The cellulases that strains of Streptomyces albogriseolus, S. nitrosporeus, and Micromonospora me... more The cellulases that strains of Streptomyces albogriseolus, S. nitrosporeus, and Micromonospora melanosporea produce when grown on untreated ballmilled bagasse were investigated. Optimum conditions for extracellular cellulase production and activity were determined to be growth at pH 6.7−7.4 and 25–35°C for 4–5 days and assay at pH 5.0−6.0 and 45–55°C, respectively. The endoglucanases were thermally stable at 50°C, but the Avicelases had a half‐life of approximately 24 h at this temperature. Nearly half of the endoglucanases and almost all of the Avicelases were absorbed on ballmilled bagasse after 15 min incubation at 50°C. The β‐glucosidases were found to be mainly intracellular or cell wall bound. These mesophilic actinomycetes concomitantly produced xylanases and β‐xylosidases with cellulases that, apart from cellobiose and glucose, also release xylose from bagasse. This feature may be advantageous in the commerical application of the enzymes of mesophilic actinomycetes for the saccharification of natural cellulosic substrates.
... Victor, 1997 Victor, D., Crous, PW, Janse, BJH & Wingfield, MJ (1997). Ge... more ... Victor, 1997 Victor, D., Crous, PW, Janse, BJH & Wingfield, MJ (1997). Genetic variation in Cylindrocladium floridanum and other morphologically similar Cylindrocladium species. Systematic and Applied Microbiology (in press).. Vilgalys and Hester, 1990 R. Vilgalys and M ...
SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated f... more SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated for the production of single-cell protein (SCP) on bagasse hydrolysates. However, the small cell volume of strain ESP-94 would complicate harvesting of the cells during a continuous fermentation process. Auxotrophic mutants of strain ESP-94 were generated and intraspecific protoplast fusion experiments performed in an attempt to increase the cell volume of strain ESP-94. The fusion products were characterised with respect to cell volume, DNA content and genetic stability. Six genetically stable fusants with bigger cell volumes and higher DNA contents were obtained. One such fusant, fnsant F 17, had a cell volume 3-times that of strain ESP-94, while exhibiting similar growth rates to strain ESP-94 on D-xylose as carbon source.
This work describes a numerical model for predicting simultaneous saccharification and fermentati... more This work describes a numerical model for predicting simultaneous saccharification and fermentation of Avicel, an insoluble crystalline cellulose polymer. Separate anoxic cultivations of 40 g/L glucose and 100 g/L Avicel were conducted to verify model predictions and obtain parameters to describe the reaction kinetics. Saccharification of Avicel was achieved with Trichoderma reesei cellulases from the enzyme preparation Spezyme CP with an enzyme loading of 10 FPU/g cellulose. Cultivations were supplemented with 50 IU/g cellulose of β-glucosidase from Novozym 188 to prevent product inhibition by cellobiose. Saccharomyces cerevisiae MH-1000 is a robust industrial strain and was used to ferment glucose to ethanol, glycerol, and carbon dioxide. The numerical model presented in this paper differs from previous models by separating the endoglucanase and exoglucanase enzyme kinetics and allowing for inhibitive site competition. Assuming all enzymes remain active and that each enzyme complex has a corresponding constant specific activity, the model is capable of predicting adsorbed enzyme concentrations with reasonable accuracy. Comparison of predicted values to experimental measurements indicated that the numerical model was capable of capturing the significant elements involved with cellulose conversion to ethanol.
Additional file 1: Figure S1. Relative transcription levels of cellulolytic enzyme-encoding genes... more Additional file 1: Figure S1. Relative transcription levels of cellulolytic enzyme-encoding genes in recombinant yeast strains. Gene ACT1 was used as the internal standard. The relative transcription levels were shown normalized to the level observed in strain EG-D-CBHI-D, whose relative transcription level was defined as 1. For each strain, data are presented as the mean Âą SD from three independent experiments.
The cellulases that strains of Streptomyces albogriseolus, S. nitrosporeus, and Micromonospora me... more The cellulases that strains of Streptomyces albogriseolus, S. nitrosporeus, and Micromonospora melanosporea produce when grown on untreated ballmilled bagasse were investigated. Optimum conditions for extracellular cellulase production and activity were determined to be growth at pH 6.7−7.4 and 25–35°C for 4–5 days and assay at pH 5.0−6.0 and 45–55°C, respectively. The endoglucanases were thermally stable at 50°C, but the Avicelases had a half‐life of approximately 24 h at this temperature. Nearly half of the endoglucanases and almost all of the Avicelases were absorbed on ballmilled bagasse after 15 min incubation at 50°C. The β‐glucosidases were found to be mainly intracellular or cell wall bound. These mesophilic actinomycetes concomitantly produced xylanases and β‐xylosidases with cellulases that, apart from cellobiose and glucose, also release xylose from bagasse. This feature may be advantageous in the commerical application of the enzymes of mesophilic actinomycetes for the saccharification of natural cellulosic substrates.
... Victor, 1997 Victor, D., Crous, PW, Janse, BJH & Wingfield, MJ (1997). Ge... more ... Victor, 1997 Victor, D., Crous, PW, Janse, BJH & Wingfield, MJ (1997). Genetic variation in Cylindrocladium floridanum and other morphologically similar Cylindrocladium species. Systematic and Applied Microbiology (in press).. Vilgalys and Hester, 1990 R. Vilgalys and M ...
SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated f... more SUMMARY The yeast Candida blank# ESP-94, capable of utilizing xylose as substrate, was isolated for the production of single-cell protein (SCP) on bagasse hydrolysates. However, the small cell volume of strain ESP-94 would complicate harvesting of the cells during a continuous fermentation process. Auxotrophic mutants of strain ESP-94 were generated and intraspecific protoplast fusion experiments performed in an attempt to increase the cell volume of strain ESP-94. The fusion products were characterised with respect to cell volume, DNA content and genetic stability. Six genetically stable fusants with bigger cell volumes and higher DNA contents were obtained. One such fusant, fnsant F 17, had a cell volume 3-times that of strain ESP-94, while exhibiting similar growth rates to strain ESP-94 on D-xylose as carbon source.
This work describes a numerical model for predicting simultaneous saccharification and fermentati... more This work describes a numerical model for predicting simultaneous saccharification and fermentation of Avicel, an insoluble crystalline cellulose polymer. Separate anoxic cultivations of 40 g/L glucose and 100 g/L Avicel were conducted to verify model predictions and obtain parameters to describe the reaction kinetics. Saccharification of Avicel was achieved with Trichoderma reesei cellulases from the enzyme preparation Spezyme CP with an enzyme loading of 10 FPU/g cellulose. Cultivations were supplemented with 50 IU/g cellulose of β-glucosidase from Novozym 188 to prevent product inhibition by cellobiose. Saccharomyces cerevisiae MH-1000 is a robust industrial strain and was used to ferment glucose to ethanol, glycerol, and carbon dioxide. The numerical model presented in this paper differs from previous models by separating the endoglucanase and exoglucanase enzyme kinetics and allowing for inhibitive site competition. Assuming all enzymes remain active and that each enzyme complex has a corresponding constant specific activity, the model is capable of predicting adsorbed enzyme concentrations with reasonable accuracy. Comparison of predicted values to experimental measurements indicated that the numerical model was capable of capturing the significant elements involved with cellulose conversion to ethanol.
Additional file 1: Figure S1. Relative transcription levels of cellulolytic enzyme-encoding genes... more Additional file 1: Figure S1. Relative transcription levels of cellulolytic enzyme-encoding genes in recombinant yeast strains. Gene ACT1 was used as the internal standard. The relative transcription levels were shown normalized to the level observed in strain EG-D-CBHI-D, whose relative transcription level was defined as 1. For each strain, data are presented as the mean Âą SD from three independent experiments.
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