Comparative proteomic analysis of Rhizopus oryzae hyphae displaying filamentous and pellet morphology

Industrial strains of Rhizopus oryzae is known for its strong ability to produce L-( +)-lactic acid, ethanol, and fumaric acid at high yields. To better understand the underlying mechanism behind the physiology of R. oryzae, we conducted the proteome changes between two different morphologies using two-dimensional polyacrylamide gel electrophoresis and mass spectrometry. R. oryzae exhibited pellet morphology and filamentous morphology when the initial pH of the culture medium was 3.0 and 5.0, respectively. The concentration of lactic acid reached 63.5 g L^-1 in the samples containing the pellet morphology, compared to 41.5 g L^-1 produced by filamentous R. oryzae. Proteomic analysis indicated that expression levels of 128 proteins changed significantly. Of these, 17 protein spots were successfully identified by mass spectrometry and were deemed to be mainly involved in carbohydrate metabolism, genetic information processing, chitin metabolism, protein catabolism, protein folding, and antioxidative pathway. L-lactate dehydrogenase (RO3G_06188), enolase (RO3G_05466) and 2, 3-bisphosphoglycerate-independent phosphoglycerate mutase (RO3G_02462) were found to be upregulated, while isocitrate dehydrogenase (RO3G_13820) was downregulated in the samples with pellet morphology compared to the filamentous hyphae. These results suggested that more carbon flow was directed towards lactic acid biosynthesis in R. oryzae hyphae with pellet morphology.