ABSTRACT
Flocculation is a desirable property in industrial yeasts and is particularly important in the fuel ethanol industry because it provides a simple and cost-free way to separate yeast cells from fermentation products. In the present study, the effect of pH and lignocellulose-derived sugars on yeast flocculation was investigated using a flocculent Saccharomyces cerevisiae, MA-R4, which has been recombinantly engineered to simultaneously co-ferment glucose and xylose to ethanol with high productivity. The flocculation level of MA-R4 dramatically decreased at pH values below 3.0 during co-fermentation of glucose and xylose. Sedimentation and microscopic observation revealed that flocculation was induced in MA-R4 when it fermented glucose, a glucose/xylose mixture, or mannose, whereas attempts to ferment xylose, galactose, and arabinose led to the loss of flocculation. MA-R4 fermented xylose and galactose more slowly than glucose and mannose. Therefore, the various flocculation behaviors shown by MA-R4 should be useful in the control of ethanol fermentation processes.
Subject(s)
Fermentation , Flocculation , Glucose/metabolism , Saccharomyces cerevisiae/metabolism , Xylose/metabolism , Hydrogen-Ion ConcentrationABSTRACT
Practical removal of radioactivity from polluted soil in Fukushima, Japan was done using a photosynthetic bacterium, Rhodobacter sphaeroides SSI, immobilized in alginate beads. The beads were put in a mesh bag and soaked in which soil was suspended (5 kg of soil/10 L of tap water). The radioactivity of the broth decreased by 31% after 15 d of aerobic treatment. When lactic acid bacterial culture broth was added to the suspend broth, about 50% of the radioactivity was transferred to a suspend broth fraction consisting of small particles from the soil after 3 d of fermentation and 20 s of sedimentation. The results suggest that organic matter in the soil was decomposed by anaerobic digestion and lactic acid fermentation simultaneously, and was then transferred into the liquid as small particles. With combined treatment by anaerobic digestion and lactic acid fermentation for 5 d and immobilized bead aerobic treatment for an additional 19 d, the radioactivity of suspend broth decreased by 66%. The radioactivity of the original soil (10.56 µSv/h) ultimately decreased by 67% (3.52 µSv/h) after the combined treatment.
Subject(s)
Cesium Radioisotopes/isolation & purification , Fukushima Nuclear Accident , Lactic Acid/metabolism , Lactobacillaceae/metabolism , Rhodobacter sphaeroides/chemistry , Soil Pollutants, Radioactive/isolation & purification , Aerobiosis , Alginates/chemistry , Anaerobiosis , Biodegradation, Environmental , Cells, Immobilized/chemistry , Cells, Immobilized/metabolism , Cesium Radioisotopes/metabolism , Fermentation , Glucuronic Acid/chemistry , Hexuronic Acids/chemistry , Humans , Hydrogen-Ion Concentration , Microspheres , Photosynthesis , Rhodobacter sphaeroides/metabolism , Soil/chemistry , Soil Pollutants, Radioactive/metabolismABSTRACT
About 90% of the radioactive Cs in the sediment mud of a school's swimming pool in Fukushima, Japan was removed by treatment for 3 d using the alginate immobilized photosynthetic bacterium Rhodobcater sphaeroides SSI. Even though batch treatment was carried out 3 times repeatedly, the activity of immobilized cells in removing Cs was maintained at levels of about 84% (second batch) and 78% (third batch). Cs was strongly attached to the sediment mud because, even with HNO(3) treatment at pH of 2.00-1.60 for 24 h, it was not eluted into the water. Furthermore, more than 75% of the Cs could be removed without solubilization with HNO(3). This suggests that the Cs attached to the sediment mud was transformed into immobilized cells via the Cs(+) ion by the negative charge of the immobilized cell surface and/or the potassium transport system of the photosynthetic bacterium.
