Zoospore Chemotaxis in the Rumen Phycomycete Neocallimastix frontalis

Abstract

Neocallimastix frontalis zoospores showed chemotaxis to a range of carbohydrates, but not to the common amino acids, purines, pyrimidines or vitamins. Four chemoreceptors were identified : the glucose receptor, sensitive to D-glucose, D-galactose, D-XylOSe, L-sorbose, D-fucose and a-deoxy-~-g~ucose; the sucrose receptor, sensitive to sucrose, D-fructose and raffinose; the mannose receptor, sensitive to u-mannose and D-glucose; and the sorbitol receptor, sensitive to D-sorbitol and D-mannitol. Growth of the vegetative stage of N . frontalis did not occur with D-xylose, L-sorbose, D-fucose, 2-deoxy-~-glucose, raffinose, u-mannose or D-sorbitol. The zoospores were attracted to carbohydrate mixtures representing the soluble carbohydrates found in different barley tissues; the highest response was with those mixtures representing carbohydrates of awn and inflorescence tissue. Chemotaxis also occurred preferentially to the awn and inflorescence tissue carbohydrate combinations rather than to carbohydrate combinations representing other tissues. Germination of the zoospores occurred in medium containing glucose in excess of I O -~ M. I N T R O D U C T l O NThe flagellated zoospores of the rumen phycomycete fungus Neocallimastix frontalis are released from sporangia borne on the vegetative stage of the organism soon after the host animal eats (Orpin, 1975). The zoospores may invade, germinate upon and grow at the expense of plant tissue present in the rumen (Orpin, 1977). Not all plant tissues are invaded by the zoospores to the same extent; a marked preference is shown for inflorescence tissue where the zoospores germinate principally at the stomata and on damaged areas. Growth of the single rhizoid results in penetration of the plant tissue through the stoma or damaged epidermis. Because of the marked substratum selection shown by the zoospores and their germination at the stomata, chemotaxis was thought likely to be operative. The chemotactic response of N . frontalis zoospores with a range of carbohydrates, amino acids, purines, pyrimidines and vitamins has now been examined. On the basis of these results, a mechanism is suggested for the preferential attraction of the zoospores to inflorescence tissues of grasses in the rumen. M E T H O D SAnimals. Sheep, Clun Forest wethers, each fitted with a permanent rumen cannula, were fed I kg hay chaff and IOO g rolled oats daily.Preparation of rumen fluid and zoospore suspensions in fresh rumen fluid. Centrifuged rumen fluid and sterile reduced rumen fluid supernatant were prepared according to Orpin (1977). Rumen fluid, used as a 8-2

Comparison of growth characteristics of anaerobic fungi isolated from ruminant and non-ruminant herbivores during cultivation in a defined medium

“…Orpin & Bountiff (1978), supported by Bauchop (1979), suggest that anaerobic fungi are the initial colonizers of forage fibre in the rumen. In vivo anaerobic rumen fungi may represent up to 8 % of the microbial biomass (Orpin, 1983(Orpin, / 1984).…”

“…Zoospores of anaerobic fungi invade freshly ingested plant tissue (Orpin & Bountiff, 1978), and the vegetative stadia closely associate with, and grow at the expense of, plant particles (Lowe et al, 1987b). The anaerobic fungi produce a range of cell-bound and extracellular polysaccharide-degrading enzymes which participate in the digestion of food particles (Lowe et al, 1987b;Williams & Orpin, 1987).…”

The Role of Haems and Related Compounds in the Nutrition and Zoosporogenesis of the Rumen Chytridiomycete Neocallimastix frontalis H8

“…Detached sporangia occur in the rumen liquor, probably broken from rhizoids during the mastication of infected digesta during rumination. Orpin (1978a) reported that one isolate of N . frontalis (strain H8) grew in a defined medium, provided haemin was included.…”

“…frontalis H8. (1979) and in the defined medium of Rochk et al (1973) modified according to Orpin (1978a), using cellobiose as carbon source. Cultures were maintained by daily sub-culture, using a 10% inoculum into fresh medium.…”

Ecologie et fonctions des champignons anaérobies du rumen

“…Quatre chimiorécepteurs ont été mis en évidence (Orpin et Bountiff, 1978) Akin, 1987b (Orpin, 1975(Orpin, , 1976(Orpin, , 1977cFonty et al, 1987). Le dosage de la chitine, constituant spécifique des parois fongiques, est fiable pour des cultures pures (Orpin, 1977b ; (Orpin, 1981 b).…”