Phylogenetic analysis of two putative Nosema isolates from Cruciferous Lepidopteran pests in Taiwan

Molecular characterization and phylogenetic analyses of MetAP2 gene and protein of Nosema bombycis isolated from Guangdong, China

Background

Pebrine, caused by microsporidium Nosema bombycis, is a devastating disease that causes serious economic damages to the sericulture industry. Studies on development of therapeutic and diagnostic options for managing pebrine in silkworms are very limited. Methionine aminopeptidase type 2 (MetAP2) of microsporidia is an essential gene for their survival and has been exploited as the cellular target of drugs such as fumagillin and its analogues in several microsporidia spp., including Nosema of honeybees.

Methods

In the present study, using molecular and bioinformatics tools, we performed in-depth characterization and phylogenetic analyses of MetAP2 of Nosema bombycis isolated from Guangdong province of China.

Results

The full length of MetAP2 gene sequence of Nosema bombycis (Guangdong isolate) was found to be 1278 base pairs (bp), including an open reading frame of 1,077 bp, encoding a total of 358 amino acids. The bioinformatics analyses predicted the presence of typical alpha-helix structural elements, and absence of transmembrane domains and signal peptides. Additionally, other characteristics of a stable protein were also predicted. The homology-based 3D models of MetAP2 of Nosema bombycis (Guangdong isolate) with high accuracy and reliability were developed. The MetAP2 protein was expressed and purified. The observed molecular weight of MetAP2 protein was found to be ~43-45 kDa. The phylogenetic analyses showed that MetAP2 gene and amino acids sequences of Nosema bombycis (Guangdong isolate) shared a close evolutionary relationship with Nosema spp. of wild silkworms, but it was divergent from microsporidian spp. of other insects, Aspergillus spp., Saccharomyces cerevisiae, and higher animals including humans. These analyses indicated that the conservation and evolutionary relationships of MetAP2 are closely linked to the species relationships.

Conclusion

This study provides solid foundational information that could be helpful in optimization and development of diagnostic and treatment options for managing the threat of Nosema bombycis infection in sericulture industry of China.

Isolation and Molecular Identification of Microsporidian Pathogen Causing Nosemosis in Muga Silkworm, Antheraea assamensis Helfer (Lepidoptera: Saturniidae)

Microsporidia are intracellular fungal parasites and they are the most common pathogens for sericulture. Microsporidian sp. can cause pebrine, a dreadful disease and lead to destructive disorder in Muga silkworm, Antheraea assamensis Helfer by vertical and horizontal transmission. This disease is the key factor obstructing the developmental progress of Muga culture in India. Nevertheless, molecular identification and characterization of pathogen associated with pebrine disease in A. assamensis is not yet established. Insect bioassay studies revealed that microsporidian infection in Muga silkworm, A. assamensis Helfer significantly reduced (P < 0.005) cocoon weight, pupal weight, shell weight and silk ratios. A new set of PCR primers suitable for amplification of small subunit ribosomal RNA (SSU-rRNA) of microsporidia infecting A. assamensis have been designed. The amplicon was cloned, sequenced and analysed. Microsporidia pathogen of wild silk moth A. assamensis has been identified at genus level as Nosema sp. AA1. Phylogeny of Nosema sp. AA1 was constructed on the basis of SSU-rRNA sequence and it has a close evolutionary relationship with microsporidian pathogens of other wild silkmoths. The arrangement and organization of the rRNA genes inferred that Nosema sp. AA1 belongs to true Nosema group and not to members of the Nosema/Vairimorpha group.

Phylogenetic Analysis of the Complete rRNA Gene Sequence of Nosema sp. SE Isolated from the Beet Armyworm Spodoptera exigua

The microsporidium Nosema sp. SE is a pathogen that infects the beet armyworm Spodoptera exigua. The complete sequence of its 4,302-base pair (bp) ribosomal ribonucleic acid (rRNA) gene region was obtained by polymerase chain reaction amplification and sequencing. The rRNA organization of Nosema sp. SE was 5'-large subunit (LSU) rRNA-internal transcribed spacer-small subunit (SSU) rRNA-intergenic spacer-5S-3', which corresponded to the pattern of Nosema bombycis. Phylogenetic analysis based on LSU rRNA and SSU rRNA both indicated that the parasite had a close relationship with other true Nosema species, confirming that Nosema sp. SE belongs to true Nosema group of the genus Nosema.

Morphological and phylogenetic analysis of a microsporidium (Nosema sp.) isolated from rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae)

A new microsporidium was isolated from Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), one of the most important rice pests in China. The morphology and molecular systematics of this novel microsporidium were described in this study. The spores were long oval and measured 3.17 × 1.64 μm on fresh smears. Ultrastructure of the spores was characteristic for the genus Nosema: a diplokaryon, 10-12 polar filament coils of the same type, and posterior vacuole. Small subunit rRNA gene sequence data and phylogenetic analysis further confirmed that the microsporidian species from C. suppressalis belong to the true Nosema sub-group of the genus Nosema. Besides, the microsporidium Nosema sp. CS could cause systemic infection of Bombyx mori and infect silkworms through vertical transmission. Therefore, mulberry field pest control should be carefully monitored, and sanitation of mulberry leaves is essential to control the pebrine disease in sericulture.

Nosema sp. PM-1, a new isolate of microsporidian from infected Papilio machaon Linnaeus, based on ultrastructure and molecular identification

A new microsporidium, Nosema sp. PM-1, was first isolated from Papilio machaon Linnaeus. The spore shape of the PM-1 isolate was a long oval with an average size of 3.22 μm × 1.96 μm. Ultrastructure observation showed that PM-1 had a typical Nosema common diplokaryotic nuclei structure with 10-13 polar filament coils, spore wall, plasma membrane, and anchoring disk. The complete rRNA gene sequences were obtained by polymerase chain reaction amplification and each rRNA unit was arrayed as follows: 5'-LSU (2497 bp)-ITS (179 bp)-SSU (1232 bp)-IGS (278 bp)-5S (115 bp)-3', which was the same as typical Nosema. The phylogenetic trees of rRNA, DNA-directed RNA polymerase II subunit, and tubulin genes all show that PM-1 was a sister to the clade comprising Nosema bombycis, Nosema spodopterae, and Nosema sp. PX1. The spore morphology, ultrastructure, and complete rRNA structure indicate that this isolate assigned to the ˝true˝ Nosema group, can parasitized in Papilio machaon Linnaeus, which provides a wider host range for Nosema.

Morphological and phylogenetic analysis of Nosema sp. HR (Microsporidia, Nosematidae): a new microsporidian pathogen of Histia rhodope Cramer (Lepidoptera, Zygaenidae)

A new microsporidium was isolated from Histia rhodope Cramer (Lepidoptera, Zygaenidae), a pest of Bischofia javanica BL. in China. The morphology and molecular systematic of this novel microsporidian isolate had been described in this study. The spores were long oval and measured 3.1 × 1.9 μm on fresh smears. Ultrastructure of the spores was characteristic for the genus Nosema: 14-15 polar filament coils, posterior vacuole, and a diplokaryon. The sequenced rRNA gene of this isolate is 4309 bp long. The organization of the rRNA gene is 5'-LSU rRNA-ITS-SSU rRNA-IGS-5S-3', which is similar to that of other Nosema species (such as Nosema bombycis). Phylogenetic analysis based on LSU rRNA gene and SSU rRNA gene both revealed that this novel micorsporidian which isolated from H. rhodope had close relationship to the genus Nosema. Additionally, this isolate can also cause systemic infection of Bombyx mori. So, we should pay attention not only to N. bombycis, but also to other microsporidian (such as Nosema sp. HR) in sericulture in the future.

Morphological and molecular studies of Vairimorpha necatrix BM, a new strain of the microsporidium V. necatrix (Microsporidia, Burenellidae) recorded in the silkworm, Bombyx mori

Vairimorpha sp. BM (2012) is a recent isolate of the microsporidia from the silkworm in Shandong, China. The ultrastructure, tissue pathology and molecular characterization of this isolate is described in this study. This pathogenic fungus causes pebrine disease in silkworms which manifests as a systemic infection. Meanwhile, the silkworm eggs produced by the infected moths were examined using a microscope and PCR amplification. Neither spores nor the expected PCR band were observed, suggesting that no vertical transmission occurred in Bombyx mori. In addition, the ultrastructure of the isolate was studied by light microscopy and transmission electron microscopy. Two types of spores were observed: diplokaroytic spores with 13-17 coils of polar tubes and monokaryotic spores with less coils of polar tubes which could form octospores; however, no sporophorous vesicles were observed. Finally, phylogenetic analysis of the small subunit rRNA genes of Vairimorpha species showed that this isolate has a closer relationship to Vairimorpha necatrix than the other species studied. This result also is supported by phylogenetic analysis based on their actin genes, heat shock protein 70 (HSP70) and RNA polymerase II (RPB1). Based on the information gained during this study, we propose that this microsporidian species infecting B. mori should be given the name V. necatrix BM.

Molecular characteristics of the alpha- and beta-tubulin genes of Nosema philosamiae

Microsporidia are intracellular parasites of insects and other higher eukaryotes. The microsporidian Nosema philosamiae Talukdar, 1961 was isolated from the eri silkworm, Philosamia cynthia ricini Grote. In the present study, alpha- and beta-tubulin genes from N. philosamiae were characterized. The identity analysis of nucleotide and amino acid sequences indicated high similarity with species of Nosema Nägeli, 1857 sensu lato (nucleotide sequences, > or = 96.0%; amino acid sequences, > or = 99.0%). However, the tubulin genes of N. philosamiae share low sequence similarity with that of N. ceranae Fries, Feng, da Silva, Slemenda et Pieniazek, 1996 (strain BRL01) and a Nosema/Vairimorpha species. Phylogenies based on alpha-, beta- and combined alpha- plus beta-tubulin gene sequences showed that N. philosamiae, along with the true Nosema species, forms a separate clade with a high bootstrap value, with N. ceranae BRL01 forming a clade of its own. The results indicated that the alpha- and beta-tubulin sequences may be useful as a diagnostic tool to discriminate the true Nosema group from the Nosema/Vairimorpha group.

Pathogenicity of a microsporidium isolate from the diamondback moth against Noctuid moths: characterization and implications for microbiological pest management

Background

Due to problems with chemical control, there is increasing interest in the use of microsporidia for control of lepidopteran pests. However, there have been few studies to evaluate the susceptibility of exotic species to microsporidia from indigenous Lepidoptera.

Methodology/Principal Findings

We investigated some biological characteristics of the microsporidian parasite isolated from wild Plutella xylostella (PX) and evaluated its pathogenicity on the laboratory responses of sympatric invasive and resident noctuid moths. There were significant differences in spore size and morphology between PX and Spodoptera litura (SL) isolates. Spores of PX isolate were ovocylindrical, while those of SL were oval. PX spores were 1.05 times longer than those of SL, which in turn were 1.49 times wider than those of the PX. The timing of infection peaks was much shorter in SL and resulted in earlier larval death. There were no noticeable differences in amplicon size (two DNA fragments were each about 1200 base pairs in length). Phylogenetic analysis revealed that the small subunit (SSU) rRNA gene sequences of the two isolates shared a clade with Nosema/Vairimorpha sequences. The absence of octospores in infected spodopteran tissues suggested that PX and SL spores are closely related to Nosema plutellae and N. bombycis, respectively. Both SL and S. exigua (SE) exhibited susceptibility to the PX isolate infection, but showed different infection patterns. Tissular infection was more diverse in the former and resulted in much greater spore production and larval mortality. Microsporidium-infected larvae pupated among both infected and control larvae, but adult emergence occurred only in the second group.

Conclusion/Significance

The PX isolate infection prevented completion of development of most leafworm and beet armyworm larvae. The ability of the microsporidian isolate to severely infect and kill larvae of both native and introduced spodopterans makes it a valuable candidate for biocontrol against lepidopteran pests.

Intraspecific polymorphism of rDNA among five Nosema bombycis isolates from different geographic regions in China

The microsporidian Nosema bombycis is the causative agent of pébrine, a highly infectious disease of the silkworm Bombyx mori. Three regions of the multicopy rDNA gene were examined in order to investigate the relationships among five Nosema isolates from various regions of China. Ribosomal DNA alleles are present on each of the 18 chromosomes of N. bombycis and show a high degree of variation. In this study the small subunit (SSU) rDNA, internal transcribed spacer (ITS) and intergenic spacer (IGS) regions for up to 10 different rDNA copies from each N. bombycis isolate were cloned and sequenced. As expected we see greater polymorphism in the ITS region (88 variable sites in 179 nucleotides) and IGS (200 variable sites in 279 nucleotides) than in the SSU rDNA (24 variable sites in 1232 nucleotides). Phylogenetic analysis shows greater differences between alleles within an isolate than between the same alleles from different isolates. The data reveal two very different groups, one from the Sichuan province and the other with a broad distribution including four provinces in southeast China and Japan. The Sichuan isolate does not have any rDNA alleles with sequences identical to those in the other isolates, implying that it is a separate, non-intermixing, population or perhaps a separate species from the other isolates. In light of the polymorphic nature of the rDNA alleles in N. bombycis and their presence on every chromosome, the rDNA gene may be useful for understanding the movement and ultimately the source of pébrine infections.

Phylogenetic characterization of a microsporidium (Nosema sp.) isolated from the mulberry pest, Hemerophila atrilineata

Microsporidia are a group of obligate intracellular unicellular eukaryotes that can parasitize a wide variety of other eukaryotes ranging from protists to invertebrates and vertebrates. In this study, we examined the microsporidium Nosema sp. isolated from the mulberry pest, Hemerophila atrilineata Butler, 1881, named herein "Nosema sp. HA". The fresh spores were long oval in shape, 3.8 +/- 0.4 microm in length and 1.9 +/- 0.3 microm in width. Analysis of tissue infection of silkworm, Bombyx mori Linnaeus, 1758, indicated that the midgut, Malpighian tubules, muscle, fat body, silk glands, hemocytes, nerve tissue and gonads of silkworm were infected with Nosema sp. HA. The complete rRNA gene sequence of this microsporidium contained 4 305 base pairs (GenBank Accession JN882299), including the large subunit rRNA (2492 bp), the internal transcribed spacer (187 bp), the small subunit rRNA (1232 bp), the intergenic spacer (279 bp) and the 5S region (115 bp). The organization of the rRNA gene is 5'-LSU-ITS-SSU-IGS-5S-3'. Phylogenetic analysis, comparison of sequence identities and the arrangement in the rRNA gene subunits suggested that this isolate is separate from other Nosema species.

Diversity of Nosema associated with bumblebees (Bombus spp.) from China

Bumblebees (Bombus spp.) are important pollinators of many economically important crops and microsporidia are among the most important infections of these hosts. Using molecular markers, we screened a large sample (n=1,009 bees) of workers of 27 different Bombus spp. from China (Sichuan, Qinghai, Inner Mongolia, and Gansu provinces). The results showed that 62 individuals representing 12 Bombus spp. were infected by microsporidia with an overall prevalence of 6.1%. Based on the haplotypes (ssrRNA sequences), we confirmed the presence of Nosema bombi, Nosema ceranae and (likely) Nosema thomsoni. In addition, four new putatively novel taxa were identified by phylogenetic reconstruction: Nosema A, Nosema B-complex, Nosema C-complex and Nosema D-complex. In many cases, hosts were infected by more than one Nosema taxon. Possible caveats of sequence analyses are discussed.

Complete sequence and gene organization of the Nosema heliothidis ribosomal RNA gene region

By sequencing the entire ribosomal RNA (rRNA) gene region of Nosema heliothidis isolated from cotton bollworm (Helicoverpa armigera), we showed that its gene organization is similar to the type species, Nosema bombycis: the 5'-large subunit rRNA (2,490 bp)-internal transcribed spacer (192 bp)-small subunit rRNA (1,232 bp)-intergenic spacer (274 bp)-5S rRNA (115 bp)-3'. We constructed two phylogenetic trees, analyzed phylogenetic relationships, examined rRNA organization of microsporidia, and compared the secondary structure of small subunit rRNA with closely related microsporidia. The latter two features may provide important information for the classification and phylogenetic analysis of microsporidia.

Phylogenetic characterization of a microsporidium (Endoreticulatus sp. Zhenjiang) isolated from the silkworm, Bombyx mori

This study examined the morphological and molecular characteristics of the microsporidium Endoreticulatus sp. Zhenjiang, isolated from the silkworm (Bombyx mori). The fresh spores were oval, 2.9 ± 0.2 μm in length and 1.2 ± 0.2 μm in width. The complete rRNA cistron has a length of 4,432 bp (GenBank accession no. FJ772431), including the large subunit rRNA (2,460 bp), the internal transcribed spacer (187 bp), the small subunit rRNA (1,254 bp), the intergenic spacer (276 bp), and the 5S region (115 bp). The organization of the rRNA gene is 5'-LSU-ITS-SSU-IGS-5S-3', which is reverse compared to the organization of most microsporidian rRNA regions. Phylogenetic analysis based on small subunit rRNA sequences showed that this isolate belongs to the genus Endoreticulatus, and is closely related to Glugoides intestinalis. Furthermore, both had a similar reverse arrangement of the rRNA gene. Our study provides another example of a microsporidian species with a novel organization of rRNA genes, demonstrating that the reverse arrangement is exhibited not only by the microsporidian genus Nosema but may also occur in a clade that contains the genera Endoreticulatus and Glugoides.

A new isolate of Nosema sp. (Microsporidia, Nosematidae) from Phyllobrotica armata Baly (Coleoptera, Chrysomelidae) from China

We studied the spore morphology and molecular systematics of a novel microsporidian isolate from Phyllobrotica armata Baly collected in China. The spores were long-oval and measured 4.7 × 2.6 μm on fresh smears. Ultrastructure of the spores was characteristic for the genus Nosema: 13-14 polar filament coils, posterior vacuole, and a diplokaryon. The complete rRNA gene sequence of the isolate was 4308 bp long. The organization of the rRNA gene was 5'-LSU rRNA-ITS-SSU rRNA-IGS-5S-3', which corresponds to that of the Nosema species. Phylogenetic analysis based on the rRNA gene sequence indicated that this isolate, designated as Nosema sp. PA, is closely related to Nosema bombycis and is correctly assigned to the "true"Nosema group.

Phylogenetic analysis of complete rRNA gene sequence of Nosema philosamiae isolated from the lepidopteran Philosamia cynthia ricini

ABSTRACT. The microsporidian Nosema philosamiae is a pathogen that infects the eri-silkworm Philosamia cynthia ricini. The complete sequence of rRNA gene (4,314 bp) was obtained by polymerase chain reaction amplification with specific primers and sequencing. The sequence analysis showed that the organization of the rRNA of N. philosamiae was similar to the pattern of Nosema bombycis. Phylogenetic analysis of rRNA gene sequences revealed that N. philosamiae had a close relationship with other Nosema species, confirming that N. philosamiae is correctly assigned to the genus Nosema.

Sequence and phylogenetic analysis of SSU rRNA gene of five microsporidia

The complete small subunit rRNA (SSU rRNA) gene sequences of five microsporidia including Nosema heliothidis, and four novel microsporidia isolated from Pieris rapae, Phyllobrotica armta, Hemerophila atrilineata, and Bombyx mori, respectively, were obtained by PCR amplification, cloning, and sequencing. Two phylogenetic trees based on SSU rRNA sequences had been constructed by using Neighbor-Joining of Phylip software and UPGMA of MEGA4.0 software. The taxonomic status of four novel microsporidia was determined by analysis of phylogenetic relationship, length, G+C content, identity, and divergence of the SSU rRNA sequences. The results showed that the microsporidia isolated from Pieris rapae, Phyllobrotica armta, and Hemerophila atrilineata have close phylogenetic relationship with the Nosema, while another microsporidium isolated from Bombyx mori is closely related to the Endoreticulatus. So, we temporarily classify three novel species of microsporidia to genus Nosema, as Nosema sp. PR, Nosema sp. PA, Nosema sp. HA. Another is temporarily classified into genus Endoreticulatus, as Endoreticulatus sp. Zhenjiang. The result indicated as well that it is feasible and valuable to elucidate phylogenetic relationships and taxonomic status of microsporidian species by analyzing information from SSU rRNA sequences of microsporidia.

Morphological and molecular studies of a microsporidium (Nosema sp.) isolated from the thee spot grass yellow butterfly, Eurema blanda arsakia (Lepidoptera: Pieridae)

A microsporidium possessing molecular and morphological characteristics of the genus Nosema was isolated from larvae of the thee-spot grass yellow butterfly, Eurema blanda arsakia. The complete rRNA gene sequences of the E. blanda isolate contained 4,428 base pairs (GenBank Accession No. EU338534). The organization of the rRNA genes is LSU rRNA-ITS-SSU rRNA-IGS-5S, which corresponds with that of Nosema species closely related to Nosema bombycis. Phylogenetic analysis based on rRNA gene sequences show that this isolate is closely related to Nosema bombycis, Nosema plutellae, Nosema spodopterae, and Nosema antheraeae. The ultrastructure of all developmental stages of this microsporidium confirmed its placement in the genus Nosema. The isolate was successfully propagated in cell lines IPLB-LD652Y (Lymantria dispar) and NTU-LY (Lymantria xylina) and, in the in vitro system, it was frequently found to develop in the nuclei of the host cells, a circumstance that seldom occurs in other Nosema species. An extra-cellular vegetative stage of this microsporidium was also observed in the culture medium after 14 days of infection. The ECMDFs might be released from disrupted host cells.

Phylogenetic characterization of Encephalitozoon romaleae (Microsporidia) from a grasshopper host: relationship to Encephalitozoon spp. infecting humans

Encephalitozoon species are the most common microsporidian pathogens of humans and domesticated animals. We recently discovered a new microsporidium, Encephalitozoon romaleae, infecting the eastern lubber grasshopper Romalea microptera. To understand its evolutionary relationships, we compared partial gene sequences of alpha- and beta-tubulin and methionine aminopeptidase 2 enzyme from this and related species. We also analyzed the rRNA internal transcribed spacer. Based on tubulin and MetAP-2 gene phylogenetic analysis, E. romaleae clustered with the Encephalitzoon group with strong bootstrap support (>99%). Within the Encephalitozoon clade, E. romaleae clustered with Encephalitozoon hellem for both the beta-tubulin and MetAP-2 phylogenies based on ML tree. The alpha-tubulin based ML tree, however, placed the new microsporidium closer to Encephalitozoon cuniculi. The rRNA internal transcribed spacer region of E. romaleae has 91% homology with E. hellem.

The comparison of rDNA spacer regions of Nosema ceranae isolates from different hosts and locations

Nosema ceranae is a common microsporidian pathogen, one of two Nosema species that cause "nosema disease" in honeybees, Apis cerana and Apis mellifera. Samples of N. ceranae rDNA from isolates collected in different locations were sequenced and one 5S rRNA was found to be upstream of SSUrRNA. The rDNA arrangement, 5'-5S rRNA-IGS-SSUrRNA-ITS-LSUrRNA-3', was found in all isolates. In order to better understand the distribution relationship between N. ceranae isolates from A. cerana and A. mellifera, their rRNA spacer regions were also sequenced for analysis. Results showed that there are no significant differences between the IGS sequences of the isolates and no difference in the ITS sequence with the exception of one transition found in an isolate from Martinique. These isolates showed consistency in the IGS phylogenic analysis suggesting that no transmission barrier exists between A. mellifera and A. cerana and there is no difference between isolates from geography separated areas.