Search Results (5)

Propionate, a critical intermediate in anaerobic digestion, and its syntrophic removal, is sensitive to stress. To our knowledge, this study investigates for the first time the response of a metabolic gene panel to organic loading rate (OLR) stress in propionate-degrading methanogenic consortia in lab-scale upflow anaerobic sludge blanket (UASB) reactors. The experimental phases included stabilisation (1.4–2.8 g COD/L/day), electroactive enrichment, OLR shock (6 g COD/L/day), and early recovery. Quantitative PCR was used to assess the abundance of key functional genes (16SrRNA, mcrA, pilA, and hgtR). During stabilisation, ~200 mLCH₄/h was produced, the mcrA/16SrRNA ratio was 0.78–2.64, and pilA and hgtR abundances were 1.29–2.27 × 10⁵ and 2.12–4.37 × 10⁴ copies/gVS. Following the OLR shock, methane production ceased entirely, accompanied by a sharp decline in the mcrA/16S ratio (0.08–0.24) and significant reductions in pilA (1.43-log) and hgtR (1.34-log) abundance. Partial recovery of pilA and hgtR abundance (1.19 × 10⁵ and 8.57 × 10⁴) was observed in the control reactor after the early recovery phase. The results highlight the utility of mcrA, 16SrRNA, pilA, and associated ratios, as reliable indicators of OLR stress in lab-scale UASB reactors. This study advances the understanding of molecular stress responses in propionate-degrading methanogenic consortia, focusing on direct interspecies electron transfer in process stability and recovery. Full article

Sulphur plays a fundamental role in the biological processes of chemolithotrophic microorganisms. Due to the redox characteristics of sulphur, microorganisms use it for metabolic processes. Such is the case of the dissimilatory processes in the anaerobic respiration of reducing microorganisms. The production of electrical energy from the metabolism of native microorganisms using sulphur as substrate from inorganic mineral sources in the form of Galena (PbS) was achieved using MR mineral medium with 15% (w/v) of PbS mineral concentrate. At 400 h of growth, the highest voltage produced in an experimental unit under anaerobic conditions was 644 mV. The inoculum was composed of microorganisms with spiral morphology, and at the final stages of energy production, the only microorganism identified was Bacillus clausii. This microorganism has not been reported in bioelectrochemical systems, but it has been reported to be present in corrosive environments and reducing anoxic environments. Full article

Iron-based nanomaterials (NMs) are increasingly used to promote extracellular electron transfer (EET) for energy production in bioelectrochemical systems (BESs). However, the composition and roles of planktonic bacteria in the solution regulated by iron-based NMs have rarely been taken into account. Herein, the changes of the microbial community in the solution by S-doped NiFe₂O₄ anodes have been demonstrated and used for constructing electroactive consortia on normal carbon cloth anodes, which could achieve the same level of electricity generation as NMs-mediated biofilm, as indicated by the significantly high voltage response (0.64 V) and power density (3.5 W m⁻²), whereas with different microbial diversity and connections. Network analysis showed that the introduction of iron-based NMs made Geobacter positively interact with f_Rhodocyclaceae, improving the competitiveness of the consortium (Geobacter and f_Rhodocyclaceae). Additionally, planktonic bacteria regulated by S-doped anode alone cannot hinder the stimulation of Geobacter by electricity and acetate, while the assistance of lining biofilm enhanced the cooperation of sulfur-oxidizing bacteria (SOB) and fermentative bacteria (FB), thus promoting the electroactivity of microbial consortia. This study reveals the effect of S-doped NiFe₂O₄ NMs on the network of microbial communities in MFCs and highlights the importance of globality of microbial community, which provides a feasible solution for the safer and more economical environmental applications of NMs. Full article

The aim of this work is the optimization of electrospun polymeric nanofibers as an ideal reservoir of mixed electroactive consortia suitable to be used as anodes in Single Chamber Microbial Fuel Cells (SCMFCs). To reach this goal the microorganisms are directly embedded into properly designed nanofibers during the electrospinning process, obtaining so called nanofiber-based bio-composite (bio-NFs). This research approach allowed for the designing of an advanced nanostructured scaffold, able to block and store the living microorganisms inside the nanofibers and release them only after exposure to water-based solutions and electrolytes. To reach this goal, a water-based polymeric solution, containing 5 wt% of polyethylene oxide (PEO) and 10 wt% of environmental microorganisms, is used as the initial polymeric solution for the electrospinning process. PEO is selected as the water-soluble polymer to ensure the formation of nanofiber mats offering features of biocompatibility for bacteria proliferation, environment-friendliness and, high ionic conductivity. In the present work, bio-NFs, based on living microorganisms directly encapsulated into the PEO nanofiber mats, were analyzed and compared to PEO-NFs made of PEO only. Scanning electron microscopy allowed researchers to confirm the rise of a typical morphology for bio-NFs, evidencing the microorganisms’ distribution inside them, as confirmed by fluorescence optical microscopy. Moreover, the latter technique, combined with optical density measurements, allowed for demonstrating that after electrospinning, the processed microorganisms preserved their proliferation capability, and their metabolic activity after exposure to the water-based electrolyte. To demonstrate that the energy-production functionality of exo-electrogenic microorganisms was preserved after the electrospinning process, the novel designed nanomaterials, were directly deposited onto carbon paper (CP), and were applied as anode electrodes in Single Chamber Microbial Fuel Cells (SCMFCs). It was possible to appreciate that the maximum power density reached by bio-NFs, which resulted in being double of the ones achieved with PEO-NFs and bare CP. SCMFCs with bio-NFs applied as anodic electrodes reached a current density value, close to (250 ± 5.2) mA m⁻², which resulted in being stable over time and was comparable with the one obtained with carbon-based electrode, thus confirming the good performance of the whole device. Full article

Microbial electrochemical technologies (METs) have a number of potential technological applications. In this work, we report the use of screen-printed electrodes (SPEs) as a tool to analyze the microbial electroactivity by using Geobacter sulfurreducens as a model microorganism. We took advantage of the small volume required for the assays (75 μL) and the disposable nature of the manufactured strips to explore short-term responses of microbial extracellular electron transfer to conductive materials under different scenarios. The system proved to be robust for identifying the bioelectrochemical response, while avoiding complex electrochemical setups, not available in standard biotechnology laboratories. We successfully validated the system for characterizing the response of Geobacter sulfurreducens in different physiological states (exponential phase, stationary phase, and steady state under continuous culture conditions) revealing different electron transfer responses. Moreover, a combination of SPE and G. sulfurreducens resulted to be a promising biosensor for quantifying the levels of acetate, as well as for performing studies in real wastewater. In addition, the potential of the technology for identifying electroactive consortia was tested, as an example, with a mixed population with nitrate-reducing capacity. We therefore present SPEs as a novel low-cost platform for assessing microbial electrochemical activity at the microscale level. Full article