Simulation of computational fluid dynamics and comparison of cephalosporin C fermentation performance with different impeller combinations

Biosynthesis of β-lactam nuclei in yeast

We have engineered brewer's yeast as a general platform for de novo synthesis of diverse β-lactam nuclei starting from simple sugars, thereby enabling ready access to a number of structurally different antibiotics of significant pharmaceutical importance. The biosynthesis of β-lactam nuclei has received much attention in recent years, while rational engineering of non-native antibiotics-producing microbes to produce β-lactam nuclei remains challenging. Benefited by the integration of heterologous biosynthetic pathways and rationally designed enzymes that catalyze hydrolysis and ring expansion reactions, we succeeded in constructing synthetic yeast cell factories which produce antibiotic cephalosporin C (CPC, 170.1 ± 4.9 μg/g DCW) and the downstream β-lactam nuclei, including 6-amino penicillanic acid (6-APA, 5.3 ± 0.2 mg/g DCW), 7-amino cephalosporanic acid (7-ACA, 6.2 ± 1.1 μg/g DCW) as well as 7-amino desacetoxy cephalosporanic acid (7-ADCA, 1.7 ± 0.1 mg/g DCW). This work established a Saccharomyces cerevisiae platform capable of synthesizing multiple β-lactam nuclei by combining natural and artificial enzymes, which serves as a metabolic tool to produce valuable β-lactam intermediates and new antibiotics.

Effects of Impeller Geometry on the 11α-Hydroxylation of Canrenone in Rushton Turbine-Stirred Tanks

The 11α-hydroxylation of canrenone can be catalyzed by Aspergillus ochraceus in bioreactors, where the geometry of the impeller greatly influences the biotransformation. In this study, the effects of the blade number and impeller diameter of a Rushton turbine on the 11α-hydroxylation of canrenone were considered. The results of fermentation experiments using a 50 mm four-blade impeller showed that 3.40% and 11.43% increases in the conversion ratio were achieved by increasing the blade number and impeller diameter, respectively. However, with an impeller diameter of 60 mm, the conversion ratio with a six-blade impeller was 14.42% lower than that with a four-blade impeller. Data from cold model experiments with a large-diameter six-blade impeller indicated that the serious leakage of inclusions and a 22.08% enzyme activity retention led to a low conversion ratio. Numerical simulations suggested that there was good gas distribution and high fluid flow velocity when the fluid was stirred by large-diameter impellers, resulting in a high dissolved oxygen content and good bulk circulation, which positively affected hyphal growth and metabolism. However, a large-diameter six-blade impeller created overly high shear compared to a large-diameter four-blade impeller, thereby decreasing the conversion ratio. The average shear rates of the former and latter cases were 43.25 s^-1 and 35.31 s^-1, respectively. We therefore concluded that appropriate shear should be applied in the 11α-hydroxylation of canrenone. Overall, this study provides basic data for the scaled-up production of 11α-hydroxycanrenone.

Oil crop wastes as substrate candidates for enhancing erythritol production by modified Yarrowia lipolytica via one-step solid state fermentation

Oil crop wastes are attractive feedstocks in microbial processes due to their low cost. However, the product yields can be limited by their undesirable nitrogen surplus. Present study proposed a one-step solid state fermentation (SSF) method for producing erythritol from unrefined oil crop wastes using a modified strain Y. lipolytica M53-S. Enhanced erythritol production (185.4 mg/gds) was obtained from peanut press cake mixed with 40% sesame meal and 10% waste cooking oil. The process was performed at pH 4.0 in 5 L flasks, with initial moisture content, NaCl addition, and inoculum size of 70%, 0.02 g/gds, and 7.5 × 10⁴ cells/gds, respectively. This procedure showed advantages in terms of lower material cost than that of submerged fermentation and shorter culture cycle (96 h) than other SSF processes. In repeated-batch fermentation, erythritol was continuously produced for seven cycles. This study presents a feasible approach in developing an efficient erythritol cultivation from nitrogen-rich wastes.

Effects of Agitation, Aeration and Temperature on Production of a Novel Glycoprotein GP-1 by Streptomyces kanasenisi ZX01 and Scale-Up Based on Volumetric Oxygen Transfer Coefficient

The effects of temperature, agitation and aeration on glycoprotein GP-1 production by Streptomyces kanasenisi ZX01 in bench-scale fermentors were systematically investigated. The maximum final GP-1 production was achieved at an agitation speed of 200 rpm, aeration rate of 2.0 vvm and temperature of 30 °C. By using a dynamic gassing out method, the effects of agitation and aeration on volumetric oxygen transfer coefficient (k_La) were also studied. The values of volumetric oxygen transfer coefficient in the logarithmic phase increased with increase of agitation speed (from 14.53 to 32.82 h⁻¹) and aeration rate (from 13.21 to 22.43 h⁻¹). In addition, a successful scale-up from bench-scale to pilot-scale was performed based on volumetric oxygen transfer coefficient, resulting in final GP-1 production of 3.92, 4.03, 3.82 and 4.20 mg/L in 5 L, 15 L, 70 L and 500 L fermentors, respectively. These results indicated that constant volumetric oxygen transfer coefficient was appropriate for the scale-up of batch fermentation of glycoprotein GP-1 by Streptomyces kanasenisi ZX01, and this scale-up strategy successfully achieved 100-fold scale-up from bench-scale to pilot-scale fermentor.