title: Bacterial cellulose synthesis by gluconacetobacter xylinus: Enhancement via fed-batch fermentation strategies in Glycerol media

authors: Adnan, Azila Binti

abstract: Bacterial cellulose (BC) is an abundant polysaccharide, which is secreted by several genera of bacteria. It has remarkable characteristics, which include high purity, high tensile strength, high biocompatibility and non-toxic. The main feature that differentiates BC and plant cellulose (PC) is the absence of contaminants such as lignin, hemicellulose and pectin. However, the main drawbacks in producing BC are low yield and expensive carbon source. Due to that, this study was carried out to enhance BC volumetric productivity in fed-batch operation mode using glycerol as a carbon source. BC was produced in fill-and-draw and pulse-feed fed-batch cultures of Gluconacetobacter xylinus DSM 46604 in a 3-L bench-top bioreactor. The fed-batch fermentation trials were conducted in agitated and aerobic conditions at 30 ºC. For fill-and-draw fed-batch culture, a total of 24.2 g/L of BC accumulated in the bioreactor after 9 days, which corresponded to a yield and productivity of 0.2 g/g and 2.69 g/L/day, respectively. Pulse-feed fed-batch fermentation resulted in a yield and volumetric productivity of 0.38 g/g and 2.71 g/L/day, respectively. The pulse-feed fed-batch culture proved to be a better fermentation system for utilizing glycerol, which is a low-cost and abundant carbon source.

text: Bacterial cellulose synthesis by gluconacetobacter xylinus: Enhancement via fed-batch fermentation strategies in Glycerol media Bacterial cellulose (BC) is an abundant polysaccharide, which is secreted by several genera of bacteria. It has remarkable characteristics, which include high purity, high tensile strength, high biocompatibility and non-toxic. The main feature that differentiates BC and plant cellulose (PC) is the absence of contaminants such as lignin, hemicellulose and pectin. However, the main drawbacks in producing BC are low yield and expensive carbon source. Due to that, this study was carried out to enhance BC volumetric productivity in fed-batch operation mode using glycerol as a carbon source. BC was produced in fill-and-draw and pulse-feed fed-batch cultures of Gluconacetobacter xylinus DSM 46604 in a 3-L bench-top bioreactor. The fed-batch fermentation trials were conducted in agitated and aerobic conditions at 30 ºC. For fill-and-draw fed-batch culture, a total of 24.2 g/L of BC accumulated in the bioreactor after 9 days, which corresponded to a yield and productivity of 0.2 g/g and 2.69 g/L/day, respectively. Pulse-feed fed-batch fermentation resulted in a yield and volumetric productivity of 0.38 g/g and 2.71 g/L/day, respectively. The pulse-feed fed-batch culture proved to be a better fermentation system for utilizing glycerol, which is a low-cost and abundant carbon source.

year: 2021

title: Monocations of bismuth and indium in arene media: A spectroscopic and EXAFS investigation

authors: Kuznetsov, Alexei N.

subjects: chemistry

abstract: The composition of In–GaCl₃–benzene and In–BiCl₃–GaCl₃–benzene solutions was investigated by Raman, UV/Vis, 71Ga and 115In NMR spectroscopy as well as by X-ray absorption fine structure spectroscopy (EXAFS). Indium metal was found to be soluble in GaCl₃–benzene solution at room temperature through the reduction of GaIII, producing Ga⁺ and In⁺ species. The subvalent cations are likely to be stabilized by the interaction with benzene. The use of these solutions as reducing media for BiCl₃ leads to the formation of Bi₅3⁺ polycations, with Bi⁺ as an intermediate product. No other subvalent bismuth species were detected. Multinuclear NMR experiments show that the reducing agent is Ga⁺ rather than In⁺. Indium K-edge EXAFS data recorded from solutions without and with subvalent bismuth species present show that In⁺ is co-ordinated by benzene (at about 2.9 Å) and chlorine atoms from chlorometalate anions (at about 3.3 Å) in a formal ratio of 1 2. Electrospray mass spectroscopic data show that In+ is most likely co-ordinated by one arene molecule.

text: Monocations of bismuth and indium in arene media: A spectroscopic and EXAFS investigation The composition of In–GaCl₃–benzene and In–BiCl₃–GaCl₃–benzene solutions was investigated by Raman, UV/Vis, 71Ga and 115In NMR spectroscopy as well as by X-ray absorption fine structure spectroscopy (EXAFS). Indium metal was found to be soluble in GaCl₃–benzene solution at room temperature through the reduction of GaIII, producing Ga⁺ and In⁺ species. The subvalent cations are likely to be stabilized by the interaction with benzene. The use of these solutions as reducing media for BiCl₃ leads to the formation of Bi₅3⁺ polycations, with Bi⁺ as an intermediate product. No other subvalent bismuth species were detected. Multinuclear NMR experiments show that the reducing agent is Ga⁺ rather than In⁺. Indium K-edge EXAFS data recorded from solutions without and with subvalent bismuth species present show that In⁺ is co-ordinated by benzene (at about 2.9 Å) and chlorine atoms from chlorometalate anions (at about 3.3 Å) in a formal ratio of 1 2. Electrospray mass spectroscopic data show that In+ is most likely co-ordinated by one arene molecule.

year: 2000

title: Voices of the land: Richard Nunns in conversation with Martin Lodge

authors: Nunns, Richard

abstract: Richard Nunns in conversation with Martin Lodge

text: Voices of the land: Richard Nunns in conversation with Martin Lodge Richard Nunns in conversation with Martin Lodge

year: 2008