Starch Hydrolysis and Fermentation by the Yeast Endomycopsis Fibuliger

Abstract

Yeasts are generally considered to be unable to ferment starch. This lack of diastatic activity is the reason for the use, in fermentation industries, of barley-malt and fungal diastase preparations for the conversion of starchy substrates to sugars which may be attacked by the yeasts. If there should exist in nature yeasts which possess active amylase systems, they might be of much scientific and industrial interest. Investigations by the authors have revealed pronounced diastatic activity by strains of the species Endomycopsis fibuliger, and the present paper presents these studies. The literature regarding the utilization of starchy substrates by yeasts and the physiological properties of yeasts of the species E. fibuliger is sparse. Guil-liermond and Tanner (1920) state that some yeasts, such as "S. exiguus ther-mantitonum, acetethylicus, Sch. pombe, mellacei, octosporus, the yeast of Logos, and some yeasts of Saaz and Mycoderma sphaeromyces" are able to ferment starch. No demonstrable-fermentation of starch has been found to occur, however, when these species are inoculated into a starch medium which is an adequate substrate for starch hydrolysis by other organisms of proved diastatic ability. Dull (1933) demonstrated the weak diastatic activity of several yeasts, including Saccharomyces cerevisiae, by flooding petri dishes containing a month-old colony with iodine solution. This was probably an evidence of intracellular amylase liberated upon autolysis of the cells, a necrobiotic reaction analogous to that shown by Beijerinck (1898) in the liquefaction of gelatin by intracellular enzymes from ruptured asci. Although strains of the species Endomycopsis fibuliger have been known for 36 years, their ability to attack starch has not been recognized. Lindner (1907), who originally isolated from spoiled bread a filamentous yeast which he named Endomyces fibuliger, reported that this organism fermented sucrose strongly, glucose less strongly, raffinose and lactose weakly, and maltose and dextrin not at all. Dombrowski (1909) reported that the yeast isolated by Lindner did not produce diastase. Saito (1913) described two new yeasts, Endomyces lindneri and Endomyces hordei, which resembled E. fibuliger to a marked degree, but differed from it in their action on carbohydrates; the new yeasts fermented maltose and dextrin, whereas E. fibuliger did not. Neither E. lindneri nor E. hordei was reported to attack starch. Stelling-Dekker (1931) reduced Saito's 1 This is one of four regional laboratories operated by the Bureau