Impact of formate on the growth and productivity of Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 grown on syngas

The current energy model based on fossil fuels is coming to an end due to the increase in global energy demand. Biofuels such as ethanol and butanol can be produced through the syngas fermentation by acetogenic bacteria. The present work hypothesizes that formate addition would positively impact kinetic parameters for growth and alcohol production in Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 by diminishing the need for reducing equivalents. Fermentation experiments were conducted using completely anaerobic batch cultures at different pH values and formate concentrations. PETC cultures were more tolerant to formate concentrations than P7, specially at pH 5.0 and 6.0. Complete growth inhibition of PETC occurred at sodium formate concentrations of 30.0 mM; however, no differences in growth rates were observed at pH 7.0 for the two strains. Incubation at formate concentrations lower than 2.0 mM resulted in increased growth rates for both strains. The most recognizable effects of formate addition on the fermentation products were the increase in the total carbon fixed into acids and alcohols at pH 5.0 and pH 6.0, as well as, a higher ethanol to total products ratio at pH 7.0. Taken all together, these results show the ability of acetogens to use formate diminishing the energy demand for growth, and enhancing strain productivity. [Int Microbiol 2014; 17(4):195-204]Keywords: Clostridium carboxidivorans · Clostridium ljungdhalii · syngas fermentation · biofuels · format

Effect of ethanol and butanol on autotrophic growth of model homoacetogens

Research efforts aimed at increasing ethanol and butanol productivity from syngas are currently gaining attention. For most model carboxydotrophic bacteria, production rates, yields and maximum product titres have been studied in detail, but little is known on alcohol toxicity in these bacteria. The aim of this work was to investigate the inhibitory effects of ethanol and butanol on the growth of Clostridium ljungdahlii PETC, C. carboxidiwrans P7, and 'Butyribacterium methylotrophicum DSM3468'. Experiments to determine inhibitory effects due to product accumulation were carried out using a synthetic mixture of CO:CO2:H-2 as a substrate. These conditions were chosen to mimic gaseous effluents of biomass and waste gasification plants. Inhibition effects were recorded as changes in growth parameters. No significant inhibition was observed for ethanol at concentrations below 15 g/L. The three species exhibited higher sensitivity to butanol. Half inhibition constants for butanol could be estimated for P7 (IC50 = 4.12 g/L), DSM3468 (IC50 = 1.79 g/L), and PETC IC50 = 9.75 g/L). In conclusion, at least for the tested strains, alcohol toxicity is not an immediate handicap for increasing alcohol production of the tested homoacetogenic strains

New fecal bacterial signature for colorectal cancer screening reduces the fecal immunochemical test false-positive rate in a screening population

Guidelines recommend routine screening for colorectal cancer (CRC) in asymptomatic adults starting at age 50. The most extensively used noninvasive test for CRC screening is the fecal immunochemical test (FIT), which has an overall sensitivity for CRC of approximately 61.0%-91.0%, which drops to 27.0%-67.0% for advanced adenomas. These figures contain a high false-positive rate and a low positive predictive value. This work aimed to develop a new, noninvasive CRC screening tool based on fecal bacterial markers capable of decreasing FIT false-positive rates in a FIT-positive population. We defined a fecal bacterial signature (RAID-CRC Screen) in a proof-of-concept with 172 FIT-positive individuals and validated the obtained results on an external cohort of 327 FIT-positive subjects. All study participants had joined the national CRC screening program. In the clinical validation of RAID-CRC Screen, a sensitivity of 83.9% and a specificity of 16.3% were obtained for the detection of advanced neoplasm lesions (advanced adenomas and/or CRC). FIT 20 μg/g produced 184 false-positive results. Using RAID-CRC Screen, this value was reduced to 154, thus reducing the false-positive rate by 16.3%. The RAID-CRC Screen test could be implemented in CRC screening programs to allow a significant reduction in the number of colonoscopies performed unnecessarily for FIT-positive participants of CRC screening programs

Insights into key parameters for bio-alcohol production in syngas fermentation using model carboxydotrophic bacteria

This doctoral thesis deals with the synthesis of two biofuels (bioethanol and biobuthanol) by bacteria. Concretely, the thesis is focused on a group of bacteria able to grow in a simple substrate such as synthesis gas or syngas. Syngas is a mixture of hydrogen, carbon monoxide, and carbon dioxide obtained through the gasification of urban and forestry wastes. The use of syngas as a substrate requires a good knowledge of bacterial metabolism to successfully control acid production and promote alcohol synthesis. To acquire this knowledge, the researcher carried out a set of experiments at lab scale, always using syngas. Among the most significant results, there is the relevance of both the temperature and the bacteria state at the start of the experiments. Additionally, new insights into bacterial metabolism which are applicable at industrial scale were gathered.Aquesta tesi doctoral tracta la producció de dos biocombustibles – el bioetanol i el bioalcohol - per mitjà de microorganismes. En concret, la tesi s'ha centrat en un grup de bacteris capaços de sintetitzar bioalcohols a partir del gas de síntesis o syngas. El syngas és una mescla d’hidrogen, diòxid de carboni i monòxid de carboni que s’obté mitjançant la gasificació de diferents tipus de residus. L’ús d’aquest gas com a substrat requereix un bon coneixement del metabolisme dels bacteris involucrats a fi de controlar amb èxit la producció d'àcids i afavorir la d'alcohols. Aquest coneixement s'ha adquirit amb una sèrie d'experiments avançats a escala de laboratori. Entre els resultats més significatius destaca la rellevància que ha demostrat tenir la temperatura en què creixen els bacteris i l’estat del bacteri en el moment d’inici dels experiments. També s’han aportat nous coneixements sobre el metabolisme bacterià que són aplicables a escala industrial

Insights into key parameters for bio-alcohol production in syngas fermentation using model carboxydotrophic bacteria

This doctoral thesis deals with the synthesis of two biofuels (bioethanol and biobuthanol) by bacteria. Concretely, the thesis is focused on a group of bacteria able to grow in a simple substrate such as synthesis gas or syngas. Syngas is a mixture of hydrogen, carbon monoxide, and carbon dioxide obtained through the gasification of urban and forestry wastes. The use of syngas as a substrate requires a good knowledge of bacterial metabolism to successfully control acid production and promote alcohol synthesis. To acquire this knowledge, the researcher carried out a set of experiments at lab scale, always using syngas. Among the most significant results, there is the relevance of both the temperature and the bacteria state at the start of the experiments. Additionally, new insights into bacterial metabolism which are applicable at industrial scale were gathered.Aquesta tesi doctoral tracta la producció de dos biocombustibles – el bioetanol i el bioalcohol - per mitjà de microorganismes. En concret, la tesi s'ha centrat en un grup de bacteris capaços de sintetitzar bioalcohols a partir del gas de síntesis o syngas. El syngas és una mescla d’hidrogen, diòxid de carboni i monòxid de carboni que s’obté mitjançant la gasificació de diferents tipus de residus. L’ús d’aquest gas com a substrat requereix un bon coneixement del metabolisme dels bacteris involucrats a fi de controlar amb èxit la producció d'àcids i afavorir la d'alcohols. Aquest coneixement s'ha adquirit amb una sèrie d'experiments avançats a escala de laboratori. Entre els resultats més significatius destaca la rellevància que ha demostrat tenir la temperatura en què creixen els bacteris i l’estat del bacteri en el moment d’inici dels experiments. També s’han aportat nous coneixements sobre el metabolisme bacterià que són aplicables a escala industrial

Impact of formate on the growth and productivity of Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 grown on syngas

The current energy model based on fossil fuels is coming to an end due to the increase in global energy demand. Biofuels such as ethanol and butanol can be produced through the syngas fermentation by acetogenic bacteria. The present work hypothesizes that formate addition would positively impact kinetic parameters for growth and alcohol production in Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 by diminishing the need for reducing equivalents. Fermentation experiments were conducted using completely anaerobic batch cultures at different pH values and formate concentrations. PETC cultures were more tolerant to formate concentrations than P7, specially at pH 5.0 and 6.0. Complete growth inhibition of PETC occurred at sodium formate concentrations of 30.0 mM; however, no differences in growth rates were observed at pH 7.0 for the two strains. Incubation at formate concentrations lower than 2.0 mM resulted in increased growth rates for both strains. The most recognizable effects of formate addition on the fermentation products were the increase in the total carbon fixed into acids and alcohols at pH 5.0 and pH 6.0, as well as, a higher ethanol to total products ratio at pH 7.0. Taken all together, these results show the ability of acetogens to use formate diminishing the energy demand for growth, and enhancing strain productivityThe authors thank the Autonomous Government of Catalonia (Generalitat de Catalunya) (2013 FI-DGR) and the Spanish Ministry of Science and Innovation (Best-Energy, CTQ2011-23632, CTM2013-43454-R) for their financial support in this study. LEQUIA and IEA have been recognized as consolidated research groups by the Catalan Government (2014-SGR-1168 and 2014-SGR-2016). RG gratefully acknowledges support from Beatriu de Pinos fellowship (BP-2011-B) and FP7 Marie Curie Career Integration Grants (PCIG13-GA-2013-618593