This study aims to augment the D-lactic acid biosynthetic capacity of Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 through random mutagenesis. The mutant strain, Mut_N23, developed through synergistic application of ultraviolet (UV) irradiation and chemical mutagenesis using N-methyl-N′-nitro-N-nitrosoguanidine (NTG), exhibited 97% increase in D-lactic acid production and 37% enhancement in glucose uptake rate at flask level. Mut_N23 consistently produced optically pure D-lactic acid across seven generations, efficiently metabolizing lactose and sucrose to yield 4.47 g L^{− 1} and 3.38 g L^{− 1} of D-lactic acid, respectively. Optimal conditions identified through One-Factor-At-a-Time (OFAT), and Response Surface Methodology (RSM) facilitated maximum D-lactic acid concentration of 7.88 g L^{− 1} (300% increase) from lactose-MRS (deMan Rogosa Sharpe) with specific productivity of 0.110 g g^{− 1} h^{− 1}. When lactose was replaced with whey permeate as an application, 4.89 g L^{− 1} (140% increase) of D-lactic acid was obtained, with specific productivity of 0.066 g g^{− 1} h^{− 1} in lab-scale bioreactor setups, achieving 99.09% optical purity. Transcriptomics and enzymatic activity analyses substantiated enhanced performance of Mut_N23 signifying beneficial random mutations. Furthermore, characterization of purified D-lactic acid derived from whey permeate using Fourier Transform Infrared (FTIR) spectroscopy and proton Nuclear Magnetic Resonance (NMR) spectroscopy demonstrated parity with commercially available standards. This study highlights Mut_N23’s potential for efficient D-lactic acid production exploiting a spectrum of carbon sources, providing a foundation for future metabolic engineering to enhance biosynthetic productivity.

The increasing worldwide problem of food waste has a substantial impact on environmental contamination, requiring the implementation of efficient management strategies. Anaerobic digestion is a potential technology for managing food waste, which is frequently more sustainable than traditional disposal methods like incineration and composting. Anaerobic digestion not only reduces the negative effects on the environment but also enables the generation of useful by-products such as biofuels, biochemicals, and enzymes. This study underscores the importance of producing biofuel from food waste, specifically focusing on the process by which anaerobic microorganisms transform organic materials into biogas, predominantly consisting of methane (60-70%), carbon dioxide (30-40%), and small amounts of other gases. Given the biogas industry’s growing emphasis on energy generation, food waste is an excellent candidate for anaerobic digestion due to its substantial energy content and widespread availability. This review paper presents a new viewpoint by combining sophisticated microbial management with state-of-the-art biotechnology methods. It is trying to justify that the digestion process efficiency can be maximized by tackling operational issues and constraints affecting microbial performance. The study demonstrates that an optimal anaerobic digestion environment can be established by optimizing the digestive process in conjunction with integrated continuous surveillance diagnostic tools and biotechnological intervention. This innovative all-encompassing strategy is a solution to the common and practical challenges in anaerobic digestion of food waste, to utilize it as a resource for sustainable biogas generation.

L-Methionine is widely used in food, agricultural and pharmaceutical industries. In this study, the L-methionine production in Corynebacterium glutamicum ATCC13032 was promoted by eliminating the feedback inhibition of key rate-limiting enzymes, blocking L-threonine biosynthesis, and strengthening the downstream pathway of L-homoserine. ATCC13032 does not accumulate L-threonine, we found that overexpressing the genes lysC and hom^G378S could accumulate 0.6 g/L L-threonine. Deleting the genes thrB, McbR, and metD in ATCC13032 could accumulate 0.49 g/L L-methionine. Next, enhancing oxaloacetate supply, overexpressing brnFE, and deleting Ncgl2640 that involved in the repression of sulphuric metabolism could accumulate 0.92 g/L L-methionine. Further overexpressing the genes related to L-homoserine downstream pathway, the resulting strain ZBW011/pEC-metYX could produce 1.82 g/L L-methionine. Finally, the gene pyk2 was deleted and the final strain ZBW014/pEC-metYX produced 7.06 g/L L-methionine in a 2.4-L fermenter. The strategies presented in this study would be useful to engineer C. glutamicum for industrial L-methionine production.

Tannase has vital importance in several industries. However, tannase production employing tannic acid as a substrate is costly. This study optimized medium components, concentration of medium components and physical parameters to yield maximum tannase production from Bacillus licheniformis AS1 in submerged fermentation utilizing low-cost agri-waste Citrus limetta (Mosambi) peels as a substrate. Tannase activity and stability parameters were also optimized. The produced crude tannase and partially purified tannase were used to reduce the bitterness (tannin content) from pomegranate juice and to remove the dye. B. licheniformis AS1 produced 0.361 U/mL under un-optimized conditions. During screening of medium components, Mosambi peels, yeast extract, potassium nitrate and sodium chloride was selected. The concentration of medium components (0.8% Mosambi peels, 0.2% yeast extract, 0.12% potassium nitrate, and 0.06% sodium chloride) was optimized using central composite design which yielded tannase up to 27.809 U/mL. Then, physical conditions were optimized (agitation, 100 µl inoculum size, 40 °C temperature, pH 3, and 72 h of incubation) and yielded tannase up to 43.83 ± 0.82 U/mL. The optimal conditions for tannase activity appeared at pH 8, at 40 °C, and 10 min incubation period with 0.3% substrate concentration. The tannase showed highest stability at 40 ºC and at pH 7. The maximum partial purified tannase activity was recorded at pH 8 and at 40 °C, while enzyme stability was at pH 7 and a temperature of 40 °C. The reduction in tannin content of pomegranate juice was noted after 2 h incubation at 37 ºC. This enzyme was also effective for the partial removal of crystal violet dye. The tannase produced in this study was cost-effective due to utilization of low cost agri-waste and showed potential in various industrial applications.

Among the 16 prioritized polycyclic aromatic hydrocarbons (PAHs), naphthalene, phenanthrene, fluoranthene, and pyrene have been used for bacterial degradation study. From the free-air CO₂ enriched (FACE) soil, five Bacillus strains were isolated and used to utilize the four model toxicants at different concentrations as the sole carbon source. Bacillus amyloliquefaciens has great resistance to different PAHs and better degradation capability. B. amyloliquefaciens can degrade naphthalene (0.5 mg mL^− 1), fluoranthene (0.1 mg mL^− 1), and pyrene (0.1 mg mL^− 1) up to 94%, 65%, and 56% respectively, while B. cereus mineralized phenanthrene (0.5 mg mL^− 1) up to 71% within seven days of incubation. B amyloliquefaciens and B. cereus have the capability of ring cleavage and they can convert PAH compounds into less toxic compounds. Based on the metabolites obtained through GC-MS, the biodegradation pathways for each PAH have been predicted to end up in the tricarboxylic acid cycle.

Anaerobic digestion (AD) systems generate biogas from protein-rich waste, with certain anaerobes modulating gene regulatory networks (GRNs) to manage ammonia toxicity. This study reconstructs GRN models for five key anaerobes—a hyper-ammonia-producing anaerobe Acetoanaerobium sticklandii H1, an anaerobic sulfur-reducing bacterium Desulfovibrio vulgaris Hildenborough, a hydrogenotrophic methanogen Methanothermobacter thermautotrophicus ΔH, a heterotrophic methanogen Methanosarcina mazei Gö1, and a methylotrophic methanogen Methanoculleus bourgensis MS2T—using genome-wide data to understand their metabolic regulation in AD processes. These GRNs integrate gene regulatory elements, thereby revealing species-specific adaptations that facilitate ammonia tolerance, substrate metabolism, and methane production. Regulatory elements, such as ExsA, PtxR, and GadW, influence pathways for carbon, nitrogen, and energy metabolism. A. sticklandii and M. mazei were crucial for carbon source utilization, whereas M. bourgensis adapted to ammonium-rich conditions without a typical ammonium uptake system. The results of our study provide insights into the metabolic interactions and regulatory roles within biogas-producing communities. This work proposes a framework for designing synthetic microbial communities to enhance biomethane yield from protein-based substrates, supporting AD efficiency improvements.

Agricultural wastes are characterized by bioactive compounds that can be used to produce different byproducts, including enzymes, which are obtained through solid state fermentation (SSF). The goal of this study was to evaluate the initial pH and moisture conditions of a substrate composed of carrot peels and corn husk residues (tusa) by SSF to obtain cellulase enzymes. Carrot and corn wastes were characterized to determine their physicochemical properties, confirming their suitability for the fermentation process. It was found that endoglucanase enzyme activity increased with time and was favored at a humidity of 75% and a pH of 5.2, reaching values above 300 U/mg protein. However, no significant trends were observed in exocellulase activity related to the study´s factors. Although the use of agro-industrial wastes to obtain high-value molecules has been widely studied, combining carrot and corn wastes as a substrate for cellulase production using Cladosporium sp. _V3 (GenBank No. PP931187) isolated from pineapple wastes has been poorly characterized.