Thermoanaerobacterium sp. Strain RBIITD as a dominant species in accelerating thermophilic dark fermentation start up through pH and substrate concentration regulation

Functional microorganisms in hydrogen production: Mechanisms and applications

The rapid growth of global energy demand accelerates the development of sustainable, clean, and renewable energy sources. Biohydrogen production, driven by functional microorganisms, offers a promising solution. Multiple species of bacteria, fungi, microalgae, and archaea were able to produce hydrogen. This study reviewed the typical strains, together with their hydrogen-production mechanisms, e.g., bio-photolysis, photo fermentation, and dark fermentation. Bacteria (e.g., purple non-sulfur bacteria) and microalgae (e.g., cyanobacteria) have been widely investigated, with respect to the limited fungi and archaea. It showed that temperature, pH, and substrate availability could all substantially influence the efficiency of biohydrogen production. Meanwhile, photo and dark fermentations are favored for future possible industrial applications. Furthermore, this review summarized practical applications of biohydrogen production, such as applications of bioreactors, waste treatments, and integrated systems for hydrogen production, highlighting the importance of functional microorganisms in advancing biohydrogen technology under global energy crisis.

Biosynthesis of Chryseno[2,1,c]oxepin-12-Carboxylic Acid from Glycyrrhizic Acid in Aspergillus terreus TMZ05-2, and Analysis of Its Anti-inflammatory Activity

Glycyrrhizic acid, glycyrrhetinic acid, and their oxo, ester, lactone, and other derivatives, are known for their anti-inflammatory, anti-oxidant, and hypoglycemic pharmacological activities. In this study, chryseno[2,1-c]oxepin-12-carboxylic acid (MG) was first biosynthesized from glycyrrhizic acid through sequential hydrolysis, oxidation, and esterification using Aspergillus terreus TMZ05-2, providing a novel in vitro biosynthetic pathway for glycyrrhizic acid derivatives. Assessing the influence of fermentation conditions and variation of strains during culture under stress-induction strategies enhanced the final molar yield to 88.3% (5 g/L glycyrrhizic acid). CCK8 assays showed no cytotoxicity and good cell proliferation, and anti-inflammatory experiments demonstrated strong inhibition of NO release (36.3%, low-dose MG vs. model), transcriptional downregulation of classical effective cellular factors tumor necrosis factor-α (TNF-α; 72.2%, low-dose MG vs. model), interleukin-6 (IL-6; 58.3%, low-dose MG vs. model) and interleukin-1β (IL-1β; 76.4%, low-dose MG vs. model), and decreased abundance of P-IKK-α, P-IKB-α, and P-P65 proteins, thereby alleviating inflammatory responses through the NF-κB pathway in LPS-induced RAW264.7 cells. The findings provide a reference for the biosynthesis of lactone compounds from medicinal plants.

Light stimulation strategy for promoting bio-hydrogen production: Microbial community, metabolic pathway and long-term application

Light stimulation strategy for promoting bio-H₂ production was firstly investigated with incandescent light. The light condition controlled by photon number (N_R, 0.63 × 10⁴-6.25 × 10⁴ μmol/(day∙L)) was applied to stimulate H₂ fermentation process. The optimal N_R of 3.75 × 10⁴ μmol/(day∙L) contributed to 1.4 folds H₂ yield of the dark reactor and promoted efficient H₂ producing pathway (acetate and nicotinamide adenine dinucleotide pathway) with increased microbial activities. Furthermore, the effect of light stimulation on microbial community was identified. Fervidobacterium, Coprothermobacter and OPB95 were the dominant genera that could be activated by light stimulation for promoting acetate pathway and contribute to higher H₂ production. Moreover, long-term operation showed more stable and higher H₂ production of light stimulated bioreactor than the dark one, which resulted from the light stimulated metabolic pathway, increased sludge conductance and promoted microbial immobilization. This novel light stimulation strategy is promising for future application on promoting bio-H₂ production.

Palm oil industrial wastes as a promising feedstock for biohydrogen production: A comprehensive review

By the year 2050, it is estimated that the demand for palm oil is expected to reach an enormous amount of 240 Mt. With a huge demand in the future for palm oil, it is expected that oil palm by-products will rise with the increasing demand. This represents a golden opportunity for sustainable biohydrogen production using oil palm biomass and palm oil mill effluent (POME) as the renewable feedstock. Among the different biological methods for biohydrogen production, dark fermentation and photo-fermentation have been widely studied for their potential to produce biohydrogen by using various waste materials as feedstock, including POME and oil palm biomass. However, the complex structure of oil palm biomass and POME, such as the lignocellulosic composition, limits fermentable substrate available for conversion to biohydrogen. Therefore, proper pre-treatment and suitable process conditions are crucial for effective biohydrogen generation from these feedstocks. In this review, the characteristics of palm oil industrial waste, the process used for biohydrogen production using palm oil industrial waste, their pros and cons, and the influence of various factors have been discussed, as well as a comparison between studies in terms of types of reactors, pre-treatment strategies, the microbial culture used, and optimum operating condition have been presented. Through biological production, hydrogen production rates up to 52 L-H₂/L-medium/h and 6 L-H₂/L-medium/h for solid and liquid palm oil industrial waste, respectively, can be achieved. In short, the continuous supply of palm oil production by-product and relatively, the low cost of the biological method for hydrogen production indicates the potential source of renewable energy.

Waste-to-energy nexus: A sustainable development

An upsurge in global population due to speedy urbanization and industrialization is facing significant challenges such as rising energy-demand, enormous waste-generation and environmental deterioration. The waste-to-energy nexus based on the 5R principle (Reduce, Reuse, Recycle, Recovery, and Restore) is of paramount importance in solving these Gordian knots. This review essentially concentrates on latest advancements in the field of 'simultaneous waste reduction and energy production' technologies. The waste-to-energy approaches (thermal and biochemical) for energy production from the agricultural residues are comprehensively discussed in terms environmental, techno-economic, and policy analysis. The review will assess the loopholes in order to come up with more sophisticated technologies that are not only eco-friendly and cost-effective, but also socially viable. The waste-to-energy nexus as a paradigm for sustainable development of restoring waste is critically discussed considering future advancement plans and agendas of the policy-makers.

Rapid recruitment of hydrogen-producing biofilms for hydrogen production in a moving bed biofilm reactor by a sequential immobilization and deoxygenization approach

To reduce start-up time and enhance hydrogen production efficiency, a sequential immobilization and deoxygenization (SIDO) strategy for hydrogen production was investigated in continuous-flow moving bed biofilm reactors (MBBRs). The pre-immobilization process accelerated the initial enrichment of hydrogen-producing bacteria (HPB) and promoted the biofilm formation, which contribute to higher hydrogen production efficiency in SIDO-MBBRs compared to a non-immobilized reactor. A similar deoxygenization effect was achieved by inoculation with Pseudomonas aeruginosa compared with N₂ sparging, and the P. aeruginosa pre-immobilized MBBR (Pse-MBBR) showed a higher H₂ yield in the initial stage of operation. Microbial community analysis found a higher abundance of putative HPB in the range of 82.82-96.56%, with the predominant populations in the SIDO-MBBR assigned to genera Clostridium and Enterobacter. The results suggest that the SIDO-MBBR is an effective approach for rapid recruitment of HPB and start-up of fermentative hydrogen production.