No abstract

Microbial fuel cells (MFCs) can be designed to combine water treatment with concomitant electricity production. Animal manure treatment has been poorly explored using MFCs, and its implementation at full-scale primarily relies on the bacterial distribution and activity within the treatment cell. This study reports the bacterial community changes at four positions within the anode of two almost identically operated MFCs fed swine manure. Changes in the microbiome structure are described according to the MFC fluid dynamics and the application of a maximum power point tracking system (MPPT) compared to a fixed resistance system (Ref-MFC). Both external resistance and cell hydrodynamics are thought to heavily influence MFC performance. The microbiome was characterised both quantitatively (qPCR) and qualitatively (454-pyrosequencing) by targeting bacterial 16S rRNA genes. The diversity of the microbial community in the MFC biofilm was reduced and differed from the influent swine manure. The adopted electric condition (MPPT vs fixed resistance) was more relevant than the fluid dynamics in shaping the MFC microbiome. MPPT control positively affected bacterial abundance and promoted the selection of putatively exoelectrogenic bacteria in the MFC core microbiome (Sedimentibacter sp. and gammaproteobacteria). These differences in the microbiome may be responsible for the two-fold increase in power production achieved by the MPPT-MFC compared to the Ref-MFC.

Natural attenuation processes alleviate the impact of fertilization practices on groundwater resources. Therefore, identifying the occurrence of denitrification has become a requirement for water quality management. Several approaches are useful for this purpose, such as isotopic and microbiological methods, each of them providing distinct but complementary information about denitrification reactions, attenuation rates and their occurrence in the aquifer. In this paper, we investigate the contribution of both approaches to describe denitrification in a consolidated rock aquifer (limestone and marls), with a porosity related to fracture networks located in the northeastern sector of the Osona basin (NE Spain). Isotopic methods indicated the origin of nitrate (fertilization using manure) and that denitrification occurred, reaching a reduction of near 25% of the nitrate mass in groundwater. The studied area could be divided in two zones with distinct agricultural pressures and, consequently, nitrate concentrations in groundwater. Denitrification occurred in both zones and at different levels, indicating that attenuation processes took place all along the whole hydrogeological unit, and that the observed levels could be attributed to a larger flow path or, in a minor extent, to mixing processes that mask the actual denitrification rates. Microbiological data showed a correlation between denitrifier genes and the isotopic composition. However, the groundwater microbiome and the distribution of denitrifying bacteria did not reveal a major influence on the denitrification level observed by isotopic methods. This focuses the interest of microbiological analysis to identify functional genes within the bacteria present in the aquifer. Results indicated that isotopic methods provide information of the overall denitrification ability of the hydrogeological unit, and that genomic data represent the processes actually acting nearby the well. A combination of both approaches is advised to support induced in situ attenuation actions in polluted sites.

Coordinated distributed experiments (CDEs) enable the study of large-scale ecological patterns in geographically dispersed areas, while simultaneously providing broad academic and personal benefits for the participants. However, the effective involvement of early-career researchers (ECRs) presents major challenges. Here, we analyze the benefits and challenges of the first CDE exclusively led and conducted by ECRs (i.e. ECR-CDE), which sets a baseline for similar CDEs, and we provide recommendations for successful CDE execution. ECR-CDEs achieve most of the outcomes identified in conventional CDEs as well as extensive benefits for the young cohort of researchers, including: (i) receiving scientific credit, (ii) peer-training in new concepts and methods, (iii) developing leadership and communication skills, (iv) promoting a peer network among ECRs, and (v) building on individual engagement and independence. We also discuss the challenges of ECR-CDEs, which are mainly derived from the lack of independence and instability of the participants, and we suggest mechanisms to address them, such as resource reallocation and communication strategies. We conclude that ECR-CDEs can be a relevant tool to empower ECRs across disciplines by fostering their training, networking and personal well-being.

Enhanced UV radiation levels and decreased rainfall in Mediterranean terrestrial ecosystems due to climate change might impact soil bacterial communities, significantly altering their structure and affecting biogeochemical cycles.The aim of this study was to evaluate the effect of UV-B and UV-A radiation on soil bacterial richness, abundance and community composition in a Typic Dystroxerept of Mediterranean shrubland and to determine whether these effects depend on reduced rainfall and/or soil physicochemical properties. Soils were subjected to long-term UV conditions: UV-A + UV-B exclusion (UV0