Rapid evolution of colistin resistance in a bioreactor model of infection of Klebsiella pneumoniae.

Colistin remains an important antibiotic for the therapeutic management of drug-resistant Klebsiella pneumoniae. Despite the numerous reports of colistin resistance in clinical strains, it remains unclear exactly when and how different mutational events arise resulting in reduced colistin susceptibility. Using a bioreactor model of infection, we modelled the emergence of colistin resistance in a susceptible isolate of K. pneumoniae. Genotypic, phenotypic and mathematical analyses of the antibiotic-challenged and un-challenged population indicates that after an initial decline, the population recovers within 24 h due to a small number of "founder cells" which have single point mutations mainly in the regulatory genes encoding crrB and pmrB that when mutated results in up to 100-fold reduction in colistin susceptibility. Our work underlines the rapid development of colistin resistance during treatment or exposure of susceptible K. pneumoniae infections having implications for the use of cationic antimicrobial peptides as a monotherapy.

Screening, identification, and characterization of molds for brewing rice wine: Scale-up production in a bioreactor.

Rice wine, well known for its unique flavor, rich nutritional value, and health benefits, has potential for extensive market development. Rhizopus and Aspergillus are among several microorganisms used in rice wine brewing and are crucial for determining rice wine quality. The strains were isolated via Rose Bengal and starch as a combined separation medium, followed by oenological property and sensory evaluation screening. The strain exhibiting the best performance can be screened using the traditional rice wine Qu. The strains YM-8, YM-10, and YM-16, which exhibited strong saccharification and fermentation performance along with good flavor and taste, were obtained from traditional rice wine Qu. Based on ITS genetic sequence analysis, the YM-8, YM-10, and YM-16 strains were identified as Rhizopus microsporus, Rhizopus arrhizus, and Aspergillus oryzae. The optimum growth temperature of each of the three strains was 30°C, 32°C, and 30°C, and the optimum initial pH was 6.0, 6.5, and 6.5, respectively. The activities of α-amylase, glucoamylase, and protease of YM-16 were highest at 220.23±1.88, 1,269.04±30.32, and 175.16±1.81 U/g, respectively. The amino acid content of rice wine fermented in a 20-L bioreactor with the three mold strains was higher than that of the control group, except for arginine, which was significantly lower than that of the control group. The total amino acid content and the total content of each type of amino acid were ranked as YM-16 > YM-8 > YM-10 > control group, and the amino acid content varied greatly among the strains. The control group had a higher content, whereas YM-8 and YM-16 had lower contents of volatile aroma components than the control group and had the basic flavor substances needed for rice wine, which is conducive to the formation of rice wine aroma. This selected strain, YM-16, has strong saccharification and fermentation ability, is a rich enzyme system, and improves the flavor of rice wine, thereby demonstrating its suitability as a production strain for brewing.

Effects of two fillers and process conditions on the water treatment efficiency of a continuous packed bed biofilm reactor.

This study evaluated the treatment efficiency of two selected fillers and their combination for improving the water quality of aquaculture wastewater using a packed bed biofilm reactor (PBBR) under various process conditions. The fillers used were nanosheet (NS), activated carbon (AC), and a combination of both. The results indicated that the use of combined fillers and the hydraulic retention time (HRT) of 4 h significantly enhanced water quality in the PBBR. The removal rates of chemical oxygen demand, NO2-─N, total suspended solids（TSS）, and chlorophyll a were 63.55%, 74.25%, 62.75%, and 92.85%, respectively. The microbiota analysis revealed that the presence of NS increased the abundance of microbial phyla associated with nitrogen removal, such as Nitrospirae and Proteobacteria. The difference between the M1 and M2 communities was minimal. Additionally, the microbiota in different PBBR samples displayed similar preferences for carbon sources, and carbohydrates and amino acids were the most commonly utilized carbon sources by microbiota. These results indicated that the combination of NS and AC fillers in a PBBR effectively enhanced the treatment efficiency of aquaculture wastewater when operated at an HRT of 4 h. The findings provide valuable insights into optimizing the design of aquaculture wastewater treatment systems.

Dynamic Energy Budget model for E. coli growth in carbon and nitrogen limitation conditions.

The simulations and predictions obtained from mathematical models of bioprocesses conducted by microorganisms are not overvalued. Mechanistic models are bringing a better process understanding and the possibility of simulating unmeasurable variables. The Dynamic Energy Budget (DEB) model is an energy balance that can be formulated for any living organism and can be classified as a structured model. In this study, the DEB model was used to describe E. coli growth in a batch reactor in carbon and nitrogen substrate limitation conditions. The DEB model provides a possibility to follow the changes in the microbes' cells including their elemental composition and content of some important cell ingredients in different growth phases in substrate limitation conditions which makes it more informative compared to Monod's model. The model can be used as an optimal choice between Monod-like models and flux-based approaches. KEY POINTS: • The DEB model can be used to catch changes in elemental composition of E. coli • Bacteria batch culture growth phases can be explained by the DEB model • The DEB model is more informative compared to Monod's based models.

Efficiency of aerobic biodegradation of sugar beet distillery stillage under dissolved oxygen tension-controlled conditions.

The efficiency of aerobic biodegradation of distillery wastewater using various microbial cultures is intricately linked to process conditions. The study aimed to examine the aerobic biodegradation by a Bacillus bacteria under controlled dissolved oxygen tension (DOT) conditions as a novel approach in the treatment of sugar beet distillery stillage. The processes were conducted in a 2-L Biostat®B stirred-tank reactor (STR), at a temperature of 36°C, with aeration of 1.0 L/(L·min), and uncontrolled pH of the medium (an initial pH of 8.0). Each experiment was performed at a different DOT setpoint: 75%, 65% and 55% saturation, controlled through stirrer rotational speed adjustments. The study showed that the DOT setpoint did not influence the process efficiency, determined by the pollutant load removal expressed as COD, BOD5 and TOC. In all three experiments, the obtained reduction values of these parameters were comparable, falling within the narrow ranges of 78.6-78.7%, 97.3-98.0% and 75.0-76.4%, respectively. However, the DOT setpoint did influence the rate of process biodegradation. The removal rate of the pollutant load expressed as COD, was the lowest when DOT was set at 55% (0.48 g O2/(L•h)), and the highest when DOT was set at 65% (0.55 g O2/(L•h)). For biogenic elements (nitrogen and phosphorus), a beneficial effect was observed at a low setpoint of controlled DOT during biodegradation. The maximum extent of removal of both total nitrogen (54%) and total phosphorus (67.8%) was achieved at the lowest DOT setpoint (55%). The findings suggest that conducting the batch aerobic process biodegradation of sugar beet stillage at a relatively low DOT setpoint in the medium might achieve high efficiency pollutant load removal and potentially lead to a reduction in the process cost.

Metatranscriptomics-guided genome-scale metabolic reconstruction reveals the carbon flux and trophic interaction in methanogenic communities.

BACKGROUND: Despite rapid advances in genomic-resolved metagenomics and remarkable explosion of metagenome-assembled genomes (MAGs), the function of uncultivated anaerobic lineages and their interactions in carbon mineralization remain largely uncertain, which has profound implications in biotechnology and biogeochemistry. RESULTS: In this study, we combined long-read sequencing and metatranscriptomics-guided metabolic reconstruction to provide a genome-wide perspective of carbon mineralization flow from polymers to methane in an anaerobic bioreactor. Our results showed that incorporating long reads resulted in a substantial improvement in the quality of metagenomic assemblies, enabling the effective recovery of 132 high-quality genomes meeting stringent criteria of minimum information about a metagenome-assembled genome (MIMAG). In addition, hybrid assembly obtained 51% more prokaryotic genes in comparison to the short-read-only assembly. Metatranscriptomics-guided metabolic reconstruction unveiled the remarkable metabolic flexibility of several novel Bacteroidales-affiliated bacteria and populations from Mesotoga sp. in scavenging amino acids and sugars. In addition to recovering two circular genomes of previously known but fragmented syntrophic bacteria, two newly identified bacteria within Syntrophales were found to be highly engaged in fatty acid oxidation through syntrophic relationships with dominant methanogens Methanoregulaceae bin.74 and Methanothrix sp. bin.206. The activity of bin.206 preferring acetate as substrate exceeded that of bin.74 with increasing loading, reinforcing the substrate determinantal role. CONCLUSION: Overall, our study uncovered some key active anaerobic lineages and their metabolic functions in this complex anaerobic ecosystem, offering a framework for understanding carbon transformations in anaerobic digestion. These findings advance the understanding of metabolic activities and trophic interactions between anaerobic guilds, providing foundational insights into carbon flux within both engineered and natural ecosystems. Video Abstract.

Enhancing Selenium Accumulation in Rhodotorula mucilaginosa Strain 6S Using a Proteomic Approach for Aquafeed Development.

It is known that selenium (Se) is an essential trace element, important for the growth and other biological functions of fish. One of its most important functions is to contribute to the preservation of certain biological components, such as DNA, proteins, and lipids, providing protection against free radicals resulting from normal metabolism. The objective of this study was to evaluate and optimize selenium accumulation in the native yeast Rhodotorula mucilaginosa 6S. Sodium selenite was evaluated at different concentrations (5-10-15-20-30-40 mg/L). Similarly, the effects of different concentrations of nitrogen sources and pH on cell growth and selenium accumulation in the yeast were analyzed. Subsequently, the best cultivation conditions were scaled up to a 2 L reactor with constant aeration, and the proteome of the yeast cultured with and without sodium selenite was evaluated. The optimal conditions for biomass generation and selenium accumulation were found with ammonium chloride and pH 5.5. Incorporating sodium selenite (30 mg/L) during the exponential phase in the bioreactor after 72 h of cultivation resulted in 10 g/L of biomass, with 0.25 mg total Se/g biomass, composed of 25% proteins, 15% lipids, and 0.850 mg total carotenoids/g biomass. The analysis of the proteomes associated with yeast cultivation with and without selenium revealed a total of 1871 proteins. The results obtained showed that the dynamic changes in the proteome, in response to selenium in the experimental medium, are directly related to catalytic activity and oxidoreductase activity in the yeast. R. mucilaginosa 6S could be an alternative for the generation of selenium-rich biomass with a composition of other nutritional compounds also of interest in aquaculture, such as proteins, lipids, and pigments.

MiDAS 5: Global diversity of bacteria and archaea in anaerobic digesters.

Anaerobic digestion of organic waste into methane and carbon dioxide (biogas) is carried out by complex microbial communities. Here, we use full-length 16S rRNA gene sequencing of 285 full-scale anaerobic digesters (ADs) to expand our knowledge about diversity and function of the bacteria and archaea in ADs worldwide. The sequences are processed into full-length 16S rRNA amplicon sequence variants (FL-ASVs) and are used to expand the MiDAS 4 database for bacteria and archaea in wastewater treatment systems, creating MiDAS 5. The expansion of the MiDAS database increases the coverage for bacteria and archaea in ADs worldwide, leading to improved genus- and species-level classification. Using MiDAS 5, we carry out an amplicon-based, global-scale microbial community profiling of the sampled ADs using three common sets of primers targeting different regions of the 16S rRNA gene in bacteria and/or archaea. We reveal how environmental conditions and biogeography shape the AD microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 692 genera and 1013 species. These represent 84-99% and 18-61% of the accumulated read abundance, respectively, across samples depending on the amplicon primers used. Finally, we examine the global diversity of functional groups with known importance for the anaerobic digestion process.

Enhancing microbial fuel cell performance through microbial immobilization.

Bio-electrochemical Systems (BES), particularly Microbial Fuel Cells (MFC), have emerged as promising technologies in environmental biotechnology. This study focused on optimizing the anode bacterial culture immobilization process to enhance BES performance. The investigation combines and modifies two key immobilization methods: covalent bonding with glutaraldehyde and inclusion in a chitosan gel in order to meet the criteria and requirements of the bio-anodes in MFC. The performance of MFCs with immobilized and suspended cultures was compared in parallel experiments. Both types showed similar substrate utilization dynamics with slight advantage of the immobilized bio-anode considering the lower concentration of biomass. The immobilized MFC exhibited higher power generation and metabolic activity, as well. Probably, this is due to improved anodic respiration and higher coulombic efficiency of the reactor. Analysis of organic acids content supported this conclusion showing significant inhibition of the fermentation products production in the MFC reactor with immobilized anode culture.

Chromosomal integration of the pSOL1 megaplasmid of Clostridium acetobutylicum for continuous and stable advanced biofuels production.

Biofuel production by Clostridium acetobutylicum is compromised by strain degeneration due to loss of its pSOL1 megaplasmid. Here we used engineering biology to stably integrate pSOL1 into the chromosome together with a synthetic isopropanol pathway. In a membrane bioreactor continuously fed with glucose mineral medium, the final strain produced advanced biofuels, n-butanol and isopropanol, at high yield (0.31 g g-1), titre (15.4 g l-1) and productivity (15.5 g l-1 h-1) without degeneration.

Mechanistic insights into tris(2-chloroisopropyl) phosphate biomineralization coupled with lead (II) biostabilization driven by denitrifying bacteria.

The ubiquity and persistence of organophosphate esters (OPEs) and heavy metal (HMs) pose global environmental risks. This study explored tris(2-chloroisopropyl)phosphate (TCPP) biomineralization coupled to lead (Pb2+) biostabilization driven by denitrifying bacteria (DNB). The domesticated DNB achieved synergistic bioremoval of TCPP and Pb2+ in the batch bioreactor (efficiency: 98 %).TCPP mineralized into PO43- and Cl-, and Pb2+ precipitated with PO43-. The TCPP-degrading/Pb2+-resistant DNB: Achromobacter, Pseudomonas, Citrobacter, and Stenotrophomonas, dominated the bacterial community, and synergized TCPP biomineralization and Pb2+ biostabilization. Metagenomics and metaproteomics revealed TCPP underwent dechlorination, hydrolysis, the TCA cycle-based dissimilation, and assimilation; Pb2+ was detoxified via bioprecipitation, bacterial membrane biosorption, EPS biocomplexation, and efflux out of cells. TCPP, as an initial donor, along with NO3-, as the terminal acceptor, formed a respiratory redox as the primary energy metabolism. Both TCPP and Pb2+ can stimulate phosphatase expression, which established the mutual enhancements between their bioconversions by catalyzing TCPP dephosphorylation and facilitating Pb2+ bioprecipitation. TCPP may alleviate the Pb2+-induced oxidative stress by aiding protein phosphorylation. 80 % of Pb2+ converted into crystalized pyromorphite. These results provide the mechanistic foundations and help develop greener strategies for synergistic bioremediation of OPEs and HMs.

Inoculum source determines the stress resistance of electroactive functional taxa in biofilms: A metagenomic perspective.

The inoculum has a crucial impact on bioreactor initialization and performance. However, there is currently a lack of guidance on selecting appropriate inocula for applications in environmental biotechnology. In this study, we applied microbial electrolysis cells (MECs) as models to investigate the differences in the functional potential of electroactive microorganisms (EAMs) within anodic biofilms developed from four different inocula (natural or artificial), using shotgun metagenomic techniques. We specifically focused on extracellular electron transfer (EET) function and stress resistance, which affect the performance and stability of MECs. Community profiling revealed that the family Geobacteraceae was the key EAM taxon in all biofilms, with Geobacter as the dominant genus. The c-type cytochrome gene imcH showed universal importance for Geobacteraceae EET and was utilized as a marker gene to evaluate the EET potential of EAMs. Additionally, stress response functional genes were used to assess the stress resistance potential of Geobacter species. Comparative analysis of imcH gene abundance revealed that EAMs with comparable overall EET potential could be enriched from artificial and natural inocula (P > 0.05). However, quantification of stress response gene copy numbers in the genomes demonstrated that EAMs originating from natural inocula possessed superior stress resistance potential (196 vs. 163). Overall, this study provides novel perspectives on the inoculum effect in bioreactors and offers theoretical guidance for selecting inoculum in environmental engineering applications.

A machine learning-based approach for improving plasmid DNA production in Escherichia coli fed-batch fermentations.

Artificial Intelligence (AI) technology is spearheading a new industrial revolution, which provides ample opportunities for the transformational development of traditional fermentation processes. During plasmid fermentation, traditional subjective process control leads to highly unstable plasmid yields. In this study, a multi-parameter correlation analysis was first performed to discover a dynamic metabolic balance among the oxygen uptake rate, temperature, and plasmid yield, whilst revealing the heating rate and timing as the most important optimization factor for balanced cell growth and plasmid production. Then, based on the acquired on-line parameters as well as outputs of kinetic models constructed for describing process dynamics of biomass concentration, plasmid yield, and substrate concentration, a machine learning (ML) model with Random Forest (RF) as the best machine learning algorithm was established to predict the optimal heating strategy. Finally, the highest plasmid yield and specific productivity of 1167.74 mg L-1 and 8.87 mg L-1/OD600 were achieved with the optimal heating strategy predicted by the RF model in the 50 L bioreactor, respectively, which was 71% and 21% higher than those obtained in the control cultures where a traditional one-step temperature upshift strategy was applied. In addition, this study transformed empirical fermentation process optimization into a more efficient and rational self-optimization method. The methodology employed in this study is equally applicable to predict the regulation of process dynamics for other products, thereby facilitating the potential for furthering the intelligent automation of fermentation processes.

Exploring the impact of magnetic fields on biomass production efficiency under aerobic and anaerobic batch fermentation of Saccharomyces cerevisiae.

In this work, the effect of moderate electromagnetic fields (2.5, 10, and 15 mT) was studied using an immersed coil inserted directly into a bioreactor on batch cultivation of yeast under both aerobic and anaerobic conditions. Throughout the cultivation, parameters, including CO2 levels, O2 saturation, nitrogen consumption, glucose uptake, ethanol production, and yeast growth (using OD 600 measurements at 1-h intervals), were analysed. The results showed that 10 and 15 mT magnetic fields not only statistically significantly boosted and sped up biomass production (by 38-70%), but also accelerated overall metabolism, accelerating glucose, oxygen, and nitrogen consumption, by 1-2 h. The carbon balance analysis revealed an acceleration in ethanol and glycerol production, albeit with final concentrations by 22-28% lower, with a more pronounced effect in aerobic cultivation. These findings suggest that magnetic fields shift the metabolic balance toward biomass formation rather than ethanol production, showcasing their potential to modulate yeast metabolism. Considering coil heating, opting for the 10 mT magnetic field is preferable due to its lower heat generation. In these terms, we propose that magnetic field can be used as novel tool to increase biomass yield and accelerate yeast metabolism.

A comparison of the performance of bacterial biofilters and fungal-bacterial coupled biofilters in BTEp-X removal.

Background: Conventional biofilters, which rely on bacterial activity, face challenges in eliminating hydrophobic compounds, such as aromatic compounds. This is due to the low solubility of these compounds in water, which makes them difficult to absorb by bacterial biofilms. Furthermore, biofilter operational stability is often hampered by acidification and drying out of the filter bed. Methods: Two bioreactors, a bacterial biofilter (B-BF) and a fungal-bacterial coupled biofilter (F&B-BF) were inoculated with activated sludge from the secondary sedimentation tank of the Sinopec Yangzi Petrochemical Company wastewater treatment plant located in Nanjing, China. For approximately 6 months of operation, a F&B-BF was more effective than a B-BF in eliminating a gas-phase mixture containing benzene, toluene, ethylbenzene, and para-xylene (BTEp-X). Results: After operating for four months, the F&B-BF showed higher removal efficiencies for toluene (T), ethylbenzene (E), benzene (B), and para-X (p-Xylene), at 96.9%, 92.6%, 83.9%, and 83.8%, respectively, compared to those of the B-BF (90.1%, 78.7%, 64.8%, and 59.3%). The degradation activity order for B-BF and F&B-BF was T > E > B > p-X. Similarly, the rates of mineralization for BTEp-X in the F&B-BF were 74.9%, 66.5%, 55.3%, and 45.1%, respectively, which were higher than those in the B-BF (56.5%, 50.8%, 43.8%, and 30.5%). Additionally, the F&B-BF (2 days) exhibited faster recovery rates than the B-BF (5 days). Conclusions: It was found that a starvation protocol was beneficial for the stable operation of both the B-BF and F&B-BF. Community structure analysis showed that the bacterial genus Pseudomonas and the fungal genus Phialophora were both important in the degradation of BTEp-X. The fungal-bacterial consortia can enhance the biofiltration removal of BTEp-X vapors.

Dirammox-dominated microbial community for biological nitrogen removal from wastewater.

Direct ammonia oxidation (Dirammox) might be of great significance to advance the innovation of biological nitrogen removal process in wastewater treatment systems. However, it remains unknown whether Dirammox bacteria can be selectively enriched in activated sludge. In this study, a lab-scale bioreactor was established and operated for 2 months to treat synthetic wastewater with hydroxylamine as a selection pressure. Three Dirammox strains (Alcaligenes aquatilis SDU_AA1, Alcaligenes aquatilis SDU_AA2, and Alcaligenes sp. SDU_A2) were isolated from the activated sludge, and their capability to perform Dirammox process was confirmed. Although these three Dirammox bacteria were undetectable in the seed sludge (0%), their relative abundances rapidly increased after a month of operation, reaching 12.65%, 0.69%, and 0.69% for SDU_A2, SDU_AA1, and SDU_AA2, respectively. Among them, the most dominant Dirammox (SDU_A2) exhibited higher nitrogen removal rate (32.35%) than the other two strains (13.57% of SDU_AA1 and 14.52% of SDU_AA2). Comparative genomic analysis demonstrated that the most dominant Dirammox bacterium (SDU_A2) possesses fewer complete metabolic modules compared to the other two less abundant Alcaligenes strains. Our findings expanded the understanding of the application of Dirammox bacteria as key functional microorganisms in a novel biological nitrogen and carbon removal process if they could be well stabilized. KEY POINTS: • Dirammox-dominated microbial community was enriched in activated sludge bioreactor. • The addition of hydroxylamine played a role in Dirammox enrichment. • Three Dirammox bacterial strains, including one novel species, were isolated.

Airlift bioreactor-based strategies for prolonged semi-continuous cultivation of edible Agaricomycetes.

Submerged cultivation of edible filamentous fungi (Agaricomycetes) in bioreactors enables maximum mass transfer of nutrients and has the potential to increase the volumetric productivity of fungal biomass compared to solid state cultivation. These aspects are paramount if one wants to increase the range of bioactives (e.g. glucans) in convenient time frames. In this study, Trametes versicolor (M9911) outperformed four other Agaricomycetes tested strains (during batch cultivations in an airlift bioreactor). This strain was therefore further tested in semi-continuous cultivation. Continuous and semi-continuous cultivations (driven by the dilution rate, D) are the preferred bioprocess strategies for biomass production. We examined the semi-continuous cultivation of T. versicolor at dilution rates between 0.02 and 0.1 h-1. A maximum volumetric productivity of 0.87 g/L/h was obtained with a D of 0.1 h-1 but with a lower total biomass production (cell dry weight, CDW 8.7 g/L) than the one obtained at lower dilution rates (12.3 g/L at D of 0.04 and vs 13.4 g/L, at a D of 0.02 h-1). However, growth at a D of 0.1 h-1 resulted in a very short fermentation (18 h) which terminated due to washout (the specific D exceeded the maximum growth rate of the fungal biomass). At a D of 0.04 h-1, a CDW of 12.3 g/L was achieved without compromising the total residence time (184 h) of the fermentation. While the D of 0.04 h-1 and 0.07 h-1 achieved comparable volumetric productivities (0.5 g/L/h), the total duration of the fermentation at D of 0.07 h-1 was only 85 h. The highest glucan content of cells (27.8 as percentage of CDW) was obtained at a D of 0.07 h-1, while the lowest glucan content was observed in T. versicolor cells grown at a D of 0.02 h-1. KEY POINTS: • The highest reported volumetric productivity for fungal biomass was 0.87 g/L/h. • Semi-continuous fermentation at D of 0.02 h-1 resulted in 13.4 g/L of fungal biomass. • Semi-continuous fermentation at D of 0.07 h-1 resulted in fungal biomass with 28% of total glucans.

Impact of long-term temperature shifts on activated sludge microbiome dynamics and micropollutant removal.

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4-40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.

Methanol as a co-substrate with CO2 enhances butyrate production in microbial electrosynthesis.

Methanol is a promising feedstock for the bio-based economy as it can be derived from organic waste streams or produced electrochemically from CO2. Acetate production from CO2 in microbial electrosynthesis (MES) has been widely studied, while more valuable compounds such as butyrate are currently attracting attention. In this study, methanol was used as a co-substrate with CO2 to enhance butyrate production in MES. Feeding with CO2 and methanol resulted in the highest butyrate production rates and titres of 0.36 ± 0.01 g L-1 d-1 and 8.6 ± 0.2 g L-1, respectively, outperforming reactors with only CO2 feeding (0.20 ± 0.03 g L-1 d-1 and 5.2 ± 0.1 g L-1, respectively). Methanol acted as electron donor and as carbon source, both of which contributed ca. 50% of the carbon in the products. Eubacterium was the dominant genus with 52.6 ± 2.5% relative abundance. Thus, we demonstrate attractive route for the use of the C1 substrates, CO2 and methanol, to produce mainly butyrate. KEY POINTS: • Butyrate was the main product from methanol and CO2 in MES • Methanol acted as both carbon and electron source in MES • Eubacterium dominating microbial culture was enriched in MES.

Altering operational conditions during protein fermentation to volatile fatty acids modifies the associated bacterial community.

In recent years, the production of volatile fatty acids (VFA) through mixed culture fermentation (MCF) has been gaining attention. Most authors have focused on the fermentation of carbohydrates, while other possible substrates, such as proteins, have not been considered. Moreover, there is little information about how operational parameters affect the microbial communities involved in these processes, even though they are strongly related to reactor performance and VFA selectivity. Hence, this study aims to evaluate how microbial composition changes according to three different parameters (pH, type of protein and micronutrient addition) during anaerobic fermentation of protein-rich side streams. For this, two continuous stirred tank reactors (CSTR) were fed with two different proteins (casein and gelatine) and operated at different conditions: three pH values (5.0, 7.0 and 9.0) with only macronutrients supplementation and two pH values (5.0 and 7.0) with micronutrients' supplementation as well. Firmicutes, Proteobacteria and Bacteroidetes were the dominant phyla in the two reactors at all operational conditions, but their relative abundance varied with the parameters studied. At pH 7.0 and 9.0, the microbial composition was mainly affected by protein type, while at acidic conditions the driving force was the pH. The influence of micronutrients was dependent on the pH and the protein type, with a special effect on Clostridiales and Bacteroidales populations. Overall, this study shows that the acidogenic microbial community is affected by the three parameters studied and the changes in the microbial community can partially explain the macroscopic results, especially the process selectivity.