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Oxygenic photosynthesis conducted by cyanobacteria has dramatically transformed the geochemistry of our planet. These organisms have colonized most habitats, including extreme environments such as the driest warm desert on Earth: the Atacama Desert. In particular, cyanobacteria highly tolerant to desiccation are of particular interest for clean energy production. These microorganisms are promising candidates for designing bioelectrodes for photocurrent generation owing to their ability to perform oxygenic photosynthesis and to withstand long periods of desiccation. Here, we present bioelectrochemical assays in which graphite electrodes were modified with the extremophile cyanobacterium Gloeocapsopsis sp. UTEXB3054 for photocurrent generation. Optimum working conditions for photocurrent generation were determined by modifying directly graphite electrode with the cyanobacterial culture (direct electron transfer), as well as using an Os polymer redox mediator (mediated electron transfer). Besides showing outstanding photocurrent production for Gloeocapsopsis sp. UTEXB3054, both in direct and mediated electron transfer, our results provide new insights into the metabolic basis of photocurrent generation and the potential applications of such an assisted bioelectrochemical system in a worldwide scenario in which clean energies are imperative for sustainable development.

Fungi are ubiquitous in the marine environment, but their role in carbon and nitrogen cycling in the ocean, and in particular the quantitative significance of fungal biomass to ocean biogeochemistry, has not yet been assessed. Determination of the biochemical and stable isotope composition of marine fungi can provide a basis for identifying fungal patterns in relation to other microbes and detritus, and thus allow evaluation of their contribution to the transformation of marine organic matter. We characterized the biochemical composition of 13 fungal strains isolated from distinct marine environments in the eastern South Pacific Ocean off Chile. Proteins accounted for 3 to 21% of mycelial dry weight, with notably high levels of the essential amino acids histidine, threonine, valine, lysine and leucine, as well as polyunsaturated fatty acids, ergosterol, and phosphatidylcholine. Elemental composition and energetic content of these marine-derived fungi were within the range reported for bacteria, phytoplankton, zooplankton and other metazoans from aquatic environments, but a distinct pattern of lipids and proteins was identified in marine planktonic fungi. These biochemical signatures, and an elemental composition indicative of a marine planktonic source, have potential applications for the assessment of fungal contribution to marine microbial biomass and organic matter reservoirs, and the cycling of carbon and nutrients.

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Abstract. We reconstructed oxygenation changes in the upwelling ecosystem off Concepción (36° S), Chile, using inorganic and organic proxies in a sediment core covering the last ca. 110 years of sedimentation in this area. Authigenic enrichments of Mo, U and Cd were observed between ca. 1935 and 1971 CE, implying a prolonged period with predominantly more reduced conditions in bottom waters and surface sediments. Significant positive correlations between redox-sensitive metals, algal sterols, biomarkers of micro-aerophilic and anaerobic microorganisms, and archaeal glycerol dialkyl glycerol tetraethers point to a tight coupling among bottom water O2 depletion and increased primary and export production. The time interval with low O2 of ca. 35 years seems to follow low-frequency interdecadal variation of the Pacific Decadal Oscillation, and it may have resulted in O2 depletion over the entire continental shelf off Concepción. Taking this together with the concurrent increase in sedimentary molecular indicators of micro-aerophilic and anaerobic microbes, we can suggest that changes in oxygenation of the water column are reflected by changes in microbial community. This study can inform our understanding of ecological consequences to projected trends in ocean deoxygenation.