Collagenase production by nematode-trapping fungi

Biological control: a novel strategy for the control of the plant parasitic nematodes

Plant parasitic nematodes (Root-knot nematodes, Meloidogyne spp.) are rounded worms, microscopic, and cause many agricultural economic losses. Their attacks have a direct impact on the productivity of cultivated crops by reducing their fruit quantity. Chemical control is widespread all over the world, but biological control is the most effective way to reduce the number of pests that infect crops, particularly by the use of microorganisms like fungi and bacteria. Biological control is rapidly evolving, and more products are being sold worldwide over time. They can be produced by fungi, bacteria, or actinomycetes that can destruct plant parasite nematodes and feed on them. Nematophagous microorganisms as the natural enemies of nematodes have a promising way of controlling nematodes. Some of them create net-like substances and traps to take the worms from outside and finally kill them. Other parasites serve as internal parasites in order to produce toxins and to produce virulence to kill nematodes. Comprehension of the molecular basis for microbial nematode interactions gives important insights into how successful biological nematode control agents can be created. We discuss recent advances in our understanding of nematodes and nematophagous microorganisms, with an emphasis on molecular mechanisms that infect nematodes with nematophagous microorganisms and on nematode safety from pathogenic attacks. Finally, we addressed numerous key areas for future research and development, including possible approaches to the application of our recent expertise in the development of successful biocontrol strategies.

Nematode-Trapping Fungi

Nematode-trapping fungi are a unique and intriguing group of carnivorous microorganisms that can trap and digest nematodes by means of specialized trapping structures. They can develop diverse trapping devices, such as adhesive hyphae, adhesive knobs, adhesive networks, constricting rings, and nonconstricting rings. Nematode-trapping fungi have been found in all regions of the world, from the tropics to Antarctica, from terrestrial to aquatic ecosystems. They play an important ecological role in regulating nematode dynamics in soil. Molecular phylogenetic studies have shown that the majority of nematode-trapping fungi belong to a monophyletic group in the order Orbiliales (Ascomycota). Nematode-trapping fungi serve as an excellent model system for understanding fungal evolution and interaction between fungi and nematodes. With the development of molecular techniques and genome sequencing, their evolutionary origins and divergence, and the mechanisms underlying fungus-nematode interactions have been well studied. In recent decades, an increasing concern about the environmental hazards of using chemical nematicides has led to the application of these biological control agents as a rapidly developing component of crop protection.

Molecular mechanisms of nematode-nematophagous microbe interactions: basis for biological control of plant-parasitic nematodes

Plant-parasitic nematodes cause significant damage to a broad range of vegetables and agricultural crops throughout the world. As the natural enemies of nematodes, nematophagous microorganisms offer a promising approach to control the nematode pests. Some of these microorganisms produce traps to capture and kill the worms from the outside. Others act as internal parasites to produce toxins and virulence factors to kill the nematodes from within. Understanding the molecular basis of microbe-nematode interactions provides crucial insights for developing effective biological control agents against plant-parasitic nematodes. Here, we review recent advances in our understanding of the interactions between nematodes and nematophagous microorganisms, with a focus on the molecular mechanisms by which nematophagous microorganisms infect nematodes and on the nematode defense against pathogenic attacks. We conclude by discussing several key areas for future research and development, including potential approaches to apply our recent understandings to develop effective biocontrol strategies.

Characterization of a neutral serine protease and its full-length cDNA from the nematode-trapping fungus Arthrobotrys oligospora

A neutral serine protease (designated Aoz1) was purified to homogeneity from a strain of Arthrobotrys oligospora, obtained from soil in Yunnan Province. The purified protein showed a molecular mass of approximately 38 000 Dalton, pI 4.9 and displayed optimal activity at 45 C and pH 6-8. The protein could hydrolyze gelatin, casein and the chromogenic substrate azocoll, and it could immobilize nematodes in vitro (Panagrellus redivivus L. [Goodey]). The level of activity in culture medium was found to increase with increasing gelatin concentration. Scanning electron micrographs demonstrated dramatic structural changes in nematode cuticle treated with the purified protease. A partial peptide sequence obtained by N-terminal sequence analysis was used to design degenerate primers for the isolation of a cDNA gene encoding the mature protease. Analysis of the cDNA and corresponding genomic sequence revealed 97% identity with PII, a gene previously described from A. oligospora, and we conclude that this gene is likely a PII ortholog.

Extracellular enzymes and the pathogenesis of nematophagous fungi

Nematophagous fungi are an important group of soil microorganisms that can suppress the populations of plant-parasitic nematodes. The pathogenic mechanisms of nematophagous fungi are diverse: They can be parasitical-mechanical through producing specialized capturing devices, or toxin-dependent. During infections, a variety of virulence factors may be involved against nematodes by nematophagous fungi. In this review, we present up-to-date information on the modes of infection by nematophagous fungi. The roles of extracellular hydrolytic enzymes and other virulence factors involved in infection against nematodes were summarized. The biochemical properties and peptide sequences of a special group of enzymes, the serine proteases, were compared, and their implications in infections were discussed. We also discussed the impact of emerging new techniques on our understanding of this unique group of fungi.

Purification and characterization of an extracellular serine protease from the nematode-trapping fungus Dactylella shizishanna

AIMS

To evaluate the production of an extracellular serine protease by Dactylella shizishanna and its potential as a pathogenesis factor.

METHODS AND RESULTS

An extracellular alkaline serine protease (Ds1) was purified and characterized from the nematode-trapping fungus D. shizishanna using cation-exchange chromatography and hydrophobic interaction chromatography. The molecular mass of the protease was approximately 35 kDa estimated by SDS-PAGE. The optimum activity of Ds1 was at pH 10 and 55 degrees C (over 30 min). The purified protease could degrade purified cuticle of Penagrellus redivivus and a broad range of protein substrates. The purified protease was highly sensitive to phenylmethyl sulfonyl fluoride (PMSF) (0.1 mmol l(-1)), indicating it belonged to the serine protease family. The N-terminal amino acid residues of Ds1 are AEQTDSTWGL and showed a high homology with Aozl and PII, two serine proteases purified from the nematode-trapping fungus Arthrobotrys oligospora.

CONCLUSIONS

Nematicidal activity of D. shizishanna was partly related to its ability to produce extracellular serine protease.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this report, we purified a new serine protease from D. shizishanna and provided a good foundation for future research on infection mechanism.

Characterization of an extracellular protease and its cDNA from the nematode-trapping fungus Monacrosporium microscaphoides

To better exploit the biocontrol potential of nematophagous fungi, it is important to fully understand the molecular background of the infection process. In this paper, several nematode-trapping fungi were surveyed for nematocidal activity. From the culture filtrate of Monacrosporium microscaphoides, a neutral serine protease (designated Mlx) was purified by chromatography. This protease could immobilize the nematode Penagrellus redivivus in vitro and degrade its purified cuticle, suggesting that Mlx could serve as a virulence factor during infection. Characterization of the purified protease revealed a molecular mass of approximately 39 kDa, an isoelectric point of 6.8, and optimum activity at pH 9 at 65 °C. Mlx has broad substrate specificity, and it hydrolyzes protein substrates, including casein, skimmed milk, collagen, and bovine serum albumin. The gene encoding Mlx was also cloned and the nucleotide sequence was determined. The deduced amino acid sequence contained the conserved catalytic triad of aspartic acid – histidine – serine and showed high similarity with two cuticle-degrading proteases (PII and Aoz1), which were purified from the nematode-trapping fungus Arthrobotrys oligospora. Research on infection mechanisms of nematode-trapping fungi has thus far only focused on A. oligospora. However, little is known about other nematode-trapping fungi. Our report is among the first to describe the purification and cloning of an infectious protease from a different nematode-trapping fungus.Key words: extracellular serine protease, Monacrosporium microscaphoides, nematode-trapping fungus, nematocidal activity.

Isolation and characterization of a serine protease from the nematophagous fungus, Lecanicillium psalliotae, displaying nematicidal activity

Lecanicillium psalliotae produced an extracellular protease (Ver112) which was purified to apparent homogeneity giving a single band on SDS-PAGE with a molecular mass of 32 kDa. The optimum activity of Ver112 was at pH 10 and 70 degrees C (over 5 min). The purified protease degraded a broad range of substrates including casein, gelatin, and nematode cuticle with 81% of a nematode (Panagrellus redivivus) being degraded after treating with Ver112 for 12 h. The protease was highly sensitive to PMSF (1 mM) indicating it to be a serine protease. The N-terminal amino acid residues of Ver112 shared a high degree of similarity with other cuticle-degrading proteases from nematophagous fungi which suggests a role in nematode infection.

Characterization of an Extracellular Serine Protease Gene from the Nematophagous Fungus Lecanicillium psalliotae

The gene encoding a cuticle-degrading serine protease was cloned from three isolates of Lecanicillium psalliotae (syn. Verticillium psalliotae) by 3' and 5' RACE (rapid amplification of cDNA ends) method. The gene encodes for 382 amino acids and the protein shares conserved motifs with subtilisin N and peptidase S8. Comparison of translated cDNA sequences of three isolates revealed one amino acid polymorphism at position 230. The deduced protease sequence shared high degree of similarities to other cuticle-degrading proteases from other nematophagous fungi.

Extracellular enzymes serving as virulence factors in nematophagous fungi involved in infection of the host

Extracellular enzymes, including serine protease, chitinase and collagenase, corresponding to the main chemical constituents of the nematode cuticle and eggshell, have been reported to be involved in the infectious process as virulence factors. This review will focus on the categories, characterization, purification, cloning and potential function of these virulence enzymes and will attempt to provide new insights into the mechanisms of fungal pathogenesis in nematodes.

Collagenase production in an antarctic strain of Arthrobotrys tortor Jarowaja

This paper describes the results of a comparative screening between the nematophagous Antarctic fungus Arthrobotrys tortor and other species of that genus for the production of extracellular collagenases. The nematode species used in this study was Caenorhabditis elegans, feeding on Escherichia coli cultures. Determination of collagenase activity was made using insoluble collagen from bovine Achilles tendon and determining the amount of solubilized hydroxyproline produced. The results show that the total amount of collagenase produced by the Antarctic strain of A. tortor was about threefold higher than that observed for the other species. In the Antarctic strain, collagenase was shown to be a constitutive enzyme.

Purification and characterization of chitinases from the nematophagous fungi Verticillium chlamydosporium and V. suchlasporium

Culture filtrates of the nematophagous fungi Verticillium chlamydosporium and V. suchlasporium growing on colloidal chitin showed increasing chitinolytic activity and production of two (32- and 43-kDa) main proteins. Maximum activity was found 18-20 days after inoculation, but V. suchlasporium always displayed higher activity. Zymography of such filtrates on carboxymethyl-chitin-Remazol brilliant violet 5R/acrylamide gels showed five bands of substrate degradation for V. suchlasporium and three for V. chlamydosporium. Filtrates with maximum activity were chromatographed on macroporous cross-linked chitin affinity matrix, showing a peak of main (50-60%) activity, which only contained a 43-kDa protein for both fungi. Zymography and colloidal chitin degradation showed that it was a single endochitinase (CHI43) with optimum pH range of 5.2-5.7. The main isoforms had pIs of 7.6 for V. suchlasporium and 7.9 for V. chlamydosporium. Eggs of the nematode Globodera pallida treated with CHI43 and the serine protease P32 from V. suchlasporium alone or in combination showed surface damage in comparison with controls when examined by scanning electron microscopy.

Proteases and Their Involvement in the Infection and Immobilization of Nematodes by the Nematophagous Fungus Arthrobotrys oligospora

The nematophagous fungus Arthrobotrys oligospora produced extracellular proteases when grown in a liquid culture, as revealed by measuring the hydrolysis of the chromogenic substrate Azocoll. The extracellular protease activity was inhibited by phenylmethylsulfonyl fluoride (PMSF) and other serine protease inhibitors and partly inhibited by the aspartate protease inhibitor pepstatin and by a cysteine protease inhibitor [ l - trans -epoxysuccinyl-leucylamide-(4-guanidino)-butane, or E-64]. Substrate gel electrophoresis showed that the fungus produced several different proteases, including multiple serine proteases. The function of proteases in the infection of nematodes was examined by treating the fungus with various protease inhibitors. None of the inhibitors tested affected the adhesion of nematodes to the traps, but incubating trap-bearing mycelium with a serine protease inhibitor, PMSF, antipain, or chymostatin, or the metalloprotease inhibitor phenanthroline significantly decreased the immobilization of nematodes captured by the fungus. Inhibitors of cysteine or aspartic proteases did not affect the immobilization of captured nematodes. The effects of PMSF on the immobilization of nematodes were probably due to serine proteases produced by the fungus, since the effects were observed when unbound inhibitor was washed away from the fungus before the nematodes were added to the system. No effects were observed when the nematodes only were pretreated with PMSF.

Differential Adhesion and Infection of Nematodes by the Endoparasitic Fungus Meria coniospora ( Deuteromycetes )

The conidia of the endoparasitic fungus Meria coniospora ( Deuteromycetes ) had different patterns of adhesion to the cuticles of the several nematode species tested; adhesion in some species was only to the head and tail regions, on others over the entire cuticle, whereas on others there was a complete lack of adhesion. After adhesion, the fungus usually infected the nematode. However, adhesion to third-stage larvae of five animal parasitic nematodes, all of which carry the cast cuticle from the previous molt, did not result in infection. M. coniospora infected animal parasitic nematodes when this protective sheath was removed. Seven preparations of sialic acid ( N -acetylneuraminic acid) gave three types of response in adhesion-infection of nematodes: (i) a significant reduction in conidial adhesions; (ii) no interference with adhesion, but a 10-day delay in infection; and (iii) a delay in infection by 2 to 3 days. The current results support previous findings indicating involvement of sialic acids localized on nematode cuticles in recognition of prey by M. coniospora.

Binding Characteristics of Lectins Involved in the Trapping of Nematodes by Fungi

Seventeen saccharides were tested for their ability to bind to the trap lectins of three species of nematode-trapping fungi and prevent nematode capture. The lectin of Arthrobotrys conoides was found to be inhibited by α- d -glucose/ d -mannose and similar saccharides. The lectins of Monacrosporium eudermatum and Monacrosporium rutgeriensis were inhibited by α- l -fucose and 2-deoxy- d -glucose, respectively. Human group O(H) erythrocytes agglutinated to traps of M. eudermatum but not A. conoides or M. rutgeriensis. There was no agglutination of group A or B to traps formed by all three fungi. Exposure of the traps to trypsin eliminated the ability to capture nematodes. The presence of d -glucose/ d -mannose and l -fucose residues on the nematode cuticle was suggested through the use of commercially prepared lectin-peroxidase conjugates.

Influence of Cadmium, Zinc, and Lead on Growth, Trap Formation, and Collagenase Activity of Nematode-Trapping Fungi

Growth and morphogenesis of seven species of nematode-trapping fungi and the activity of a collagenase produced by Arthrobotrys amerospora were measured in the presence of various concentrations of divalent cadmium, zinc, or lead. In general, growth varied with species and was dependent on the metal present and the concentration at which it was tested. Cadmium was found to exhibit the greatest toxicity followed by zinc and lead, respectively. In most cases, inhibition of growth was directly correlated with a decreased capacity to form traps. However, in a few cases, trap formation was inhibited either more or less than was growth. The activity of the collagenase was less sensitive than was growth or trap formation to heavy-metal inhibition.