Using DNA-based stable isotope probing to reveal novel propionate- and acetate-oxidizing bacteria in propionate-fed mesophilic anaerobic chemostats

Abstract

Propionate is one of the most important intermediates of anaerobic fermentation. Its oxidation performed by syntrophic propionate-oxidizing bacteria coupled with hydrogenotrophic methanogens is considered to be a rate-limiting step for methane production. However, the current understanding of SPOB is limited due to the difficulty of pure culture isolation. In the present study, two anaerobic chemostats fed with propionate as the sole carbon source were operated at different dilution rates (0.05 d−1 and 0.15 d−1). The propionate- and acetate-oxidizing bacteria in the two methanogenic chemostats were investigated combining DNA-stable isotope probing (DNA-SIP) and 16S rRNA gene high-throughput sequencing. The results of DNA-SIP with 13C-propionate/acetate suggested that, Smithella, Syntrophobacter, Cryptanaerobacter, and unclassified Rhodospirillaceae may be putative propionate-oxidizing bacteria; unclassified Spirochaetaceae, unclassified Synergistaceae, unclassified Elusimicrobia, Mesotoga, and Gracilibacter may contribute to acetate oxidation; unclassified Syntrophaceae and Syntrophomonas may be butyrate oxidizers. By DNA-SIP, unclassified OTUs with 16S rRNA gene abundance higher than 62% of total Bacteria in the PL chemostat and 38% in the PH chemostat were revealed to be related to the degradation of propionate. These results suggest that a variety of uncultured bacteria contribute to propionate degradation during anaerobic digestion. The functions and metabolic characteristics of these bacteria require further investigation.

Enrichment and description of novel bacteria performing syntrophic propionate oxidation at high ammonia level

“…“ Ca . Syntrophopropionicum ammoniitolerans” was shown to distinctly diverge from SPOB affiliating with Pelotomaculum , Smithella , Syntrophobacter, Syntrophobacterium and “ Candidatus Cloacamonas”, which are known to represent dominant syntrophic propionate degraders in low‐ammonia and mesophilic (30–40°C) anaerobic digesters (Ariesyady et al ., 2007b; Ban et al ., 2015; Ahlert et al ., 2016; Wang et al ., 2019). Our results also suggest that conversion of propionate to methane at high ammonia was conducted through cooperation between “ Ca .…”

Syntrophic propionate-oxidizing bacteria in methanogenic systems

“…In this context, higher susceptibility to increased dilution rate (from 0.025 to 0.05 day -1 ) in a thermophilic community compared with a mesophilic community has been reported (Chen et al 2020). In a mesophilic propionate enrichment study, Syntrophobacter and Smithella were found to be favored at high dilution rate (0.15 day -1 ), while at lower rates (0.05 day -1 ) unclassified Syntrophaceae were more abundant (Wang et al 2019a). Shortening the retention time from 10 to 4 h is reported to cause a shift in dominance from Pelotomaculum to Syntrophobacter and Smithella (Ban, Zhang and Li 2015).…”

Effect of magnetite addition on transcriptional profiles of syntrophic Bacteria and Archaea during anaerobic digestion of propionate in wastewater sludge

“…Butyrate oxidation was included as it is a part of the C6-dismutation pathway for syntrophic propionate catabolism that is so far only known from Smithella (de Bok et al, 2001). The intermediate butyrate from the C6-dismutation pathway is either oxidized by the SPOB itself or is available for SBOB (Wang et al, 2019;Xia et al, 2019;Chen et al, 2020).…”

“…Smithella propionica is the only known SPOB so far that degrades propionate via a C6 dismutation pathway to acetate and butyrate (de Bok et al, 2001). The intermediate butyrate is eventually oxidized through beta-oxidation by Smithella itself or it is available for syntrophic butyrate-oxidizing bacteria (SBOB) (Wang et al, 2019;Xia et al, 2019;Chen et al, 2020). All other SPOBs encode the methylmalonyl CoA (MMC) pathway for propionate oxidation producing acetate, H 2 and CO 2 as direct precursors for methanogenesis (Li et al, 2012).…”