Investigation of sugar metabolism in Rhizopus oryzae

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Rhizopus oryzae is a filamentous fungus, which can produce high amounts of
L(+) lactic acid and produces ethanol as the main by-product. In an effort to
understand the pyruvate branch point of this organism, fermentations under different
inoculum and glucose concentrations were carried out.
At low inoculum size (1×103 spores/ml), high amount of lactate (78 g/l) was
produced, whereas high ethanol concentration (37 g/l) was obtained at high inoculum
sizes (1×106 spores/ml). Decreasing working volume increased lactate production
significantly at high inoculum sizes (1×105 and 1×106 spores/ml), but did not
influenced the physiology at low inoculum sizes (1×103 and 1×104 spores/ml).
In shake flask cultures, at low initial glucose concentrations biomass yield
was high and lactate and ethanol yields were low. Higher lactate and ethanol and
lower biomass yields were obtained by increasing the initial glucose concentrations.
In alginate immobilized, semi-continuous cultures with cell retention, glucose level
in the medium was kept at low values. Like in shake flask cultures, as the glucose
concentration decreased lactate and ethanol yields decreased and biomass yields
increased. Increasing the glucose concentration by a pulse of glucose caused
increases in branch point enzyme activities, as well as in concentrations of the
metabolites. In fed batch cultures higher biomass yield (0.25 g DCW/g glucose)
could be obtained.
Lactate dehydrogenase was influenced by the inoculum size and glucose
concentration more than pyruvate decarboxylase and alcohol dehydrogenase. It
showed higher activity at lactate producing fermentations. Unlike lactate
dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase showed high
activity even at low glucose concentrations.
Ali Oğuz Büyükkileci
Investigation of sugar metabolism in Rhizopus oryzae · 2007 · 94 sayfa.
Danışman: Prof. Dr. Haluk Hamamcı ; Prof. Dr. Şebnem Harsa

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