Weexaminedthe changeof the compositionof the cell wall polysaccharides prepared from cells of the salt-tolerant yeast Zygosaccharomycesrouxii grown in two media containing 20%NaCl and 0%NaCl.Comparative analysis of their walls showedthat the wall obtainedfromsalt-free medium had greater quantities of alkali-insoluble fraction and smaller quantities of mannanthan the walls obtained from 20%NaClmedium.The alkali-insoluble fractions from the cell walls obtained from salt-free mediumcontained a large amountof glucosamineand a smaller amount of linear /M,3-glucosidic linkage than the fractions from the cell walls obtained from 20% Nap medium. Structural analyses showed that the mannans from each cell wall contained an a-l,6-mannbsidic linked backbone to which single mannoseand mannobiose units were connected as side chains by a-l,2-mannosidic linkages. However, when cells were grown in the presence of 20% NaCl, the side chains of the mannans consisting of a mannobiose unit were largely reduced.These results indicated that the structure of alkali-insoluble glucan and mannanwere greatly affected by the presence of NaCl in the final medium.It is well known that Zygosaccharomyces rouxii, a salt-tolerant yeast, is important for the fermentation of shoyu and miso. It has been reported that the shape ofZ. rouxii cells change from spherical to spheroidal with an increase in NaClconcentration of the mediumand the chemical structure of cell walls may play some role in the regulation of the shape of cells under the salt-stress condition.1>2) In spite of many investigations on the structure of the cell wall mannans from Z. rouxii,2~5) there has been no report on the comparison of the other carbohydrate composition of the cell walls under the salt-stress conditions. The purpose of this paper was to compare the chemical composition and the structure of cell wall polysaccharides obtained from cells of Z. rouxii before and after a shift to the presence of 20% NaCl and to the absence ofNaCl.
Materials and MethodsOrganisms and culture methods.Zygosaccharomyces 2757 rouxii IFO-505wasmaintained in a refrigerator on an agar slant containing (w/v) yeast extract (1%), peptone (1%), glucose (2%) (YEPD), and NaCl (18%). First, the cells were transferred to YEPD-agar medium with or without 20% NaCl, and cultivated at 30°C for 3 days. For preculture, the cells were transferred from the agar media to YEPDmedium with (20% NaCl medium) or without salt (salt-free medium), in a test tube conaining 10ml of the medium, and cultivated at 30°C for 48hr. The cells obtained were washed with the same fresh medium, separately, and transferred, with an inoculum size of 105 cells per ml, to 100ml of salt-free medium and 20% NaCl medium in 500-ml conical flasks. Late exponential phase cultures were washed by centrifugation (620 x g, 5min), and shifted to salt-free medium or 20% NaCl medium by adding an equal density of cells. All liquid cultivations were done at 30°C on a rotary shaker (220rpm, 6-cm amplitude).Growth was monitored by measuring the optical den...