Nutritional requirements of the nematophagous fungus Hirsutella rhossiliensis

Six natural media were examined for growth and sporulation of six isolates of the nematophagous fungus Hirsutella rhossiliensis, using solid and/or liquid culture. Twenty carbohydrates, 19 nitrogen (N) compounds, and nine vitamins were also tested for their effects on growth, sporulation, and spore germination of a further three isolates (ATCC46487, OWVT-1 and JA16-1). Variations in nutritional requirements existed among the fungal isolates. In general, V-8 juice agar (VA), cornmeal agar and potato dextrose agar were good media for growth, and malt extract agar, VA and yeast dextrose agar were good for sporulation of all six isolates. Glycogen was the best and sucrose, inulin, D-(+)-trehalose and soluble starch were also good carbon (C) sources for growth and spore germination of the three isolates ATCC46487, OWVT-1 and JA16-1 in both liquid and solid culture. None of the isolates utilized D-(+)-xylose as a C source. L-sorbose, D-ribose, citric acid and D-fructose were poor for growth of all isolates. The best C source for sporulation was D-(+)-trehalose for ATCC46487, D-sorbitol for OWVT-1 and D-(+)-cellobiose for JA16-1. Casein was the best N source for growth of ATCC46487 and OWVT-1, while peptone was best for JA16-1. L-asparagine, L-proline, and peptone were also good for growth of all three isolates. L-cystine was not utilized by H. rhossiliensis and DL-methionine inhibited growth of all isolates. Spore germination of all isolates was well supported by most N compounds examined but was inhibited by L-cystine. No significant difference in sporulation of ATCC46487 was observed among the N sources. DL-threonine was the best N source for spore production by OWVT-1 and L-phenylalanine was best for JA16-1. Vitamins generally enhanced fungal growth and sporulation, with thiamine having the greatest influence. Excluding some vitamins individually from the medium containing all other test vitamins sometimes increased growth and/or sporulation of certain isolates.