Dactylellina haptotyla

Dactylellina haptotyla is a common soil-living fungus that develops structures to capture nematodes as nutrient source. In the presence of nematodes, spores can germinate into sticky knobs or non-constricting loops. The fungus traps nematodes with sticky knobs and non-constricting loops, then breakdown the cuticle, and penetrates the body of nematodes to obtain nutrients. For its predatory nature, Dactylellina haptotyla is also considered as nematode-trapping fungus or carnivorous fungus. Dactylellina haptotyla belongs to the family Orbiliaceae. Before nematode-trapping fungi were studied phylogenetically, Dactylellina haptotyla had been classified with more than five synonyms, and it is commonly known as Arthrobotrys candida, Monacrosporium haptotyla and Dactylella haptotyla. The classification was ambiguous because the fungus does not form non-constricting loops all the time. For example, M. candidum and M.yunnanense form stalk adhesive knobs and non-constricting rings, while M. sclerohypha and M.haptotylum only form adhesive knobs. Yet, these four species are all synonyms of Dactylellina haptotyla. In 1999, the carnivorous fungi of Orbiliaceae has been reclassified based on rDNA and β-tubulin datasets. Nematode-trapping fungi can be grouped into four monophyletic clade (Arhtrobotrys, Monacrosporium, Dactylella and Dactylellina) which correspond to their nematode-trapping structures. Therefore, Dactylellina haptotyla has been classified as genus Dactylellina because of its non-constricting loops and sticky knobs structure. Dactylellina haptotyla can be isolated on corn meal agar. After fifteen days of incubation, the colour of colonies changes from hyaline (unpigmented) to whitish or faintly pink colour. Colony diameter can expand by 4 cm at 25 °C within 10 days. Conidiophores are hyaline branches that are constructed by 5-7 septate. It is about 100–335μm long, 2–3.7 μm wide at the base. 2-12 (mostly 3-5) branches can grow near apex with conidia. Macroconidia are also hyaline and in spindle-shape (truncate at the base and narrow down at the basal end). It is usually constructed by 2-5 septate, and approximately 27.5–57.5 × 7.5–12.5μm2 (mostly 35 × 9μm2) in size. No chlamydospores have been observed in cultures. The spindle spores can develop into adhesive knob in the presence of nematodes. The adhesive knob is a globose adhesive cell locates at the end of non-adhesive stalk which is composed by one to three cells. The adhesive knob contains membrane-bound vesicles which is approximately 0.2-0.5μm. The other trapping structure, non-constricting loop, is constructed by three cells which elongate from stalk and fuse back to base. The inner area of the loop is sticky. Dactyllelina haptotyla traps nematodes by adhesive knobs and non-constricting loops. When nematodes thrust into non-constricting loops or adhesive knobs, the trapping structures wedge the nematodes by the sticky surface. Nematodes struggle and sometimes become more tightly wedged because they contact other loops or knobs. In some cases, the struggle may be so violent that the nematode can escape and detach the knobs or loops from stalks. The detached knobs or loops stay on the nematode's body and travel along. Eventually, the fungus will paralyze and digest the nematode. Evolutionary, this assist the Dactylellina haptotyla to migrate to new sites and explore food sources.