The Ifchit1 chitinase gene acts as a critical virulence factor in the insect pathogenic fungus Isaria fumosorosea

Role of chitinase expression in the virulence of Lecanicillium lecanii against citrus black aphid (Toxoptera aurantii)

Chitinase plays a vital role in the virulence of entomopathogenic fungi (EPF) when it infects host insects. We used gene recombination technology to express chitinase of three strains of Lecanicillium lecanii: Vl6063, V3450, and Vp28. The ORF of ChitVl6063, ChitV3450 and ChitVp28 were inserted into the fungal expression vector pBARGPE-1, which contained strong promoter and terminator, respectively, to construct a chitinase overpressing plasmid, then transformed the wild-type strain with blastospore transformation method. The virulence of the three recombinant strains against Toxoptera aurantii was improved by overproduction of ChitVl6063, ChitV3450, and ChitVp28, as demonstrated by significantly lower 3.43 %, 1.72 %, and 1.23 % fatal doses, respectively, according to an insect bioassay. Similarly, lethal times of recombinants (ChitVl6063, ChitV3450 and ChitVp28) were also decreased up to 29.51 %, 30.46 % and 33.90 %, respectively, compared to the wild-type strains. Improving the expression of chitinase is considered as an effective method for the enhancement of the EPF value. The efficacy could be enhanced using recombinant technology, which provides a prospecting view for future insecticidal applications.

Chitinases as key virulence factors in microbial pathogens: Understanding their role and potential as therapeutic targets

Chitinases are crucial for the survival of bacterial and fungal pathogens both during host infection and outside the host in the environment. Chitinases facilitate adhesion onto host cells, act as virulence factors during infection, and provide protection from the host immune system, making them crucial factors in the survival of microbial pathogens. Understanding the mechanisms behind chitinase action is beneficial to design novel therapeutics to control microbial infections. This review explores the role of chitinases in the pathogenesis of bacterial, fungal, and viral infections. The mechanisms underlying the action of chitinases of bacterial, fungal, and viral pathogens in host cells are thoroughly reviewed. The evolutionary relationships between chitinases of various bacterial, fungal, and viral pathogens are discussed to determine their involvement in processes, such as adhesion and host immune system modulation. Gaining a better understanding of the distribution and activity of chitinases in these microbial pathogens can help elucidate their role in the invasion and infection of host cells.

Identification of Virulence Factors in Entomopathogenic Aspergillus flavus Isolated from Naturally Infected Rhipicephalus microplus

Aspergillus flavus has been found to be an effective entomopathogenic fungus for various arthropods, including ticks. In particular, natural fungal infections in cattle ticks show promise for biocontrol of the Rhipicephalus (Boophilus) microplus tick, which is a major ectoparasite affecting cattle worldwide. Our study aimed to elucidate the specific entomopathogenic virulence factors encoded in the genome of an A. flavus strain isolated from naturally infected cattle ticks. We performed morphological and biochemical phenotyping alongside complete genome sequencing, which revealed that the isolated fungus was A. flavus related to the L morphotype, capable of producing a range of gene-coded entomopathogenic virulence factors, including ribotoxin, aflatoxin, kojic acid, chitinases, killer toxin, and satratoxin. To evaluate the efficacy of this A. flavus strain against ticks, we conducted experimental bioassays using healthy engorged female ticks. A morbidity rate of 90% was observed, starting at a concentration of 105 conidia/mL. At a concentration of 107 conidia/mL, we observed a 50% mortality rate and a 21.5% inhibition of oviposition. The highest levels of hatch inhibition (30.8%) and estimated reproduction inhibition (34.64%) were achieved at a concentration of 108 conidia/mL. Furthermore, the tick larval progeny that hatched from the infected tick egg masses showed evident symptoms of Aspergillus infection after incubation.

Shell disease syndromes of decapod crustaceans

The term shell disease subsumes a number of debilitating conditions affecting the outer integument (the carapace) of decapod crustaceans, such as lobsters and crabs. Herein, we seek to find commonality in the aetiology and pathology of such conditions, and those cases that result in the progressive erosion of the cuticle through to the visceral tissues by a cocktail of microbial-derived enzymes including lipases, proteases and chitinases. Aquimarina spp. are involved in shell disease in many different crustaceans across a wide geographical area, but the overall view is that the condition is polymicrobial in nature leading to dysbiosis within the microbial consortium of the damaged cuticle. The role of environment, decapod behaviour and physiology in triggering this disease is also reviewed. Finally, we provide a conceptual model for disease aetiology and suggest several avenues for future research that could improve our understanding of how such factors trigger, or exacerbate, this condition.

Chitinase Is Involved in the Fruiting Body Development of Medicinal Fungus Cordyceps militaris

Cordyceps militaris is a famous traditional edible and medicinal fungus in Asia, and its fruiting body has rich medicinal value. The molecular mechanism of fruiting body development is still not well understood in C. militaris. In this study, phylogenetically analysis and protein domains prediction of the 14 putative chitinases were performed. The transcription level and enzyme activity of chitinase were significant increased during fruiting body development of C. militaris. Then, two chitinase genes (Chi1 and Chi4) were selected to construct gene silencing strain by RNA interference. When Chi1 and Chi4 genes were knockdown, the differentiation of the primordium was blocked, and the number of fruiting body was significantly decreased approximately by 50% compared to wild-type (WT) strain. The length of the single mature fruiting body was shortened by 27% and 38% in Chi1- and Chi4-silenced strains, respectively. In addition, the chitin content and cell wall thickness were significantly increased in Chi1- and Chi4-silenced strains. These results provide new insights into the biological functions of chitinase in fruiting body development of C. militaris.

Genomic Determinants of Entomopathogenic Fungi and Their Involvement in Pathogenesis

Entomopathogenic fungi offer an effective and eco-friendly alternative to curb insect populations in biocontrol strategy. The evolutionary history of selected entomopathogenic fungi indicates their ancestral relationship with plant endophytes. During this host shifting, entomopathogenic fungi must have acquired multiple mechanisms, including a combination of various biomolecules that make them distinguishable from other fungi. In this review, we focus on understanding various biochemical and molecular mechanisms involved in entomopathogenesis. In particular, we attempt to explain the indispensable role of enlarged gene families of various virulent factors, viz. chitinases, proteases, lipases, specialized metabolites, and cytochrome P450, in entomopathogenesis. Our analysis suggests that entomopathogenic fungi recruit a different set of gene products during the progression of pathogenesis. Knowledge of these bio-molecular interactions between fungi and insect hosts will allow researchers to execute pointed efforts towards the development of improved entomopathogenic fungal strains.

Proteomic Analysis of a Hypervirulent Mutant of the Insect-Pathogenic Fungus Metarhizium anisopliae Reveals Changes in Pathogenicity and Terpenoid Pathways

Metarhizium anisopliae is a commercialized entomopathogenic fungus widely used for the control of insect pests. Significant efforts have been expended to screen and/or select for isolates that display increased virulence toward target insect hosts. UV-induced mutagenesis has resulted in the isolation of a number of hypervirulent M. anisopliae mutants; however, the underlying mechanisms that have led to the desired phenotype have yet to be characterized. Here, we performed a comparative proteomic analysis of an M. anisopliae UV-induced hypervirulent mutant (MaUV-HV) and its wild-type parent using tandem mass tag (TMT)-based quantitative proteomics. A total of 842 differentially abundant proteins were identified, with 360 being more abundant in the hypervirulent mutant and 482 in the wild-type parent. In terms of differential abundance, the critical pathways affected included those involved in secondary metabolite production, virulence, and stress response. In addition, a number of genes involved in terpenoid biosynthesis pathways were identified as significantly mutated in the MaUV-HV strain. In particular, mutations in the farnesyl pyrophosphate synthase (FPPS1) and geranylgeranyl diphosphate synthase (GGPPS5) genes were seen. The effects of the FPPS1 mutation were confirmed via the construction and characterization of a targeted gene knockout strain (ΔMaFPPS1). The overall effects of the mutations were increased resistance to UV stress, faster growth, and increased virulence. These results provide mechanistic insights and new avenues for modulating fungal virulence in efforts to increase the biological control potential of insect-pathogenic fungi. IMPORTANCE The mechanisms that underlie and contribute to microbial (fungal) virulence are known to be varied; however, the identification of contributing pathways beyond known virulence factors remains difficult. Using TMT-based proteomic analyses, changes in the proteomes of an M. anisopliae hypervirulent mutant and its wild-type parent were determined. These data revealed alterations in pathogenicity, stress, and growth/developmental pathways, as well as pathways not previously known to affect virulence. These include terpenoid pathways that can be manipulated to increase the efficacy of fungal insect biological control agents for increased sustainable pest control.

Development of Cordyceps javanica BE01 with enhanced virulence against Hyphantria cunea using polyethylene glycol-mediated protoplast transformation

Cordyceps javanica has promising application prospects as an entomopathogenic fungus with a wide range of hosts. To enhance the virulence of C. javanica, a polyethylene glycol (PEG)-mediated protoplast genetic transformation system was constructed. Strains overexpressing the subtilisin-like protease genes CJPRB and CJPRB1 and the tripeptidyl peptidase gene CJCLN2-1 were constructed with this system, and the effects of these strains on Hyphantria cunea were tested. The aminoglycoside G418 was used at 800 μg ml⁻¹ to screen the transformants. C. javanica hyphae were degraded with an enzyme mixture to obtain protoplasts at 1.31 × 10⁷ protoplasts ml⁻¹. The transformation of 2 μg of DNA into 1,000 protoplasts was achieved with 20% PEG2000, and after 6 h of recovery, the transformation efficiency was 12.33 ± 1.42 transformants μg⁻¹ plasmid. The LT₅₀ values of CJPRB, CJPRB1, and CJCLN2-1-overexpressing C. javanica strains were 1.32-fold, 2.21-fold, and 2.14-fold higher than that of the wild-type (WT) strain, respectively. The three overexpression strains showed no significant differences from the WT strain in terms of colony growth, conidial yield, and conidial germination rate. However, the infection rate of the CJPRB1 strain was faster than that of the WT strain, with infection occurring within 4–5 days. The CJCLN2-1 strain had a significantly higher mortality rate than the WT strain within 4–10 days after infection. A C. javanica genetic transformation system was successfully constructed for the first time, and an overexpression strain exhibited enhanced virulence to H. cunea compared with the WT strain.

A Contemporary Appraisal on Impending Industrial and Agricultural Applications of Thermophilic-Recombinant Chitinolytic Enzymes from Microbial Sources

The ability of chitinases to degrade the second most abundant polymer, chitin, into potentially useful chitooligomers and chitin derivatives has not only rendered them fit for chitinous waste management but has also made them important from industrial point of view. At the same time, they have also been recognized to have an imperative role as promising biocontrol agents for controlling plant diseases. As thermostability is an important property for an industrially important enzyme, various bacterial and fungal sources are being exploited to obtain such stable enzymes. These stable enzymes can also play a role in agriculture by maintaining their stability under adverse environmental conditions for longer time duration when used as biocontrol agent. Biotechnology has also played its role in the development of recombinant chitinases with enhanced activity, thermostability, fungicidal and insecticidal activity via recombinant DNA techniques. Furthermore, a relatively new approach of generating pathogen-resistant transgenic plants has opened new ways for sustainable agriculture by minimizing the yield loss of valuable crops and plants. This review focuses on the potential applications of thermostable and recombinant microbial chitinases in industry and agriculture.

Mutation of a prenyltransferase results in accumulation of subglutinols and destruxins and enhanced virulence in the insect pathogen, Metarhizium anisopliae

The insect pathogenic fungus, Metarhizium anisopliae is a commercialized microbial agent used in biological control efforts targeting a diverse range of agricultural and other insect pests. The second step in the synthesis of a group of M. anisopliae α-pyrone diterpenoids (termed subglutinols) involves the activity of a prenyltransferase family geranylgeranyl diphosphate synthase (product of the subD/MaGGPPS5 gene). Here, we show that targeted gene disruption of MaGGPPS5 results in earlier conidial germination and faster greater vegetative growth compared to the wild type (WT) parent and complemented strains. In addition, insect bioassays revealed that the ΔMaGGPPS5 mutant strain displayed significantly increased virulence, with a ~50% decrease in the mean lethal time (LT₅₀ , from 6 to 3 days) to kill (50% of) target insects, and an ~15-40-fold decrease in the mean lethal dose (LC₅₀ ). Metabolite profiling indicated increased accumulation in the ΔMaGGPPS5 mutant of select subglutinols (A, B and C) and destruxins (A, A2, B and B2), the latter a set of fungal secondary metabolites that act as insect toxins, with a concomitant loss of production of subglutinol 'analogue 45'. These data suggest that the increased virulence phenotype seen for the ΔMaGGPPS5 strain can, at least in part, be attributed to a combination of faster growth and increased insect toxin production, linking the production of two different secondary metabolite pathways, and represent a novel approach for the screening of isolates with enhanced virulence via modulation of terpenoid secondary metabolite biosynthesis.

The Tudor Domain-Containing Protein BbTdp1 Contributes to Fungal Cell Development, the Cell Cycle, Virulence, and Transcriptional Regulation in the Insect Pathogenic Fungus Beauveria bassiana

Beauveria bassiana is an insect pathogenic fungus that serves as a model system for exploring the mechanisms of fungal development and host-pathogen interactions. Clinical and experimental studies have indicated that SND1 is closely correlated with the progression and invasiveness of common cancers as a potential oncogene, but this gene has rarely been studied in fungi. Here, we characterized the contributions of an SND1 ortholog (Tdp1) by constructing a BbTdp1 deletion strain and a complemented strain of B. bassiana. Compared with the wild-type (WT) strain, the ΔBbTdp1 mutant lost conidiation capacity (∼87.7%) and blastospore (∼96.3%) yields, increased sensitivity to chemical stress (4.4 to 54.3%) and heat shock (∼44.2%), and decreased virulence following topical application (∼24.7%) and hemocoel injection (∼40.0%). Flow cytometry readings showed smaller sizes of both conidia and blastospores for ΔBbTdp1 mutants. Transcriptomic data revealed 4,094 differentially expressed genes (|log2 ratio| > 2 and a q value of <0.05) between ΔBbTdp1 mutants and the WT strain, which accounted for 41.6% of the total genes, indicating that extreme fluctuation in the global gene expression pattern had occurred. Moreover, deletion of BbTdp1 led to an abnormal cell cycle with a longer S phase and shorter G2/M and G0/G1 phases of blastospores, and enzyme-linked immunosorbent assay confirmed that the level of phosphorylated cyclin-dependent kinase 1 (Cdk1) in the ΔBbTdp1 strain was ∼31.5% lower than in the WT strain. In summary, our study is the first to report that BbTdp1 plays a vital role in regulating conidia and blastospore yields, fungal morphological changes, and pathogenicity in entomopathogenic fungi. IMPORTANCE In this study, we used Beauveria bassiana as a biological model to report the role of BbTdp1 in entomopathogenic fungi. Our findings indicated that BbTdp1 contributed significantly to cell development, the cell cycle, and virulence in B. bassiana. In addition, deletion of BbTdp1 led to drastic fluctuations in the transcriptional profile. BbTdp1 can be developed as a novel target for B. bassiana development and pathogenicity, which also provides a framework for the study of Tdp1 in other fungi.

Sustainable control of the rice pest, Nilaparvata lugens, using the entomopathogenic fungus Isaria javanica

BACKGROUND

The brown planthopper (Nilaparvata lugens) is an insect pest of rice (Oryza sativa) that is distributed worldwide and is responsible for significant crop yield losses. Of particular concern, N. lugens has developed high resistance to several commonly used insecticides. The entomopathogenic fungus, Isaria javanica, offers an alternative to insecticides for the control of rice plant pests.

RESULTS

We show that I. javanica caused high mortality of N. lugens nymphs and reduced the survival and fecundity of newly emerged adults in I. javanica-treated insects. I. javanica persisted on plants up to 17 days after its inoculation under greenhouse conditions carried out in summer and autumn. Rice metabolites supported conidial germination and mycelia growth of I. javanica. A granular formulation of I. javanica conidia controlled N. lugens populations in a field experiment. The granular formulation promoted fungal survival and growth in the field up to 28 days post inoculation, resulting in increased fungal persistence and greater pest control coverage.

CONCLUSION

These data indicate that a granular formulation of I. javanica is able to control N. lugens populations in rice fields. Therefore, this granular formulation can be an alternative to insecticides and can be used in organic fields. © 2020 Society of Chemical Industry.

Host-dependent contributions of the Cfcdp1 protease gene to virulence in the entomopathogenic fungus Cordyceps fumosorosea

BACKGROUND

The genomes of broad host range insect pathogenic fungi, including Cordyceps fumosorosea, encode for a suite of secreted proteases implicated in targeting, penetration, and degradation of the host exoskeleton or cuticle. These cuticle-degrading proteases act as critical virulence factors, but their functions within the biological context, particularly in relation to host specificity, remain poorly characterized.

RESULT

A C. fumosorosea protease gene, Cfcdp1, was identified and a targeted gene-knockout strain constructed. Minor growth defects were observed for the ΔCfcdp1 strain when compared to the wild-type parent and complemented (ΔCfcdp1::Cfcdp1) strains, with delayed and decreased sporulation noted for the mutant. Decreased subtilisin-like protease activity was seen for the ΔCfcdp1 strain, although total secreted protease activity was similar between the mutant and wild-type strains. Insect bioassays using whitefly, Bemisia tabaci, and cabbageworm, Pieris rapae, showed decreased infectivity, i.e. 2.4-3.4-fold increase in lethal dose (LC₅₀ ) and an increased time to death (LT₅₀ ), for the ΔCfcdp1 strain. In contrast, insect bioassays using the diamondback moth, Plutella xylostella, or the brown planthopper, Nilaparvata lugens, showed increased infectivity, i.e. a 3-5-fold decrease in LC₅₀ , and a decreased LT₅₀ . Differential effects were also seen on the fecundity of B. tabaci infected by the different fungal strains.

CONCLUSION

These data reveal host-dependent effects of a protease implicated in cuticle degradation on C. fumosorosea virulence. The implications of these findings in suggesting context-dependent requirements of cuticle-degrading enzymes and their potentially differential roles in mediating virulence towards different hosts are discussed. © 2019 Society of Chemical Industry.

Identification and characterization of the glycoside hydrolase family 18 genes from the entomopathogenic fungus Isaria cicadae genome

Fungal chitinases play essential roles in chitin degradation, cell wall remodeling, chitin recycling, nutrition acquisition, autolysis, and virulence. In this study, 18 genes of the glycoside hydrolase 18 (GH18) family were identified in the Isaria cicadae genome. Seventeen of the genes belonged to chitinases and one was an endo-β-N-acetylglucosaminidase (ENGase). According to phylogenetic analysis, the 17 chitinases were designated as subgroups A (7 chitinases), B (7), and C (3). The exon-intron organizations of these genes were analyzed. The conserved regions DxxDxDxE and S/AxGG and the domains CBM1, CBM18, and CBM50 were detected in I. cicadae chitinases and ENGase. The results of analysis of expression patterns showed that genes ICchiA1, ICchiA6, ICchiB1, and ICchiB4 had high transcript levels in the different growth conditions or developmental stages. Subgroup A chitinase genes had higher transcript levels than the genes of all other chitinases. Subgroup B chitinase genes (except ICchiB7) presented higher transcript levels in chitin medium compared with other conditions. ICchiC2 and ICchiC3 were mainly transcribed in autolysis medium and in blastospores, respectively. Moreover, ICchiB1 presented higher transcript levels than genes of other chitinases. This work provides an overview of the GH18 chitinases and ENGase in I. cicadae and provides a context for the chitinolytic potential, functions, and biological controls of these enzymes of entomopathogenic fungi.

Genome sequence of Isaria javanica and comparative genome analysis insights into family S53 peptidase evolution in fungal entomopathogens

The fungus Isaria javanica is an important entomopathogen that parasitizes various insects and is effective for pest control. In this study, we sequenced and assembled the genomes (IJ1G and IJ2G) of two I. javanica strains isolated from different insects. The genomes were approximately 35 Mb in size with 11,441 and 11,143 protein-coding genes, respectively. Using a phylogenomic approach, we evaluated genome evolution across five entomopathogenic fungi in Cordycipitaceae. By comparative genome analysis, it was found that family S53 serine peptidases were expanded in Cordycipitaceae entomopathogens, particularly in I. javanica. Gene duplication events were identified based on phylogenetic relationships inferred from 82 S53 peptidases within six entomopathogenic fungal genomes. Moreover, we found that carbohydrate-active enzymes and proteinases were the largest secretory protein groups encoded in the I. javanica genome, especially chitinases (GH18), serine and aspartic peptidases (S53, S08, S10, A01). Pathogenesis-related genes and genes for bacterial-like toxins and secondary metabolites were also identified. By comparative transcriptome analysis, differentially expressed genes in response to insect nutrients (in vitro) were identified. Moreover, most S53 peptidases were detected to be significantly upregulated during the initial fungal infection process in insects (in vivo) by RT-qPCR. Our results provide new clues about understanding evolution of pathogenic proteases and may suggest that abundant S53 peptidases in the I. javanica genome may contribute to its effective parasitism on various insects.

In vitro Trypanocidal Activity, Genomic Analysis of Isolates, and in vivo Transcription of Type VI Secretion System of Serratia marcescens Belonging to the Microbiota of Rhodnius prolixus Digestive Tract

Serratia marcescens is a bacterium with the ability to colonize several niches, including some eukaryotic hosts. S. marcescens have been recently found in the gut of hematophagous insects that act as parasite vectors, such as Anopheles, Rhodnius, and Triatoma. While some S. marcescens strains have been reported as symbiotic or pathogenic to other insects, the role of S. marcescens populations from the gut microbiota of Rhodnius prolixus, a vector of Chagas’ disease, remains unknown. Bacterial colonies from R. prolixus gut were isolated on BHI agar. After BOX-PCR fingerprinting, the genomic sequences of two isolates RPA1 and RPH1 were compared to others S. marcescens from the NCBI database in other to estimate their evolutionary divergence. The in vitro trypanolytic activity of these two bacterial isolates against Trypanosoma cruzi (DM28c clone and Y strain) was assessed by microscopy. In addition, the gene expression of type VI secretion system (T6SS) was detected in vivo by RT-PCR. Comparative genomics of RPA1 and RPH1 revealed, besides plasmid presence and genomic islands, genes related to motility, attachment, and quorum sensing in both genomes while genes for urea hydrolysis and type II secretion system (T2SS) were found only in the RPA1 genome. The in vitro trypanolytic activity of both S. marcescens strains was stronger in their stationary phases of growth than in their exponential ones, with 65–70 and 85–90% of epimastigotes (Dm28c clone and Y strain, respectively) being lysed after incubation with RPA1 or RPH1 in stationary phase. Although T6SS transcripts were detected in guts up to 40 days after feeding (DAF), R. prolixus morbidity or mortality did not appear to be affected. In this report, we made available two trypanolytic S. marcescens strains from R. prolixus gut to the scientific community together with their genomic sequences. Here, we describe their genomic features with the purpose of bringing new insights into the S. marcescens adaptations for colonization of the specific niche of triatomine guts. This study provides the basis for a better understanding of the role of S. marcescens in the microbiota of R. prolixus gut as a potential antagonist of T. cruzi in this complex system.

Dual Biocontrol Potential of the Entomopathogenic Fungus, Isaria javanica, for Both Aphids and Plant Fungal Pathogens

Dual biocontrol of both insects and plant pathogens has been reported for certain fungal entomopathogens, including Beauveria bassiana and Lecanicillum spp. In this study, we demonstrate, for the first time, the dual biocontrol potential of two fungal isolates identified by morphological and phylogenetic analyses as Isaria javanica. Both these isolates caused mortality in the greater wax moth, and hence can be considered entomopathogens. Spores of the isolates were also pathogenic to nymphs of the green peach aphid (Myzus persicae), with an LC50 value of 107 spores/mL 4 days after inoculation and an LT50 of 4.2 days with a dose of 108 spores/mL. In vitro antifungal assays also demonstrated a strong inhibitory effect on the growth of two fungi that are pathogenic to peppers, Colletotrichum gloeosporioides and Phytophthora capsici. These results indicate that I. javanica isolates could be used as novel biocontrol agents for the simultaneous control of aphids and fungal diseases, such as anthracnose and Phytophthora blight, in an integrated pest management framework for red pepper.

Specialisation events of fungal metacommunities exposed to a persistent organic pollutant are suggestive of augmented pathogenic potential

BACKGROUND

The impacts of man-made chemicals, in particular of persistent organic pollutants, are multifactorial as they may affect the integrity of ecosystems, alter biodiversity and have undesirable effects on many organisms. We have previously demonstrated that the belowground mycobiota of forest soils acts as a buffer against the biocide pollutant pentachlorophenol. However, the trade-offs made by mycobiota to mitigate this pollutant remain cryptic.

RESULTS

Herein, we demonstrate using a culture-dependent approach that exposure to pentachlorophenol led to alterations in the composition and functioning of the metacommunity, many of which were not fully alleviated when most of the biocide was degraded. Proteomic and physiological analyses showed that the carbon and nitrogen metabolisms were particularly affected. This dysregulation is possibly linked to the higher pathogenic potential of the metacommunity following exposure to the biocide, supported by the secretion of proteins related to pathogenicity and reduced susceptibility to a fungicide. Our findings provide additional evidence for the silent risks of environmental pollution, particularly as it may favour the development of pathogenic trade-offs in fungi, which may impose serious threats to animals and plant hosts.

Isaria fumosorosea KCh J2 Entomopathogenic Strain as an Effective Biocatalyst for Steroid Compound Transformations

The catalytic activity of enzymes produced by an entomopathogenic filamentous fungus (Isaria fumosorosea KCh J2) towards selected steroid compounds (androstenedione, adrenosterone, progesterone, 17α-methyltestosterone and dehydroepiandrosterone) was investigated. All tested substrates were efficiently transformed. The structure of the substrate has a crucial impact on regio- and stereoselectivity of hydroxylation since it affects binding to the active site of the enzyme. Androstenedione was hydroxylated in the 7α-position to give a key intermediate in the synthesis of the diuretic-7α-hydroxyandrost-4-ene-3,17-dione with 82% conversion. Adrenosterone and 17α-methyltestosterone were hydroxylated in the 6β-position. Hydroxylated derivatives such as 15β-hydroxy-17α-methyltestosterone and 6β,12β-dihydroxy-17α-methyltestosterone were also observed. In the culture of Isaria fumosorosea KCh J2, DHEA was effectively hydroxylated in the C-7 position and then oxidized to give 7-oxo-DHEA, 3β,7α- and 3β,7β-dihydroxy-17a-oxa-d-homo-androst-5-ene-17-one. We obtained 7β-OH-DHEA lactone with 82% yield during 3 days transformation of highly concentrated (5 g/L) DHEA.

Lack of resistance development in Bemisia tabaci to Isaria fumosorosea after multiple generations of selection

The emergence of insecticide resistant insect pests is of significant concern worldwide. The whitefly, Bemisia tabaci, is an important agricultural pest and has shown incredible resilience developing resistance to a number of chemical pesticides. Entomopathogenic fungi such as Isaria fumosorosea offer an attractive alternative to chemical pesticides for insect control, and this fungus has been shown to be an effective pathogen of B. tabaci. Little is known concerning the potential for the development of resistance to I. fumosorosea by B. tabaci. Five generations of successive survivors of B. tabaci infected by I. fumosorosea were assayed with I. fumosorosea. No significant differences in susceptibility to I. fumosorosea, number of ovarioles, or ovipostioning were seen between any of the generations tested. Effects of I. fumosorosea and cell-free ethyl acetate fractions derived from the fungus on the B. tabaci fat body, ovary, and vitellogenin were also investigated. These data revealed significant deformation and degradation of ovary tissues and associated vitellogenin by the fungal mycelium as well as by cell-free ethyl acetate fungal extracts. These data indicate the lack of the emergence of resistance to I. fumosorosea under the conditions tested and demonstrate invasion of the insect reproductive tissues during fungal infection.