An exopolysaccharide depolymerase of Rhizobium trifolii is induced in the host bacterial cells by virulent phage infection. The action of this depolymerase appeared only when exopolysaccharide contained glucuronic acid in the exopolysaccharide chains. The reaction was completely inhibited by ethylenediaminetetraacetic acid (EDTA) and this inhibitory effect was abrogated by Ca2+. This enzyme has a molecular weight of about 4.4×105. Optimum pH, optimum temperature, and minimum dose for the activity of this enzyme were elucidated. No difference in the elution pattern on column chromatography and molar ratio of component materials was found between oligosaccharides of infectious and non-infectious bacterial strains obtained after hydrolysis by the depolymerase.
To obtain thermophilic methanol-assimilating yeasts of high growth rate, soil sources collected from various regions were examined by two kinds of enrichment methods and two kinds of screening methods. Its results showed that the soil samples collected from the tropical region were rich in thermophilic yeasts. An ordinary enrichment culture using a test tube was more effective for this purpose than a continuous enrichment culture using a mini-fermentor, because many prominent yeasts were lost through the continuous enrichment culture. After the screening test of isolates by comparing the growth rate of the culture in a flask, properties of selected strains were examined, comparing them with those in continuous culture. They were divided into three types from their growth properties. Among them, the type of yeasts which grew at a low growth rate in batch culture and at high dilution rate in continuous culture was lost during screening in batch culture. Little correspondence was found between the data from the batch culture and those from the continuous culture. It would be better to omit screening by flask cultivation.
Bacillus polymyxa did not grow in a medium containing nitrate as a sole nitrogen source if kept under anaerobic condition, although it grew in the same medium under aerobic condition. The bacteria grew aerobically or anaerobically in media containing nitrite or ammonium nitrogen. When both nitrate and nitrite were supplied in various combinations under anaerobic condition, cell yield at the stationary growth phase was limited only by the amount of nitrite and independent of the amount of nitrate added. Washed cells that had been grown aerobically in nitrate-containing media could reduce nitrate either aerobically or anaerobically when glucose was used as an electron donor. During the nitrate reduction, little or no nitrite accumulated. When the gas phase in cultures that were growing aerobically on nitrate was changed to anaerobic condition, cells continued to grow and nitrate was continued to be assimilated, but cellular activity of nitrate reductase distinctly decreased. These results show that oxygen is required, not for the reaction, but for the formation of assimilatory nitrate reductase system of B. polymyxa.
Metabolic origin of sterols found in rumen protozoa was investigated by the use of 14C-labeled precursors. Hydrogenation of unsaturated sterols by protozoa was shown by incubation with 14C-cholesterol and 14C-β-sitosterol, suggesting that stigmastanol and campestanol in protozoa could be derived from exogenous C29 and C28 sterols, respectively. Low redox potential was found to be required for this hydrogenation reaction. No evidence was obtained for the assumption that protozoal cholestanol is formed by dealkylation of C(24)-alkyl-sterols. Incorporation of the label from 14C-acetate and 14C-mevalonate into the sterol fraction of protozoa was shown. Therefore, it appears highly probable that cholestanol is formed by de novo synthesis. The radioactivity in the protozoal sterol fraction, however, was not high enough to conclude with definite certainty that rumen protozoa possess a sterol-synthesizing capacity; the possibility that contaminating organisms such as yeasts and fungi were responsible for the reaction could not be denied. Attempts to prove cholestanol synthesis by radio gas-liquid chromatography were unsuccessful due to low specific radioactivity of the protozoal sterols labeled. Thus, poor or no capacity of rumen protozoa to synthesize sterols may, at least in part, explain the sterol requirement of these protozoa. In addition, other conversion and degradation reactions of sterols are described.
Substrate specificity of the two forms of glucoamylase (GA-I and GA-II) obtained from the culture of Monascus kaoliang F-1 on wheat bran was examined. Both glucoamylases hydrolyzed amylopectin, amylose, glycogen, soluble starch, maltotriose, and maltose but not isomaltose. The Km values of GA-I for maltose, amylose, amylopectin, and glycogen were 1.0×10-1%, 3.6×10-1%, 6.1×10-1%, and 1.6%, respectively, and the values of GA-II for these substrates were 1.0×10-1%, 1.9×10-2%, 3.0×10-3%, and 8.5×10-3%, respectively. The ratio of Vmax values of GA-I for various substrates with maltose as a standard was not so different from that of GA-II. The limits of hydrolysis of soluble starch, amylopectin, amylose, and glycogen by each glucoamylase were 70%, 90%, 100%, and 100%, respectively. GA-II hydrolyzed raw starch from wheat, corn, sweet potato, and potato more rapidly than GA-I. Both enzymes hydrolyzed soluble starch with the inversion of configuration, producing the β-anomer of glucose.
Edited and published by : Applied Microbiology, Molecular and Cellular Biosciences Research Foundation/Center for Academic Publications Japan Produced and listed by : TERRAPUB, Center for Academic Publications Japan/Shobi Printing Co., Ltd. (-Vol.60,No12), Center for Academic Publications Japan/InternationalAcademic Printing Co., Ltd.(-Vol.54,No1)