The current work evaluates the production of ligninolytic enzyme optimization via response surface methodology using different inducers: acid cellulignin (CA); MnSO₄ (Mn²⁺); CuSO₄·5H₂O (Cu²⁺); veratryl (3, 4-dimethoxybenzyl); alcohol (VA); Tween 80% (T80); and the carbon-to-nitrogen ratio (C/N). A further goal was implementing a fed-batch strategy to produce ligninolytic enzyme extracts from P. sanguineus 2512 using a bubble column reactor (BCR). The best optimized experimental condition in the shake flasks was a 7.5 C/N ratio, 0.025 g/L Cu²⁺, 1.5 mM Mn²⁺, 3.0 mM VA and 0.025 mM T80, resulting in 64,580, 9.10 and 80.72 U/L for Laccase (Lac), Manganese (MnP) and Lignin peroxidase (LiP) activities, respectively. In the BCR, three feedings were performed at 24 h intervals on the 6th, 7th and 8th days with a significant increase in Lac (99,600 U/L) and MnP (47.53 U/L) activities on the 8th day and a reduction on the 9th day of cultivation. The LiP activity peak was achieved on the 5th day (416 U/L) of cultivation, decreasing thereafter. Enzyme cocktails concentrated in hollow fiber in the third cultivation batch showed contents of 4 × 10⁵ U/L, 220 U/L and 2.5 g/L for Lac, MnP and total proteins, respectively. The enzymatic cocktail with the highest LiP activity (1200 U/L) was obtained in the first batch. The results showed that the optimization of the biosynthesis of the ligninolytic enzymes provided satisfactory improvement in terms of Lac and MnP production per run.

This study focuses on optimizing the medium composition for cellular biomass production and bioconversion of ethylene glycol (EG) to glycolic acid (GA) using Gluconobacter oxydans CCT 0552. The improvement in cellular growth in the presence of yeast extract and peptone led to a 35.7% and 32.7% increase, respectively, compared to the medium with each of these carbon sources separately. Negligible growth was produced when (NH₄)₂SO₄ and urea were used. Optimal bioconversion results were very similar for both the stirred tank and bubble column bioreactors, with GA concentrations reaching 49.4 g/L and 47.7 g/L, volumetric productivities of 0.35 g/L∙h and 0.33 g/L∙h, and product yield factors of 1.08 g/g and 0.94 g/g, respectively. An extended fed-batch strategy using a STR-type bioreactor achieved a concentration of glycolic acid of 94.2 g/L, corresponding to a volumetric productivity of 0.41 g/L∙h and a yield factor of 1.19 g/g. The resulting efficiency of this biological transformation process achieved a remarkable value of 97.3%, simultaneously with a significant decrease in the substrate amount by 90.5%. This study demonstrates the efficiency of G. oxydans in producing GA, offering a cost-effective and environmentally sustainable production method.

Propionic acid (PA) is a valuable chemical with wide industrial applications, and its sustainable production via microbial fermentation has gained increasing attention. This study aimed to develop and improve a bioprocess for PA production using Acidipropionibacterium acidipropionici DSM 4900 and renewable carbon sources, namely xylose and glycerol. Shake-flask and bioreactor experiments were conducted to evaluate the effects of substrate ratios and operational strategies on process performance. Among the tested conditions, the fed-batch bioreactor using glycerol as the main substrate showed the best results, reaching a final PA concentration of 24.5 g/L, productivity of 0.18 g/(L·h), yield of 0.57 g/g, and bioconversion efficiency of 71%. These findings highlight the potential of optimizing substrate composition and feeding strategies to enhance microbial catalysis and process efficiency. This work advances current knowledge by revealing the synergy between xylose and glycerol co-utilization and demonstrating that integrated process design, combining redox-balanced substrates with fed-batch operation, can overcome end-product inhibition and enhance carbon flux toward propionic acid synthesis. Overall, this study demonstrates the feasibility of using low-cost, renewable feedstocks for PA production, contributing to the development of sustainable and circular biorefinery platforms in line with green chemistry and process intensification principles.