Propionate is a key intermediate in anaerobic digestion processes and often accumulates in association with perturbations, such as elevated levels of ammonia. Under such conditions, syntrophic ammonia-tolerant microorganisms play a key role in propionate degradation. Despite their importance, little is known about these syntrophic microorganisms and their cross-species interactions. Here, we present metagenomes and metatranscriptomic data for novel thermophilic and ammonia-tolerant syntrophic bacteria and the partner methanogens enriched in propionate-fed reactors. A metagenome for a novel bacterium for which we propose the provisional name ‘Candidatus Thermosyntrophopropionicum ammoniitolerans’ was recovered, together with mapping of its highly expressed methylmalonyl-CoA pathway for syntrophic propionate degradation. Acetate was degraded by a novel thermophilic syntrophic acetate-oxidising candidate bacterium. Electron removal associated with syntrophic propionate and acetate oxidation was mediated by the hydrogen/formate-utilising methanogens Methanoculleus sp. and Methanothermobacter sp., with the latter observed to be critical for efficient propionate degradation. Similar dependence on Methanothermobacter was not seen for acetate degradation. Expression-based analyses indicated use of both H₂ and formate for electron transfer, including cross-species reciprocation with sulphuric compounds and microbial nanotube-mediated interspecies interactions. Batch cultivation demonstrated degradation rates of up to 0.16 g propionate L⁻¹ day⁻¹ at hydrogen partial pressure 4–30 Pa and available energy was around −20 mol⁻¹ propionate. These observations outline the multiple syntrophic interactions required for propionate oxidation and represent a first step in increasing knowledge of acid accumulation in high-ammonia biogas production systems.

Summary: To enrich syntrophic acetate‐oxidizing bacteria ( SAOB ), duplicate chemostats were inoculated with sludge from syntrophic acetate oxidation ( SAO )‐dominated systems and continuously supplied with acetate (0.4 or 7.5 g l ⁻¹ ) at high‐ammonia levels. The chemostats were operated under mesophilic (37°C) or thermophilic (52°C) temperature for about six hydraulic retention times ( HRT 28 days) and were sampled over time. Irrespective of temperature, a methane content of 64–69% and effluent acetate level of 0.4–1.0 g l ⁻¹ were recorded in chemostats fed high acetate. Low methane production in the low‐acetate chemostats indicated that the substrate supply was below the threshold for methanization of acetate via SAO . Novel representatives within the family Clostridiales and genus Syntrophaceticus (class Clostridia) were identified to represent putative SAOB candidates in mesophilic and thermophilic conditions respectively. Known SAOB persisted at low relative abundance in all chemostats. The hydrogenotrophic methanogens Methanoculleus bourgensis (mesophilic) and Methanothermobacter thermautotrophicus (thermophilic) dominated archaeal communities in the high‐acetate chemostats. In line with the restricted methane production in the low‐acetate chemostats, methanogens persisted at considerably lower abundance in these chemostats. These findings strongly indicate involvement in SAO and tolerance to high ammonia levels of the species identified here, and have implications for understanding community function in stressed anaerobic processes.

The objective was to determine the effects on rumen microbiome and milk quality of reducing the methane (CH₄) produced from enteric fermentation by the addition of Asparagopsis taxiformis (AT) to the diets of dairy cows. Six Nordic Red cows at 122 ± 13.7 (mean ± SD) days in milk, of parity 2.7 ± 0.52 and producing 36 kg ± 2.5 kg milk per day at the start of the trial were divided into three blocks by milk yield and assigned to an extra-period Latin-square change-over design comprising two dietary treatments. An extra period of observation was added to the Latin-square change-over design to control for carry-over effects. The dietary treatments were a diet consisting of grass silage and a commercial concentrate mixture (60:40) either not supplemented or supplemented with 0.5% AT on an organic matter intake basis. On average, daily CH₄ production, CH₄ yield, and CH₄ intensity decreased by 60%, 54%, and 58%, respectively, in cows fed the diet supplemented with AT. Furthermore, hydrogen gas emitted by cows fed diets supplemented with AT increased by more than five times compared with cows fed a non-AT-supplemented diet. Feed intake was decreased and milk production altered, reflecting a decreased yield of milk fat in cows fed an AT-supplemented diet, but feed efficiency increased. Rumen fermentation parameters were changed to promote propionate rather than acetate and butyrate fermentation. The most prominent change in milk quality was an increase in bromine and iodine when the diet was supplemented with AT. The reduction in CH₄ was associated with a shift from Methanobrevibacter to Methanomethylophilaceae in the archaeal population and a lower relative abundance of Prevotella in the bacterial population. Changes in milk fat odd-numbered and branched-chain fatty acids in the current study of AT supplementation support observed differences in ruminal archaeal and bacterial populations.

The enrichment of CO ₂ -reducing microbial biocathodes is challenging. Previous research has shown that a promising approach could be to first enrich bioanodes and then lower the potential so the electrodes are converted into biocathodes. However, the effect of such a transition on the microbial community on the electrode has not been studied. The goal of this study was thus to compare the start-up of biocathodes from preenriched anodes with direct start-up from bare electrodes and to investigate changes in microbial community composition. The effect of three electrode materials on the long-term performance of the biocathodes was also investigated. In this study, preenrichment of acetate-oxidizing bioanodes did not facilitate the start-up of biocathodes. It took about 170 days for the preenriched electrodes to generate substantial cathodic current, compared to 83 days for the bare electrodes. Graphite foil and carbon felt cathodes produced higher current at the beginning of the experiment than did graphite rods. However, all electrodes produced similar current densities at the end of the over 1-year-long study (2.5 A/m ² ). Methane was the only product detected during operation of the biocathodes. Acetate was the only product detected after inhibition of the methanogens. Microbial community analysis showed that Geobacter sp. dominated the bioanodes. On the biocathodes, the Geobacter sp. was succeeded by Methanobacterium spp., which made up more than 80% of the population. After inhibition of the methanogens, Acetobacterium sp. became dominant on the electrodes (40% relative abundance). The results suggested that bioelectrochemically generated H ₂ acted as an electron donor for CO ₂ reduction. IMPORTANCE In microbial electrochemical systems, living microorganisms function as catalysts for reactions on the anode and/or the cathode. There is a variety of potential applications, ranging from wastewater treatment and biogas generation to production of chemicals. Systems with biocathodes could be used to reduce CO ₂ to methane, acetate, or other high-value chemicals. The technique can be used to convert solar energy to chemicals. However, enriching biocathodes that are capable of CO ₂ reduction is more difficult and less studied than enriching bioanodes. The effect of different start-up strategies and electrode materials on the microbial communities that are enriched on biocathodes has not been studied. The purpose of this study was to investigate two different start-up strategies and three different electrode materials for start-up and long-term operation of biocathodes capable of reducing CO ₂ to valuable biochemicals.

Summary: Inefficient syntrophic propionate degradation causes severe operating disturbances and reduces biogas productivity in many high‐ammonia anaerobic digesters, but propionate‐degrading microorganisms in these systems remain unknown. Here, we identified candidate ammonia‐tolerant syntrophic propionate‐oxidising bacteria using propionate enrichment at high ammonia levels (0.7–0.8 g NH ₃ L ⁻¹ ) in continuously‐fed reactors. We reconstructed 30 high‐quality metagenome‐assembled genomes (MAGs) from the propionate‐fed reactors, which revealed two novel species from the families Peptococcaceae and Desulfobulbaceae as syntrophic propionate‐oxidising candidates. Both MAGs possess genomic potential for the propionate oxidation and electron transfer required for syntrophic energy conservation and, similar to ammonia‐tolerant acetate degrading syntrophs, both MAGs contain genes predicted to link to ammonia and pH tolerance. Based on relative abundance, a Peptococcaceae sp. appeared to be the main propionate degrader and has been given the provisional name “ Candidatus Syntrophopropionicum ammoniitolerans”. This bacterium was also found in high‐ammonia biogas digesters, using quantitative PCR. Acetate was degraded by syntrophic acetate‐oxidising bacteria and the hydrogenotrophic methanogenic community consisted of Methanoculleus bourgensis and a yet to be characterised Methanoculleus sp. This work provides knowledge of cooperating syntrophic species in high‐ammonia systems and reveals that ammonia‐tolerant syntrophic propionate‐degrading populations share common features, but diverge genomically and taxonomically from known species.

The global spread and diversification of multidrug-resistant Gram-negative (MRGN) bacteria poses major challenges to healthcare. In particular, carbapenem-resistant Klebsiella pneumoniae strains have been frequently identified in infections and hospital-wide outbreaks. The most frequently underlying resistance gene (bla_KPC) has been spreading over the last decade in the health care setting. bla_KPC seems to have rapidly diversified and has been found in various species and on different plasmid types. To review the progress and dynamics of this diversification, all currently available KPC plasmids in the NCBI database were analysed in this work. Plasmids were grouped into 257 different representative KPC plasmids, of which 79.4% could be clearly assigned to incompatibility (Inc) group or groups. In almost half of all representative plasmids, the KPC gene is located on Tn4401 variants, emphasizing the importance of this transposon type for the transmission of KPC genes to other plasmids. The transposons also seem to be responsible for the occurrence of altered or uncommon fused plasmid types probably due to incomplete transposition. Moreover, many KPC plasmids contain genes that encode proteins promoting recombinant processes and mutagenesis; in consequence accelerating the diversification of KPC genes and other colocalized resistance genes.