Microbiology of thermophilic anaerobic syngas conversion

Biological syngas fermentation can be used for novel biotechnological applications. Syngas can be produced from biomass and recalcitrant wastes; fermentation of this gas is therefore an environmentally friendly process with foreseen applications in the production of biofuels and chemicals. This thesis reports the use of thermophilic anaerobic mixed cultures for syngas and carbon monoxide (CO) conversion, as well as the isolation and characterization of two new thermophilic bacterial strains - one CO-utilizing bacterium and one CO-tolerant bacterium. Stable thermophilic enrichments converting syngas or CO at 55 oC were obtained by long term exposure of a thermophilic anaerobic suspended sludge to these substrates. Enrichments were successively transferred (for over a year) with syngas and pure CO, as sole carbon and energy source. CO partial pressure was increased from 0:09 to 0:88 bar during the enrichment procedure. Enrichment cultures initiated with syngas produced mainly acetate, while hydrogen was the main product detected in enrichment cultures initially incubated with CO. Bacteria branching within the families Peptococcaceae and Thermoanaerobacteraceae were present in syngas and CO enrichment cultures. Syngas enrichment cultures were composed of two predominant species related to Desulfotomaculum and Caloribacterium genera, while bacteria assigned to Thermincola and Thermoanaerobacter genera were abundant in CO enrichment cultures. The e ect of sulfate on CO conversion by the obtained syngas-degrading enriched culture was also investigated. Although the enrichment culture could convert CO into mainly acetate both in the presence and in the absence of sulfate, CO conversion was faster when sulfate was present. Identi cation of the predominant microorganisms revealed the presence of Desulfotomaculum-like bacteria. A novel CO-tolerating bacterium, Thermoanaerobacter carboxyditolerans, was isolated from the syngasdegrading enriched culture. This bacterium is closest related to Thermoanaerobacter thermohydrosulfu- ricus (97% identity based on 16S rRNA gene sequence). Although T. carboxyditolerans does not utilize CO, it is able to grow in the presence of high CO concentrations (pCO = 1:7 bar). Other Thermoanaer- obacter species showed tolerance to CO, namely T. thermohydrosulfuricus, T. brockii subsp. nnii, T. pseudethanolicus and T. wiegelii ; growth of these bacteria was not substantially a ected by CO concentrations ranging from 25% to 100% (pCO from 0:425 to 1:7 bar). Nevertheless, hydrogen production by those species decreased with increasing CO partial pressure. A new thermophilic hydrogenogenic carboxydotrophic bacterium, Moorella stamsii, could be isolated from the CO-degrading enrichment. This bacterium is able to utilize CO coupled to the production of hydrogen. M. stamsii is phylogenetically related to Moorella glycerini (97% identity based on 16S rRNA gene sequences). With this PhD research we gained insight in the ecophysiology of thermophilic anaerobic conversion of syngas and CO. Results presented in this thesis are important for prospecting biotechnological processes for the production of added-values compounds, such as hydrogen and/or acetate.

Name thesis:degree_name

Doutoramento em Engenharia Química e Biológica

Year dc:date.issued

2013

Author dc:creator

• Alves, J. I.

Advisors dc:contributor.advisor

• Sousa, Diana Zita Machado
• Alves, M. M.
• Plugge, Caroline M.

Statement dc:rights

• openAccess

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1822/28642

OAI record oai:identifier

http://repositorium.sdum.uminho.pt/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepositorium.uminho.pt%3A1822%2F28642