Metabolic flux of Bacillus subtilis under poised potential in electrofermentation system: Gene expression vs product formation

Whole genome sequencing of the poly-γ-glutamic acid-producing novel Bacillus subtilis Tamang strain, isolated from spontaneously fermented kinema

Kinema, a traditional fermented soybean food from the Himalayas, is well-liked for its sticky texture and flavourful umami taste. Among 175 bacterial strains from spontaneously fermented kinema samples, Bacillus subtilis Tamang strain stood out for its high stickiness and viscosity. The strain's Poly-γ-glutamic acid (γ-PGA) contains various groups of glutamic acid and has a molecular weight of 660 kDa. It demonstrates the ability to solubilize iron, preserve ferritin in Caco-2 cells, and exhibit antibacterial properties. The genome of B. subtilis Tamang is devoid of plasmid elements but does feature nine insert elements. Noteworthy is the presence of unique secondary metabolites with potential antimicrobial effects, such as amyloliquecidin GF610, bogorol A, and thermoactinoamide A. A total of 132 carbohydrate-active enzymes (CAZy) were identified, hinting at possible prebiotic characteristics. The genome analysis revealed genes responsible for γ-PGA production via the capBCA complex. Furthermore, genes associated with fibrinolytic activity, taste enhancement, biopeptides, immunomodulators, and vitamins like B12 and K2 were found, along with probiotics and various health benefits. The genetic material for L-asparaginase production, known for its anti-cancer properties, was also detected, as well as CRISPR-Cas systems. The absence of virulence factors and antimicrobial resistance genes confirms the safety of consuming B. subtilis Tamang as a food-grade bacterium.

Electric wiring of bacteria using redox polymers and selective measurement of metabolic activity in the presence of surrounding planktonic bacteria

Non-electroactive bacteria (n-EAB), constituting the majority of known bacteria to date, have been underutilized in electrochemical conversion technologies due to their lack of direct electron transfer to electrodes. In this study, we established an electric wiring between n-EAB (gram-positive Bacillus subtilis and gram-negative Escherichia coli) and an extracellular electrode via a ferrocene-polyethyleneimine-based redox polymer (Fc-PEI). Chronoamperometry recordings indicated that Fc-PEI can transfer intracellular electrons to the extracellular electrode regardless of the molecular organization of PEI (linear or branched) and the membrane structure of bacteria (gram-positive or -negative). As fluorescence staining suggested, Fc-PEI improves the permeability of the bacterial cell membrane, enabling electron carriers in the cell to react with Fc. In addition, experiments with Fc-immobilized electrodes without PEI suggested the existence of an alternative electron transfer pathway from B. subtilis to the extracellular Fc adsorbed onto the cell membrane. Furthermore, we proposed for the first time that the bacteria/Fc-linear PEI modified structure enables selective measurement of immobilized bacterial activity by physically blocking contact between the electrode surface and planktonic cells co-existing in the surrounding media. Such electrodes can be a powerful analytical tool for elucidating the metabolic activities of specific bacteria wired to the electrode even within complex bacterial communities.

Purification of Waste-Generated Biogas Mixtures Using Covalent Organic Framework's High CO2 Selectivity

Development of crystalline porous materials for selective CO2 adsorption and storage is in high demand to boost the carbon capture and storage (CCS) technology. In this regard, we have developed a β-keto enamine-based covalent organic framework (VM-COF) via the Schiff base polycondensation technique. The as-synthesized VM-COF exhibited excellent thermal and chemical stability along with a very high surface area (1258 m2 g-1) and a high CO2 adsorption capacity (3.58 mmol g-1) at room temperature (298 K). The CO2/CH4 and CO2/H2 selectivities by the IAST method were calculated to be 10.9 and 881.7, respectively, which were further experimentally supported by breakthrough analysis. Moreover, theoretical investigations revealed that the carbonyl-rich sites in a polymeric backbone have higher CO2 binding affinity along with very high binding energy (-39.44 KJ mol-1) compared to other aromatic carbon-rich sites. Intrigued by the best CO2 adsorption capacity and high CO2 selectivity, we have utilized the VM-COF for biogas purification produced by the biofermentation of municipal waste. Compared with the commercially available activated carbon, VM-COF exhibited much better purification ability. This opens up a new opportunity for the creation of functionalized nanoporous materials for the large-scale purification of waste-generated biogases to address the challenges associated with energy and the environment.

Sustainable Production of Biofuels and Biochemicals via Electro-Fermentation Technology

The energy crisis and climate change are two of the most concerning issues for human beings nowadays. For that reason, the scientific community is focused on the search for alternative biofuels to conventional fossil fuels as well as the development of sustainable processes to develop a circular economy. Bioelectrochemical processes have been demonstrated to be useful for producing bioenergy and value-added products from several types of waste. Electro-fermentation has gained great attention in the last few years due to its potential contribution to biofuel and biochemical production, e.g., hydrogen, methane, biopolymers, etc. Conventional fermentation processes pose several limitations in terms of their practical and economic feasibility. The introduction of two electrodes in a bioreactor allows the regulation of redox instabilities that occur in conventional fermentation, boosting the overall process towards a high biomass yield and enhanced product formation. In this regard, key parameters such as the type of culture, the nature of the electrodes as well as the operating conditions are crucial in order to maximize the production of biofuels and biochemicals via electro-fermentation technology. This article comprises a critical overview of the benefits and limitations of this emerging bio-electrochemical technology and its contribution to the circular economy.

Hydrothermal Processing of Agar Waste to Levulinic acid and Fermentation of Hydrolysate to Bioethanol

Increasing global energy consumption and depleting fossil-fuel supplies prompted the search for green-alternatives. This study focuses on conversion of waste agar using different acids/alkalis (0.5% and 1%) as catalysts under varied temperature and time towards galactose (Gal), 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) production in a sequential reaction. The optimized process for agar depolymerisation was achieved using 1 % acid (H₂SO₄/HCl) catalysed conditions with a maximum of 11 g/L Gal yield (121 °C; 15 min). Increase in temperature (150 °C) and time (180 min) with 1% HCl/H₂SO₄ catalyst resulted in improved LA production along with Gal and HMF. The hydrolysis process was optimised for the selective production of LA (10 g/L) at 175 °C; 180 min. Further, galactose-rich hydrolysates were assessed for bioethanol fermentation using Saccharomyces cerevisiae and resulted 3 g/L ethanol. Thus, the study comprehensively demonstrates waste agar utilization to yield biochemicals/fuels in a circular bio-based economy approach.

New insights into mycelial pellets for aerobic sludge granulation in membrane bioreactor: Bio-functional interactions among metazoans, microbial communities and protein expression

Direct cultivation of aerobic granular sludge (AGS) in membrane bioreactor (MBR) has gained increasing attention. Mycelial pellets (MPs) has been shown capable of promoting rapid granulation of aerobic sludge in MBR, yet mechanisms remain unclear and in-depth insight into cross-scale interactions between MPs and indigenous microbiota as well as the corresponding protein expression functions is necessary. Herein, we found that the addition of MPs in MBR resulted in massive growth of metazoans with 40-400 /mL for rotifers, 20-140 /mL for nematodes and 2-420 /mL for oligochaetes in the initial phase of granulation. This facilitated the MPs to rapidly aggregate with bacteria to form defensive granules for physical protection from predation by metazoans, which inhibited the overgrowth of filamentous bacteria Thiothrix and promoted the reproduction of functional bacteria related to nitrogen removal (Nitrospira, Trichococcus and Acinetobacter). Proteomic analysis demonstrated that the upregulation of functional proteins was mainly ascribed to the decrease of Thiothrix and the increase of Nitrospira, resulting in the enhancement of metabolic pathways involved in glycolysis/gluconeogenesis, citrate (TCA) cycle, oxidative phosphorylation, pyruvate metabolism, nitrogen metabolism and biosynthesis of amino acids, which was responsible for MPs-induced AGS with denser structure, more abundant proteins and β-polysaccharides, higher species diversity, significant nitrogen removal (33.12-42.33%) and lower membrane fouling potential. This study provided a novel and comprehensive insight into the enhanced granulation of aerobic sludge by MPs and the functional superiority of MPs-induced AGS in MBR system.

Deeper insight into the effect of salinity on the relationship of enzymatic activity, microbial community and key metabolic pathway during the anaerobic digestion of high strength organic wastewater

The threshold salt concentration to inhibit the anaerobic digestion (AD) has been intensively investigated, but its insight mechanism is not fully revealed. Therefore, this study systematically investigated the effect of salinity on acidogenesis and methanogenesis and its mechanism. Results showed that low salinity level (i.e. 0.6%) had stimulatory effect on volatile fatty acids (VFA) and methane production, while significant inhibition was observed with further increased salinity. Moreover, high salinity limited the butyric acid degradation at acidogenesis process. The decreases of enzymes (AK and PTA) activity and functional genes (ackA, pta and ACOX) expression that related to β-oxidation explained the butyric acid accumulation at high salinity levels. Microbial community analysis revealed high salinity levels significantly inhibited the proliferation of Syntrophomonas sp., which are known to be associated with butyric acid degradation. Similarly, the relative abundance of acetoclastic methanogen (Methanothrix sp.) and methylotrophic methanogen (Methanolinea sp.) significantly decreased at salinity condition.

Recent advances in electro-fermentation technology: A novel approach towards balanced fermentation

Biotransformation of organic substrates via acidogenic fermentation (AF) to high-value products such as C1-C6 carboxylic acids and alcohol serves as platform chemicals for various industrial applications. However, the AF technology suffers from low product titers due to thermodynamic constraints. Recent studies suggest that augmenting AF redox potential can regulate the metabolic pathway and provide seamless electron flow by lowering the activation energy barrier, thus positively influencing the substrate utilization rate, product yield, and speciation. Hence, the augmented AF system with an exogenous electricity supply is termed as electro-fermentation (EF), which has enormous potential to strengthen the fermentation technology domain. Therefore, this critical review systematically discusses the current understanding of EF with a special focus on the extracellular electron transfer mechanism of electroactive bacteria and provides perspectives and research gaps to further improve the technology for green chemical synthesis, sustainable waste management, and circular bio-economy.

Design and evaluation of gas fermentation systems for CO2 reduction to C2 and C4 fatty acids: Non-genetic metabolic regulation with pressure, pH and reaction time

Addressing the carbon emissions through microbial mediated fermentation is an emerging interest. Custom designed and fabricated gas fermentation (GF) systems were evaluated to optimize the headspace pressure, pH (6.5, 7.5, and 8.5), fermentation time, and substrate concentration by employing enriched homoacetogenic chemolithoautotrophs in non-genetic approach. Headspace pressure showed marked influence on the metabolic conversion of inorganic carbon to acetic and butyric acids with 26% higher productivity than the control (atmospheric pressure). Maximum volatile fatty acid (VFA) yield of 3.7 g/L was observed at alkaline pH (8.5) under 2 bar pressure at carbon load of 10 g/L, 96 h). Acetic (3.0 g/L) and butyric (0.7 g/L) acids were the major products upon conversion of 85% of the inorganic substrate. A better in-situ buffering (β = 0.048) at pH 8.5 along with higher reductive current (RCC: -4.4 mA) depicted better performance of GF towards CO₂ reduction.