Comparative studies of the physiology of Sapromyces and related genera.

In recent years increasing attention has been directed to nutritional and physiological characteristics as an aid in tracing phylogenetic relationships among aquatic phycomycetes; and as a result of this interest, reports on the physiology of the group have become increasingly numerous. An exception has been the leptomitales, on which the last report was made over a decade ago by Schade and Thimann (1940). Moreover, their work and that of their predecessors were concerned with only one family in the order, the leptomitaceae. As a result, very little, if any, data are available on the second important family in the leptomitales, the rhipidiaceae. Among the leptomitaceae, Leptomitus lacteus has received the most attention, probably because of its role in sewage treatment and consequent greater frequency of being encountered. One of the earliest studies on the nutrition of the organism dates back to Kolkwitz (1903), who was interested in the organism because of its possibilities as a biological indicator in sewage influent. He concluded from his observations that the organism grew best on complex organic nitrogen compounds and less satisfactorily on amino acids. Tiegs and Dorries (1926) gave evidence that, as Kolkwitz had maintained, albuminoid material and other high molecular compounds constituted the most favorable nitrogen and carbon sources. In a study of the nutrition of L. lacteus and Apodachlya brachynema, Schade (1940) demonstrated that both organisms could use only organic compounds as sources of nitrogen. He also showed that A. brachynema was limited to three of the five sugars tested (glucose, fructose, and sucrose), and confirmed Kolkwitz's finding that L. lacteus is unable to utilize sugars as carbon sources. The latest published report on the leptomitaceae was the result of a quantitative analytical study on the metabolism of L. lacteus by Schade and Thimann (1940). They were able to demonstrate that DL-alanine underwent oxidative deamination, whereas leucine was partially oxidixed to a product of the stage of oxidation of alanine, which was then assimilated. Especially noteworthy are their observations on the fate of the inorganic ammonium ion. They showed that when oxidative assimilation of fatty acids was taking place, ammonia was absorbed from the medium and converted to an assimilation product. However, such assimilation did not result in the increase in dry wt to be normally expected from the amount of nitrogen used. The organisms studied in the present investigation were Sapromyces elongatus (Cornu) Coker, Rhipidium sp., and Apodachlya sp. Sapromyces and Rhipidium were selected because their physiology had not been studied previously and because such a study would make possible a comparison between two of the important genera constituting the rhipidiaceae. Apodachlya sp. was added because, as a representative of the leptomitaceae, it could be used in comparing the leptomitaceae and the rhipidiaceae.