Novel properties of photofermentative biohydrogen production by purple bacteria Rhodobacter sphaeroides: effects of protonophores and inhibitors of responsible enzymes

Living Therapeutics for Synergistic Hydrogen-Photothermal Cancer Treatment by Photosynthetic Bacteria

Hydrogen gas (H2) therapy, recognized for its inherent biosafety, holds significant promise as an anti-cancer strategy. However, the efficacy of H2 treatment modalities is compromised by their reliance on systemic gas administration or chemical reactions generation, which suffers from low efficiency, poor targeting, and suboptimal utilization. In this study, living therapeutics are employed using photosynthetic bacteria Rhodobacter sphaeroides for in situ H2 production combined with near-infrared (NIR) mediated photothermal therapy. Living R. sphaeroides exhibits strong absorption in the NIR spectrum, effectively converting light energy into thermal energy while concurrently generating H2. This dual functionality facilitates the targeted induction of tumor cell death and substantially reduces collateral damage to adjacent normal tissues. The findings reveal that integrating hydrogen therapy with photothermal effects, mediated through photosynthetic bacteria, provides a robust, dual-modality approach that enhances the overall efficacy of tumor treatments. This living therapeutic strategy not only leverages the therapeutic potential of both hydrogen and photothermal therapeutic modalities but also protects healthy tissues, marking a significant advancement in cancer therapy techniques.

Enhanced photo-fermentative hydrogen production by constructing Rhodobacter capsulatus-ZnO/ZnS hybrid system

This study incorporated ZnO/ZnS nanoparticles with Rhodobacter capsulatus SB1003, forming a hybrid system to promote photo-fermentative hydrogen production. The results indicate that the material's photocatalytic activity and concentration significantly affected hydrogen yield. The addition of ZnO/ZnS exhibited a more significant auxiliary effect than ZnO and achieved an approximately 30% increase in hydrogen production compared to the control group. ZnO/ZnS enhanced the production of extracellular polymers, thereby strengthening the synergy between the nanomaterials and the bacteria. The photogenerated electrons from ZnO/ZnS were utilized by the photosynthetic bacteria. Furthermore, the activity of nitrogenase was enhanced, resulting in improved hydrogen production performance. This study provides insights into hydrogen production by photosynthetic bacteria with the assistance of inorganic semiconductor nanomaterials.

Bacterial Electrophysiology

Bacterial ion fluxes are involved in the generation of energy, transport, and motility. As such, bacterial electrophysiology is fundamentally important for the bacterial life cycle, but it is often neglected and consequently, by and large, not understood. Arguably, the two main reasons for this are the complexity of measuring relevant variables in small cells with a cell envelope that contains the cell wall and the fact that, in a unicellular organism, relevant variables become intertwined in a nontrivial manner. To help give bacterial electrophysiology studies a firm footing, in this review, we go back to basics. We look first at the biophysics of bacterial membrane potential, and then at the approaches and models developed mostly for the study of neurons and eukaryotic mitochondria. We discuss their applicability to bacterial cells. Finally, we connect bacterial membrane potential with other relevant (electro)physiological variables and summarize methods that can be used to both measure and influence bacterial electrophysiology.

Bioconversion of volatile fatty acids from organic wastes to produce high-value products by photosynthetic bacteria: A review

Anaerobic fermentation of organic waste to produce volatile fatty acids (VFAs) production is a relatively mature technology. VFAs can be used as a cheap and readily available carbon source by photosynthetic bacteria (PSB) to produce high value-added products, which are widely used in various applications. To better enhance the VFAs obtained from organic wastes for PSB to produce high value-added products, a comprehensive review is needed, which is currently not available. This review systematically summarizes the current status of microbial proteins, H2, poly-β-hydroxybutyrate (PHB), coenzyme Q10 (CoQ10), and 5-aminolevulinic acid (ALA) production by PSB utilizing VFAs as a carbon resource. Meanwhile, the metabolic pathways involved in the H2, PHB, CoQ10, and 5-ALA production by PSB were deeply explored. In addition, a systematic resource utilization pathway for PSB utilizing VFAs from anaerobic fermentation of organic wastes to produce high value-added products was proposed. Finally, the current challenges and priorities for future research were presented, such as the screening of efficient PSB strains, conducting large-scale experiments, high-value product separation, recovery, and purification, and the mining of metabolic pathways for the VFA utilization to generate high value-added products by PSB.

Regulation of biohydrogen production by protonophores in novel green microalgae Parachlorella kessleri

The green microalgae Parachlorella kessleri RA-002 isolated in Armenia can produce biohydrogen (H₂) during oxygenic photosynthesis. Addition of protonophores, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNF) enhances H₂ yield in P. kessleri. The maximal H₂ yield of ~2.20 and 2.08 mmol L^-1 was obtained in the presence of 15 μM CCCP and 50 μM DNF, respectively. During dark conditions H₂ production by P. kessleri was not observed even in the presence of protonophores, indicating that H₂ formation in these algae was mediated by light conditions. The enhancing effect of protonophores can be coupled with dissipation of proton motive force across thylakoid membrane in P. kessleri, facilitating the availability of protons and electrons to [Fe-Fe]-hydrogenase, which led to formation of H₂. At the same time H₂ production was not observed in the presence of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a specific inhibitor of PS II. Moreover, diuron inhibits H₂ yield in P. kessleri in the presence of protonophores. The inhibitory effect of diuron coupled with suppression of electron transfer from PS II. The results showed that in these algae operates PS II-dependent pathway of H₂ generation. This study is important for understanding of the mechanisms of H₂ production by green microalgae P. kessleri and developing of its biotechnology.

Comparative effects of Ni(II) and Cu(II) ions and their combinations on redox potential and hydrogen photoproduction by Rhodobacter sphaeroides

The aim of the present work was the study of comparative effects of Cu(II) and Ni(II) and their mixture on growth, redox potential, hydrogen (H₂) yield and ATPase activity in phototrophic purple bacteria R. sphaeroides MDC6522 from Jermuk mineral spring in Armenia. It was ascertained, that Cu²⁺ and Ni²⁺ have different effects on bacterial specific growth rate: in the presence of 5μM Cu²⁺ growth rate was ~3.2-fold lower in comparison with control (no addition), and increased ~1.5-fold in medium with 5μM Ni²⁺. These changes may be resulted by action of the ions on redox potential (E_h). Low concentrations of Ni²⁺ had an enhancing effect on the E_h drop and H₂ production. The increase of concentration from 1 to 5μM enhanced the stimulatory effect of Ni²⁺. H₂ yield in R. sphaeroides (72h of growth) was enhanced ~3-fold with 5μM Ni²⁺, whereas in the presence of 5μM Cu²⁺ H₂ yield was ~1.2 fold lower in comparison with control. Cu²⁺+Ni²⁺ combinations effects were differed from the effect when ions used separately. When Cu²⁺ and Ni²⁺ were added together, the Ni²⁺ stimulatory effect disappeared, which indicated that heavy metal ions mixture may have different action mechanisms. Moreover, N,N'-dicyclohexylcarbodiimide-sensitive ATPase activity of R. sphaeroides membrane vesicles has been increased in the presence of both ions, but in the presence of Сu²⁺ the influence was feebly marked in comparison with Ni²⁺. The results suggest an interaction between these ions and the F_OF₁-ATPase. Thus, the results obtained point out discrimination between Cu²⁺ and Ni²⁺ and their combinations effects and reveal new regulatory pathways to enhance H₂ yield in R. sphaeroides.

Biohydrogen production by purple non-sulfur bacteria Rhodobacter sphaeroides: Effect of low-intensity electromagnetic irradiation

The present work was focused on the effects of low-intensity (the flux capacity was of 0.06mWcm(-2)) electromagnetic irradiation (EMI) of extremely high frequencies or millimeter waves on the growth and hydrogen (H2) photoproduction by purple non-sulfur bacteria Rhodobacter sphaeroides MDC6521 (from Armenian mineral springs). After exposure of R. sphaeroides, grown under anaerobic conditions upon illumination, to EMI (51.8GHz and 53.0GHz) for 15min an increase of specific growth rate by ~1.2-fold, in comparison with control (non-irradiated cells), was obtained. However, the effect of EMI depends on the duration of irradiation: the exposure elongation up to 60min caused the delay of the growth lag phase and the decrease specific growth rate by ~1.3-fold, indicating the bactericidal effect of EMI. H2 yield of the culture, irradiated by EMI for 15min, determined during 72h growth, was ~1.2-fold higher than H2 yield of control cells, whereas H2 production by cultures, irradiated by EMI for 60min was not observed during 72h growth. This difference in the effects of extremely high frequency EMI indicates a direct effect of radiation on the membrane transfer and the enzymes of these bacteria. Moreover, EMI increased DCCD-inhibited H(+) fluxes across the bacterial membrane and DCCD-sensitive ATPase activity of membrane vesicles, indicating that the proton FoF1-ATPase is presumably a basic target for extremely high frequency EMI related to H2 production by cultures.