Abstract
BackgroundBiochemical conversion of lignocellulose hydrolysates remains challenging, largely because most microbial processes have markedly reduced efficiency in the presence of both hexoses and pentoses. Thus, identification of microorganisms capable of efficient and simultaneous utilization of both glucose and xylose is pivotal to improving this process.ResultsIn this study, we found that the oleaginous yeast strain Trichosporon cutaneum AS 2.571 assimilated glucose and xylose simultaneously, and accumulated intracellular lipid up to 59 wt% with a lipid coefficient up to 0.17 g/g sugar, upon cultivation on a 2:1 glucose/xylose mixture in a 3-liter stirred-tank bioreactor. In addition, no classic pattern of diauxic growth behavior was seen; the microbial cell mass increased during the whole culture process without any lag periods. In shake-flask cultures with different initial glucose:xylose ratios, glucose and xylose were consumed simultaneously at rates roughly proportional to their individual concentrations in the medium, leading to complete utilization of both sugars at the same time. Simultaneous utilization of glucose and xylose was also seen during fermentation of corn-stover hydrolysate with a lipid content and coefficient of 39.2% and 0.15 g/g sugar, respectively. The lipid produced had a fatty-acid compositional profile similar to those of conventional vegetable oil, indicating that it could have potential as a raw material for biodiesel production.ConclusionEfficient lipid production with simultaneous consumption of glucose and xylose was achieved in this study. This process provides an exciting opportunity to transform lignocellulosic materials into biofuel molecules, and should also encourage further study to elucidate this unique sugar-assimilation mechanism.
Highlights
Biochemical conversion of lignocellulose hydrolysates remains challenging, largely because most microbial processes have markedly reduced efficiency in the presence of both hexoses and pentoses
Utilization of a glucose:xylose mixture for lipid production by T. cutaneum The experiments started with cultivation of T. cutaneum using a mixture of 47 g/L glucose and 23 g/L xylose as the carbon source in a phosphate-buffered solution at pH 5.5 to 6.0
After cultivation of T. cutaneum for 120 hours, the culture produced 23.8 g/L cell mass with a cellular lipid content of 49.7%, comparable with earlier results in which both glucose and xylose were present in the medium [12,21]
Summary
Biochemical conversion of lignocellulose hydrolysates remains challenging, largely because most microbial processes have markedly reduced efficiency in the presence of both hexoses and pentoses. The sugar streams produced upon hydrolysis of lignocellulose are mixtures of hexoses and pentoses, mostly glucose and xylose, with a typical mass ratio around 2:1 [2] Unless both the glucose and xylose are utilized, the economics of converting lignocellulosic biomass into bio-based products are unfavorable [3,4,5]. In recent years, Lipomyces starkeyi [12], Trichosporon fermentans [13] and R. glutinis [14] have been assessed for the production of lipid using carbon sources containing glucose and xylose Both hexose and pentose were converted into lipid in those examples, the sequential manner of substrate uptake significantly increased the cultivation time
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