A preliminary study of the nutritional requirements of Myxotrichum uncinatum
Certain nutritional requirements of one strain ofMyxotrichum uncinatum were established. Growth was measured on a dry weight basis. The approximate optimum medium for growth consisted of 5% KNO3, 4% sucrose, 0.1% K2HPO4, 0.05% MgSO4. 7 H2O, 0.2 mg % biotin and 1.0 mg % uracil. The best initial pH range was 6.0–7.0. Approximately three to five days incubation on a rotary shaker permitted excellent growth.
Comparative physiology of some representatives of the gymnoascaceae
A comparative nutritional study was made of the following fungi:Arachniotus reticulatus, Myxotrichum uncinatum, Eidamella deflexa, Gymnoascus reessii, Ctenomyces serratus andPenicillium spiculisporum. Sodium nitrate, ammonium nitrate, ammonium sulfate, asparagine, glycine, casein hydrolysate and an amino acid mixture were supplied singly as sources of nitrogen. All of the fungi grew on the organic nitrogen sources. The amino acid mixture was the best source for growth ofM. uncinatum, G. reessii, C. serratus andA. reticulatus. Asparagine was the best source forE. deflexa andP. spiculisporum, although the latter grew on all 7 sources of nitrogen tested. Of the inorganic nitrogen sources tested sodium nitrate was assimilated only byM. uncinatum andE. deflexa. Glucose, fructose, galactose, maltose, sucrose, lactose, raffinose, xylose, dextrin and sodium lactate were the ten carbon sources which were tested.Myxotrichum uncinatum failed to assimilate only lactose, and grew best on raffinose, dextrin and sucrose.Eidamella deflexa used all carbohydrates but not sodium lactate.Gymnoascus reessii either did not grow at all or else grew only poorly on all carbon sources tested.Ctenomyces serratus assimilated only fructose.Arachniotus reticulatus grew on maltose, fructose and glucose in that order.Penicillium spiculisporum used galactose, sucrose, xylose, glucose, maltose, dextrin and raffinose and failed to use lactose and sodium lactate. Thiamin, biotin, inositol, pyridoxine and calcium pantothenate were used in vitamin requirement studies.Myxotrichum uncinatum andEidamella deflexa appeared to be autotrophic for all vitamins,G. reessii was heterotrophic for biotin and pyridoxine,C. serratus for thiamin andA. reticulatus for thiamin and pyridoxine.Penicillium spiculisporum showed a partial deficiency for pyridoxine and pantothenate. The trace elements which were tested included iron, zinc, copper and manganese. Probably only the results withE. deflexa are valid since the carbon and nitrogen sources were inadequate forG. reessii, C. serratus andA. reticulatus. Zinc and copper were essential for growth ofE. deflexa. Manganese and copper seemed essential for growth ofP. spiculisporum, while zinc was toxic.
The assimilation by plants of various forms of nitrogen
SOME YEARS AGO (1926) the author became interested in the possible effect of hydrogen-ion concentration on the assimilation by plants of nitrogen as ammonia or as nitrate. In an experiment 2 designed to attack this problem, mineral nutrient solutions containing dextrose were prepared in which the nitrogen was furnished as ammonium nitrate, ammonium sulfate, or sodium nitrate, and the hydrogen-ion concentration of the solutions was varied by intervals of 0.2 or 0.3 pH from pH 4.0 to pH 7.6. The organism used, Rhizopus nigricans, grew well at all reactions in the solutions which contained ammonium sulfate or ammonium nitrate (somewhat better in the more alkaline solutions) but not at all in those which contained sodium nitrate. This confirmed earlier reports (Bach, 1927; Ritter, 1909) of the inability of Rhizopus nigricans to assimilate nitrogen as nitrate (at least under ordinary laboratory conditions) and encouraged the writer to plan an investigation of the ability of organisms to use various forms of nitrogen. Circumstances made it impossible to carry out the investigation as planned. Nevertheless, the preliminary work may be of sufficient interest to encourage further investigations in this field. A survey of the literature (space precludes summarizing all the available literature) suggested to the author that organisms may be arranged in four groups 3 according to their ability to assimilate various forms of nitrogen. GROIJP I. NITROGEN-FIXING ORGANISMS. These organisms are capable of assimilating gaseous nitrogen and also nitrates, ammonium salts, and certain organic nitrogenous compounds. Attention should be called to the assumption that everv organism capable of fixing gaseous nitrogen is capable also of assimilating nitrogen in the form of nitrates, ammonium compounds, and 'suitable forms of organic nitrogen. Though the evidence available supports it, this assumption needs further confirmation since considerably more attention has been devoted to the relation to gaseous nitrogen of the organisms generally accepted as nitrogen fixers than to their ability to assimilate combined nitrogen. However, it is generally agreed (Waksman, 1927; Lohnis, 1926; Stephenson, 1930) that Azotobacter can assimilate nitrogen as nitrates, as ammonium salts. and as orgLanic nitrogen (for