title: Kluyveromyces lactis cells entrapped in Ca-alginate beads for the continuous production of a heterologous glucoamylase.
abstract: Viable cells of Kluyveromyces lactis, transformed with the glucoamylase gene from Arxula adeninivorans, were entrapped in beads of Ca-alginate and employed on a lab scale in a continuous stirred and a fluidised bed reactor (FBR), both fed with a rich medium (YEP) containing lactose as carbon source. Experiments with freely suspended cells in batch and chemostat had demonstrated that glucoamylase production was favoured in the presence of lactose and YEP medium. Employing controlled-sized beads having a 2.13 mm diameter, specific glucoamylase productivity was higher in the stirred reactor (CSTR) than in the FBR; in the latter a higher volumetric productivity was achieved, due to the lower void degree. The performance of the immobilised cell systems, in terms of specific glucoamylase productivity, was strongly affected by mass transfer limitations occurring throughout the gel due to the high molecular weight of the product. In the perspective to improve and scale-up the immobilised cell system proposed, a mathematical model, which takes into account substrate transfer limitations throughout the gel, has been developed. The effective lactose diffusivity was related to the bead reactive efficiency by means of the Thiele modulus. The regression of the model parameters on the experimental data of substrate consumption obtained both in the CSTR and in the FBR allowed to estimate lactose diffusivity and the kinetic parameters of the immobilised yeast.
authors.affiliation: Sez. Igiene e Microbiologia, Dip.to di Fisiologia Generale ed Ambientale, Università degli Studi di Napoli Federico II, Via Mezzocannone 16, 80134 Naples, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: de Alteriis
authors.forename: Giovanni
authors.initials: G
authors.lastname: Silvestro
authors.forename: Massimo
authors.initials: M
authors.lastname: Poletto
authors.forename: Vittorio
authors.initials: V
authors.lastname: Romano
authors.forename: Daniele
authors.initials: D
authors.lastname: Capitanio
authors.forename: Concetta
authors.initials: C
authors.lastname: Compagno
authors.forename: Palma
authors.initials: P
authors.lastname: Parascandola
mesh_terms: D000464:Alginates / Q000737:chemistry; D018914:Cells, Immobilized / Q000378:metabolism; D005285:Fermentation; D005087:Glucan 1,4-alpha-Glucosidase / Q000096:biosynthesis* / Q000235:genetics; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D007716:Kluyveromyces / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008863:Microspheres; D011994:Recombinant Proteins / Q000096:biosynthesis*
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D011994:Recombinant Proteins; D020723:Glucuronic Acid; D005087:Glucan 1,4-alpha-Glucosidase