Sonia Mohamadnia

Methanotrophs are of fundamental importance in the global methane cycle and hold promise for the bioconversion of methane into valuable products. This study elucidates the impact of alternating aerobic-anoxic conditions on metabolism of the two phylogenetically distinct groups of methanotrophs: Methylomonas koyamae (type I, γ-proteobacteria) and Methylocystis bryophila (type II, α-proteobacteria). Using batch cultivations with single and repeated oxygen pulses, we demonstrated that cyclic aerobic-anoxic alternation significantly increased the secretion of organic compounds. Notably, acetate secretion by the type II methanotroph M. bryophila was observed for the first time. Genome-scale metabolic modeling and flux balance analysis revealed that acetate secretion serves as an auxiliary ATP-generating pathway for M. bryophila under oxygen limitation. We further uncovered a dynamic mechanism: aerobic phases trigger methane uptake and build up intracellular organic carbon pools, while anoxic phases redirect these pools toward acetate and/or hydrogen release to sustain survival under oxygen limitation. This cyclic regimen effectively channels more methane-derived carbon into extracellular acetate. Our findings underscore that redox conditions critically shape methanotrophic metabolism, influencing both the biological methane cycle and the global climate.

Isoprenoids constitute a large and various number of bio-compounds, with many profitable applications in pharmaceutical, nutraceutical, and industrial fields. The complexity of isoprenoid molecules leads to a challenging, expensive, and environmentally unfriendly chemical synthesis of these metabolites. In addition, the awareness and desire of many consumers for products generated by natural microbial processes has increased recently. Metabolic engineering tools and synthetic biology strategies have been used as a means for the enhancement and optimization of the natural isoprenoid biosynthetic pathways of wild strains. Microalgae as production organisms have been manipulated for the bioproduction of diverse isoprenoids. Particularly when cultivated in unsuitable conditions (such as wastewater, unbalanced nutritional sources, and distinct environmental conditions), microalgae can adjust their metabolic pathways and generate compounds with significant technological potential. Several metabolic engineering approaches have been developed, modifying the metabolic pathways in microalgae to redirect the flow of carbon toward isoprenoid biosynthesis, including pathway engineering, strain improvement, and synthetic biology. In this review, some beneficial features of these high-value metabolites are summarized. Besides, recent advancements in metabolic engineering approaches for the biosynthesis of isoprenoids are discussed in detail. At last, the viewpoints and challenges for the biosynthesis of novel compositions with isoprene units in the microalgae are also included.

Although the skin has a high healing capacity, severe skin wounds often require external interventions to heal properly. Tissue-engineered wound dressings have indeed gained significant attention among various treatment strategies for wound healing. This study focuses on the integration of polyvinyl pyrrolidone (PVP), quaternized chitosan (QCS), and dextran (DEX) to prepare a ternary composite (PVP/QCS/DEX) as a wound dressing hydrogels with varying concentration of PVP and DEX. A variety of analytical methods, including infrared spectroscopy (FTIR), scanning electron microscopy (SEM), contact angle, and water vapor transmission rate (WVTR) were employed to assess the characteristics of the samples. The uniform and interconnected porous structure of the samples was confirmed by the SEM results. All the samples showed high porosity and water vapor transition rate, demonstrating their ability to provide a suitable moist environment and efficient exudate handling for wound healing. The antibacterial test conducted on hydrogels demonstrated the antibacterial activity of hydrogels and drug-loaded hydrogel samples including Escherichia coli and Staphylococcus aureus. The in vitro cytotoxicity evaluation using the MTT assay demonstrated that the developed PVP/QCS/DEX hydrogels exhibit satisfactory cytocompatibility and promote cell viability. The results of the scratch assay indicated that the samples had promoted the cell migration and would improve and accelerate wound healing process. The in vivo healing tests conducted by the drug-loaded hydrogel sample revealed a promising healing performance. Therefore, based on the favorable performance observed throughout the various tests and analysis, the as-prepared PVP/QCS/DEX hydrogels show significant promise in the field of wound dressings.

Wastewater from the potato processing industry called protamylasse is rich in proteins and carbohydrates that potentially can be valorized through cultivation of microalgae by mixotrophic metabolism. However, the complex organic compounds are a challenge, as algae grow best on simple compounds such as volatile fatty acids (VFA). This study demonstrates a new two-stage system. First, VFA production was achieved by testing mesophilic and thermophilic anaerobic acidification (AA) at a short hydraulic retention time (HRT; 3.3 and 5 days) resulting in the release of ammonium and phosphate. HRT of 5 days and thermophilic conditions was optimal considering the high acetate yield of 0.23 g and 22 ml CH₄ per g volatile solids (VS). Then, Chlorella sorokiniana was chosen based on the obtained growth rate, and better adaption in ammonium-rich AA effluent after screening several tested microalgae (Chlorella sorokiniana, Chlorella vulgaris, Scenedesmus obliquus, and Haematococcus pluvialis). It was cultivated for valorization of nutrients and organics and successfully upscaled to 25 L photobioreactor (PBR) scale under both batch and continuous operation with high dosage of 25% (8.2 g L⁻¹ of VS) of AA effluent at an HRT of 5 days in the PBR. Chlorella sorokiniana removed more than 99% of the chemical oxygen demand (COD) and the VFA during continuous flow PBR operation. This approach contributed to the final removal efficiency of 71%, 91%, and 78% for phosphorus, nitrate, and ammonia, respectively, and production of microalgae biomass with more than 73% protein. Thus, a promising process for simultaneous treatment of high strength wastewater for microalgal protein production.