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All biological hydroxylation reactions are thought to derive the oxygen atom from one of three inorganic oxygen donors, O2, H2O2 or H2O. Here, we have identified the organic compound prephenate as the oxygen donor for the three hydroxylation steps of the O2-independent biosynthetic pathway of ubiquinone, a widely distributed lipid coenzyme. Prephenate is an intermediate in the aromatic amino acid pathway and genetic experiments showed that it is essential for ubiquinone biosynthesis in Escherichia coli under anaerobic conditions. Metabolic labeling experiments with 18O-shikimate, a precursor of prephenate, demonstrated the incorporation of 18O atoms into ubiquinone. The role of specific iron--sulfur enzymes belonging to the widespread U32 protein family is discussed. Prephenate-dependent hydroxylation reactions represent a unique biochemical strategy for adaptation to anaerobic environments. [ABSTRACT FROM AUTHOR]

Photogeneration of hydrogen in microalgae is thought to be among the mechanisms increasing their resilience to stresses including those caused by nutrient deprivation by re-routing the flow of electrons and reducing power in the cell. Metabolism of phosphorus (P), an essential nutrient, and its reserve forms such as polyphosphate (PolyP), is affected by and plays a role in the responses to diverse stresses, too. However, the potential interplay of the capability of photogeneration of hydrogen and turnover of phosphorus-rich inclusions in stressed microalgae cells so far escaped the attention of researchers. Here, we present a quantitative ultrastructural view of the turnover of P-rich inclusions in the model microalga Chlamydomonas reinhardtii strains, the parent strain CC-425 and its hydEF-1 mutant lacking hydrogenase activity as a function of sulfur and oxygen availability in the medium. In addition to the electron microscopy cell image analysis of the studied strains, we followed the elemental composition of the inclusions in different (sub) compartments of the cells obtained with energy dispersive X-ray spectroscopy. The stress caused by sulfur deprivation and subsequent transition of the microalgae culture to anaerobic conditions declined the size of phosphorus-containing inclusions but increased their number in the parent strain. Overall, the accumulation of the phosphorus-rich inclusions in hydEF-1 mutant was much lower than in the fully functional parent strain regardless of the cultivation conditions. We believe that impaired hydrogenase activity and correspondingly reduced sink of electrons and reducing power in the mutant strain indirectly affects the turnover of P and its reserves in the cell. These effects were manifested by the changes in the abundance, morphology, and elemental composition of the P-containing inclusions. We hypothesized that the sulfur-deprivation stress increased the initiation of the biosynthesis of PolyP chains, but their elongation and hence the formation of large PolyP-containing inclusions was hindered by anaerobiosis. [ABSTRACT FROM AUTHOR]

Molasses are a source of fermentable sugars, the substrate utilized for this study, as it is a subproduct from sugarcane processing for sucrose recovery. These sugars can be metabolized for bioH 2 production by bacterial strains, particularly strict-anaerobe Clostridium acetobutylicum (Clac) and its media preparation requires chemical of O 2 removal and N 2 flushing to promote anaerobiosis. Bacillus subtilis (Bsub) can deplete O 2 from culture media and promotes anaerobiosis, which is an aspect that would benefit from further research. Clac was grown in an anaerobic medium and produced 269 mL of hydrogen at 72 h. By co-culturing Clac and Bsub , 502 mL of bioH 2 were produced in a cysteine/N 2 flushed medium, while 203 mL of bioH 2 at 72 h were produced by aerobic co-culture. Additionally, in an untreated/aerobic conventional growth culture for Clac , no production of H 2 was detected, reinforcing the utility of Bsub for anaerobiosis generation. • Clostridium acetobutylicum consumes substrate approximately 6x faster than Bacillus subtilis. • Clostridium acetobutylicum produced 202 mL of bioH 2 in a culture with anaerobiosis assisted by Bacillus subtilis. • Bacillus subtilis CBB5555 can act as a biological O 2 depleter for anaerobic bioprocesses. [ABSTRACT FROM AUTHOR]

Anaeramoebae is a recently described phylum of anaerobic, marine amoebae, and amoeboflagellates belonging to the Metamonada supergroup. So far, six species have been described based on light microscopic morphology and sequences of the SSU rRNA gene. Here we present three new strains of Anaeramoeba with a description of their morphology, ultrastructure, and phylogenetic position based on the analysis of SSU rRNA gene sequences. Two of the strains represent a new species, Anaeramoeba pumila sp. nov., that has the smallest cells of all known Anaeramoeba species, and one that represents a species from the newly recognized Anaeramoeba flamelloides complex. Anaeramoebae are known to have a syntrophic relationship with prokaryotes. Our strains display two novel, remarkable types of symbioses, previously unknown from Anaeramoebae. [ABSTRACT FROM AUTHOR]

Green hydrogen, produced during microalgal photosynthesis, is regarded as one of the most promising sustainable energy sources. It utilizes sunlight and water, which are essentially unlimited, and its combustion results in only water as a waste product. In microalgal hydrogen energy production systems, the sensitivity of hydrogenase to O2 poses a significant challenge, limiting sustained photosynthetic H2 production in microalgae. Additionally, efficient photosynthetic H2 production in anaerobic microalgal cells is hindered by impaired electron source (photosystem II) and electron loss through the Calvin‐Benson cycle, cyclic electron transfer around photosystem I, and O2 photoreduction, which are identified as the other key challenges. Over the past eight decades, considerable progress has been made in addressing these challenges and regulating electron transfer to achieve sustainable and efficient photosynthetic H2 production in microalgae. In this review, we discuss a range of regulatory methods for achieving sustainable and efficient photosynthetic H2 production in microalgae. Emphasizing the significant progress made over the past eight decades, we also address current challenges and propose potential future solutions. [ABSTRACT FROM AUTHOR]

Vibrio cholerae can form biofilms in the aquatic environment and in the human intestine, facilitating the release of hyper-infectious aggregates. Due to the increasing antibiotic resistance, alternatives need to be found. One of these alternatives is antimicrobial peptides, including polymyxin B (PmB). In this study, we first investigated the resistance of V. cholerae O1 El Tor strain A1552 to various antimicrobials under aerobic and anaerobic conditions. An increased resistance to PmB is observed in anaerobiosis, with a 3-fold increase in the dose required for 50 % growth inhibition. We then studied the impact of the PmB on the formation and the degradation of V. cholerae biofilms to PmB. Our results show that PmB affects more efficiently biofilm formation under anaerobic conditions. On the other hand, preformed biofilms are susceptible to degradation by PmB at concentrations close to the minimal inhibitory concentration. At higher concentrations, we observe an opacification of the biofilm structures within 20 min post-treatment, suggesting a densification of the structure. This densification does not seem to result from the overexpression of matrix genes but rather from DNA release through massive cell lysis, likely forming a protective shield that limits the penetration of the PmB into the biofilm. [ABSTRACT FROM AUTHOR]

The waste generated by the mezcal and seafood restaurant industries has significant negative environmental impacts on soils, water, and air. However, these waste materials offer the potential for methane production through anaerobic digestion. This research focuses on evaluating a methodological strategy that involves using an enriched inoculum, co-digesting waste materials, and applying specific pretreatment (chemical, thermal, and adjusting the volumetric ratio of residues) to produce biogas with a high methane content, as assessed through the Biochemical Methane Potential (BMP) test. The results demonstrate that the enriched inoculum used in the test exhibited a pH of 8.18, an Alkalinity of 31 g CaCO3/L, and an alpha (α) ratio of 0.75. The BMP test was conducted over 29 days. In the most successful test, which involved pretreatment at a temperature of 50 °C, a residue ratio of 1 VSW (Volume of Seafood Waste)/2 VMV (Volume of Mezcal Vinasses), and a pH of 6.5, we achieved a methane production of 1420.51 ± 0.038 N mL CH4, with a biogas containing 81.5% methane. This process also yielded 175.37 N mL CH4 per gram of Volatile Solids (VS) and a degradation kinetic constant of 0.14 1/d. Through the methodological strategy used with the combination of an enriched and stabilized inoculum, the co-digestion of the waste for nutrient complementation, and the application of pretreatments, it was achieved that the different stages that constitute the anaerobic process allowed for the establishment of optimal conditions for the generation of biogas with a high methane content.Graphical Abstract: The waste generated by the mezcal and seafood restaurant industries has significant negative environmental impacts on soils, water, and air. However, these waste materials offer the potential for methane production through anaerobic digestion. This research focuses on evaluating a methodological strategy that involves using an enriched inoculum, co-digesting waste materials, and applying specific pretreatment (chemical, thermal, and adjusting the volumetric ratio of residues) to produce biogas with a high methane content, as assessed through the Biochemical Methane Potential (BMP) test. The results demonstrate that the enriched inoculum used in the test exhibited a pH of 8.18, an Alkalinity of 31 g CaCO3/L, and an alpha (α) ratio of 0.75. The BMP test was conducted over 29 days. In the most successful test, which involved pretreatment at a temperature of 50 °C, a residue ratio of 1 VSW (Volume of Seafood Waste)/2 VMV (Volume of Mezcal Vinasses), and a pH of 6.5, we achieved a methane production of 1420.51 ± 0.038 N mL CH4, with a biogas containing 81.5% methane. This process also yielded 175.37 N mL CH4 per gram of Volatile Solids (VS) and a degradation kinetic constant of 0.14 1/d. Through the methodological strategy used with the combination of an enriched and stabilized inoculum, the co-digestion of the waste for nutrient complementation, and the application of pretreatments, it was achieved that the different stages that constitute the anaerobic process allowed for the establishment of optimal conditions for the generation of biogas with a high methane content. [ABSTRACT FROM AUTHOR]