Enrichment of anaerobic syngas-converting bacteria from thermophilic bioreactor sludge

Thermophilic (55 °C) anaerobic microbial communities were enriched with a synthetic syngas mixture (composed of CO, H2, and CO2) or with CO alone. Cultures T-Syn and T-CO were incubated and successively transferred with syngas (16 transfers) or CO (9 transfers), respectively, with increasing CO partial pressures from 0.09 to 0.88 bar. Culture T-Syn, after 4 successive transfers with syngas, was also incubated with CO and subsequently transferred (9 transfers) with solely this substrate – cultures T-Syn-CO. Incubation with syngas and CO caused a rapid decrease in the microbial diversity of the anaerobic consortium. T-Syn and T-Syn-CO showed identical microbial composition and were dominated by Desulfotomaculum and Caloribacterium species. Incubation initiated with CO resulted in the enrichment of bacteria from the genera Thermincola and Thermoanaerobacter. Methane was detected in the first two to three transfers of T-Syn, but production ceased afterward. Acetate was the main product formed by T-Syn and T-Syn-CO. Enriched T-CO cultures showed a two-phase conversion, in which H2 was formed first and then converted to acetate. This research provides insight into how thermophilic anaerobic communities develop using syngas/CO as sole energy and carbon source can be steered for specific end products and subsequent microbial synthesis of chemicals.This study has been financially supported by FEDER funds through the Operational Competitiveness Programme (COMPETE) and by national funds through the Portuguese Foundation for Science and Technology (FCT) in the frame of the project FCOMP-01-0124-FEDER-027894. Financial support from FCT and the European Social Fund (POPH-QREN) through the PhD grant SFRH/BD/48965/2008 attributed to J.I.A. is gratefully acknowledged. A.J.M. Stams acknowledges grants from CW-TOP 700.55.343 and ALW 819.02.014 of the Netherlands Science Foundation (NWO), Consolider-CSD 2007-00055 and ERC (323009)

Methane cycling in lake sediments and its influence on chironomid larval δ13C

Stable carbon isotope analysis of chironomid larvae gave rise to the hypothesis that methane-oxidizing bacteria can provide an important food source for higher trophic levels in lakes. To investigate the importance of the methane cycle for the larval stable carbon signatures, isotope analysis and microbiological and biogeochemical investigations were combined. The study was based on comparison of a dimictic lake (Holzsee) and a polymictic, shallow lake (Großer Binnensee), both located in northern Germany. Both lakes are inhabited by Chironomus plumosus larvae, which exhibited a stronger 13C-depletion in Holzsee than in Großer Binnensee, indicating a greater contribution of methane–carbon in the former. Indeed, the processes involved in the microbial methane cycle were found to be more active in Holzsee, showing higher potential methane production and methane oxidation rates. Consistently, cell numbers of methane-oxidizing bacteria were with 0.5 − 1.7 × 106 cells Embedded Image about one order of magnitude higher in Holzsee than in Großer Binnensee. Molecular analysis of the microbial community structure revealed no differences in the methanotrophic community between the two lakes, with a clear dominance of type I methanotrophs. The methanogenic population seemed to be adapted to the prevailing substrate in the respective lake (H2/CO2 in Holzsee and acetate in Großer Binnensee), even though differences were minor. In conclusion, the stronger larval 13C-depletion in Holzsee was not reflected in differences in the microbial community structure, but in the activity and size of the methanogenic and methanotrophic populations in the lake sediment