Interaction between CO2-consuming autotrophy and CO2-producing heterotrophy in non-axenic phototrophic biofilms

As the effects of climate change become increasingly evident, the need for effective CO2 management is clear. Microalgae are well-suited for CO2 sequestration, given their ability to rapidly uptake and fix CO2. They also readily assimilate inorganic nutrients and produce a biomass with inherent commercial value, leading to a paradigm in which CO2-sequestration, enhanced wastewater treatment, and biomass generation could be effectively combined. Natural non-axenic phototrophic cultures comprising both autotrophic and heterotrophic fractions are particularly attractive in this endeavour, given their increased robustness and innate O2-CO2 exchange. In this study, the interplay between CO2-consuming autotrophy and CO2-producing heterotrophy in a non-axenic phototrophic biofilm was examined. When the biofilm was cultivated under autotrophic conditions (i.e. no organic carbon), it grew autotrophically and exhibited CO2 uptake. After amending its growth medium with organic carbon (0.25 g/L glucose and 0.28 g/L sodium acetate), the biofilm rapidly toggled from net-autotrophic to net-heterotrophic growth, reaching a CO2 production rate of 60 μmol/h after 31 hours. When the organic carbon sources were provided at a lower concentration (0.125 g/L glucose and 0.14 g/L sodium acetate), the biofilm exhibited distinct, longitudinally discrete regions of heterotrophic and autotrophic metabolism in the proximal and distal halves of the biofilm respectively, within 4 hours of carbon amendment. Interestingly, this upstream and downstream partitioning of heterotrophic and autotrophic metabolism appeared to be reversible, as the position of these regions began to flip once the direction of medium flow (and hence nutrient availability) was reversed. The insight generated here can inform new and important research questions and contribute to efforts aimed at scaling and industrializing algal growth systems, where the ability to understand, predict, and optimize biofilm growth and activity is critical.

Taxonomic and denitrifying bacteria communities associated with the interception of nitrate leaching by carbon amendment in the subsoil

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Taxonomic and denitrifying bacteria communities associated with the interception of nitrate leaching by carbon amendment in the subsoil

Nitrate leaching is severe in greenhouse agriculture where excessive nitrogen is often applied to maintain high crop productivities. Carbon amendment in the subsoil, where denitrification is limited by the availability of carbon, might mitigate nitrate leaching. In this study, we investigated the effects of carbon amendment in the subsoil on nitrate leaching and the emission of greenhouse gases (CH 4 and N 2 O) emissions using a soil column experiment. Diversity and abundance of total and nirS-, nirK- , and nosZ -type denitrifying bacteria were investigated by high throughput sequencing of PCR amplicons and quantitative real-time PCR. The amounts of nitrate leaching were >39% less in the treatments with carbon amendment than in the non-amended control without fertilization or in treatments fertilized by two doses (1600 or 3200 kg N ha - 1 ) of ammonia or nitrate. No effects of carbon amendment on the emissions of CH 4 or N 2 O were observed. The total N content in the subsoil zone with carbon amendment increased from 20.74% to 70.54%. Strikingly, the abundance of nirS , nosZ and 16S rRNA was higher in the treatment than the corresponding controls while no significant effects were detected for nirK . Carbon amendment rather than fertilization was the primary factor that influenced the community composition of the three denitrifying bacterial communities and explained 14%, 10%, and 4% of the variation in the community of nosZ, nirS , and nirK, respectively. Decreased alpha-diversity and increased variability in beta-diversity were observed for the carbon amended treatment for total and denitrifying bacteria. On average, genera such as Anaerovorax, Pseudobacteroides, Magnetospirillum, Prolixibacter, Sporobacter, Ignavibacterium, Syntrophobacter, Oxobacter, Hydrogenispora, Desulfosporomusa, Mangrovibacterium, and Sporomusa were enriched more than seven times in soil amended with carbon. In summary, carbon amendment in the subsoil mitigated nitrate leaching and increased the nitrogen pool by possible activation of denitrifying and anaerobic bacterial populations.

Nitrate Removal by Floating Treatment Wetlands Amended with Spent Coffee: A Mesocosm-Scale Evaluation

HighlightsA floating treatment wetland design was evaluated for water quality improvements.Nitrate-N removal rates were quantified using spent coffee grounds as a carbon source.Nitrate-N removal rates increased throughout the growing season Abstract. The Midwestern U.S. is vulnerable to eutrophic conditions from high nutrient concentrations. Floating treatment wetlands (FTWs) are an innovative wetland design for nutrient removal from nonpoint sources and provide a unique treatment. The objectives of this project were to quantify nitrate removal in traditional and carbon-amended FTWs planted with Midwestern plant species during the establishment year. Three greenhouse experiments were conducted throughout the growing season using 18 mesocosms. Two vegetation designs were evaluated: rush species ( and ) and diverse species (, , , , , and ). Spent coffee grounds were applied to 9 of the 18 mesocosms as a carbon amendment. Nitrate-N removal increased during the establishment growing season in the FTW systems (Spring: 15.0% to 17.3%, Summer 1: 82.8% to 92.6%, Summer 2: 86.4% to 94.7%). Nitrate-N removal was also impacted by carbon amendments (FTW without amendment: 82.8% to 94.7%, FTW with amendment: 88.4% to 96.1%). Carbon additions were found to enhance denitrifying conditions even in the absence of FTWs (decreased dissolved oxygen, increased available organic carbon). Significant differences in nitrate-N removal were not observed between FTW vegetation designs. This study provides new insight on the impacts of the growing season, plant species, and carbon amendments on FTW nitrate-N removal performance during the establishment year. Keywords: Best management practices, Carbon amendment, Floating treatment wetlands, Nitrogen removal, Spent coffee grounds