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Cryoconite holes, ponds full of melting water with sediment on the bottom, are hotspots of biodiversity on glacier surfaces and host dynamic micro-ecosystems. They have been extensively investigated in different areas of the world (e.g., the Arctic, Antarctic, Alps, and Himalaya), but so far no study has described the bacterial communities of the glaciers in the Andes, the world’s longest mountain range. In this study, we describe the bacterial communities of three small (< 2 km2) high-elevation (< 4200 m a.s.l.) glaciers of the Central Andes (Iver, East Iver and Morado glaciers) and two large (> 85 km2) glaciers of the Patagonian Andes (Exploradores and Perito Moreno glaciers) whose ablation tongues reach low altitude (< 300 m a.s.l.). Results show that the bacterial communities were generally similar to those observed in the cryoconite holes of other continents, but with few cyanobacteria (0.5% of sequences). The most abundant orders were Betaproteobacteriales, Cytophagales, Chitinophagales, Acetobacterales, Frankiales, Armatimonadales, Sphingobacteriales, Rhizobiales, Bacteroidales, Sphingomonadales, and Micrococcales. The bacterial communities differed between glaciers and both water pH and O2 concentration appeared to influence the bacterial community composition. This work thus provides the first description of the bacterial communities in cryoconite holes of South American glaciers.

Selective export and retrieval of proteins between the endoplasmic reticulum (ER) and Golgi apparatus is indispensable for eukaryotic cell function. An essential step in the retrieval of ER luminal proteins from the Golgi is the pH-dependent recognition of a carboxyl-terminal Lys-Asp-Glu-Leu (KDEL) signal by the KDEL receptor. Here, we present crystal structures of the chicken KDEL receptor in the apo ER state, KDEL-bound Golgi state, and in complex with an antagonistic synthetic nanobody (sybody). These structures show a transporter-like architecture that undergoes conformational changes upon KDEL binding and reveal a pH-dependent interaction network crucial for recognition of the carboxyl terminus of the KDEL signal. Complementary in vitro binding and in vivo cell localization data explain how these features create a pH-dependent retrieval system in the secretory pathway.

Bioelectrochemical systems (BESs) have proven to be a useful tool for bioremediation and have been applied to achieve the oxidation of hydrocarbons at the anode. Microbial metabolism can be stimulated in a BES when overpotential is applied, increasing the rate of pollutant degradation. The aim of this work was to test the exoelectrogenic capacity of Cupriavidus metallidurans CH34 and to determine if the application of overpotential stimulates bioremediation of toluene-polluted water. Exoelectrogenic activity was studied with succinate as sole carbon source. C. metallidurans CH34 showed exoelectrogenic activity (maximum current density obtained was 0.65 mA/m2), reaching a 92% of succinate removal after 42 h. Although the upper pathway of toluene degradation from C. metallidurans CH34 has not been reported, C. metallidurans CH34 significantly reduced the concentration of toluene (from 100 to 42 ppm in 27 days) under denitrifying conditions. The concentration of toluene in the abiotic control remained stable. A Microbial Fuel Cell (MFC) was set with a pure culture of C. metallidurans CH34 using toluene as sole carbon source. When C. metallidurans CH34 was inoculated in a MFC containing toluene as sole carbon source, current densities reached 0.80 mA/m2. Conversely, in the abiotic control no current was detected. Toluene concentration in the control remained stable (38 ppm) while in inoculated MFC toluene decreased by 37% after 10 days. A Microbial Electrolysis Cell (MEC) was set with a pure culture of C. metallidurans CH34 using toluene as sole carbon source. In the MEC, overpotential (+800 mV) was applied between the anode and the cathode. In the biotic MEC, seven respikes were performed. Current density reached a maximum of 45 mA/m2 after the 7th respike, while in the control, current densities remained constant at 10 mA/m2. Current density increased when toluene was further spiked in the reactors. After the initial adsorption of toluene on the anodes of both inoculated and abiotic MECs, above 90% of the initial toluene in the biotic MEC was removed, while this compound remained stable in the abiotic reactor. Coulombic efficiencies of the toluene mineralization process increased with time. The coulombic efficiency between the second and the third respike was 18.9%, while the coulombic efficiency of the last period increased to 76.9%. These results showed that C. metallidurans CH34 is an exoelectrogen able to degrade toluene under anaerobic conditions and that the application of an external overpotential increased the rate of toluene removal and current production.

Bioelectrochemical systems (BESs) have proven to be a useful tool for bioremediation and have been applied to achieve the oxidation of organic compounds (e.g. hydrocarbons) at the anode. Microbial metabolism can be stimulated in a BES when overpotential is applied, increasing the rate of pollutant degradation. The aim of this work was to test the exoelectrogenic capacity of five hydrocarbonoclastic strains of the genera Cupriavidus and Pseudomonas and to determine if the applications of overpotential stimulates microbial metabolism, analyzing current density and substrate consumption. Exoelectrogenic activity was studied with succinate as sole carbon source. Three of the five strains (Cupriavidus metallidurans CH34, Pseudomonas sp. DN34 and Pseudomonas sp. DN36) showed exoelectrogenic activity. Comparing the current densities obtained with the three exoelectrogenic strains, Pseudomonas sp. DN36 reached a maximum of 1.00 mA/m2, followed by Cupriavidus metallidurans CH34 (0.65 mA/m2) and Pseudomonas sp. DN34 (0.23 mA/m2). C. metallidurans CH34, Pseudomonas sp. DN34 and Pseudomonas sp. DN36 reached a 91.74%, 89.38% and 35.28% of succinate removal respectively in 42 h. The application of overpotentials between the anode and the cathode lead to an increase in substrate consumption, turbidity and current density production. Although whole genome sequencing reveal that C. metallidurans CH34 lacks in the upper pathway of toluene degradation in anaerobic conditions, C. metallidurans CH34 significantly reduced (from 100 to 42 ppm in 27 days) the concentration of toluene under denitrifying conditions, while the abiotic control maintained toluene concentration around 100 ppm. A Microbial Fuel Cell (MFC) and a Microbial Electrolysis Cell (MEC) were set with a pure culture of C. metallidurans CH34 and with toluene as sole carbon source. In the MEC, overpotential (+800 mV) was applied between the anode and the cathode. When C. metallidurans CH34 was inoculated in a MFC containing toluene as sole carbon source, current densities reached 0.80 mA/m2. Conversely, in the abiotic control no current was detected. Toluene concentration in the control remained stable (38 ppm) while in inoculated MFC toluene decreased by 36.6% in 10 days. In the biotic MEC, current densities increased from 21 to 30 mA/m2 in 20 days, while in the control, current densities remained constant at 10 mA/m2. After the initial adsorption of toluene on the anodes of both inoculated and sterile control MECs, 63.3% of the initial toluene in the biotic MEC was removed, while it remained stable in the abiotic reactor. The current density increased when toluene was further spiked in the reactors. These data showed that C. metallidurans CH34 was able to degrade toluene under anaerobic conditions and to transfer electrons to a solid electrode.