Hansenula polymorpha cells lacking the ER-localized peroxins Pex23 or Pex29 show defects in mitochondrial function and morphology.

Pex23 family proteins localize to the endoplasmic reticulum and play a role in peroxisome and lipid body formation. The yeast Hansenula polymorpha contains four members: Pex23, Pex24, Pex29 and Pex32. We previously showed that loss of Pex24 or Pex32 results in severe peroxisomal defects, caused by reduced peroxisome-endoplasmic reticulum contact sites. We now analyzed the effect of the absence of all four Pex23 family proteins on other cell organelles. Vacuoles were normal in all four deletion strains. The number of lipid droplets was reduced in pex23 and pex29, but not in pex24 and pex32 cells, indicating that peroxisome and lipid droplet formation require different Pex23 family proteins in H. polymorpha. In pex23 and pex29 cells mitochondria were fragmented and clustered accompanied by reduced levels of the fusion protein Fzo1. Deletion of DNM1 suppressed the morphological phenotype of pex23 and pex29 cells, suggesting that mitochondrial fusion is affected. pex23 and pex29 cells showed retarded growth and reduced mitochondrial activities. The growth defect was partially suppressed by DNM1 deletion as well as by an artificial mitochondrion-endoplasmic reticulum tether. Hence, the absence of Pex23 family proteins may influence mitochondrion-endoplasmic reticulum contact sites.

Scaling-up batch conditions for efficient sucrose hydrolysis catalyzed by an immobilized recombinant Pichia pastoris cells in a stirrer tank reactor

Background: Invert sugar is used greatly in food and pharmaceutical industries. This paper describes scaling-up batch conditions for sucrose inversion catalyzed by the recombinant Pichia pastoris BfrA4X whole cells expressing Thermotoga maritima invertase entrapped in calcium alginate beads. For the first time, we describe the application of a kinetic model to predict the fractional conversion expected during sucrose hydrolysis reaction in both, a model and a prototype bioreactor with 0.5- and 5-L working volume, respectively. Results: Different scaled-up criteria used to operate the 0.5-L bioreactor were analyzed to explore the invert sugar large scale production. After model inversion studies, a 5-L scaled-up reaction system was performed in a 7-L stirred reactor. Both scaled-up criteria, immobilized biocatalyst dosage and stirring speed, were analyzed in each type of bioreactors and the collected data were used to ensure an efficient scale-up of this biocatalyst. Conclusions: To date, there is not enough information to describe the large-scale production of invert sugar using different scaled-up criteria such as dose of immobilized biocatalyst and stirring speed effect on mass transfer. The present study results constitute a valuable tool to successfully carry out this type of high-scale operation for industrial purposes.