Physiological and Nutritional Studies with an Isolate of Leptolegnia sp. from the Freshwater Nematode Neomesomermis flumenalis

Abstract

The basic physiological responses and nutritional requirements for mycelial growth of an isolate of Leptolegnia sp. were determined. The optimum temperature was 19 C, and the optimum pH range was 4.7 to 5.7. The optimum level of vitamin-free casamino acids in the presence of glucose was 20 g/1, and the optimum glucose concentration was 8 g/1. When organic nitrogen sources were supplied either individually or as a mixture (vitamin-free casamino acids), &L-proline, L-arginine, L-histidine, L-threonine, L-serine, L-glutamic acid, glycine, L-leucine, L-alanine, L-glutamine, L-valine, and L-aspartic acid were utilized, L-phenylalanine, L-tyrosine, L-isoleucine, L-lysine, and L-a-amino-n-butyric acid were utilized only from the mixture and not as individual sources. Ammonium chloride functioned as a nitrogen source but neither potassium nitrate nor potassium nitrite were utilized, L-methionine (optimum concentration of 50 ppm) did not serve as either a carbon or a nitrogen source, but of the sulfur sources tested, it supported the best growth. Glucose, maltose, starch, glycogen, and sucrose were readily utilized as carbon sources. When glucose was omitted from a growth medium containing casamino acids, L-threonine, L-alanine, L-isoleucine, L-leucine, L-lysine, L-tryptophan, urea, L-serine, glycine, cysteic acid, L-aspartic acid, L-glutamic acid, and L-ornithine were utilized earlier than in the presence of glucose, and, thus, probably served as carbon sources. A requirement for a high level of organic nitrogen was also found when individual organic nitrogen sources were used in the presence of glucose, L-proline and L-alanine had optimum concentrations of 20 g (2400 mg N/1) and 7.5 g (1200 mg N/1), respectively. The optimal concentration for an inorganic nitrogen source was much lower. A basal medium adjusted to pH 5.2 and composed of glucose, methionine, potassium phosphate, a standard complement of micronutrients and either L-proline, L-alanine, or ammonium chloride was devised.