The global waste crisis is a significant concern driven by urbanization and economic expansion. Untreated waste poses major environmental, economic, and societal challenges, especially affecting agriculture and industry. Addressing this crisis necessitates innovative waste management strategies and sustainable practices to mitigate the impending waste burden on ecosystems and societies worldwide. Recent advancements in biofuels and biochemicals intensified research into the conversion of biogenic waste into bio-carboxylic acid/volatile fatty acids (VFAs), driven by the dual imperatives of sustainable waste management and renewable resource development. This study presents a comparative analysis of three waste streams: cheese whey from the cheese-making industry, lignocellulosic brewery spent grains (BSG), and agricultural by-products like wheat straw (WS) assessing their efficacy in carboxylic acid production by mixed culture fermentation. Each substrate produced a diverse array of carboxylic acids, including acetic, propionic, butyric, valeric, iso-valeric, and caproic acids exhibiting unique fermentation efficiencies in carboxylic acid production. The experimental results reveal distinct fermentation efficiencies, the highest concentration of short-chain carboxylic acids (SCCA) production of 11.84 gCOD per L from CW, alongside a medium-chain carboxylic acid (MCCA) production of 3.95 gCOD per L. Notably, despite the lignocellulosic composition of the substrates, both BSG and WS demonstrated substantial and competitive yields of SCCA and MCCA. Specifically, BSG produced 10.68 gCOD per L of SCCA and 3.54 gCOD per L of MCCA, while WS yielded 11.51 gCOD per L of SCCA and 3.84 gCOD per L of MCCA. These findings highlight the viability of lignocellulosic substrates for carboxylic acid production, suggesting significant opportunities for enhancing bioprocessing strategies in biochemical and industrial applications. Taxonomic analysis of microbial communities showed a significant predominance of Firmicutes, Bacteroidota, and Actinobacteriota. The Clostridiaceae family exhibited dominance across all reactors, with respective abundances of 82.72%, 27.67%, and 61.29%. The BSG uniquely showcased an enrichment of Lactobacillaceae (23.86%), Ruminococcaceae (7.72%), and Prevotellaceae (3.24%). Key genera contributing to carboxylic acid production included Clostridium sensu stricto 1, Romboutsia, and Enterococcus. This diversity highlights the influence of substrate composition on microbial community structure, highlighting the intricate relationships between substrate nature and microbial metabolites suggesting that strategic substrate selection could optimize fermentation efficiency and enhance product yield.

The production of biogas through anaerobic digestion (AD) of organic-renewable feedstocks is recognized as a viable solution within the renewable energy sector. Biogas typically contains a methane concentration ranging from 60 to 70%, presenting a significant opportunity for energy generation. However, the co-generated carbon dioxide (CO2), which constitutes approximately 30–40% of biogas, poses challenges to overall energy efficiency, thus necessitating the implementation of purification methods to enhance methane concentrations. It is noteworthy that the production of one ton of biomethane results in the generation of approximately two tons of biogenic CO2. This reality opens avenues for carbon capture, storage, and valorization strategies. The biogas industry is beginning to recognize CO2 not merely as a byproduct to be discarded, but as a valuable resource for the synthesis of biomethane, chemicals, fuels, and even building materials. There is a growing interest in utilizing biogenic CO2 as a climate-friendly feedstock, with “bio-Carbon Capture and Utilization” (bio-CCU) practices facilitating the development of sustainable fuels, chemicals, and materials. The article extends to various methods of valorization for biogenic CO2, providing an analysis of techniques for separating and upgrading CO2 derived from biogas. This assessment encompasses both physical and biological methodologies within the carbon capture, utilization, and storage (CCUS) framework. The article further demonstrates both in-situ and ex-situ processes, including biological methodologies that employ microorganisms for CO2 conversion, as well as thermo-physicochemical processes that transform CO2 into biobased products. Additionally, the article demonstrates the economic and environmental advantages associated with the strategic utilization of biogenic CO2. Repurposing this resource is vital for achieving sustainability goals, particularly in renewable energy sectors, where it can significantly enhance energy efficiency and reduce waste. Finally, the article emphasizes the importance of these practices in climate change mitigation, advocating for a circular economy that prioritizes carbon reuse over atmospheric emissions, thus contributing to the advancement of a sustainable future.

CO2 absorption in aqueous alkaline solutions promoted by carbonic anhydrase (CA) has received increased attention as a solution for post-combustion CO2 capture. In particular, accelerated weathering has emerged as an alternative approach for CO2 capture, mimicking nature’s way to sequestrate CO2. In this study, an evolved CA from Desulfovibrio vulgaris was immobilized on magnetic nanoparticles (MNPs) offering a promising solution for the effective enzyme separation and recovery from complex and heterogeneous reaction media. The immobilization yields were high (86–98 %) and MNPs-DvCA8.0 were characterized based on standardized CO2 release and CO2 absorption assays and compared to the free enzyme. As a following step, MNPs-DvCA8.0 were applied as promoter in the accelerated weathering of insoluble lime mud, originating as a residue from a paper and pulp industry. MNPs-DvCA8.0 could be efficiently separated, washed and reused for up to 10 consecutive reaction cycles, offering a biocatalyst productivity equal to 2.83 g captured CO2/g CA opposite to the free enzyme that offered only 1.01 g captured CO2/g CA. CA immobilization could offer a mitigation strategy for the non-selective adsorption of the free enzyme on lime mud particles during the CO2 capturing reaction. The highly reproducible and robust immobilization method, that provides material separation based on its magnetic properties, could be a viable solution for the recovery of enzyme and its separation from the lime mud slurry, aiding in obtaining a highly pure solution rich in bicarbonate, as product.

The escalating global environmental crisis demands transformative biotechnological solutions that are both sustainable and scalable. This perspective advocates Data-Driven Synthetic Microbes (DDSM); engineered microorganisms designed through integrating omics, machine learning, and systems biology to tackle challenges like PFAS degradation, greenhouse gas mitigation, and sustainable biomanufacturing. DDSMs offer a rational framework for developing robust microbial systems, reshaping the future of synthetic biology toward environmental resilience and circular bioeconomy.

Carbonic anhydrases (CAs) have been proved as a highly efficient and selective promoter for conventional Carbon Capture Utilization and Storage (CCUS) industrial processes. The aim of this work was to demonstrate a high-throughput screening system for detecting engineered CAs with resistance to common inhibitors (SO42-, SO32-, NO3-, NO2-) present as major impurities in post-combustion flue gases, maintaining their initial thermostability. We established a screening protocol on solid and liquid assays for selecting mutants generated with error-prone PCR (epCA8.0) maintaining the thermostability of the parent DvCA8.0 but having improved resistance to flue gas inhibitors. A library of around 1000 mutants was created. The mutant E12 (G7D) showed 50 % increased stability for a mix of inhibitors corresponding to total concentration of 300–600 mM and 65 % increased stability to 150 mM, compared to the parent DvCA8.0. To our knowledge, this is the first time that a CA was evolved by protein engineering methods to increase its stability to common flue gas inhibitors. Additionally, we have established a premise for screening and characterization of CA libraries, which has not been clearly addressed previously, as presence of ionic inhibitors significantly change the pH of enzyme assays, while the nature of such screening assays is pH dependent. We envision that this study will open the pathway for the development of highly resistant CAs in the near future, overcoming stability and cost issues that are associated with their limited application in CCUS technologies.

Lignin is a potential sustainable alternative to polyacrylonitrile (PAN) precursor for the production of carbon fibers. The high purity lignin extracted from residual forest biomass via organosolv process undergoes stabilization and carbonization treatment to produce carbon fibers. Recent developments suggest the potential of producing organosolv lignin carbon fibers (OLCF) with competing mechanical properties similar to PAN carbon fibers. This is likely to enable the use of OLCF in structurally demanding applications such as wind turbine blades. In this work, a life cycle assessment (LCA) is performed with a threefold objective. First, the environmental footprint of OLCF is quantified and results are compared with PAN-CF produced in Sweden and elsewhere in Europe i.e., electricity demands met by European average electrical grid (RER). Second, the environmental performance of OLCF reinforced wind turbine blades (referred as BIOMAT) to be installed in 0.8 MW capacity is evaluated against incumbent variants: glass fiber turbine blade (GFTB), PAN-CF based turbine blades manufactured in Sweden (CFTB-SE), and other parts of Europe (CFTB-RER). Finally, the total environmental externality costs (EEC) of these blades and corresponding lifetime electricity generation when they are installed in 0.8 MW capacity wind turbine blade are calculated. Our results indicate that the environmental impacts of OLCF are lower by 71–94% than PAN-CF-RER in nine, and lower by 43–90% than PAN-CF-SE in six out of ten impact categories quantified respectively. BIOMAT blades also have better overall environmental performance than existing blade variants and particularly lucrative because of their negative total climate change impact. The total EEC of BIOMAT blades is 74%, 83% and 88% lower than GFTB, CFTB-SE and CFTB-RER respectively. Correspondingly, the total EEC of lifetime electricity generated by wind turbine equipped with BIOMAT blades is 11%, 17% and 23% lower than the respective blade variants.

The inert nature, durability, low cost, and wide applicability of plastics have made this material indispensable in our lives. This dependency has resulted in a growing number of plastic items, of which a substantial part is disposed in landfills or dumped in the environment, thereby affecting terrestrial and aquatic ecosystems. Among plastic materials, polyolefins are the most abundant and are impervious to biodegradation, owing to the presence of strong C C and C H bonds. Nevertheless, naturally occurring biodegradation of polyolefins, albeit limited, has been reported. This observation has sparked research on microbial polyolefin degradation. More efficient and targeted versions of this process could be developed also in the laboratory by designing synthetic microbial consortia with engineered enzymes. In this review, we discuss strategies for the development of such microbial consortia and identification of novel polyolefin-degrading microorganisms, as well as the engineering of polyethylene-oxidizing enzymes with greater catalytic efficacy. Finally, different techniques for the design of synthetic microbial consortia capable of successful polyolefin bioremediation will be outlined.

The focus on sustainability and circular economy renders the microalgal biorefinery concept highly attractive. Although the diversity of microalgal composition makes them ideal feedstocks, their metabolic versatility challenges bioprocess optimization. To address this, an integrated, strain-specific approach was used to evaluate key cultivation parameters (nitrogen source, C/N ratio, and light intensity) as their interactions affect growth performance and biochemical composition. Heterotrophic cultivation of A. protothecoides (AP) and C. sorokiniana (CS) in glucose showed enhanced cell growth with organic N-sources. Biomass was consistently elevated across C/N ratios from 5 to 60 with corn steep liquor (CSL) (8.1 g L-1) and yeast extract (YE) (7.0 g L-1), while with urea it maximized at C/N 5 (6.2 g L-1). Protein synthesis increased at C/N 5, whereas lipid accumulation at C/N 60. Beechwood hydrolysate, a renewable glucose alternative, produced an average of 4.1 g L-1 protein (C/N 5) and 3.5 g L-1 lipids (C/N 60) between YE and CSL. Mixotrophic cultivation indicated better photosynthetic adaptation of AP at C/N 5, yielding 13.2 g L-1 biomass at 400 μmol m-2 s-1, whereas at C/N 60 growth was favored at 50 μmol m-2 s-1. The fatty acid profile of microalgal oil revealed de novo biosynthesis of odd-chain fatty acids at C/N 5 in both cultivation modes, while biodiesel-grade lipids produced in heterotrophic condition. These findings advance microalgal bioprocessing by emphasizing the importance of fine-tuning cultivation strategies and utilizing renewable nutrients to maximize resource efficiency and optimize the biosynthesis of valuable bioproducts, such as proteins, pigments, carbohydrates, and high-quality lipids.

Background

Triacylglycerol lipases (E.C. 3.1.1.3) are serine hydrolases, universally present in animals, plants and microbes and are an integral part of lipid metabolism. They are industrially relevant enzymes that cleave ester bonds of triacylglycerides to release free fatty acids and glycerol. Thraustochytrid Aurantiochytrium limacinum SR21 has previously been reported to utilize 120 g L− 1 of oil substrate. Previously, thraustochytrid specific lipases was reported that allowed the microbe to thrive on oil substrate, however the structural characteristics of these enzymes remain undetermined.

Results

In this study, we identified nearly 30 genes that encode TAG lipases with Lipase_3 domain, allowing the marine microbe to thrive on oil substrate. The lipases were predicted to localize at several subcellular compartments such as extracellular (31293), membrane-bound and cytosolic. Phylogenomic analysis revealed that lipases from thraustochytrids form distinct clades, diverging significantly from the well-characterized lipases from yeast Yarrowia lipolytica. Motif enrichment analysis confirmed the presence of the conserved ‘GXSXG’ motif in all lipases, where serine serves as the catalytic residue. Notably, histidine (H) or tyrosine (Y) was found at the second position of the motif in A. limacinum SR21 lipases 34357 (cytosolic) and 31293 (extracellular) respectively, suggesting functional differences. Docking analysis with tripalmitoylglycerol (4RF) revealed lower binding energy (ΔG = -5.7 kcal/mol) for cytoplasmic lipase 34357, indicating a stronger ligand interaction compared to ΔG = -3.4 kcal/mol for the extracellular lipase 31293. This suggests that substituting histidine for tyrosine in the active site affects lipase catalytic efficiency and substrate specificity.

Conclusions

Our study provides novel insights regarding the structure and ligand binding affinities for thraustochytrid specific lipases which are diversified attributed to the heterogeneity within the catalytic triads. In conclusion, we hypothesize that differential localization and higher binding efficiency of thraustochytrid specific lipases allow the microbe to efficiently utilize oil substrates. These thraustochytrid-specific lipases are potential candidates for commercialization as large-scale production of thraustochytrids can be achieved sustainably by cultivating on sustainable substrates and these enzymes are highly efficient and robust.

Microbial biotransformation of waste streams into nutraceuticals appears to be a more viable approach to attaining sustainability. Thraustochytrids are leading producers of docosahexaenoic acid (DHA); an essential ω-3 fatty acid with several health benefits. A surge in identifying alternatives to glucose was observed for these heterotrophs in the past decade with little focus on their metabolic routes. In this study, Aurantiochytrium limacinum SR21 was evaluated for converting glycerol, acetic acid, and waste cooking oil into DHA. Compared to glucose, glycerol resulted in a similar biomass yield (9.53 g L-1) with higher biomass and DHA yield coefficients (YX/S & YP/S) i.e., 0.81 and 0.14 respectively. In contrast, acetic acid resulted in significantly lower biomass yields (5.07 g L-1) while lipid content was comparable. To explore synergistic effects, substrate combinations were tested, with glucose, glycerol, and acetic acid (GlcGlyAA) yielding the highest lipid (48.3 % DCW) and DHA content (45.6 % total fatty acids), approximately 1.2-fold higher than acetate alone. Conversely, WCO suppressed the effect of glycerol on lipid metabolism, resulting in lower DHA content (30.0 % total fatty acids). Further, untargeted metabolomics was performed for 12 combinations to understand the metabolic crosstalk between these substrates. The pentose phosphate pathway metabolites were enriched in glycerol, while fatty acid oxidation and the TCA cycle were more pronounced in WCO metabolism. Multivariate analysis exhibited that acetate combinations had a distinct metabolite profile enriched in γ-aminobutyric acid (GABA), suggesting its role in pathway regulation. GlcGlyAA showed significant accumulation of metabolites related to the pentose phosphate pathway and TCA cycle, yielding abundant acetyl-CoA and NADPH to support higher DHA. In conclusion, this study provides a roadmap and identifies key metabolic nodes that can be fine-tuned to enhance DHA yield.