From grass to gas: microbiome dynamics of grass biomass acidification under mesophilic and thermophilic temperatures

Abstract

BackgroundSeparating acidification and methanogenic steps in anaerobic digestion processes can help to optimize the process and contribute to producing valuable sub-products such as methane, hydrogen and organic acids. However, the full potential of this technology has not been fully explored yet. To assess the underlying fermentation process in more detail, a combination of high-throughput sequencing and proteomics on the acidification step of plant material (grass) at both mesophilic and thermophilic temperatures (37 and 55 °C, respectively) was applied for the first time.ResultsHigh-strength liquor from acidified grass biomass exhibited a low biodiversity, which differed greatly depending on temperature. It was dominated by Bacteroidetes and Firmicutes at 37 °C, and by Firmicutes and Proteobacteria at 55 °C. At the methane stage, Methanosaeta, Methanomicrobium and Methanosarcina proved to be highly sensitive to environmental changes as their abundance in the seed sludges dropped dramatically after transferring the seed sludges from the respective reactors into the experimental setup. Further, an increase in Actinobacteria coincided with reduced biogas production at the end of the experiment. Over 1700 proteins were quantified from the first cycle of acidification samples using label-free quantitative proteome analysis and searching protein databases. The most abundant proteins included an almost complete set of glycolytic enzymes indicating that the microbial population is basically engaged in the degradation and catabolism of sugars. Differences in protein abundances clearly separated samples into two clusters corresponding to culture temperature. More differentially expressed proteins were found under mesophilic (120) than thermophilic (5) conditions.ConclusionOur results are the first multi-omics characterisation of a two-stage biogas production system with separated acidification and suggest that screening approaches targeting specific taxa such as Methanosaeta, Methanomicrobium and Methanosarcina could be useful diagnostic tools as indicators of environmental changes such as temperature or oxidative stress or, as in the case of Actinobacteria, they could be used as a proxy of the gas production potential of anaerobic digesters. Metaproteome analyses only detected significant expression differences in mesophilic samples, whereas thermophilic samples showed more stable protein composition with an abundance of chaperones suggesting a role in protein stability under thermal stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0859-0) contains supplementary material, which is available to authorized users.

Liquid co-substrates repower sewage microbiomes

“…As shown in Fig. 3D, microscopic analysis revealed a high number of rod-shaped methanogens in solid-fed batches, indicating a high number of Methanosaeta , a typical genus observed in sewage sludge (Abendroth et al, 2015; Abendroth et al, 2017a). Interestingly, liquid-fed batches showed decreasing numbers of rod-shaped methanogens and increasing numbers of Methanosarcina -like complexes.…”

“…The key microorganisms in the methanogenesis phase are methanogenic archaea, whose composition depends on the operation conditions and strongly changes when co-digestion with additional substrates occurs (Sundberg et al, 2013). Mesophilic methanogens that can be found in especially high abundances belong to the genus Methanosaeta, Methanoculleus, and Methanosarcina (Abendroth et al, 2015; Abendroth et al, 2017a). A strong microbial shift can be observed under thermophilic conditions, in which methanogens such as Methanothermobacter or Methanobacterium show an increased abundance (Maus et al, 2016; Lin et al, 2017; Xiao et al, 2018).…”

“…Based on this idea, a number of works showing the possibility to repower sewage sludge digesters by using cosubstrates have been published recently. The proposed co-substrates include grass biomass (Hidaka et al, 2016; Abendroth et al, 2017), food waste (Zahan et al, 2016), municipal solid waste (Cabbai et al, 2016), glycerol (Jensen et al, 2014), microalgae (Mahdy et al, 2015), or pear residues (Arhoun et al, 2013). To make such repowering approaches applicable for the industry, and to meet the high standards of water treatment plants regarding process stability, a better understanding of the microbial changes ocurring during the transition from typical sewage digestion to high-load digestion processes is still needed.…”

“…For example, under mesophilic conditions digestion processes with high amounts of chemical oxygen demand (COD) tend to have high amounts of Methanosarcina and Methanoculleus . On the other hand, sewage sludge, which has typically lower amounts of COD compared to typical industrial co-digesters, tends to have higher amounts of archaea corresponding to the genus Methanosaeta (Abendroth et al, 2015; Abendroth et al, 2017a).…”

Identification and cultivation of hydrogenotrophic methanogens from palm oil mill effluent for high methane production

“…[30][31][32]60 The uncultured proteiniborus detected in this study might be related to P. ethanoligenes and P. indolifex, which had been found in the thermophilic biogas reactor. 33,61 However, the involvement of uncultured clostridium in biogas production has not been reported. The relative proportion of uncultured bacterium accounted for more than 33.35% of bacterial species ( Figure 4).…”