Quantitative analysis of previously identified propionate-oxidizing bacteria and methanogens at different temperatures in an UASB reactor containing propionate as a sole carbon source

Syntrophic propionate-oxidizing bacteria in methanogenic systems

The mutual nutritional cooperation underpinning syntrophic propionate degradation provides a scant amount of energy for the microorganisms involved, so propionate degradation often acts as a bottleneck in methanogenic systems. Understanding the ecology, physiology and metabolic capacities of syntrophic propionate-oxidizing bacteria (SPOB) is of interest in both engineered and natural ecosystems, as it offers prospects to guide further development of technologies for biogas production and biomass-derived chemicals, and is important in forecasting contributions by biogenic methane emissions to climate change. SPOB are distributed across different phyla. They can exhibit broad metabolic capabilities in addition to syntrophy (e.g. fermentative, sulfidogenic and acetogenic metabolism) and demonstrate variations in interplay with cooperating partners, indicating nuances in their syntrophic lifestyle. In this review, we discuss distinctions in gene repertoire and organization for the methylmalonyl-CoA pathway, hydrogenases and formate dehydrogenases, and emerging facets of (formate/hydrogen/direct) electron transfer mechanisms. We also use information from cultivations, thermodynamic calculations and omic analyses as the basis for identifying environmental conditions governing propionate oxidation in various ecosystems. Overall, this review improves basic and applied understanding of SPOB and highlights knowledge gaps, hopefully encouraging future research and engineering on propionate metabolism in biotechnological processes.

Response of Microbial Community to Induced Failure of Anaerobic Digesters Through Overloading With Propionic Acid Followed by Process Recovery

In order to effectively use microbial-based strategies to manage anaerobic digesters, it is necessary to distinguish between community shifts that are part of the natural dynamic of the system and shifts caused by environmental or operational disturbances. The objective of this research study was to evaluate the significance of changes in the microbial community of anaerobic digesters during failure in correlation to operational parameters such as an organic acid overload. Five continuously stirred 0.5 L reactors were set-up as semi-continuously-fed, mesophilic dairy manure digesters with a 30-day hydraulic retention time. After a 120-day stabilization period, two digesters were kept as controls, while the organic loading rates in the triplicate set were increased step-wise to ultimately provide a shock-load leading to failure using propionic acid spikes. Acidosis resulting in near cessation of biogas and termination of methane production occurred between 4 and 7 weeks, after which all the digesters continued to be fed only dairy manure. The shock loading of propionic acid led to an accumulation of mainly acetate and propionate, with low levels of iso-butyrate, butyrate, iso-valerate, and valerate. High-throughput Illumina sequencing of the V4 region of the bacterial and archaeal 16S rRNA gene in digester samples showed a significant change in the microbial community composition during propionic acid overload, followed by a return to the original composition with regular feedstock. Bacterial genera whose relative abundance decreased during the inhibition stage included Sedimentibacter, Syntrophomonas, TSCOR003.O20, and Marinilabiaceae, while the relative abundance of Lachnospiraceae, Ruminococcus, Mogibacteriaceae, Pyramidobacter, and Bacteroides increased. The relative abundance of dominant methanogens, Methanosarcina and Methanobacterium, although initially resistant, were decreased (from 91.71 to 12.14% and from 2.98 to 0.73%, respectively) during inhibition, while Methanobrevibacter and Methanosphaera that were prominent in the manure feedstock increased from 17.36 to 79.45% and from 0.14 to 1.12%, respectively. Shifts in bacterial and archaeal compositions, back to their pre-shock steady state after failure, highlight the digester's microbial resilience and recovery potential.

Vertical distribution of microbial community and metabolic pathway in a methanogenic propionate degradation bioreactor

The methanogenic propionate degradation consortia were enriched in a propionate-fed semi-continuous bioreactor. The microbial community shift with depth, the microbial network and its correlation with metabolic pathway were also investigated. The results demonstrated that the maximum organic loading rate (OLR) of the reactor was 2.5g propionic acid (HPr) L^-1d^-1 with approximately 1.20LL^-1d^-1 of volumetric methane production (VMP). The organisms in the enrichment were spanning 36 bacterial phyla and 7 archaeal orders. Syntrophobacter, the main Hpr oxidizer in the digester, dominated bacteria with relative abundance changing from 63% to 37% with depth. The predominant methanogens shift from hydrogenotrophic Methanoculleus (∼60%) at the upper liquid layer to acetoclastic Methanothrix (∼51%) at the lower sediment layer in the bioreactor. These methanogens syntrophically support Syntrophobacter by degrading HPr catabolism by-products (H₂ and acetate). Other bacteria could scavenge anabolic products (carbohydrate and protein) presumably derived from detrital biomass produced by the HPr-degrading community.

A review: Driving factors and regulation strategies of microbial community structure and dynamics in wastewater treatment systems

The performance and stabilization of biological wastewater treatment systems ¹are closely related to the microbial community structure and dynamics. In this paper, the effects and mechanisms of influent composition, process configuration, operating parameters (dissolved oxygen [DO], pH, hydraulic retention time [HRT] and sludge retention time [SRT]) and environmental condition (temperature) to the change of microbial community structure and process performance (nitrification, denitrification, biological phosphorus removal, organics mineralization and utilization, etc.) are critically reviewed. Furthermore, some strategies for microbial community structure regulation, mainly bioaugmentation, process adjustment and operating parameters optimization, applied in the current wastewater treatment systems are also discussed. Although the recent studies have strengthened our understanding on the relationship between microbial community structure and wastewater treatment process performance, how to fully tap the microbial information, optimize the microbial community structure and maintain the process performance in wastewater treatment systems are still full of challenges.

Ammonium level induces high purity propionate production in mixed culture glucose fermentation

Propionate is an important chemical widely applied in industry and its productionviafermentation is economic.

Microbial Community Shifts during Biogas Production from Biowaste and/or Propionate

Propionate is the most delicate intermediate during anaerobic digestion as its degradation is thermodynamically unfavorable. To determine its maximum possible degradation rates during anaerobic digestion, a reactor was fed Monday to Friday with an organic loading rate (OLR) of 12/14 kg COD_biowaste·m⁻³·d⁻¹ plus propionate up to a final OLR of 18 kg COD·m⁻³·d⁻¹. No feed was supplied on weekends as it was the case in full-scale. To maintain permanently high propionate oxidizing activity (POA), a basic OLR of 3 kg COD_propionate·m⁻³·d⁻¹ all week + 11 kg COD_biowaste·m⁻³·d⁻¹ from Monday to Friday was supplied. Finally a reactor was operated with an OLR of 12 kg COD_biowaste·m⁻³·d⁻¹ from Monday to Friday and 5 kg COD_propionate·m⁻³·d⁻¹ from Friday night to Monday morning to maintain a constant gas production for permanent operation of a gas engine. The propionate degradation rates (PDRs) were determined for biowaste + propionate feeding. Decreasing PDRs during starvation were analyzed. The POA was higher after propionate supply than after biowaste feeding and decreased faster during starvation of a propionate-fed rather than a biowaste-fed inoculum. Shifts of the propionate-oxidizing and methanogenic community were determined.