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Kluyveromyces lactis is broadly considered as a safe yeast in food and a suitable organism for the production of food enzymes. The K. lactis enzyme production strains of DSM are used to produce a variety of enzymes, for example beta-galactosidase (lactase), chymosin and esterase. All of these production strains are derived from the same lineage, meaning they all originate from the same ancestor strain after classical mutagenesis and/or genetic engineering. Four different enzyme preparations produced with strains within this lineage were toxicologically tested. These enzyme preparations were nontoxic in repeated-dose oral toxicity studies performed in rats and were non-genotoxic in vitro. These studies confirm the safety of the DSM K. lactis strains as a production platform for food enzymes, as well as the safety of the genetic modifications made to these strains through genetic engineering or classical mutagenesis. The outcome of the toxicity studies can be extended to other enzyme preparations produced by any strain from this lineage through read across. Therefore, no new toxicity studies are required for the safety evaluation, as long as the modifications made do not raise safety concerns. Consequently, this approach is in line with the public ambition to reduce animal toxicity studies., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The bifunctional hexokinase KlHxk1 is a key component of glucose-dependent signal transduction in Kluyveromyces lactis. KlHxk1 is phosphorylated in vivo and undergoes ATP-dependent autophosphorylation-inactivation in vitro. This study identifies serine-15 as the site of in vivo phosphorylation and serine-157 as the autophosphorylation-inactivation site. X-ray crystallography of the in vivo phosphorylated enzyme indicates the existence of a ring-shaped symmetrical homodimer carrying two phosphoserine-15 residues. In contrast, small-angle X-ray scattering and equilibrium sedimentation analyses reveal the existence of monomeric phosphoserine-15 KlHxk1 in solution. While phosphorylation at serine-15 and concomitant homodimer dissociation are likely to be involved in glucose signalling, mechanism and putative physiological significance of KlHxk1 inactivation by autophosphorylation at serine-157 remain to be established., (Copyright © 2013 Elsevier Inc. All rights reserved.)