NEMATOPHAGOUS ACTIVITY ON MOSS AS CULTURAL SUBSTRATUM OF Arthrobotrys tortor Jarowaja ISOLATED IN ANTARCTICA

Mycological investigations of Antarctic material coIlected in localities ofthe Mid Victoria Land during the Italian antarctic expeditions (1988-1993) have indicated that the highest ocurrence of fungi was recorded from mosses and soil when mosses were present. Acremonium strictum W. Gams, Engyodontium alhum (Limber) De Hoog, Paecilomycesfarinosus (Holm) Brown & G. Sm., and Arthrohotrys tortor Jarowaja were only or mainIy isolated from soil moss (Del Frate and Caretta, 1990). The rooss was shown to be an optimal substratum suitable for the growth of these fungi particularIy for A. tortor. In cultural laboratory experiments the growth ofthese fungus within 5 days at a range of temperatures between 5 and 25° C. This fact was previously reported by Duddington (1951); bryophytes, especiaIly when moist, have proved to be the most fruitful material for supplying predacious fungi, asA. oligospora Fres. andA. rohusta Duddington. A. robusta was recorded by (Gray et al., 1982; Gray & Srnith 1984; Gray, 1985), as nematophagous fungus froro the maritime antarctic; this species ofArthrohotrys was only isolated froro bird-associated sites. In RESUMEN


INTRODUCTION
Mycological investigations of Antarctic material coIlected in localities ofthe Mid Victoria Land during the Italian antarctic expeditions (1988)(1989)(1990)(1991)(1992)(1993) have indicated that the highest ocurrence of fungi was recorded from mosses and soil when mosses were present.Acremonium strictum W. Gams, Engyodontium alhum (Limber) De Hoog, Paecilomycesfarinosus (Holm) Brown & G. Sm., and Arthrohotrys tortor Jarowaja were only or mainIy isolated from soil moss (Del Frate and Caretta, 1990).The rooss was shown to be an optimal substratum suitable for the growth of these fungi particularIy for A. tortor.In cultural laboratory experiments the growth ofthese fungus within 5 days at a range of temperatures between 5 and 25° C.This fact was previously reported by Duddington (1951); bryophytes, especiaIly when moist, have proved to be the most fruitful material for supplying predacious fungi, asA.oligospora Fres.andA.rohusta Duddington. A. robusta was recorded by (Gray et al., 1982;Gray & Srnith 1984;Gray, 1985), as nematophagous fungus froro the maritime antarctic; this species ofArthrohotrys was only isolated froro bird-associated sites.In
Continental Antarctica, two species of Arthrobotrys were isolated, both from moss. A. tortor (Caretta et al. , 1994) andA.ferox a new predaceous hyphomycete ofthe springtail Gressittacantha terranovae (Onofri & Tosi, 1992).A. tortor was isolated originally by Jarowaja (1968) from sandy garden soil from Swider (Warsaw) and reported as a nematophagous fungus.In a subsequent survey of predaceous fungi in Poland (1970), seven strains of A. tortor were isolated by Jarowaja from loess soil; two of them were nematophagous, trapping nematodes by means of adhesive threedimensional nets.
In this work predatory activityofA.tortor, antarctic strains was studied.Organs and way of capture of live .nematodes have been demonstrated on a plate culture containing the fungus, the nematodes feeding on bacteria and the moss as a natural substratum for the fungus.

MATERIAL AND METHODS
A strain of A. tortor isolated from moss sampit:s coIlected in 1988 at Edmondson Point (Mid victoria Land, Ross Sector 160-170° E) and cultured at 15° C on malt extract agar (MEA formula I Oxoid) was used.A series of sterile plates has been prepared as follows : water agar plates (in 12 g of agar in l litre of water, sterilized and poured into 9 cm Petri dishes, 15 mIlplate) with the moss (Brachytecium rutabulum (Hedw.)Bruch et al.) previously sterilized and dispersed on the agar surface.Another series of pi ates was prepared, according to Duddington technique (l955),by using coro meal agar (Oxoid) as a medium to which the moss was added.Nematodes were collected from rabbit dung by means of the Baermann Funnel technique reported in Goodey (1949), and identified in the genus Rhabditis Dujardin; bacteria were always present in the plate, to provide food for the nematodes.
Fungus, nematodes and bacteria' inoculations were completed in all plates of the two series by using these procedures.A. tortorwas appliedas a conidial suspension, and by rnicelial disks, both from a 72-hr-old culture ofthe fungus.A conidial suspension was prepared from conidia collected from cultures grown in Erlenmeyer flasks containing 20 mI of MEA.The suspension \vas washed in sterile tap water by centrifugation (1500 g) and adjusted to lxlO6 conidia per millilitre and sprinkled on moss.Micelial disks from MEA cUlture were placed in the center of Petri plates.Nematodes and bacteria cultured on coro meal agar were transferred to the plates by using a sterilized spatula.The plates were incubated at 20c.°

RESULTS
Leaves and stems of Brachithecium were swiftly colonized by the fungus (fig.1).On the moss, A. tortor developed and sporulated abundantly, both in the.coro meal agar plates and in the water agar plates.It was possible to distinguish two different morphological aspects ofthe fungus; on the agar and on the moss.On the agar surface the fungus gave rise to three-dimensional adhesive networks and hyphal loops, generally in an upright position above the generallevel ofthe mycelium, according to the description of Jarowaja (1968Jarowaja ( , 1970)).Abundant nematode-graveyards have been observed in areas with a lot oftrapping organs.On moss the fungus formed strong and •thick fasciculate aerial hyphae on which drops or sheath of sticky secretion were evident.AH over the moss the aerial hyphae of the fungus was organized in a sort of spider's web.
Adhesive networks, developing by anastomosis of the recurved branch tips, were common, but simple adhesive loops were more frequent (fig, 2, 3, 4).Coiled hyphae arranged on one plane, were also boro by the fasciculate hyphae.Nematodes crawling on the aerial mycelium were observed, and many of them have thrusted their bodies into such a loop or have become.tightly wedged insideit (fig. 5, 6,7, 8,10).Trappingorganswere distributed a1l over the moss as well as on the thick and 38 strong fasciculate hyphae extending fron one leaf moss to another.Drops of mucilaginous material along the hyphae and above all of the hyphal branches have been observed.Microscopical observation of the mucilagineous drops have revealed the presence of eggs (fig.9), spawned at interval along the aerial hyphae, or young swirnrning nematodes.

DISCUSSION
Arthrobotrys Corda, is known to be one ofthe most .interesting genus because ofits many predaceous species.
As mentioned by van Oorschot (1985), various types of trapping organs are produced by different species of Arthrobotrysj three species produce constricting rings .andA.entomopagaDrechsler,A.ItaptosporaDrechsler and A. ferox, produce adhesive knobs.Nematode traps are intimately connected witn an adhesive phase that appears to be a .prerequisitefor organisms to penetrate and colonize the host in the more general panisiticsymbiotic relationships (Tunlid et al., 1992).Trapping organs do not develop in pure culture; the addition of nematodes or their extracts induces the development of them within 24-48 hr (Duddington, 1955;Pramer & Stollm, 1959;Nordbring-Herz, 1973).This fact shows that the series of interaction events between nematode and predaceous fungi may be initiated by a chemotactic/ chemotropic response occuring at sorne distance from . the host.Tunlid et al. (1992) reviewed several of the interaction steps in the nematode-nemotophagous attachment ofthe fungi to nematodes and the biological and biochemical/molecular background to this adhesion.The above mentioned observations were conducted in cultural experiments on agar or liquid media.In our work the nernatophagous activity of the fungus is studied on moss.
In the extreme dryness and low temperature conditions of Antarctica, the moss cushions are cornfortable habitat.Moss can retain much water in its capillary spaces,.formed between the partly overlapping leaves and the stems.These spaces possess considerable suction power and capacity (Overgaard, 1948).Moreover solar radiation on the water droplets in the moss may increase the temperature values.Thesefacts can help to realize the life cycle of antarctic moss-fauna-mycobiota.
A. tortor and nematodes, are two important components in the antarctic moss biotope and closely related to it.Rhabditis is a nematode genus previously recorded for Antarctica (Vinciguerra etal., 1989) The study oftheA.tortor ability to form nematode trapping organs on moss, revealed new aspects in the relationships between the fungus, nematodes and the moss.The architecture of the ' furigal mycelium and ' disposition of trapping organs on the moss have been pointed out. A. tortor, captures nematodes not only by means of threedimentional adhesive nets and loops but also of the entire adhesive fasciculate aerial hyphae complexo It can be supposed the coiled hyphae, that are usually present in our strains, are a new kind oftrapping organ, although nematodes have never been seen captured by such a structure.Moreover, the nematode is not only a prey for the fungus but it seems to utilize the fungus as a support for its eggs and larvae.It can be argued that eggs have more protection aboye the general soillevel, being far from soil dangerous bacteria and other organisms.A possible equilibrium might be established between nematodes and the predacious fungus in this peculiar and limited habitat.Further researches will be carried out in order to studythe econutritional relationships betweenA.tortor and nematodes in Antarctica.