Alejandra Arancibia

Some sulfate-reducing bacteria (SRB), mainly belonging to the Desulfovibrionaceae family, have evolved the capability to conserve energy through microbial extracellular electron transfer (EET), suggesting that this process may be more widespread than previously believed. While previous evidence has shown that mobile genetic elements drive the plasticity and evolution of SRB and iron-reducing bacteria (FeRB), few have investigated the shared molecular mechanisms related to EET. To address this, we analyzed the prevalence and abundance of EET elements and how they contributed to their differentiation among 42 members of the Desulfovibrionaceae family and 23 and 59 members of Geobacteraceae and Shewanellaceae, respectively. Proteins involved in EET, such as the cytochromes PpcA and CymA, the outer membrane protein OmpJ, and the iron–sulfur cluster-binding CbcT, exhibited widespread distribution within Desulfovibrionaceae. Some of these showed modular diversification. Additional evidence revealed that horizontal gene transfer was involved in the acquiring and losing of critical genes, increasing the diversification and plasticity between the three families. The results suggest that specific EET genes were widely disseminated through horizontal transfer, where some changes reflected environmental adaptations. These findings enhance our comprehension of the evolution and distribution of proteins involved in EET processes, shedding light on their role in iron and sulfur biogeochemical cycling.

Technical advances have converted bioremediation into a large-scale ecosystem service suitable for the treatment of polluted soils worldwide; however, its application in Chile is scarce. The main hurdles that must be addressed include the capacities of such approaches for the treatment of polluted soils, the lack of knowledge about key factors affecting bioremediation costs and the lack of a legal framework to regulate this activity. In this study, the economic performance of the bioremediation of chronically hydrocarbon-polluted urban soils based on bioaugmentation, biostimulation or the combination of both approaches projected to an industrial scale was evaluated. The cost of bioremediation ranged between USD 50.7 and USD 310.4 per m³ of contaminated soil. In addition, the items and activities that had the most significant impacts on the final bioremediation cost, such as compost for biostimulation and bacterial growth media for bioaugmentation-based approaches, were identified. The projected costs were compared against an extensive database of 130 soil bioremediation projects. The bioremediation treatment costs fell within the top 60% of the more expensive projects, highlighting the high effort involved in bioremediation of chronically contaminated soils. This framework can facilitate the decision making of entrepreneurs, consultants, researchers and governmental authorities when launching initiatives to develop a local bioremediation industry capable of cleaning up a high number of polluted sites in Chile.