Xylose metabolism in the fungus Rhizopus oryzae : effect of growth and respiration on l (+)-lactic acid production

The fungus Rhizopus oryzae converts both glucose and xylose under aerobic conditions into chirally pure l(+)-lactic acid with by-products such as xylitol, glycerol, ethanol, carbon dioxide and fungal biomass. In this paper, we demonstrate that the production of lactic acid by R. oryzae CBS 112.07 only occurs under growing conditions. Deprivation of nutrients such as nitrogen, essential for fungal biomass formation, resulted in a cessation of lactic acid production. Complete xylose utilisation required a significantly lower C/N ratio (61/1) compared to glucose (201/1), caused by higher fungal biomass yields that were obtained with xylose as substrate. Decreasing the oxygen transfer rate resulted in decline of xylose consumption rates, whereas the conversion of glucose by R. oryzae was less affected. Both results were linked to the fact that R. oryzae CBS 112.07 utilises xylose via the two-step reduction/oxidation route. The consequences of these effects for R. oryzae as a potential lactic acid producer are discussed

Lactic acid production from xylose by the fungus Rhizopus oryzae

Lignocellulosic biomass is considered nowadays to be an economically attractive carbohydrate feedstock for large-scale fermentation of bulk chemicals such as lactic acid. The filamentous fungus Rhizopus oryzae is able to grow in mineral medium with glucose as sole carbon source and to produce optically pure l(+)-lactic acid. Less is known about the conversion by R. oryzae of pentose sugars such as xylose, which is abundantly present in lignocellulosic hydrolysates. This paper describes the conversion of xylose in synthetic media into lactic acid by ten R. oryzae strains resulting in yields between 0.41 and 0.71 g g¿1. By-products were fungal biomass, xylitol, glycerol, ethanol and carbon dioxide. The growth of R. oryzae CBS 112.07 in media with initial xylose concentrations above 40 g l¿1 showed inhibition of substrate consumption and lactic acid production rates. In case of mixed substrates, diauxic growth was observed where consumption of glucose and xylose occurred subsequently. Sugar consumption rate and lactic acid production rate were significantly higher during glucose consumption phase compared to xylose consumption phase. Available xylose (10.3 g l¿1) and glucose (19.2 g l¿1) present in a mild-temperature alkaline treated wheat straw hydrolysate was converted subsequently by R. oryzae with rates of 2.2 g glucose l¿1 h¿1 and 0.5 g xylose l¿1 h¿1. This resulted mainly into the product lactic acid (6.8 g l¿1) and ethanol (5.7 g l¿1

Spontaneous formation of a mannitol-producing variant of Leuconostoc pseudomesenteroides grown in the presence of fructose

We report the spontaneous formation of a stable mannitol-producing variant of Leuconostoc pseudomesenteroides. The mannitol-producing variant showed mannitol dehydrogenase activity which was absent in the parental strain. It was also able to use fructose and glucose simultaneously, whereas the parental strain showed diauxic growth with these sugars. A possible explanation of these observations is discussed

The alcohol acetyltransferase Eat1 is located in yeast mitochondria

Eat1 is a recently discovered alcohol acetyltransferase responsible for bulk ethyl acetate production in yeasts such as Wickerhamomyces anomalus and Kluyveromyces lactis. These yeasts have the potential to become efficient biobased ethyl acetate producers. However, some fundamental features of Eat1 are still not understood, which hampers the rational engineering of efficient production strains. The cellular location of Eat1 in yeast is one of these features. To reveal its location, Eat1 was fused with yEGFP to allow intracellular tracking. Despite the current assumption that bulk ethyl acetate production occurs in the yeast cytosol, most of Eat1 localised to the mitochondria of K. lactis CBS 2359 Δku80. We then compared five bulk ethyl acetate-producing yeasts in iron-limited chemostats with glucose as carbon source. All yeasts produced ethyl acetate under these conditions. This strongly suggests that the mechanism and location of bulk ethyl acetate synthesis are similar in these yeast strains. Furthermore, an in silico analysis showed that Eat1 proteins from various yeasts were mostly predicted as mitochondrial. Altogether, it is concluded that Eat1-catalyzed ethyl acetate production occurs in yeast mitochondria. This study has added new insights to bulk ethyl acetate synthesis in yeast, which is relevant for developing efficient production strains

Disaccharide fermentation by yeasts

Applied Science

Production of a product in a microbial fuel cell

The invention relates to a specific use of a microbial fuel cell for fermenting a substrate into a product, wherein said product is oxidised compared to the substrate present in the microbial fuel cell and wherein electrical energy i s produced

Production of a product in a microbial fuel cell

The invention relates to a specific use of a microbial fuel cell for fermenting a substrate into a product, wherein said product is oxidised compared to the substrate present in the microbial fuel cell and wherein electrical energy i s produced