The effect of surfactant on fermentation of kitasamycin in Streptomyces kitasatoensis

Effect of catalase on CPC production during fermentation of Acremonium chrysogenum

Cephalosporin C (CPC) is a critical raw material for cephalosporin antibiotics produced by Acremonium chrysogenum. During fermentation, the oxygen supply is a crucial factor limiting the efficient biosynthesis of CPC. This study demonstrated that the addition of exogenous surfactants significantly increased the dissolved oxygen (DO) level, extracellular catalase content, and final CPC titer. Consequently, we hypothesized and examined a correlation between catalase and CPC biosynthesis in A. chrysogenum through both the exogenous addition of hydrogen peroxide (H₂O₂) and the endogenous modulation of the catA expression level. The results indicated that both the addition of H₂O₂ and the ∆catA mutation exhibited similar fermentation trends, leading to decreased extracellular catalase activity and increased intracellular reactive oxygen species (ROS) content, which resulted in reduced CPC production. Conversely, strains that overexpress varying levels of the catA accelerated hyphal differentiation under DO-limiting conditions, reducing intracellular ROS accumulation and decreasing cellular apoptosis, which stabilized CPC yield during the later stages of fermentation. This study provides a critical foundation for further investigations into the regulatory mechanisms governing CPC biosynthesis in A. chrysogenum.

Surfactants in biorefineries: Role, challenges & perspectives

The use of lignocellulosic biomass (LCB) as feedstock has received increasing attention as an alternative to fossil-based refineries. Initial steps such as pretreatment and enzymatic hydrolysis are essential to breakdown the complex structure of LCB to make the sugar molecules available to obtain bioproducts by fermentation. However, these steps increase the cost of the bioproduct and often reduces its competitiveness against synthetic products. Currently, the use of surfactants has shown considerable potential to enhance lignocellulosic biomass processing. This review addresses the main mechanisms and role of surfactants as key molecules in various steps of biorefinery processes, viz., increasing the removal of lignin and hemicellulose during the pretreatments, increasing enzymatic stability and enhancing the accessibility of enzymes to the polymeric fractions, and improving the downstream process during fermentation. Further, technical advances, challenges in application of surfactants, and future perspectives to augment the production of several high value-added bioproducts have been discussed.

Engineering Bafilomycin High-Producers by Manipulating Regulatory and Biosynthetic Genes in the Marine Bacterium Streptomyces lohii

Bafilomycin A₁ is the representative compound of the plecomacrolide natural product family. This 16-membered ring plecomacrolide has potent antifungal and vacuolar H⁺-ATPase inhibitory activities. In our previous work, we identified a bafilomycin biosynthetic gene cluster (baf) from the marine bacterium Streptomyces lohii ATCC BAA-1276, wherein a luxR family regulatory gene orf1 and an afsR family regulatory gene bafG were revealed based on bioinformatics analysis. In this study, the positive regulatory roles of orf1 and bafG for bafilomycin biosynthesis are characterized through gene inactivation and overexpression. Compared to the wild-type S. lohii strain, the knockout of either orf1 or bafG completely abolished the production of bafilomycins. The overexpression of orf1 or bafG led to 1.3- and 0.5-fold increased production of bafilomycins, respectively. A genetically engineered S. lohii strain (SLO-08) with orf1 overexpression and inactivation of the biosynthetic genes orf2 and orf3, solely produced bafilomycin A₁ with the titer of 535.1 ± 25.0 mg/L in an optimized fermentation medium in shaking flasks. This recombinant strain holds considerable application potential in large-scale production of bafilomycin A₁ for new drug development.

Effect of sodium dodecyl sulfate on the production of L-isoleucine by the fermentation of Corynebacterium glutamicum

Corynebacterium glutamicum is a safe and popular industrial microorganism that it is gram-positive bacteria with thick cell walls, which hinder the extracellular secretion of products. Surfactant has good surface or interface activity and can destroy the cell membrane of microorganisms. In this study, the surfactant SDS was used to artificially destroy the cell membrane of Corynebacterium glutamicum, increase the permeability of the cell membrane, and increase the ability of the strain to secrete L-isoleucine. This is the first time that surfactants have been applied to the fermentation of Corynebacterium glutamicum. Results indicated that after optimization, the output of L-isoleucine reached 43.67 g/L, which was 13.01% higher than that without sodium dodecyl sulfate. The yield of the by-products, such as valine, leucine, and alanine, was reduced by 72.30%, 64.30%, 71.70%, respectively. This method can promote the production of L-isoleucine while minimizing the damage of SDS to the strain.