Editorial: natural compounds in food safety and preservation

Research Areas: Nutrition & Dieteticsinfo:eu-repo/semantics/publishedVersio

Anaerobic microbial LCFA degradation in bioreactors

This paper reviews recent results obtained on long-chain fatty acids (LCFA) anaerobic degradation. Two LCFA were used as model substrates: oleate, a mono-unsaturated LCFA, and palmitate, a saturated LCFA, both abundant in LCFA-rich wastewaters. 16S rRNA gene analysis of sludge samples submitted to continuous oleate- and palmitate-feeding followed by batch degradation of the accumulated LCFA demonstrated that bacterial communities were dominated by members of the Clostridiaceae and Syntrophomonadaceae families. Archaeal populations were mainly comprised of hydrogen-consuming microorganisms belonging to the genus Methanobacterium, and acetate-utilizers from the genera Methanosaeta and Methanosarcina. Enrichment cultures growing on oleate and palmitate, in the absence or presence of sulfate, gave more insight into the major players involved in the degradation of unsaturated and saturated LCFA. Syntrophomonas-related species were identified as predominant microorganisms in all the enrichment cultures. Microorganisms clustering within the family Syntrophobacteraceae were identified in the methanogenic and sulfate-reducing enrichments growing on palmitate. Distinct bacterial consortia were developed in oleate and palmitate enrichments, and observed differences might be related to the different degrees of saturation of these two LCFA. A new obligately syntrophic bacterium, Syntrophomonas zehnderi, was isolated from an oleatedegrading culture and its presence in oleate-degrading sludges detected by 16S rRNA gene cloning and sequencing.Fundação para a Ciência e a Tecnologia (FCT)Fundo Social Europeu (FSE) - SFRH/BD/8726/2006, SFRH/BPD/14591/200

Enrichment and microbial characterization of syngas converting anaerobic cultures

Bioconversion of recalcitrant biomass/waste into bulk chemicals or biofuels is often not feasible. By gasification of these materials, syngas (mainly composed of CO2, CO and H2) is generated and can be used for the production of high value compounds by thermochemical or biotechnological processes. Here, three thermophilic cultures enriched with syngas mixtures or pure CO (T-Syn, T-Syn-CO and T-CO) were studied. Stable enriched cultures obtained by subsequent transfers for over a year, convert syngas/CO to mainly acetate and hydrogen (CO partial pressure up to 0.88 bar). 16S rRNA based techniques (PCR-DGGE) showed that predominant microorganisms in the cultures belonged to Desulfotomaculum, Caloribacterium, Thermincola and Thermoanaerobacter genera. Moreover, from the syngas- and CO-degrading cultures, a novel Thermoanaerobacter sp. (strain PCO) and a novel Moorella sp. (strain E3-O) were isolated

Microbial diversity of anaerobic syngas-converting enrichments from a multi-orifice baffled bioreactor (MOBB)

Syngas fermentation can be used to produce fuels and chemicals from lignocellulosic biomass or other poorly biodegradable wastes. The aim of this study was to identify and characterize carboxydotrophic microorganisms in enrichments and evaluate their potential for syngas bioconversion. Anaerobic sludge that efficiently converted syngas (60% CO, 30% H2, 10% CO2) to methane, in a multi-orifice baffled bioreactor (MOBB), was used as inoculum to start enrichments with CO as carbon and energy source. Enrichments were started under a headspace containing 40% CO. Bottles amended with vancomycin and/or erythromycin were also inoculated to test the potential for enriching CO-converting methanogens. Methane and acetate were produced in the enrichment, but no growth or methane production was detected in incubation with antibiotics. In the enrichment, organisms related to Acetobacterium and Sporomusa species were the predominant bacterial species and Methanobacterium and Methanospirillum were the dominant archaea. The enrichment was subcultured and pasteurized to select for spore-forming bacteria and to inactivate methanogens. A stable enrichment culture was obtained that converted up to 100% CO. This enrichment produced hydrogen and acetate. The pasteurized culture showed a low microbial diversity; more than 90% of the community was related to Sporomusa ovata (97% identity). The results suggest that methane production from CO in the MOBB is a combined activity of carboxydotrophic acetogenic bacteria and hydrogenotrophic methanogens. Interestingly, growth of S. ovata with high concentrations of CO was never shown before.info:eu-repo/semantics/publishedVersio

Enrichment of syngas-converting communities from a multi-orifice baffled bioreactor

The substitution of natural gas by renewable biomethane is an interesting option to reduce global carbon footprint. Syngas fermentation has potential in this context, as a diverse range of low-biodegradable materials that can be used. In this study, anaerobic sludge acclimatized to syngas in a multi-orifice baffled bioreactor (MOBB) was used to start enrichments with CO. The main goals were to identify the key players in CO conversion and evaluate potential interspecies metabolic interactions conferring robustness to the process. Anaerobic sludge incubated with 0.7 × 105 Pa CO produced methane and acetate. When the antibiotics vancomycin and/or erythromycin were added, no methane was produced, indicating that direct methanogenesis from CO did not occur. Acetobacterium and Sporomusa were the predominant bacterial species in CO-converting enrichments, together with methanogens from the genera Methanobacterium and Methanospirillum. Subsequently, a highly enriched culture mainly composed of a Sporomusa sp. was obtained that could convert up to 1.7 × 105 Pa CO to hydrogen and acetate. These results attest the role of Sporomusa species in the enrichment as primary CO utilizers and show their importance for methane production as conveyers of hydrogen to methanogens present in the culture.Nederlandse Organisatie voor Wetenschappelijk Onderzoek (024.002.002); FP7 Ideas: European Research Council (323009); Norte 2020 - Sistema de Apoio a Investigação Científica e Tecnol ogica (NORTE-01-0145-FEDER-000004); Fundação para a Ciência e a Tecnologia (PD/BD/128030/2016, SFRH/BPD/104837/ 2014).info:eu-repo/semantics/publishedVersio

Anaerobic LCFA degradation: a role for non-syntrophic conversions?

For many years the focus of lipids/long-chain fatty-acids (LCFA) wastewater treatment was on technological and process developments. More recently, promising results on the anaerobic treatment of LCFA-containing wastewaters[1] widened the attention to the microbiology aspects as well. In anaerobic bioreactors, LCFA can be β-oxidized to acetate and H2 by acetogenic bacteria, in obligatory syntrophy with methanogens. Presently, 14 species have been described that grow on fatty-acids in syntrophy with methanogens, all belonging to the families Syntrophomonadaceae and Syntrophaceae[2]. Among these, only 4 species are able to degrade mono- and/or polyunsaturated LCFA. The reason why the degradation of unsaturated LCFA is not more widespread remains unknown. Early studies suggested that degradation of unsaturated LCFA requires complete chain saturation prior to β-oxidation[2]. Unsaturated LCFA, such as linoleate (C18:2) and oleate (C18:1), would be metabolized through a hydrogenation step yielding stearate (C18:0), then entering the β-oxidation cycle. However, this theory is inconsistent with the observed accumulation of palmitate (C16:0) in continuous bioreactors fed with oleate[1]. We hypothesize that LCFA chain saturation might be a non-syntrophic process, i.e. unsaturated LCFA can function as electron donors and acceptors, as protons released in a first β-oxidation step can be used to hydrogenate the unsaturated hydrocarbon. To test this, linoleate (C18:2), oleate (C18:1) and a mixture of stearate (C18:0) and palmitate (C16:0) were continuously fed to bioreactors with methanogenesis-active or -inhibited anaerobic sludge. In the reactors fed with linoleate and oleate, palmitate accumulated in methanogenesis-active and -inhibited bioreactors up to concentrations of approximately 2 mM and 8 mM, respectively. In methanogenesis-inhibited bioreactors fed with a mixture of saturated LCFA (stearate and palmitate) no biological activity occurred. These results suggest the occurrence of a non-syntrophic step during the degradation of unsaturated LCFA in anaerobic bioreactors. The identification of microbial communities involved in non-syntrophic linoleate/oleate to palmitate conversion will give more insights into this novel biochemical mechanism

Freeze tolerance of the yeast Torulaspora delbrueckii : cellular and biochemical basis

The freeze-stress responses to prolonged storage at - 20 °C in Torulaspora delbrueckii PYCC5323 were investigated. In this yeast no loss of cell viability was observed for at least 120 days during freezing at - 20ºC, whereas a loss of 80% was observed in a commercial baker's yeast after 15 days. In the former strain, freeze resistance was dependent on an adaptation process. The primary cell target of freeze stress was the plasma membrane, preservation of it’s integrity being related with a lower increase of lipid peroxidation and with higher resistance to H2O2, but not with intracellular trehalose concentration.Fundação para a Ciência e a Tecnologia (FCT) - grant (PRAXIS XXI/BD/21543/99)