual textile wastewater. Thus, development of biodegradation systems holds promise for application of affordable wastewater treatment in polluted environments.

Plant phenolic acids induce programmed cell death of a fungal pathogen: MAPK signaling and survival of Cochliobolus heterostrophus

Plant aromatic compounds provide signals and a nutrient source to pathogens, and also act as stressors. Structure-activity relationships suggest two pathways sensing these compounds in the maize pathogen Cochliobolus heterostrophus, one triggering a stress response, and one inducing enzymes for their degradation. Focusing on the stress pathway, we found that ferulic acid causes rapid appearance of TUNEL-positive nuclei, dispersion of histone H1:GFP, hyphal shrinkage, and eventually membrane damage. These hallmarks of programmed cell death (PCD) were not seen upon exposure to caffeic acid, a very similar compound. Exposure to ferulic acid dephosphorylated two MAP kinases: Hog1 (stress activated) and Chk1 (pathogenicity related), while increasing phosphorylation of Mps1 (cell integrity related). Mutants lacking Hog1 or Chk1 are hypersensitive to ferulic acid while Mps1 mutants are not. These results implicate three MAPK pathways in the stress response. Ferulic acid and the antifungal fludioxonil have opposite additive effects on survival and on dephosphorylation of Hog1, which is thus implicated in survival. The results may explain why some fungal pathogens of plants undergo cell death early in host invasion, when phenolics are released from plant tissue.

CCR4-Not Complex Subunit Not2 Plays Critical Roles in Vegetative Growth, Conidiation and Virulence in Watermelon Fusarium Wilt Pathogen Fusarium oxysporum f. sp. niveum

CCR4-Not complex is a multifunctional regulator that plays important roles in multiple cellular processes in eukaryotes. In the present study, the biological function of FonNot2, a core subunit of the CCR4-Not complex, was explored in Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon wilt disease. FonNot2 was expressed at higher levels in conidia and germinating conidia and during infection in Fon-inoculated watermelon roots than in mycelia. Targeted disruption of FonNot2 resulted in retarded vegetative growth, reduced conidia production, abnormal conidial morphology, and reduced virulence on watermelon. Scanning electron microscopy observation of infection behaviors and qRT-PCR analysis of in planta fungal growth revealed that the ΔFonNot2 mutant was defective in the ability to penetrate watermelon roots and showed reduced fungal biomass in root and stem of the inoculated plants. Phenotypic and biochemical analyses indicated that the ΔFonNot2 mutant displayed hypersensitivity to cell wall perturbing agents (e.g., Congo Red and Calcofluor White) and oxidative stress (e.g., H₂O₂ and paraquat), decreased fusaric acid content, and reduced reactive oxygen species (ROS) production during spore germination. Our data demonstrate that FonNot2 plays critical roles in regulating vegetable growth, conidiogenesis and conidia morphology, and virulence on watermelon via modulating cell wall integrity, oxidative stress response, ROS production and FA biosynthesis through the regulation of transcription of genes involved in multiple pathways.

Hydroxycinnamic Acid Degradation, a Broadly Conserved Trait, Protects Ralstonia solanacearum from Chemical Plant Defenses and Contributes to Root Colonization and Virulence

Plants produce hydroxycinnamic acid (HCA) defense compounds to combat pathogens, such as the bacterium Ralstonia solanacearum. We showed that an HCA degradation pathway is genetically and functionally conserved across diverse R. solanacearum strains. Further, a feruloyl-CoA synthetase (Δfcs) mutant that cannot degrade HCA was less virulent on tomato plants. To understand the role of HCA degradation in bacterial wilt disease, we tested the following hypotheses: HCA degradation helps the pathogen i) grow, as a carbon source; ii) spread, by reducing HCA-derived physical barriers; and iii) survive plant antimicrobial compounds. Although HCA degradation enabled R. solanacearum growth on HCA in vitro, HCA degradation was dispensable for growth in xylem sap and root exudate, suggesting that HCA are not significant carbon sources in planta. Acetyl-bromide quantification of lignin demonstrated that R. solanacearum infections did not affect the gross quantity or distribution of stem lignin. However, the Δfcs mutant was significantly more susceptible to inhibition by two HCA, namely, caffeate and p-coumarate. Finally, plant colonization assays suggested that HCA degradation facilitates early stages of infection and root colonization. Together, these results indicated that ability to degrade HCA contributes to bacterial wilt virulence by facilitating root entry and by protecting the pathogen from HCA toxicity.

Immunoproteomic analysis reveals a convergent humoral response signature in the Sporothrix schenckii complex

Sporotrichosis is a polymorphic disease that affects both humans and animals worldwide. The fungus gains entry into a warm-blooded host through minor trauma to the skin, typically by contaminated vegetation or by scratches and bites from a diseased cat. Cellular and humoral responses triggered upon pathogen introduction play important roles in the development and severity of the disease. We investigated molecules expressed during the host-parasite interplay that elicit the humoral response in human sporotrichosis. For antigenic profiling, Sporothrix yeast cell extracts were separated by two-dimensional (2D) gel electrophoresis and probed with pooled sera from individuals with fixed cutaneous and lymphocutaneous sporotrichosis. Thirty-five IgG-seroreactive spots were identified as eight specific proteins by MALDI-ToF/MS. Remarkable cross-reactivity among Sporothrix brasiliensis, Sporothrix schenckii, and Sporothrix globosa was noted and antibodies strongly reacted with the 70-kDa protein (gp70), irrespective of clinical manifestation. Gp70 was successfully identified in multiple spots as 3-carboxymuconate cyclase. In addition, 2D-DIGE characterization suggested that the major antigen of sporotrichosis undergoes post-translational modifications involving glycosylation and amino acid substitution, resulting in at least six isoforms and glycoforms that were present in the pathogenic species but absent in the ancestral non-virulent Sporothrix mexicana. Although a primary environmental function related to the benzoate degradation pathway of aromatic polymers has been attributed to orthologs of this molecule, our findings support the hypothesis that gp70 is important for pathogenesis and invasion in human sporotrichosis. We propose a diverse panel of new putative candidate molecules for diagnostic tests and vaccine development.

BIOLOGICAL SIGNIFICANCE

Outbreaks due to Sporothrix spp. have emerged over time, affecting thousands of patients worldwide. A sophisticated host-pathogen interplay drives the manifestation and severity of infection, involving immune responses elicited upon traumatic exposure of the skin barrier to the pathogen followed by immune evasion. Using an immunoproteomic approach we characterized proteins of potential significance in pathogenesis and invasion that trigger the humoral response during human sporotrichosis. We found gp70 to be a cross-immunogenic protein shared among pathogenic Sporothrix spp. but absent in the ancestral environmental S. mexicana, supporting the hypothesis that gp70 plays key roles in pathogenicity. For the first time, we demonstrate with 2D-DIGE that post-translational modifications putatively involve glycosylation and amino acid substitution, resulting in at least six isoforms and glycoforms, all of them IgG-reactive. These findings of a convergent humoral response highlight gp70 as an important target serological diagnosis and for vaccine development among phylogenetically related agents of sporotrichosis.

Plant phenolic compounds and oxidative stress: integrated signals in fungal-plant interactions

Upon invasion of a host, fungal pathogens are exposed to a variety of stresses. Plants release reactive oxygen species, and mount a variety of preformed and induced chemical defenses. Phenolic compounds are one example: they are ubiquitous in plants, and an invading pathogen encounters them already at the leaf surface, or for soil-borne pathogens, in the rhizosphere. Phenolic and related aromatic compounds show varying degrees of toxicity to cells. Some compounds are quite readily metabolized, and others less so. It was known already from classical studies that phenolic substrates induce the expression of the enzymes for their degradation. Recently, the ability to degrade phenolics was shown to be a virulence factor. Conversely, phenolic compounds can increase the effectiveness of antifungals. Phenolics are known antioxidants, yet they have been shown to elicit cellular responses that would usually be triggered to counter oxidant stress. Here, we review the evidence for a connection between the fungal response to phenolics as small-molecule signals, and the response to oxidants. The connections proposed here should enable genetic screens to identify specific fungal receptors for plant phenolics. Furthermore, understanding how the pathogen detects plant phenolic compounds as a stress signal may facilitate new antifungal strategies.

Proteomic identification of potential target proteins regulated by the SCF(F) (bp1) -mediated proteolysis pathway in Fusarium oxysporum

F-box proteins function in the recruitment of proteins for SCF ubiquitination and proteasome degradation. Here, we studied the role of Fbp1, a nonessential F-box protein of the tomato pathogen Fusarium oxysporum f. sp. lycopersici. The Δfbp1 mutant showed a significant delay in the production of wilt symptoms on tomato plants and was impaired in invasive growth on cellophane membranes and on living plant tissue. To search for target proteins recruited by Fbp1, a combination of sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) was used to compare proteins in mycelia of the wild-type and Δfbp1 mutant. The proteomic approach identified 41 proteins differing significantly in abundance between the two strains, 17 of which were more abundant in the Δfbp1 mutant, suggesting a possible regulation by proteasome degradation. Interestingly, several of the identified proteins were related to vesicle trafficking. Microscopic analysis revealed an impairment of the Δfbp1 strain in directional growth and in the structure of the Spitzenkörper, suggesting a role of Fbp1 in hyphal orientation. Our results indicate that Fbp1 regulates protein turnover and pathogenicity in F. oxysporum.

Differences in cell morphometry, cell wall topography and gp70 expression correlate with the virulence of Sporothrix brasiliensis clinical isolates

Sporotrichosis is a chronic infectious disease affecting both humans and animals. For many years, this subcutaneous mycosis had been attributed to a single etiological agent; however, it is now known that this taxon consists of a complex of at least four pathogenic species, including Sporothrix schenckii and Sporothrix brasiliensis. Gp70 was previously shown to be an important antigen and adhesin expressed on the fungal cell surface and may have a key role in immunomodulation and host response. The aim of this work was to study the virulence, morphometry, cell surface topology and gp70 expression of clinical isolates of S. brasiliensis compared with two reference strains of S. schenckii. Several clinical isolates related to severe human cases or associated with the Brazilian zoonotic outbreak of sporotrichosis were genotyped and clustered as S. brasiliensis. Interestingly, in a murine subcutaneous model of sporotrichosis, these isolates showed a higher virulence profile compared with S. schenckii. A single S. brasiliensis isolate from an HIV-positive patient not only showed lower virulence but also presented differences in cell morphometry, cell wall topography and abundant gp70 expression compared with the virulent isolates. In contrast, the highly virulent S. brasiliensis isolates showed reduced levels of cell wall gp70. These observations were confirmed by the topographical location of the gp70 antigen using immunoelectromicroscopy in both species. In addition, the gp70 molecule was sequenced and identified using mass spectrometry, and the sequenced peptides were aligned into predicted proteins using Blastp with the S. schenckii and S. brasiliensis genomes.

Crossover fungal pathogens: the biology and pathogenesis of fungi capable of crossing kingdoms to infect plants and humans

The outbreak of fungal meningitis associated with contaminated methylprednisolone acetate has thrust the importance of fungal infections into the public consciousness. The predominant pathogen isolated from clinical specimens, Exserohilum rostratum (teleomorph: Setosphaeria rostrata), is a dematiaceous fungus that infects grasses and rarely humans. This outbreak highlights the potential for fungal pathogens to infect both plants and humans. Most crossover or trans-kingdom pathogens are soil saprophytes and include fungi in Ascomycota and Mucormycotina phyla. To establish infection, crossover fungi must overcome disparate, host-specific barriers, including protective surfaces (e.g. cuticle, skin), elevated temperature, and immune defenses. This review illuminates the underlying mechanisms used by crossover fungi to cause infection in plants and mammals, and highlights critical events that lead to human infection by these pathogens. Several genes including veA, laeA, and hapX are important in regulating biological processes in fungi important for both invasive plant and animal infections.