Sunday 18 December 2022

Drechslerella daliensis & Drechslerella xiaguanensis: Two new species of predatory Fungi from Yunnan Province, China.

Predatory Fungi are important controls on Nematode populations in many soil ecosystems. The majority of these Fungi belong to the Ascomycote Family Orbiliaceae, which currently includes 116 predatory species, divided into three genera. Arthrobotrys, which contains 67 species, and which traps Nematodes in a network of sticky hyphae, Dactylellina, which contains 34 species and which captures Nematodes with sticky knobs, and Drechslelrella, which contains 15 species, and which produces constricting rings, used to trap Nematodes in a lasso-like action.

The genus Drechslelrella was first described by the Indian mycologist Chirayathumadom Venkatachalier Subramanian in 1963, and has been found in a wide variety of ecosystems, including forest soils, Mangrove sediments, freshwater sediments, brackish water sediments, heavy metal polluted areas and even in tree trunks and animal faeces. They are typically found in the upper part of the soil or overlying humus layer, where the density of Nematodes appears to be highest. The constricting rings produced by these Fungi are made up of three cells, which swell rapidly when a Nematode is detected. 

In a paper published in the Biodiversity Data Journal on 16 December 2022, Fa Zhang of the Institute of Eastern-Himalaya Biodiversity Research at Dali University, and the Center of Excellence in Fungal Research and School of Science at Mae Fah Luang UniversitySaranyaphat Boonmee, also of the Center of Excellence in Fungal Research and School of Science at Mae Fah Luang University, Jutamart Monkai, again of the Center of Excellence in Fungal Research at Mae Fah Luang University, and Xiao-Yan Yang and Wen Xiao, also of the Institute of Eastern-Himalaya Biodiversity Research, and of the Key Laboratory of Yunnan State Education Department on Er’hai Lake Basin Protection and the Sustainable Development Research, at Dali University, describe two new species of Drechslerella from fire-disturbed forest soil from the slopes of Cangshan Mountain, to the west of Dali city in Yunnan Province, China.

The new Fungi were cultivated from soil samples spread on agar, and prompted to produce traps by the introduction of the free-living Nematode Panagrellus redivivus as bait. They were confirmed as new species by the extraction of DNA, and comparison to other species on the GenBank database, using the BLASTn online tool. The phylogenetic relationships of the new species were established using the MrBayes software package.

The first new species is named Drechslerella daliensis, where 'daliensis' means 'from Dali', in reference to the city. This Fungus formed white, cottony colonies on the cultivation medium, reaching a diameter of 50 mm after 18 days. Two types of conidia (spore producing bodies) were produced, both on conidiophores (conidia-bearing hyphae) 125-335 µm in length. The macroconidia were roughly 20-49.5 µm long and 8.5-15 µm wide, smooth, ellipsoid, broadly rounded at the apex and truncated at the base. The microconidia were 6.5-22 µm long and 3.5-7 µm wide, smooth, clavate or bottle-shaped, broadly rounded at the apex and truncated at the base. Drechslerella daliensis was observed to trap Nematodes with constricting rings on stalks 5.5–11 µm long, with an outer diameter of 21–32 µm and an inner diameter of 2–21 µm.

Drechslerella daliensis (holotype, CGMCC3.20131). (a) Culture colony; (b), (c) Macroconidia; (d) Microconidia; (e) Constricting rings; (f), (g) Conidiophores. Scale bars: (a) 1 cm; (b)–(g) 10 µm. Zhang et al, (2022).

The second species is named Drechslerella xiaguanensis, where 'xiaguanensis' means 'from Xiaguan' in reference to the district where the soil samples were collected. This Fungus also formed white, cottony colonies on the growth medium, reaching 50 mm in diameter after 15 days. The conidia of this species were born on conidiophores 145-315 µm in length, with a single type of conidia being produced, these being 33-52 µm in length and 9.5–28 µm in width. Constricting rings were born on stalks 5–11.5 µm long, and had an outer diameter of 19–27.5 µm and an inner diameter of 12.5–20.5 µm.

Drechslerella xiaguanensis (holotype, CGMCC3.20132). (a) Culture colony; (b), (c) Conidia; (d) Germinating conidia; (e) Constricting rings; (f), (g) Conidiophore. Scale bars: (a) 1 cm; (b)–(g) 10 µm. Zhang et al. (2022).

The phylogenetic analysis confirmed that both species could be placed within the genus Drechslerella, with Drechslerella daliensis being recovered as the sister species to Drechslerella hainanensis, known from Hainan, an island province of China in the South China Sea, and Drechslerella xiaguanensis as the sister species to Drechslerella bembicodes, a species from New Zealand.

Maximum Likelihood tree, based on combined ITS, TEF1-α and RPB2 sequence data from 42 Nematode-trapping taxa in Orbiliaceae. Bootstrap support values for Maximum Parsimony (red) and Maximum Likelihood (black) equal or greater than 50% and Bayesian posterior probabilities values (green) greater than 0.90 are indicated above the nodes. New isolates are in blue, ex-type strains are in bold. Zhang et al. (2022).

Zhang et al. note the the network of sticky hyphae used by the genus Arthrobotrys appears to be a more efficient trap than the methods used by Drechslerella or Dactylellina, and that, under normal circumstances, this genus is the most abundant in the upper soil layer, where Nematodes are most abundant. However, in the fire-damaged forest soils, the reverse appeared to be the case, with Arthrobotrys almost absent, while Drechslerella and Dactylellina are abundant. They theorise that in this environment, Arthrobotrys has been killed off by the burning of the upper soil layer, allowing the other two genera to invade rapidly from colonies in deeper soil layers.

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