Bo Young Jeon

Development of a serial bioreactor system for direct ethanol production from starch usingAspergillus niger andSaccharomyces cerevisiae

Aspergillus niger hyphae were found to grow with unliquefied potato starch under aerobic conditions, but did not grow under anaerobic conditions. The raw culture ofA. niger catalyzed saccharification of potato starch to glucose, producing approximately 12 g glucose/L/day/ The extracellular enzyme activity was decreased in proportion to incubation time, and approximately 64% of initial activity was maintained after 3 days. At 50°C,A. niger hyphae growth stopped, while the extracellular enzyme activity peaked. On the basis of theA. niger growth property and enzyme activity, we designed a serial bioreactor system composed of four different reactors. Fungal hyphae were cultivated in reactor I at 30°C, uniquefied starch was saccharified to glycose by a fungal hyphae culture in reactors II and III at 50°C, and glucose was fermented to ethanol bySaccharomyces cerevisiae in reactor IV. The total glucose produced by fungal hyphae in reactor I and saccharification in reactor II was about 42 g/L/day. Ethanol production in reactor IV was approximately 22 g/L/day, which corresponds to about 79% of the theoretical maximum produced from 55 g starch/L/day.

Estimation on metabolic pathway of Pseudomonas sp. SMIC-3 for 1-methyl-2-pyrrolidinone based on physiological and biochemical analyses

Pseudomonas sp. SMIC-3 grown on NMP was physiologically differentiated from that on glucose. Growth of SMIC-3 in an NMP-defined medium was approximately three times lower than that in a glucose-defined medium. Methylamine and 1-methyl succinimide were detected in culture fluid of SMIC-3 grown in an NMP-defined medium. Methylamine content in the culture fluid was very similar to NMP consumed by SMIC-3, but 1-methyl succinimide content was much less than the consumed NMP. Crude enzyme isolated from SMIC-3 grown on NMP catalyzed production of methylamine, 1-methyl succinimide, and succinate from NMP but that on glucose did not. Crude enzyme isolated from SMIC-3 grown on glucose and NMP commonly catalyzed dehydrogenation of pyruvate, isocitrate, and malate coupled to reduction of NAD+ to NADH. 2D-SDS-PAGE pattern of total soluble proteins isolated from SMIC-3 grown on glucose was significantly different from that on NMP. Physiological function of SMIC-3 for catabolizing NMP may be selectively induced and activated by NMP.

Effects of an electric pulse on variation of bacterial community and metabolite production in kimchi-making culture

Three, six, nine, and twelve V of electric pulse (EP) was applied to a culture of Weissella cibaria SKkimchi1 in MRS medium and kimchi-making culture (KMC). Viable cell number of SKkimchi1 in MRS medium was decreased in proportion to pulse intensity but that of bacteria in KMC was not. Lactic acid and ethanol produced by SKkimchi1 tended to be decreased in proportion to EP intensity but acetic acid was proportionally increased to EP intensity. Lactic acid, ethanol, and propionic acid produced in KMC were proportionally decreased, but acetic acid was proportionally increased to the EP intensity. Bacterial community and diversity in KMC were analyzed based on culture time by a temperature gradient gel electrophoresis (TGGE) technique. Most bacterial communities grown in freshly prepared kimchi belonged to Bacillus genus. Lactic acid bacteria responsible for kimchi fermentation began to grow on day 4, and were completely substituted for Bacillus genus on day 8, but some Bacillus genus began to grow again on day 12. However, bacterial community diversities were not different based on varying EP intensity.

Symbiotic relationship between Microbacterium sp. SK0812 and Candida tropicalis SK090404.

A bacterium growing inside yeast cytoplasm was observed by light microscope without staining. The bacterium was separately stained from yeast cell by a fluorescent dye, 4′,6-diamidino-2-phenylindole (DAPI). The bacterium actively moved inside yeast cytoplasm and propagated in company with the yeast growth. The bacterium was separated from the yeast cytoplasm by selective disruption of yeast cells and the yeast without the intracellular bacterium (YWOB) was obtained by selective inactivation of bacterial cells. The yeast and the intracellular bacterium were identified as Candida tropicalis and Microbacterium sp., respectively. The length of Microbacterium sp. and C. tropicalis measured with SEM image was smaller than 0.5 μm and was larger than 5 μm, respectively. The yeast with the intracellular bacterium (YWIB) grew in a starch-based medium but the YWOB was not C. tropicalis has neither extracellular nor intracellular saccharification enzyme. Glucose was produced from starch by the extracellular crude enzyme (culture fluid) of Microbacterium sp. YWIB produced significantly more ethanol from glucose than YWOB but did not from starch. Conclusively, C. tropicalis is thought to catabolize starch dependent upon Microbacterium sp. growing in its cytoplasm and furnish stable habitat for the Microbacterium sp.

Bioelectrochemical Fixation of Carbon Dioxide with Electric Energy Generated by Solar Cell

Atmospheric carbon dioxide has been increased and was reached approximately to 390 mg/L at December 2010 (Tans, 2011). Rising trend of carbon dioxide in past and present time may be an indicator capable of estimating the concentration of atmospheric carbon dioxide in the future. Cause for increase of atmospheric carbon dioxide was already investigated and became general knowledge for the civilized peoples who are watching TV, listening to radio, and reading newspapers. Anybody of the civilized peoples can anticipate that the atmospheric carbon dioxide is increased continuously until unknowable time in the future but not in the near future. Carbon dioxide is believed to be a major factor affecting global climate variation because increase of atmospheric carbon dioxide is proportional to variation trend of global average temperature (Cox et al., 2000). Atmospheric carbon dioxide is generated naturally from the eruption of volcano (Gerlach et al., 2002; Williams et al., 1992), decay of organic matters, respiration of animals, and cellular respiration of microorganisms (Raich and Schlesinger, 2002; Van Veen et al., 1991); meanwhile, artificially from combustion of fossil fuels, combustion of organic matters, and cement making-process (Worrell et al., 2001). Theoretically, the natural atmospheric carbon dioxide generated biologically from the decay of organic matter and the respirations of organisms has to be fixed biologically by land plants, aquatic plants, and photosynthetic microorganisms, by which cycle of atmospheric carbon dioxide may be nearly balanced (Grulke et al., 1990). All of the human-emitted carbon dioxide except the naturally balanced one may be incorporated newly into the pool of atmospheric greenhouse gases that are methane, water vapor, fluorocarbons, nitrous oxide, and carbon dioxide (Lashof and Ahuja, 1990). The airborne fraction of carbon dioxide that is the ratio of the increase in atmospheric carbon dioxide to the emitted carbon dioxide variation was typically about 45% over 5 years period (Keeling et al., 1995). Canadell at al (2007) reported that about 57% of human-emitted carbon dioxide was removed by the biosphere and oceans. These reports indicate that the airborne fraction of carbon dioxide is at least 43-45%, which may be the balance emitted by human activity. The land plants are the largest natural carbon dioxide sinker, which have been decreased globally by deforestation (Cramer et al., 2004). Especially, tropical and rainforests are being