Functional characterization of starvation-induced lysosomal activity in Saccharomyces cerevisiae

Starvation induces significant alterations in lysosomal enzymes, and reduced concentrations of glucose increases the activity of several lysosomal enzymes. Therefore, to evaluate the lysosomal antimicrobial activity under starvation conditions, we added 0, 5, 10, 20, or 40 g/l of glucose (0%, 0.5%, 1%, 2%, or 4% glucose) supplemented YP medium to cultured Saccharomyces cerevisiae, and lysosomal fractions were isolated from S. cerevisiae grown under the various culture conditions. The lysosomes isolated from each condition exhibited increased antimicrobial activity against Escherichia coli as determined by a decrease in glucose concentration. In addition, a starvation-dependent increase in lysosomal activity coincided with increased lysosome intensity at the cytosol and distinct protein expression from lysosomes in S. cerevisiae. It also was determined found that the lysosomes have antimicrobial activity against seven different microorganisms, including E. coli, and starvation-induced lysosomes showed enhanced antimicrobial activity compared to those from normal lysosomes. These results suggest the possibility that lysosomal alterations during starvation may induce conditions that activate lysosomes for future development of efficient antimicrobial agents.     

Blue LED and succinic acid enhance the growth of Rhodobacter sphaeroides

Rhodobacter sphaeroides is a purple non-sulfur photosynthetic bacteria that participates in the anoxic cycling of carbon both as the primary producer and as the light-stimulated consumers of the reduced organic compounds. In this study, six different organic acids, i.e. acetate, lactate, oxaloacetate, malate, succinate, and citrate, were selected and used to analyze the relationships between the organic acid source and the cell growth. The C₄ compound exhibited an enhanced cell growth compared to the other organic acids, and the growth rate of R. sphaeroides that was grown with 0.03 M succinic acid was significantly 3.2-fold faster than the C₆ compound of 0.03 M citrate. Additionally, the cell growth of R. sphaeroides was enhanced with increasing light intensity, and the growth rate and the dry cell weight of R. sphaeroides that were grown under the light conditions of 15 W/m² were 2.0- and 1.2-fold higher than R. sphaeroides at 3 W/m². Therefore, the high light intensity probably affected the growth of R. sphaeroides. Moreover, the blue-colored light emitting diode (LED) exhibited a highest growth rate and cell concentration of R. sphaeroides among the various types of LEDs, and the enhanced cell growth phenomenon under the blue LED conditions was dramatically stimulated at low concentrations of succinic acid, which was compensatory for succinic acid. Therefore, a high light intensity and a blue LED as the light source were necessary for the enhanced cell growth for the C₄ organic acid, i.e. succinic acid.