System optimization of an embedding protocol to immobilize cells from Candida bombicola to improve the efficiency of sophorolipids production

Advances in high-throughput screening approaches for biosurfactants: current trends, bottlenecks and perspectives

The market size of biosurfactants (BSs) has been expanding at an extremely fast pace due to their broad application scope. Therefore, the re-construction of cell factories with modified genomic and metabolic profiles for desired industrial performance has been an intriguing aspect. Typical mutagenesis approaches generate huge mutant libraries, whereas a battery of specific, robust, and cost-effective high-throughput screening (HTS) methods is requisite to screen target strains for desired phenotypes. So far, only a few specialized HTS assays have been developed for BSs that were successfully applied to obtain anticipated mutants. The most important milestones to reach, however, continue to be: specificity, sensitivity, throughput, and the potential for automation. Here, we discuss important colorimetric and fluorometric HTS approaches for possible intervention on automated HTS platforms. Moreover, we explain current bottlenecks in developing specialized HTS platforms for screening high-yielding producers and discuss possible perspectives for addressing such challenges.

Preparation and characterization of EI-Co/Zr@AC and the mechanisms underlying its removal for atrazine in aqueous solution

Atrazine, a widely used herbicide in agriculture, is detrimental to both the ecological environment and human health owing to its extensive use, poor degradability, and biotoxicity. The technology commonly used to remove atrazine from water is activated carbon adsorption, but it has the problems of difficult recovery, secondary contamination, and a low removal rate. To efficiently remove atrazine from agricultural wastewater, in this study, a new environmental material, embedding immobilization (EI)-Co- and Zr-modified activated carbon powder (Co/Zr@AC), was prepared by immobilizing the bimetallic Co/Zr@AC via EI technique and employed to remove atrazine. When preparing EI-Co/Zr@AC, the single-factor experiment was conducted and determined the optimal preparation conditions: sodium alginate 2.5% (wt), calcium chloride 4.0% (wt), Co/Zr@AC 1.0% (wt), and bentonite 2.0% (wt). The prepared EI-Co/Zr@AC has a three-dimensional mesh structure and many pores and also possesses good mass transfer performance and mechanical properties. The removal efficiency by EI-Co/Zr@AC for the removal of 5.0 mg/L atrazine from 50 mL was 94.1% at pH 7.0 and 25°C, with an EI-Co/Zr@AC dosage of 0.8 g. The mechanistic study showed that the pseudo-second-order kinetic model could describe the removal process better than the pseudo-first-order kinetic model, and the Freundlich isotherm model fit better than other isotherm models. Additionally, the synthesized EI-Co/Zr@AC spheres demonstrated good reusability, with the atrazine removal rate remaining 70.4% after five cycles, and the mechanical properties of the spheres were stable.

Precise fermentation coupling with simultaneous separation strategy enables highly efficient and economical sophorolipids production

Sophorolipids (SLs) represent highly promising biosurfactants. However, its widespread production and application encounter obstacles due to the significant costs involved. Here, an intelligent and precise regulation strategy was elucidated for the fermentation process coupled with in-situ separation production mode, to achieve cost-effective SLs production. Firstly, a mechanism-assisted data-driven model was constructed for "on-demand feeding of cells". Moreover, a strategy of step-wise oxygen supply regulation based on the demand for cell metabolic capacity was developed, which accomplished "on-demand oxygen supply of cells", to optimize the control of energy consumption. Finally, a systematic approach was implemented by integrating a semi-continuous fermentation mode with in-situ separation technology for SLs production. This strategy enhanced SLs productivity and yield, reaching 2.30 g/L/h and 0.57 g/g, respectively. These values represented a 40.2% and 18.7% increase compared to fed-batch fermentation. Moreover, the concentration of crude SLs after separation reached 793.12 g/L, facilitating downstream separation and purification processes.

Difference in calcium ion precipitation between free and immobilized Halovibrio mesolongii HMY2

Biomineralization has become a research focus in wastewater treatment due to its much lower costs compared to traditional methods. However, the low sodium chloride (NaCl)-tolerance of bacteria limits applications to only water with low NaCl concentrations. Here, calcium ions in hypersaline wastewater (10% NaCl) were precipitated by free and immobilized Halovibrio mesolongii HMY2 bacteria and the differences between them were determined. The results show that calcium ions can be transformed into several types of calcium carbonate with a range of morphologies, abundant organic functional groups (C-H, C-O-C, C=O, etc), protein secondary structures (β-sheet, α-helix, 3₁₀ helix, and β-turn), P=O and S-H indicated by P2p and S2p, and more negative δ¹³C_PDB (‰) values (-16.8‰ to -18.4‰). The optimal conditions for the immobilized bacteria were determined by doing experiments with six factors and five levels and using response surface method. Under the action of two groups of immobilized bacteria prepared under the optimal conditions, by the 10^th day, Ca²⁺ ion precipitation ratios had increased to 79%-89% and 80%-88% with changes in magnesium ion cencentrations. Magnesium ions can significantly inhibit the calcium ion precipitation, and this inhibitory effect can be decreased under the action of immobilized bacteria. Minerals induced by immobilized bacteria always aggregated together, had higher contents of Mg, P, and S, lower stable carbon isotope values and less well-developed protein secondary structures. This study demonstrates an economic and eco-friendly method for recycling calcium ions in hypersaline wastewater, providing an easy step in the process of desalination.

Corncob biocarriers with available carbon release for Chlamydopodium sp. microalgae towards enhanced nitrogen removal from low C/N rare earth element tailings (REEs) wastewater

Low nitrogen (N) removal efficiency limits the potential of microalgae technology for the treatment of high nitrogen and low carbon rare earth tailings (REEs) wastewater. In this study, waste corncob was utilized as a biocarrier immobilizing Chlamydopodium sp. microalgae to realize high-efficient treatment of the REEs wastewater. In only 2.5 d, corncob-immobilized microalgae allowed the residual concentrations of N lower than the emission standards, and ammonia nitrogen (NH4+-N) removal rate is 83.3 mg L-1·d-1, total inorganic nitrogen (TIN) removal rate is 86.7 mg L-1·d-1, which was 18.5 times that of the previously-reported microalgae (4.68 mg L-1·d-1). Compared with other microalgae immobilization carriers, corncob possesses the ability to release available carbon sources for microalgae. Composition analysis and sugar verification experiments showed that the main content of TOC released by corncob was monosaccharide, and in a certain range, the removal rate of N was positively correlated with the TOC concentration. The utilization of biomass wastes with dual functions as biological carriers has great potential to improve the performance of microalgae, and is conducive to the development of engineering applications.

Efficient production of inositol from glucose via a tri-enzymatic cascade pathway

Inositol is an essential intermediate in cosmetics, food, medicine and other industries. However, developing an efficient biotransformation system for large-scale production of inositol remains challenging. Herein, a tri-enzymatic cascade route with three novel enzymes including polyphosphate glucokinase (PPGK) from Thermobifida fusca, inositol 3-phosphate synthase (IPS) from Archaeoglobus profundus DSM 5631 and inositol monophosphatase (IMP) from Thermotoga petrophila RKU-1 was designed and reconstructed for the production of inositol from glucose. The problem of poor cooperativity of the cascade reactions was addressed by ribosome binding site (RBS) optimization of PPGK and replication of IPS. Under the optimum biotransformation conditions, the engineered whole-cell immobilized with colloidal chitin transformed 120 g/L glucose to 110.8 g/L inositol with 92.3% conversion in four cycles of reuse, representing the highest titer of inositol to date. Furthermore, this is the first study for inositol production using a three-enzyme coordinated immobilized single-cell.

Sophorolipids bioproduction in the yeast Starmerella bombicola: Current trends and perspectives

Sophorolipids are highly active green surfactants (glycolipid biosurfactants) getting tremendous appreciation worldwide due to their low toxicity, biodegradability, broad spectrum of applications, and significant biotechnological potential. Sophorolipids are mainly produced by an oleaginous budding yeast Starmerella bombicola using low-cost substrates. Therefore, the recent state-of-art literature information about S. bombicola yeast is hereby provided, especially the underlying production pathways, biosynthetic gene cluster, and regulatory enzymes. Moreover, the S. bombicola offers flexibility for regulating the structural diversity of sophorolipids, either genetically or by varying fermentative conditions. The emergence of advanced technologies like 'Omics and CRISPR/Cas have certainly boosted rational engineering research for designing high-performing platform strains. Therefore, currently available genetic engineering tools in S. bombicola were reviewed, thereby opening up exciting new possibilities for improving the overall bioproduction titers, structural variability, and stability of sophorolipids. Finally, some technical perspectives to address the current challenges were discussed.