7 research outputs found
Morphological analysis of Yarrowia lipolytica under stress conditions through image processing
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.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação para a Ciência e a Tecnologia (FCT); CAPES
Yarrowia lipolytica growth under increased air pressure: influence on enzymes production
Improvement of microbial cell cultures oxygenation can be achieved by the
increase of total air pressure, which increases oxygen solubility in the medium. In this
work, a pressurized bioreactor was used for Yarrowia lipolytica batch cultivation under
increased air pressure from 1 to 6 bar. Cell growth was strongly enhanced by the pressure
rise. Fivefold and 3.4-fold increases in the biomass production and in specific growth rate,
respectively, were observed under 6 bar. The increase of oxygen availability caused the
induction of the antioxidant enzyme superoxide dismutase, which indicates that the
defensive mechanisms of the cells against oxidative stress were effective and cells could
cope with increased pressure. The pregrowth of Y. lipolytica under increased pressure
conditions did not affect the lipase production ability of the cells. Moreover, the
extracellular lipase activity increased 96% using a 5-bar air pressure instead of air at 1-
bar pressure during the enzyme production phase. Thus, air pressure increase in bioreactors
is an effective mean of cell mass and enzyme productivity enhancement in bioprocess based
in Y. lipolytica cultures
Dynamics of filler size and spatial distribution in a plasticating single screw extruder : modeling and experimental observations
A model of agglomerate break-up, incorporating both rupture and erosion, is employed to predict the dynamics of filler size distribution in a plasticating single screw extruder. Filler spatial distribution along the extruder length was also ascertained and direct comparison of experimental and computational data proved to be satisfactory. The method was also used to investigate the effect of material properties, operating conditions and extruder geometry on the dynamics of agglomerate dispersion along a single screw extruder. Generally, dispersion levels were primarily governed by the magnitude of the hydrodynamic stresses developed in the extruder and the residence time in the melt.The financial support provided by FCT (Fundacao para a Ciencia e Tecnologia), Portugal, under project POCTI CTM/48448/2002 and scholarship SFRH/BD/19605/2004, is acknowledged