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The Non-Photosynthetic Algae Helicosporidium spp.: Emergence of a Novel Group of Insect Pathogens.

Tartar A - Insects (2013)

Bottom Line: The ability to produce large quantity of biological material has led to very significant advances in the understanding of Helicosporidium biology and its interactions with insect hosts.In particular, the unique infectious process has been well documented; the highly characteristic cyst and its included filamentous cell have been shown to play a central role during host infection and have been the focus of detailed morphological and developmental studies.In addition, phylogenetic analyses inferred from a multitude of molecular sequences have demonstrated that Helicosporidium are highly specialized non-photosynthetic algae (Chlorophyta: Trebouxiophyceae), and represent the first described entomopathogenic algae.

View Article: PubMed Central - PubMed

Affiliation: Division of Math, Science, and Technology, Nova Southeastern University, 3301 College Avenue, Fort Lauderdale, FL 33314, USA. aurelien@nova.edu.

ABSTRACT
Since the original description of Helicosporidium parasiticum in 1921, members of the genus Helicosporidium have been reported to infect a wide variety of invertebrates, but their characterization has remained dependent on occasional reports of infection. Recently, several new Helicosporidium isolates have been successfully maintained in axenic cultures. The ability to produce large quantity of biological material has led to very significant advances in the understanding of Helicosporidium biology and its interactions with insect hosts. In particular, the unique infectious process has been well documented; the highly characteristic cyst and its included filamentous cell have been shown to play a central role during host infection and have been the focus of detailed morphological and developmental studies. In addition, phylogenetic analyses inferred from a multitude of molecular sequences have demonstrated that Helicosporidium are highly specialized non-photosynthetic algae (Chlorophyta: Trebouxiophyceae), and represent the first described entomopathogenic algae. This review provides an overview of (i) the morphology of Helicosporidium cell types, (ii) the Helicosporidium life cycle, including the entire infectious sequence and its impact on insect hosts, (iii) the phylogenetic analyses that have prompted the taxonomic classification of Helicosporidium as green algae, and (iv) the documented host range for this novel group of entomopathogens.

No MeSH data available.


Related in: MedlinePlus

(A) Scanning electron micrograph of a diagnostic Helicosporidium cyst. (B) Transmission electron micrograph (cross section) detailing the core of three stacked ovoid cells (O) and the filamentous cell (F) contained within a pellicle (P).
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insects-04-00375-f001: (A) Scanning electron micrograph of a diagnostic Helicosporidium cyst. (B) Transmission electron micrograph (cross section) detailing the core of three stacked ovoid cells (O) and the filamentous cell (F) contained within a pellicle (P).

Mentions: Virtually all reports of Helicosporidium infection in invertebrate hosts rely on the observation of unique and characteristic four-cell structures [1,3,4,5,6,7,8,9,10,11,12,13]. These structures have been alternatively termed spores [1,3,4,5,6,7,9] or cysts [8,10,11,12,13]. Although the term spore was used during the original description of Helicosporidium parasiticum [1], and can still be found in occasional modern reports [9], most current studies, including this review, refer to the diagnostic feature of Helicosporidium as cyst. The Helicosporidium cyst is a barrel-shape structure that contains a core of three superposed ovoid cells surrounded by a single elongated, filamentous cell. These four cells are enclosed in a pellicle. The original H. parasiticum description featured elaborate drawings and microphotographs of the cyst and the filamentous cell [1]. Since then, electron microscopy photographs of the characteristic cyst have routinely been provided to support the identification of Helicosporidium in insect and other invertebrates. Recent reports of Helicosporidium sp. in various Coleopteran hosts, including the great European spruce bark beetle Dendroctonus micans (Coleoptera: Curculionidae), the predator beetle Rhizophagus grandis (Coleoptera: Rhizophaginae), and the weevil Cyrtobagous salviniae (Coleoptera: Curculionidae), all incorporated transmission electron micrographs (TEM) depicting cysts with the peripheral filamentous cell surrounding the three ovoid cells [10,11,12]. Cell measurements [7,8,10,12] indicated that the cysts are rather small, and range from 3 to 6 μm, although some of this variation might be due to differences in preparation methods [7]. Inside the cysts, the filamentous cell typically wraps around the core of ovoid cells three or four times, and can be distinguished on the narrow outer surface of the cysts (Figure 1).


The Non-Photosynthetic Algae Helicosporidium spp.: Emergence of a Novel Group of Insect Pathogens.

Tartar A - Insects (2013)

(A) Scanning electron micrograph of a diagnostic Helicosporidium cyst. (B) Transmission electron micrograph (cross section) detailing the core of three stacked ovoid cells (O) and the filamentous cell (F) contained within a pellicle (P).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4553470&req=5

insects-04-00375-f001: (A) Scanning electron micrograph of a diagnostic Helicosporidium cyst. (B) Transmission electron micrograph (cross section) detailing the core of three stacked ovoid cells (O) and the filamentous cell (F) contained within a pellicle (P).
Mentions: Virtually all reports of Helicosporidium infection in invertebrate hosts rely on the observation of unique and characteristic four-cell structures [1,3,4,5,6,7,8,9,10,11,12,13]. These structures have been alternatively termed spores [1,3,4,5,6,7,9] or cysts [8,10,11,12,13]. Although the term spore was used during the original description of Helicosporidium parasiticum [1], and can still be found in occasional modern reports [9], most current studies, including this review, refer to the diagnostic feature of Helicosporidium as cyst. The Helicosporidium cyst is a barrel-shape structure that contains a core of three superposed ovoid cells surrounded by a single elongated, filamentous cell. These four cells are enclosed in a pellicle. The original H. parasiticum description featured elaborate drawings and microphotographs of the cyst and the filamentous cell [1]. Since then, electron microscopy photographs of the characteristic cyst have routinely been provided to support the identification of Helicosporidium in insect and other invertebrates. Recent reports of Helicosporidium sp. in various Coleopteran hosts, including the great European spruce bark beetle Dendroctonus micans (Coleoptera: Curculionidae), the predator beetle Rhizophagus grandis (Coleoptera: Rhizophaginae), and the weevil Cyrtobagous salviniae (Coleoptera: Curculionidae), all incorporated transmission electron micrographs (TEM) depicting cysts with the peripheral filamentous cell surrounding the three ovoid cells [10,11,12]. Cell measurements [7,8,10,12] indicated that the cysts are rather small, and range from 3 to 6 μm, although some of this variation might be due to differences in preparation methods [7]. Inside the cysts, the filamentous cell typically wraps around the core of ovoid cells three or four times, and can be distinguished on the narrow outer surface of the cysts (Figure 1).

Bottom Line: The ability to produce large quantity of biological material has led to very significant advances in the understanding of Helicosporidium biology and its interactions with insect hosts.In particular, the unique infectious process has been well documented; the highly characteristic cyst and its included filamentous cell have been shown to play a central role during host infection and have been the focus of detailed morphological and developmental studies.In addition, phylogenetic analyses inferred from a multitude of molecular sequences have demonstrated that Helicosporidium are highly specialized non-photosynthetic algae (Chlorophyta: Trebouxiophyceae), and represent the first described entomopathogenic algae.

View Article: PubMed Central - PubMed

Affiliation: Division of Math, Science, and Technology, Nova Southeastern University, 3301 College Avenue, Fort Lauderdale, FL 33314, USA. aurelien@nova.edu.

ABSTRACT
Since the original description of Helicosporidium parasiticum in 1921, members of the genus Helicosporidium have been reported to infect a wide variety of invertebrates, but their characterization has remained dependent on occasional reports of infection. Recently, several new Helicosporidium isolates have been successfully maintained in axenic cultures. The ability to produce large quantity of biological material has led to very significant advances in the understanding of Helicosporidium biology and its interactions with insect hosts. In particular, the unique infectious process has been well documented; the highly characteristic cyst and its included filamentous cell have been shown to play a central role during host infection and have been the focus of detailed morphological and developmental studies. In addition, phylogenetic analyses inferred from a multitude of molecular sequences have demonstrated that Helicosporidium are highly specialized non-photosynthetic algae (Chlorophyta: Trebouxiophyceae), and represent the first described entomopathogenic algae. This review provides an overview of (i) the morphology of Helicosporidium cell types, (ii) the Helicosporidium life cycle, including the entire infectious sequence and its impact on insect hosts, (iii) the phylogenetic analyses that have prompted the taxonomic classification of Helicosporidium as green algae, and (iv) the documented host range for this novel group of entomopathogens.

No MeSH data available.


Related in: MedlinePlus