Microbiological conversion of CO 2 into biofuels and/or organic industrial feedstock is an excellent carbon-cycling strategy. Here, autotrophic anaerobic bacteria in the membrane biofilm reactor (MBfR) transferred electrons from hydrogen gas (H 2 ) to inorganic carbon (IC) and produced organic acids and alcohols. We systematically varied the H 2 -delivery, the IC concentration, and the hydraulic retention time in the MBfR. The relative availability of H 2 versus IC was the determining factor for enabling microbial chain elongation (MCE). When the H 2 :IC mole ratio was high (>2.0 mol H 2 /mol C), MCE was an important process, generating medium-chain carboxylates up to octanoate (C8, 9.1 ± 1.3 mM C and 28.Conversely, products with two carbons were the only ones present when the H 2 :IC ratio was low (<2.0 mol H 2 /mol C), so that H 2 was the limiting factor. The biofilm microbial community was enriched in phylotypes most similar to the well-known acetogen Acetobacterium for all conditions tested, but phylotypes closely related with families capable of MCE (e.g., Bacteroidales, Rhodocyclaceae, Alcaligenaceae, Thermoanaerobacteriales, and Erysipelotrichaceae) became important when the H 2 :IC ratio was high. Thus, proper management of IC availability and H 2 supply allowed control over community structure and function, reflected by the chain length of the carboxylates and alcohols produced in the MBfR.

No abstract

Pd 0 catalysis and microbially catalyzed reduction of nitrate (NO 3 − -N) were combined as a strategy to increase the kinetics of NO 3 − reduction and control selectivity to N 2 gas versus ammonium (NH 4 + ). Two H 2 -based membrane biofilm reactors (MBfRs) were tested in continuous mode: one with a biofilm alone (H 2 -MBfR) and the other with biogenic Pd 0 nanoparticles (Pd 0 NPs) deposited in the biofilm (Pd−H 2 -MBfR). Solid-state characterizations of Pd 0 NPs in Pd−H 2 -MBfR documented that the Pd 0 NPs were uniformly located along the outer surfaces of the bacteria in the biofilm. Pd−H 2 -MBfR had a higher rate of NO 3 − reduction compared to H 2 -MBfR, especially when the influent NO 3 − concentration was high (28 mg-N/L versus 14 mg-N/L). Pd−H 2 -MBfR enriched denitrifiers of Dechloromonas, Azospira, Pseudomonas, and Stenotrophomonas in the microbial community and also increased abundances of genes affiliated with NO 3 − -N reductases, which reflected that the denitrifying bacteria could channel their respiratory electron flow to NO 3 − reduction to NO 2 − . N 2 selectivity in Pd−H 2 -MBfR was regulated by the H 2 /NO 3 − flux ratio: 100% selectivity to N 2 was achieved when the ratio was less than 1.3 e − equiv of H 2 /e − equiv N, while the selectivity toward NH 4 + occurred with larger H 2 /NO 3 − flux ratios. Thus, the results with Pd−H 2 -MBfR revealed two advantages of it over the H 2 -MBfR: faster kinetics for NO 3 − removal and controllable selectivity toward N 2 versus NH 4 + . By being able to regulate the H 2 /NO 3 − flux ratio, Pd−H 2 -MBfR has significant implications for improving the efficiency and effectiveness of the NO 3 − reduction processes, ultimately leading to more environmentally benign wastewater treatment.

The use of prebiotics and probiotics to improve symptoms associated with autism spectrum disorder (ASD) has varied from study to study, indicating the complex and heterogeneous nature of the disorder and the behaviors and gastrointestinal symptoms associated with ASD. There is a wide variety in the severity of symptoms and developmental impediments across the population. Gut microbiome studies have also shown unique but varied microbial signatures in ASD. While there have been successes in pre-clinical and clinical trials with prebiotic and probiotic components, the limited population sizes have promising yet inconclusive results. This study addresses this issue by 1) enrolling an ASD cohort of 296 children and adults and comparing their deep DNA metagenomic sequencing of gut microbiomes to that of an age-matched neurotypical cohort and 2) individually formulating a precision synbiotic (probiotic and prebiotic) tailored towards each individual's needs and conducting pre/post evaluations of ASD and GI symptoms and longitudinal whole genome microbiome sequencing. At baseline, there was significantly lower microbiome diversity in the ASD group relative to controls. Microbes, pathways, and gene families significantly differed between the two populations. The ASD microbiome had higher abundances of pathogens, such as Shigella, Klebsiella, Mycobacterium, and Clostridium, but lower abundances of beneficial microbes, including Faecalibacterium. With a 3-month synbiotic supplementation, the microbiome diversity of the 170 ASD participants completing the study increased and became closer to the neurotypical controls. Significant shifts in microbial and pathway abundances were also measured at the second ASD timepoint. In addition to changes in the gut microbiome, there was a significant reduction in gastrointestinal discomfort. There were also improvements in some ASD-related symptoms; however, we cannot exclude that these were potentially due to the open-label nature of the study. Changes in the gut microbiome composition and functional capacity, along with a reduction in gastrointestinal symptoms and potential changes in behavior, highlight the importance of metagenomics, longitudinal studies, and the potential for therapeutic microbial supplementation in ASD.