Waste valorization as low-cost media engineering for auxin production from the newly isolated Streptomyces rubrogriseus AW22: Model development

Transforming Agricultural Waste from Mediterranean Fruits into Renewable Materials and Products with a Circular and Digital Approach

The Mediterranean area is one of the major global producers of agricultural food. However, along the entire supply chain-from farming to food distribution and consumption-food waste represents a significant fraction. Additionally, plant waste residues generated during the cultivation of specific fruits and vegetables must also be considered. This heterogeneous biomass is a valuable source of bioactive compounds and materials that can be transformed into high-performance functional products. By analyzing technical and scientific literature, this review identifies extraction, composite production, and bioconversion as the main strategies for valorizing agricultural by-products and waste. The advantages of these approaches as well as efficiency gains through digitalization are discussed, along with their potential applications in the Mediterranean region to support new research activities and bioeconomic initiatives. Moreover, the review highlights the challenges and disadvantages associated with waste valorization, providing a critical comparison of different studies to offer a comprehensive perspective on the topic. The objective of this review is to evaluate the potential of agricultural waste valorization, identifying effective strategies while also considering their limitations, to contribute to the development of sustainable and innovative solutions in Mediterranean bioeconomy.

Analysis of secondary metabolites and morphology in Streptomyces rimosus microparticle-enhanced cultivation (MPEC) at various initial organic nitrogen concentrations

The influence of talc microparticles on metabolism and morphology of S. rimosus at various initial organic nitrogen concentrations was investigated. The shake flask cultivations were conducted in the media with yeast extract (nitrogen source) concentration equal to 1 g YE L- 1 and 20 g YE L- 1. Two talc microparticle concentrations of 5 g TALC L- 1 and 10 g TALC L- 1 were tested in microparticle-enhanced cultivation (MPEC) runs. A high nitrogen concentration of 20 g YE L- 1 promoted the development of small agglomerates (pellets) of projected area lower than 105 µm2 and dispersed pseudohyphae. A low nitrogen concentration of 1 g YE L- 1 led to the limitation of S. rimosus growth and, in consequence, the development of the smaller number of large pseudohyphal agglomerates (pellets) of projected area higher than 105 µm2 compared to the culture containing a high amount of nitrogen source. In both cases talc microparticles were embedded into pellets and caused the decrease in their sizes. The lower amount of talc (5 g TALC L- 1) usually caused the weaker effect on S. rimosus morphology and metabolite production than the higher one. This correlation between the microparticles effect on morphology and metabolism of S. rimosus was especially noticeable in the biosynthesis of oxytetracycline, 2-acetyl-2-dicarboxamide oxytetracycline (ADOTC) and spinoxazine A. Compared to the control run, in MPEC their levels increased 4-fold, 5-fold and 1.6-fold respectively. The addition of talc also improved the production of 2-methylthio-cis-zeatin, lorneic acid J and milbemycin A3.

Harnessing artificial intelligence-driven approach for enhanced indole-3-acetic acid from the newly isolated Streptomyces rutgersensis AW08

Indole-3-acetic acid (IAA) derived from Actinobacteria fermentations on agro-wastes constitutes a safer and low-cost alternative to synthetic IAA. This study aims to select a high IAA-producing Streptomyces-like strain isolated from Lake Oubeira sediments (El Kala, Algeria) for further investigations (i.e., 16S rRNA gene barcoding and process optimization). Subsequently, artificial intelligence-based approaches were employed to maximize IAA bioproduction on spent coffee grounds as high-value-added feedstock. The specificity was the novel application of the Limited-Memory Broyden-Fletcher-Goldfarb-Shanno Box (L-BFGS-B) optimization algorithm. The new strain AW08 was a significant producer of IAA (26.116 ± 0.61 μg/mL) and was identified as Streptomyces rutgersensis by 16S rRNA gene barcoding and phylogenetic inquiry. The empirical data involved the inoculation of AW08 in various cultural conditions according to a four-factor Box Behnken Design matrix (BBD) of Response surface methodology (RSM). The input parameters and regression equation extracted from the RSM-BBD were the basis for implementing and training the L-BFGS-B algorithm. Upon training the model, the optimal conditions suggested by the BBD and L-BFGS-B algorithm were, respectively, L-Trp (X1) = 0.58 %; 0.57 %; T° (X2) = 26.37 °C; 28.19 °C; pH (X3) = 7.75; 8.59; and carbon source (X4) = 30 %; 33.29 %, with the predicted response IAA (Y) = 152.8; 169.18 μg/mL). Our findings emphasize the potential of the multifunctional S. rutgersensis AW08, isolated and reported for the first time in Algeria, as a robust producer of IAA. Validation investigations using the bioprocess parameters provided by the L-BFGS-B and the BBD-RSM models demonstrate the effectiveness of AI-driven optimization in maximizing IAA output by 5.43-fold and 4.2-fold, respectively. This study constitutes the first paper reporting a novel interdisciplinary approach and providing insights into biotechnological advancements. These results support for the first time a reasonable approach for valorizing spent coffee grounds as feedstock for sustainable and economic IAA production from S. rutgersensis AW08.