Description
Yarrowia lipolytica is an aerobic microrganism capable to produce important metabolites, has
an intense secretory activity which drives efforts to be employed in industry (as a biocatalyst),
in molecular biology and genetics studies. Dimorphism is refeered to fungi ability to growth
in two distinct forms, usually as single oval cells os as a filament and to be reversible between
each one. The cell shape is controlled by environmental factors and has been seeked by some
authors [1,2,3].
Y. lipolytica has been considered an adequate model for dimorphism studies in yeasts since it
has an efficient system for transformation and is easy to distinct between its morphological
forms, on opposite to S. cerevisiae that do not produce true filaments and exhibits pseudohyphae
growth under nitrogen limited conditions. Y. lipolytica has an hyphae diameter
corresponding 60 to 100% of its single cell stage [4,5]. It is believed that Y. lipolytica
dimorphism is related to defense mechanism from adverse conditions.
The aim of this work resides on investigate morphological changes in Y. lipolytica under
thermal and oxidative stress conditions. Yarrowia lipolytica (IMUFRJ 50682) was cultivated
in YPD medium (glucose 2%, peptone 0.64%, yeast extract 1%) at 29oC and 160 rpm.
Thermal stress experiments were carried employing a temperature shift (37oC / 1 h.). For
oxidative ones, an addition of H2O2 was used to reach final concentration of 10mM. Both
stress conditions were applied at exponential growth phase. Morphology was observed in a
optic microscope (Axiolab, Zeiss) and cell characteristics were determined employing image
processing analysis (Matlab v. 6.1, The Mathworks Inc.) and comparisons were carried on to
a control system.
A net increase around 22% on hyphae formation was detected as well as a significant
increment in its length in relation to control system, when both thermal and oxidative stress
was applied. The results herein obtained drives to consider a possible relationship between
dimorphism and a cell response mechanism to stress conditions.
; Amaral, P. F. 
