Microbial and Phenyl Acid Dynamics during the Start-up Phase of Anaerobic Straw Degradation in Meso- and Thermophilic Batch Reactors

Abstract

Aromatic compounds like phenyl acids derived from lignocellulose degradation have been suspected to negatively influence biogas production processes. However, results on this topic are still inconclusive. To study phenyl acid formation in batch reactors during the start-up phase of anaerobic degradation, different amounts of straw from grain were mixed with mesophilic and thermophilic sludge, respectively. Molecular biological parameters were assessed using next-generation sequencing and qPCR analyses. Metagenomic predictions were done via the program, piphillin. Methane production, concentrations of phenylacetate, phenylpropionate, phenylbutyrate, and volatile fatty acids were monitored chromatographically. Methanosarcina spp. was the dominant methanogen when high straw loads were effectively degraded, and thus confirmed its robustness towards overload conditions. Several microorganisms correlated negatively with phenyl acids; however, a negative effect, specifically on methanogens, could not be proven. A cascade-like increase/decrease from phenylacetate to phenylpropionate, and then to phenylbutyrate could be observed when methanogenesis was highly active. Due to these results, phenylacetate was shown to be an early sign for overload conditions, whereas an increase in phenylbutyrate possibly indicated a switch from degradation of easily available to more complex substrates. These dynamics during the start-up phase might be relevant for biogas plant operators using complex organic wastes for energy exploitation.

Microbial community dynamics in mesophilic and thermophilic batch reactors under methanogenic, phenyl acid-forming conditions

“…Furthermore, 288 genomes and 359 KEGG pathways were observed for this data set, including all mesophilic as well as all thermophilic normalised samples. These numbers are comparable to a previous study focusing on the two meso-and thermophilic methanogenic systems [40]. Generally, the orthology counts for peripheral and central benzoyl-CoA pathways were considerably higher in mesophilic than in thermophilic samples (Fig.…”

“…The small subunit rRNA gene primers 515f and 806r [69], according the Earth microbiome project [70], were used to target the V4 region. The first PCR step, including the 16S rRNA primers and the Illumina ® adapter sequences, was performed as described previously [40]. 25 µL PCR solution contained 12 µL PCR Mix (MyTaq ™ Mix 2× (Bioline), 250 nM of each primer-adapter combination, 20% Betaine Enhancer Solution (5×) (VWR International, Germany), and PCR-grade water to reach a final volume of 24 µL, as well as 1 µL DNA template (2.5 ng DNA µL −1 ).…”

“…For that purpose, the Illumina ® barcodes (i5 and i7) were attached. The same PCR procedure as in the first PCR step [40] was conducted except that only five cycles were applied and that the annealing temperature was set to 56 °C. PCR products were again checked with a 1.5% agarose gel.…”

Lignin intermediates lead to phenyl acid formation and microbial community shifts in meso- and thermophilic batch reactors

“…One group of monocyclic aromatic compounds are phenyl acids that include phenylacetate (PAA), phenylpropionate (PPA), or phenylbutyrate (PBA). Studies on PPA [ 18 ] and especially on PBA [ 19 ] are very rare, even though they represent relevant intermediates in the AD cascade prior to the anaerobic ring cleavage. A cascade-like increase/decrease from PAA to PPA to PBA could be observed when straw from grain was anaerobically degraded under overload conditions.…”

“…A cascade-like increase/decrease from PAA to PPA to PBA could be observed when straw from grain was anaerobically degraded under overload conditions. It was concluded that an increase in PAA concentration was an early indicator for overload conditions, whereas an increase in PBA concentration indicated a switch from using easier degradable substrates to more recalcitrant (lignocellulosic) materials [ 19 ].…”