Dodecanol, metabolite of entomopathogenic fungus Conidiobolus coronatus, affects fatty acid composition and cellular immunity of Galleria mellonella and Calliphora vicina

Oxidative stress is intrinsic to staphylococcal adaptation to fatty acid synthesis antibiotics

Antibiotics inhibiting the fatty acid synthesis pathway (FASII) of the major pathogen Staphylococcus aureus reach their enzyme targets, but bacteria continue growth by using environmental fatty acids (eFAs) to produce phospholipids. We assessed the consequences and effectors of FASII-antibiotic (anti-FASII) adaptation. Anti-FASII induced lasting expression changes without genomic rearrangements. Several identified regulators affected the timing of adaptation outgrowth. Adaptation resulted in decreased expression of major virulence factors. Conversely, stress responses were globally increased and adapted bacteria were more resistant to peroxide killing. Importantly, pre-exposure to peroxide led to faster anti-FASII-adaptation by stimulating eFA incorporation. This adaptation differs from reports of peroxide-stimulated antibiotic efflux, which leads to tolerance. In vivo, anti-FASII-adapted S. aureus killed the insect host more slowly but continued multiplying. We conclude that staphylococcal adaptation to FASII antibiotics involves reprogramming, which decreases virulence and increases stress resistance. Peroxide, produced by the host to combat infection, favors anti-FASII adaptation.

The Entomopathogenic Fungus Conidiobolus coronatus Has Similar Effects on the Cuticular Free Fatty Acid Profile of Sensitive and Resistant Insects

The mechanisms underlying the recognition of a susceptible host by a fungus and the role of cuticular compounds (CCs) in this process remain unclear; however, accumulated data suggest that this is influenced to a great degree by cuticular lipids. Two insect species differing in their sensitivity to fungal infection, viz. the highly sensitive Galleria mellonella Linnaeus (Lepidoptera: Pyralidae) and the resistant Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae), exhibited significant qualitative and quantitative changes in cuticular free fatty acid (FFA) profiles after exposure to Conidiobolus coronatus (Constantin) Batko (Entomopthorales). Despite being systematically distant, leading different lifestyles in different habitats, both insect species demonstrated similar changes in the same FFAs following exposure to the fungus (C12:0, C13:0, C14:0, C15:0, C16:1, C16:0, C18:1, C18:0), suggesting that these are involved in a contact-induced defense response. As it was not possible to distinguish the share of FFAs present in the conidia that were attached to the cuticle from the FFAs of the cuticle itself in the total number of extracted FFAs, further research is necessary.

Feasibility of using volatile urine fingerprints for the differentiation of sexually transmitted infections

Sexually transmitted infections (STIs) are a public health problem worldwide, and current diagnostic methods have certain limitations. In recent years, volatile organic compounds (VOCs) have been studied as an alternative diagnostic method. Due to this, this study aimed to detect, in vaginal swabs and urine samples, VOCs emitted by highly prevalent STIs-causing bacteria (Chlamydia trachomatis, Mycoplasma genitalium, and Neisseria gonorrhoeae) to identify potential biomarkers that allow the detection of these STIs. VOCs detected in urine samples showed a better differentiation of patients with STIs due to C. trachomatis from those not infected, with 2,6-dimethyl-4-heptanone as the volatile compound most related to the presence of this bacterium. Among the VOCs most related to M. genitalium in urine, 4-methyltetradecane and 2-methylpentadecane stood out, while 3,4,4-trimethyl-2-cyclohexen-1-one was the VOC most closely related to N. gonorrhoeae infection. Moreover, C12 alcohols were the main VOC family associated with positive samples in all three bacteria, which could indicate the presence of aldehyde reductases in their metabolism. In contrast, alcohols such as 3-methyl-1-heptanol and 1-octanol, as well as dimethyl esters, were more associated with negative samples and may be useful in ruling out an STI caused by one of these three bacteria. In short, the VOCs identified as potential biomarkers in patients with infection by C. trachomatis, M. genitalium, or N. gonorrhoeae could be used in the early diagnosis of these STIs, quickly interrupting the chain of transmission, especially interesting in asymptomatic patients. KEY POINTS: • Sexually transmitted infections are a serious public health problem worldwide. • The study of VOCs in multiple infections is increasing in recent years. • The identification of volatile biomarkers could allow new diagnostic methods.

Biocontrol effect of entomopathogenic fungi Metarhizium anisopliae ethyl acetate-derived chemical molecules: An eco-friendly anti-malarial drug and insecticide

Insect pests represent a major threat to human health and agricultural production. With a current over-dependence on chemical insecticides in the control of insect pests, leading to increased chemical resistance in target organisms, as well as side effects on nontarget organisms, the wider environment, and human health, finding alternative solutions is paramount. The employment of entomopathogenic fungi is one such potential avenue in the pursuit of greener, more target-specific methods of insect pest control. To this end, the present study tested the chemical constituents of Metarhizium anisopliae fungi against the unicellular protozoan malaria parasite Plasmodium falciparum, the insect pests Anopheles stephensi Listen, Spodoptera litura Fabricius, and Tenebrio molitor Linnaeus, as well as the nontarget bioindicator species, Eudrilus eugeniae Kinberg. Fungal crude chemical molecules caused a noticeable anti-plasmodial effect against P. falciparum, with IC50 and IC90 values of 11.53 and 7.65 µg/mL, respectively. The crude chemical molecules caused significant larvicidal activity against insect pests, with LC50 and LC90 values of 49.228-71.846 µg/mL in A. stephensi, 32.542-76.510 µg/mL in S. litura, and 38.503-88.826 µg/mL in T. molitor at 24 h posttreatment. Based on the results of the nontarget bioassay, it was revealed that the fungal-derived crude extract exhibited no histopathological sublethal effects on the earthworm E. eugeniae. LC-MS analysis of M. anisopliae-derived crude metabolites revealed the presence of 10 chemical constituents. Of these chemicals, three major chemical constituents, namely, camphor (15.91%), caprolactam (13.27%), and monobutyl phthalate (19.65%), were highlighted for potential insecticidal and anti-malarial activity. The entomopathogenic fungal-derived crude extracts thus represent promising tools in the control of insect pests and malarial parasites.

Acaricidal activity of bioactive compounds isolated from Aspergillus oryzae against poultry red mites, Dermanyssus gallinae (Acari: Dermanyssidae)

Dermanyssus gallinae, the poultry red mite (PRM), is an obligate ectoparasite feeding on poultry blood, seriously affecting the health of layers and egg production. The control of PRMs mainly relies on chemical drugs, which is facing several challenges such as the environment pollution and drug resistance. Using fungal metabolites is an environmentally friendly alternative for the control of pests. However, few studies have been conducted on the efficacy of fungal metabolites against D. gallinae. In this study, five strains of fungi were isolated from D. gallinae under laboratory conditions, and their extracts with ethyl acetate were tested for acaricidal activity on D. gallinae. The crude extract of Aspergillus oryzae caused 75.55 ± 6.94% mortality of mites at a concentration of 12.5 mg/mL, showing the highest acaricidal effect in all extracts. Subsequently, the extract of A. oryzae was isolated by bio-guided fractionation, and ten major compounds were identified by LC-MS/MS analysis. The results of bioassays indicated that five compounds exhibited acaricidal activity against D. gallinae. N, N-dimethyldecylamine N-oxide was the optimal acaricidal compound with LC₅₀ of 0.568 mg/mL. Additionally, palmitic acid, triethanolamine, cuminaldehyde, and 2,4-dimethylbenzaldehyde also showed acaricidal activity. These compounds have great application potential in the mite control, and the analysis of these fungal acaricidal substances provides a new idea and basis for the subsequent development of PRM control technology.

The plant protection preparation GZM improves crop immunity, yield, and quality

Lauryl alcohol, a natural compound found in plants and other organisms, is widely used to make surfactants, food, and pharmaceuticals. GZM, a plant protection preparation with lauryl alcohol as its major component is thought to establish a physical barrier on the plant surface, but its physiological functions are unknown. Here, we show that GZM improves the performance of peanut (Arachis hypogaea) plants in both the laboratory and the field. We demonstrate that the treatment with GZM or lauryl alcohol raises the contents of several specific lysophospholipids and induces the biosynthesis of phenylpropanoids, flavonoids, and wax in various plant species. In the field, GZM improves crop immunity, yield, and quality. In addition, GZM and lauryl alcohol can inhibit the growth of some pathogenic fungi. Our findings provide insights into the physiological and biological effects of GZM treatment on plants and show that GZM and lauryl alcohol are promising preparations in agricultural production.

Lipids as a key element of insect defense systems

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule.

Debilitation of Galleria mellonella hemocytes using CytCo a cytolytic-like protein derived from the entomopathogen Conidiobolus obscurus

Cytolytic (Cyt)-like genes are present in both pathogenic bacteria and fungi. Bacterial Cyt proteins can destroy insect midgut epithelial cells after ingestion by hosts and some of them have been developed as biopesticides; however, few studies have investigated their functions in fungal pathogens. This study investigated the effects of a Cyt-like protein (CytCo) derived from Conidiobolus obscurus (Entomophthoromycotina) on the hemocytes of the greater wax moth Galleria mellonella larvae. The results showed a significant decline in hemocyte viability after treatment with CytCo in vivo or in vitro. The hemocyte density in the hemolymph was reduced by 65.2% and 50.2% after 12 h in vivo and 6 h in vitro treatments, respectively. Apoptosis/necrosis tests using fluorescence microscopy demonstrated that CytCo-treated hemocytes displayed apoptosis, and many of them also showed necrosis after 6 h in vitro treatment. Based on transcriptome analysis, several genes involved in the programmed cell death signaling pathway were upregulated in the CytCo-treated hemocytes. Meanwhile, the differentially expressed genes related to energy production, signal transduction, transcription regulation, and melanization were upregulated, demonstrating activated immune responses; those putatively related to hemocyte adhesion were downregulated, possibly in response to the reduction of hemocytes in hemolymph. In conclusion, CytCo as a virulence factor, could irreversibly incapacitate host hemocytes, playing an important role in debilitating insect immunity. This novel insecticidal protein holds a potential to develop biopesticide for controlling agroforestry pests.

Insect cuticular compounds affect Conidiobolus coronatus (Entomopthorales) sporulation and the activity of enzymes involved in fungal infection

Mycoses are a global problem that affects humans and animals. In the present study, the entomopathogenic soil fungus Conidiobolus coronatus (Entomophthorales), infecting in tropics also humans, sheep and horses, was cultivated with the addition of insect cuticular compounds (CCs) previously detected in the cuticle of C. coronatus-resistant fly species (C10-C30 fatty alcohols, butyl oleate, butyl stearate, glycerol oleate, squalene, tocopherol acetate). Our findings indicate that CCs have diversified and complex effects on the growth and sporulation of C. coronatus and its ability to infect the larvae of Galleria mellonella (Lepidoptera). The CCs affected protein content and cuticle-degrading enzymes (CDEs) activity in the conidia. Some CCs inhibited fungal growth (0.1% C10), decreased sporulation (C12, C16, C24, C28, C30, butyl stearate, squalene), virulence (C12, C14, butyl oleate, butyl stearate) and protein content (C18). They also reduced conidial CDE activity: elastase (C24, butyl oleate, butyl stearate, squalene, tocopherol acetate), chitobiosidase (C12, C14, C20) and lipase (C12, C18, C26, squalene, tocopherol acetate). Several CCs enhanced sporulation (C14, C18, C22, C26, C30), virulence (C18, C26, squalene), conidial protein content (C16, C24, C30, squalene) and CDE activity: elastase (C10, C16, C18), NAGase (C16, C20), chitobiosidase (C16) and lipase (C10, C14, C16, C20, butyl oleate). Our findings indicate that C. coronatus colonies grown on media supplemented with CCs employ various compensation strategies: colonies grown with C16 alcohol demonstrated reduced sporulation but greater conidial protein accumulation and increased elastase, NAGase, chitobiosidase and lipase activity, thus preserving high virulence. Also, colonies supplemented with C18 alcohol demonstrated high virulence and enhanced sporulation and elastase activity but slightly decreased conidial protein content. CCs that inhibit the activity of lipases and proteases show promise in the fight against conidiobolomycosis.

Octanoic Acid-An Insecticidal Metabolite of Conidiobolus coronatus (Entomopthorales) That Affects Two Majors Antifungal Protection Systems in Galleria mellonella (Lepidoptera): Cuticular Lipids and Hemocytes

The food flavour additive octanoic acid (C8:0) is also a metabolite of the entomopathogenic fungus Conidiobolus coronatus, which efficiently infects and rapidly kills Galleria mellonella. GC-MS analysis confirmed the presence of C8:0 in insecticidal fraction FR3 extracted from C. coronatus filtrate. Topical administration of C8:0 had a dose-dependent effect on survival rates of larvae but not on pupation or adult eclosion times of the survivors. Topically applied C8:0 was more toxic to adults than larvae (LD100 for adults 18.33 ± 2.49 vs. 33.56 ± 2.57 µg/mg of body mass for larvae). The administration of C8:0 on the cuticle of larvae and adults, in amounts corresponding to their LD50 and LD100 doses, had a considerable impact on the two main defense systems engaged in protecting against pathogens, causing serious changes in the developmental-stage-specific profiles of free fatty acids (FFAs) covering the cuticle of larvae and adults and damaging larval hemocytes. In vitro cultures of G. mellonella hemocytes, either directly treated with C8:0 or taken from C8:0 treated larvae, revealed deformation of hemocytes, disordered networking, late apoptosis, and necrosis, as well as caspase 1-9 activation and elevation of 8-OHdG level. C8:0 was also confirmed to have a cytotoxic effect on the SF-9 insect cell line, as determined by WST-1 and LDH tests.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Galleria mellonella as a Good Model to Study Acinetobacter baumannii Pathogenesis

The invertebrate model, Galleria mellonella, has been widely used to study host-pathogen interactions due to its cheapness, ease of handling, and similar mammalian innate immune system. G. mellonella larvae have been proven to be useful and a reliable model for analyzing pathogenesis mechanisms of multidrug resistant Acinetobacter baumannii, an opportunistic pathogen difficult to kill. This review describes the detailed experimental design of G. mellonella/A. baumannii models, and provides a comprehensive comparison of various virulence factors and therapy strategies using the G. mellonella host. These investigations highlight the importance of this host-pathogen model for in vivo pathogen virulence studies. On the long term, further development of the G. mellonella/A. baumannii model will offer promising insights for clinical treatments of A. baumannii infection.

The Impact of the Entomopathogenic Fungus Conidiobolus coronatus on the Free Fatty Acid Profile of the Flesh Fly Sarcophaga argyrostoma

Simple Summary

The interaction between insect and fungus is characterised on the one hand by the parasite developing more effective strategies of host exploitation, and on the other, by the host mounting increasingly robust defences though Red Queen dynamics or coevolutionary arms races. Furthermore, depending on gene flow and differences in selection pressure between sites, both host and parasite may demonstrate local adaptation to their counterpart or develop more general resistance or offensive traits. As the cuticle is considered the first line of defence of the insect, changes in the FFA profile may well influence susceptibility or resistance to fungal invasion. Our findings indicate that Sarcophaga argyrostoma demonstrates stage-specific resistance to Conidiobolus coronatus infection and suggests that FFAs play a role in resistance to fungal infection in flesh flies. These findings not only increase our knowledge of the entomopatogenic potential of fungi, but also of the growing level of infection by C. coronatus in humans and other mammals. Also, the presented research suggests that FFAs demonstrate antifungal activity which may be helpful in designing new antifungal treatments.

Abstract

The chemical composition of the insect cuticle varies remarkably between species and their life stages. It can affect host resistance and substrate utilization by invading entomopathogen fungi, such as the soil fungus Conidiobolus coronatus. In this study, Sarcophaga argyrostoma flies were exposed to sporulating C. coronatus colonies for 24 h; the pupae were resistant, but the adults demonstrated 60% mortality. Although the pupae demonstrated no sign of infection nor any abnormal development, our findings indicate that after 24 h of contact with the fungus, the pupae demonstrated a 25.2-fold increase in total cuticular free fatty acids (FFAs) and a 1.9-fold decrease in total internal FFAs. Also, the cuticular FFA increased from 26 to 30, while the internal FFA class increased from 13 to 23. In exposed adults, the total mass of cuticular FFAs increased 1.7-fold, while the number of FFAs stayed the same (32 FFAs). Also, the internal FFA class increased from 26 to 35 and the total FFA mass increased 1.1-fold. These considerable differences between adults and pupae associated with C. coronatus exposure indicate developmental changes in the mechanisms governing lipid metabolism and spatial distribution in the organism, and suggest that cuticular lipids play a vital role in the defence against pathogenic fungi.