Lipid and carotenoid production by Rhodosporodium toruloides ATCC 204091 using C5 and C6 sugars obtained from lignocellulosic hydrolysate

Aim: This study investigated the production of lipids and carotenoids and associated growth properties by the oleaginous red yeast Rhodosporodium toruloides strain ATCC 204091, using C5 and C6 sugar streams of lignocellulosic waste hydrolysate separately and in combination (C5+C6). Methodology: Cell density, wet and dry biomass weight, concentration of total sugars and reducing sugars were determined at various time intervals during cell growth in media containing C5, C6 and mixed sugars. Lipid and carotenoids were extracted and the media were compared with respect to production. Results: Production of lipid (22.25%) and carotenoids (19 mg l-1) was highest in C6 sugar, as compared to mixed sugars and C5 sugar. Interpretation: Due to the versatility of Rhodosporodium toruloides strain ATCC 204091 for utilizing C6 and C5 sugars present in waste hydrolysates, it has been projected as a good choice for cultivation in “waste” hydrolysates.

Efficient Co-Utilization of Biomass-Derived Mixed Sugars for Lactic Acid Production by Bacillus coagulans Azu-10

Lignocellulosic and algal biomass are promising substrates for lactic acid (LA) production. However, lack of xylose utilization and/or sequential utilization of mixed-sugars (carbon catabolite repression, CCR) from biomass hydrolysates by most microorganisms limits achievable titers, yields, and productivities for economical industry-scale production. This study aimed to design lignocellulose-derived substrates for efficient LA production by a thermophilic, xylose-utilizing, and inhibitor-resistant Bacillus coagulans Azu-10. This strain produced 102.2 g/L of LA from 104 g/L xylose at a yield of 1.0 g/g and productivity of 3.18 g/L/h. The CCR effect and LA production were investigated using different mixtures of glucose (G), cellobiose (C), and/or xylose (X). Strain Azu-10 has efficiently co-utilized GX and CX mixture without CCR; however, total substrate concentration (>75 g/L) was the only limiting factor. The strain completely consumed GX and CX mixture and homoferemnatively produced LA up to 76.9 g/L. On the other hand, fermentation with GC mixture exhibited obvious CCR where both glucose concentration (>25 g/L) and total sugar concentration (>50 g/L) were the limiting factors. A maximum LA production of 50.3 g/L was produced from GC mixture with a yield of 0.93 g/g and productivity of 2.09 g/L/h. Batch fermentation of GCX mixture achieved a maximum LA concentration of 62.7 g/L at LA yield of 0.962 g/g and productivity of 1.3 g/L/h. Fermentation of GX and CX mixture was the best biomass for LA production. Fed-batch fermentation with GX mixture achieved LA production of 83.6 g/L at a yield of 0.895 g/g and productivity of 1.39 g/L/h.

Dynamic Simulation of Continuous Mixed Sugar Fermentation with Increasing Cell Retention Time for Lactic Acid Production using Enterococcus mundtii QU 25

Background: The simultaneous and effective conversion of both pentose and hexose in fermentation is a critical and challenging task towards the lignocellulosic economy. This study aims to investigate the feasibility of an innovative co-fermentation process featuring with a cell recycling unit (CF/CR) for mixed sugar utilization. A l-lactic acid producing strain Enterococcus mundtii QU 25, was applied in the continuous fermentation process, and the mixed sugars were utilized at different productivities after the flowing conditions were changed. A numerical platform was constructed with the experiments to optimize the biological process and clarify the cell metabolism through kinetics analysis. The structured model, kinetic parameters, and achievement of the fermentation strategy shall provide new insights towards whole sugar fermentation via real-time monitoring for process control and optimization. Results: Significant carbon catabolite repression in co-fermentation using a glucose/xylose mixture was overcome by replacing glucose with cellobiose, and the ratio of consumed pentose to consumed hexose increased significantly from 0.096 to 0.461 by mass. An outstanding product concentration of 65.2 g·L-1 and productivity of 13.03 g·L-1·h-1 were achieved with 50 g·L-1 cellobiose and 30 g·L-1 xylose at an optimized dilution rate of 0.2 h-1, and the cell retention time gradually increased. Among the total lactic acid production, xylose contributed to more than 34% of the mixed sugars, which was close to the related contents in agricultural residuals. The model successfully simulated the transition of sugar consumption, cell growth, and lactic acid production among the batch, continuous process, and CF/CR systems. Conclusion: Cell retention time played a critical role in balancing pentose and hexose consumption, cell decay, and lactic acid production in the CF/CR process. With increasing cell concentration, consumption of mixed sugars increased with the productivity of the final product; hence, the impact of substrate inhibition was reduced. With the validated parameters, the model showed the highest accuracy simulating the CF/CR process, and significantly longer cell retention times compared to hydraulic retention time were tested.

Dynamic Simulation of Continuous Mixed Sugars Fermentation with Increasing Cell Retention Time for Lactic Acid Production using Enterococcus mundtii QU 25

Background: Simultaneous and effective conversion of both pentose and hexoses in fermentation is a critical and challenging task toward the lignocellulosic economy. This study aims to investigate the feasibility of an innovative co-fermentation process featured with cell recycle unit (CF/CR) for mixed sugar utilization. A l-lactic acid producing strain Enterococcus mundtii QU 25 was applied in the continuous fermentation process to utilize the mixed sugar at different productivities over the changes of flowing conditions. Structured numerical platform were constructed with the experiments to optimize the biological process and clarify the cell metabolisms through kinetics analysis. The structured model, kinetic parameters, and achievement of the fermentation strategy shall provide new insights towards whole sugar fermentation via real-time monitoring for process control and optimization.Results: Significant carbon catabolite repression of co-fermentation using glucose/xylose mixture was overcome by replacing glucose with cellobiose, of which the consumption ratio of hexose to pentose was improved dramatically from 10.4:1 to 2.17:1. An outstanding product concentration of 65.15 g·L -1 and productivity of 13.03 g·L -1 ·h -1 were achieved with 50 g·L -1 cellobiose and 30 g·L -1 xylose, at an optimized dilution rate of 0.2 h -1 with gradually increased cell retention time. Among the total lactic acid production, xylose contributed to more than 34% of the mixed sugars, which was close to the related contents in agricultural residuals. The model successfully simulated the transition of sugar consumption, cell growth, and lactic acid production among the batch, continuous process, and CF/CR system.Conclusion: Cell retention time played a critical role in balancing pentose and hexose consumption, cell decay, and lactic acid production in the CF/CR process. With the increase of cell concentration, consumption of mixed sugars increased with the productivity of final products, hence the impacts of substrate inhibiting reduced. With the validated parameters, the model showed highest accuracy simulating the CF/CR process, of which significantly longer cell retention times over hydraulic retention time were tested.