Kirsten Kottmeier

Asymmetric division of Hansenula polymorpha reflected by a drop of light scatter intensity measured in batch microtiter plate cultivations at phosphate limitation

Hansenula polymorpha RB11 pC10‐FMD (PFMD− GFP) (FMD promoter gfp gene) was simultaneously cultivated in the Respiration Activity Monitoring System (RAMOS) and in the microtiter plate cultivation system “BioLector” under phosphate limitation. The light scatter signal of the BioLector, for the determination of the biomass concentration in the wells, shows a significant decrease with the onset of the phosphate limitation until a stationary level is reached. At lower initial phosphate concentration this effect is more pronounced and longer time is required until the stationary level of the scattered light is achieved. The oxygen transfer rate signal of the RAMOS and the light scatter signal of the BioLector correlate with respect to the points of time where the maxima and the stationary levels of the courses are reached. In order to understand the effect causing this light scatter behavior, the forward and side scatter properties were investigated off line by flow cytometry. The decay in the light scatter of the BioLector seems to correlate with the formation of two subpopulations of different scatter intensities detected by a flow cytometer. With ongoing cultivation the fraction of cells possessing higher light scattering properties decreases until only a population of lower light scattering properties exists. The rate of transition of the yeast from one subpopulation to the other appears to be correlated with the rate of decrease in the BioLector light scatter signal. The formation of the subpopulations may be caused by an increased asymmetry in the cell cycle due to phosphate limitation. Biotechnol. Bioeng. 2009; 104: 554–561

Constitutive expression of hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris and its pre-purification by foam separation during cultivation

Hydrophobins are small surface‐active proteins that have considerable potential for use in applications ranging from medical and technical coatings, separation technologies, biosensors, and personal care. Their wider use would be facilitated by the availability of recombinant tailor‐made hydrophobins. We successfully expressed the class II hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris under the control of the constitutive GAP (glyceraldehyde 3‐phosphate dehydrogenase) promoter. Avoiding the use of the AOX1 (alcohol oxidase 1) promoter prevents the costs and risks associated with the storage and delivery of methanol used as an inducer. Efficient secretion of hydrophobin was achieved using either the alpha‐factor prepro‐peptide or the native secretion signal of HFB1. The secreted hydrophobins have been isolated with a purity of up to 70% using in situ foam separation during the cultivation process. Coating experiments and surface pressure measurements demonstrated the activity of the hydrophobins. An immunodot assay showed the accessibility of carboxyterminally fused tags of the hydrophobin, which is necessary for potential applications using functionalized hydrophobins. The presented data show that Pichia pastoris is a suitable system for production of constitutively expressed and secreted active hydrophobin, allowing for in situ pre‐purification using foam separation.