Rhizopus oryzae is a filamentous fungus, belonging to the
order Mucorales. It can ferment a wide range of carbohydrates hydrolyzed from
lignocellulosic materials and even cellobiose to produce ethanol. However, R.oryzae also produces lactic acid as a major metabolite, which reduces the yield
of ethanol. In this study, we show that significant reduction of lactic acid
production could be achieved by short (25nt) synthetic siRNAs targeting the
ldhA gene.
The average yield of lactic acid production by R. oryzae during the
batch fermentation process, where glucose had been used as a sole carbon
source, diminished from 0.07gm/gm in wild type to 0.01gm/gm in silenced
samples. In contrast, the average yield of ethanol production increased from
0.39gm/gm in wild type to 0.45gm/gm in silenced samples. These results show
85.7% (gm/gm) reduction in lactic acid production as compared with the wild
type R. oryzae, while an increase of 15.4% (gm/gm) in ethanol yield.
