Angelo Fontana, Laura Dipasquale and Giuliana d'Ippolito
Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche, Itlay
The heterotrophic bacterium Thermotoga neapolitana produces hydrogen (H2) by fermentation of organic substrates. The process is referred to as dark fermentation and is completed by synthesis organic acids whose composition varies in agreement with the culture conditions. Here we show that dark fermentation is shunted by an unprecedented mechanism of capture and sequestration of carbon dioxide into lactic acid [1, 2]. This novel pathway is based on direct coupling of CO2 with C2 substrates, such as exogenous acetate or acetyl-CoA derived from fermentation of carbon-rich materials. In fact, when the bacterial cultures are supplemented only with carbohydrates, synthesis of lactic acid occurs to the detriment of acetic acid levels but, in contrast with the currently accepted DF model, synthesis of lactic acid does not affect H2 productivity. On the contrary, when exogenous acetate is added under CO2-enriched conditions, the bacterial cells perform as microscopic reactors that are able to synthesize lactic acid through elongation of the acetic acid molecule by addition of carbon dioxide. This mechanism could represent an unprecedented way of non-photothrophic CO2 fixation in the thermophilic bacterium. The bacterium can also use bicarbonate but incorporation levels suggest CO2 as substrate for the coupling reaction. The CO2-dependent fermentation process, which we named capnophilic lactic fermentation, achieves at the same time production of H2 and conversion of CO2 into added value chemicals without biomass deconstruction [3].
Keywords: Biohydrogen, CO2 capture, lactic fermentation.
REFERENCES
[1] Dipasquale L., d''Ippolito G., Fontana A. Capnophilic lactic fermentation and hydrogen synthesis by Thermotoga neapolitana:
an unexpected deviation from dark fermentation. International Journal of Hydrogen Energy 2014, 39: 4857-4862.
[2] d''Ippolito G., Dipasquale L., Fontana A. Recycling of carbon dioxide and acetate to lactic acid by the hydrogen-producing
bacterium Thermotoga neapolitana. ChemSusChem 2014, 7, 2678-2683.
[3] Fontana A., d''Ippolito G., Dipasquale L. Process for non photosynthetic biosequestration of carbon dioxyde, PCT/IB2014/058519 of
23 January 2013.