Impact of dissolved hydrogen partial pressure on mixed culture fermentations

Kok, Stefan de; Meijer, J.A.M.; Loosdrecht, M.C.M. van; Kleerebezem, Robbert

doi:10.1007/s00253-012-4400-x

Cited by 48 publications

(23 citation statements)

References 32 publications

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“…Thermodynamic analysis of product formation pathways combined with product transport considerations enabled these authors to identify the optimal product spectrum in terms of bioenergy conservation potential. Based on experimental evidence (de Kok et al 2013) electron carriers other than NADH/NAD were included in the second version of the model , resulting in dominant production of butyrate and acetate mixtures as fermentation products. This fermentation pattern typically is associated with Clostridium fermentations that indeed are often found to dominate at acid and around neutral pH-values and mesophilic temperatures.…”

Section: Controlling the Product Spectrum In Anaerobic Fermentationsmentioning

confidence: 99%

Anaerobic digestion without biogas?

Kleerebezem

Joosse

Rozendal

et al. 2015

Rev Environ Sci Biotechnol

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320

171

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Section: Controlling the Product Spectrum In Anaerobic Fermentationsmentioning

confidence: 99%

Anaerobic digestion without biogas?

Kleerebezem

Joosse

Rozendal

et al. 2015

Rev Environ Sci Biotechnol

Self Cite

320

171

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“…Trend line is for ATP production at pH 8.00 only. propionate and ethanol at basic pH to butyrate at acidic pH may again result from the 6-105 maintenance energy) in the same way that a stable NAD pool is maintained 26 . This could imply that there are additional pH-related maintenance tasks at high pH, such as maintenance of the cellular membrane 185 , which require even greater ATP generation than does intracellular pH maintenance.…”

Section: Hpr-type Fermentationmentioning

confidence: 99%

“…Measurements of the redox states of bacterial EMCs have shown that the Fd and NADP pools are generally maintained at 90% or more reduced 42 , while the NAD pool is maintained at 80% or more oxidized 26,42 . This shifts the intracellular reduction potential of these EMCs down to around (vs SHE) -500 mV for Fd and -360 mV for NADP, while shifting NAD up to around -280 mV 43 .…”

Section: -6mentioning

confidence: 99%

“…Additionally, outside of electron mediation mechanisms, there has been limited investigation of the metabolic mechanisms through which various fermentation pathways are regulated. Even within the area of electron mediation, this has been limited to investigation of the mediator pools 26 and mechanistic assumptions in fermentation models 27 .…”

Section: Statement Of Part Of the Thesis Submitted To Qualify For Thementioning

confidence: 99%

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Metabolic mechanisms and regulation of mixed culture fermentation

Hoelzle¹

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Fermentation of waste streams is an emerging method for production of biofuels and commodity chemicals, and mixed-culture fermentation allows for robustness and flexibility in the range of waste streams that can be processed, and in varying product mix from the fermenter. However, mechanistic models of mixed culture fermentation are limited, with mixed culture fermentation generally resulting in acetate, butyrate, and ethanol, with even these production modes are not clearly understood. Results from pure-culture fermentation, as well as those from methanogenic reactors indicate the possibility to produce high-value lactate and propionate if the cellular mechanisms which control the expression of these production modes can be harnessed and understood. Lactate and propionate are key chemicals in production of bioplastics, pesticides, preservatives, and food additives, among many other uses. Their production by mixed cultures has been observed at high substrate concentrations (shock loads), and inconsistently at high pH. They are produced via metabolic pathways which branch off of the primary energy-generation pathways. In general, they are thought to be produced by microbes as a way to redirect excess carbon flow in transient states, and are also thought to be produced as an electron sink. In this work, both of these possible production influences are explored for steady state production of lactate and propionate.By increasing substrate from limiting to non-limiting quantities, and thereby increasing the carbon load on a fermentation system, lactate production was successfully achieved and maintained during steady state only when substrate was in excess. Substrate consumption at this point was 14.1±0.8 gCOD·L -1 , and lactate accounted for 25±1% of the total product COD. Upon return to substrate-limiting conditions, the process returned to butyrate production. This demonstrates the reversibility of this production mode. Taxonomic analysis via Illumina pyrosequencing of the 16S rRNA gene revealed that the microbial community experienced a shift from Megasphaera-dominant during butyrate production to Ethanoligenens-dominant during lactate production. Taxonomy was also regained upon return to substrate-limiting conditions. However, taxonomy alone could not explain the product shift because Ethanoligenens produces little to no lactate in cultured references. A mechanistic description of the product shift therefore required molecular analysis of the metabolic mechanisms, and this was achieved through metaproteomics via SWATH-MS.The evidence suggests that at high carbon loads, toxic methylglyoxal is formed in many microbe groups, including Megasphaera, due to limited processing capacity of the ii dihydroxyacetone-P intermediate of glycolysis. The methylglyoxal is converted into lactate for disposal. This detoxification need is abated upon return to substrate-limited conditions. The impact of redox stress was examined using cathodic electro-fermentation with soluble mediator chemicals ranging from slightly negati...

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“…Apart from the unreliable product prediction under certain conditions, the interaction between microbial populations in MCF is also not well understood (Rafrafi et al, 2013. Thermodynamic was considered as the major driving force determining product mix and previously utilized to develop theoretical models for MCF (Costello et al, 1991, Mosey, 1983.As an example, pathways that produce more hydrogen (acetate type fermentation) are favoured at low hydrogen partial pressures (Ruzicka, 1996, de Kok et al, 2013. However, these models often fail in validating experiments, indicating that: (a) the full range of thermodynamic factors is not included, or (b) the influence of physiological and phylogenetic factors needs to be included.…”

Section: Application Barriers and Research Gapmentioning

confidence: 99%

Regulation of mixed culture fermentation

Zaki¹

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Fermentation is commonly used to produce food materials (beverages, dairy products), renewable fuels (hydrogen, ethanol), pharmaceuticals (antibiotics) and industrial chemicals (acetate, butyrate). In industrial fermentation, a specialised, pure microbial culture is normally used to generate specific products. This requires expensive, sterile production conditions with high-quality raw materials. In contrast, Mixed Culture Fermentation (MCF) uses environmentally ubiquitous organisms to produce a mixture of products depending on the environmental conditions. As they are sourced from the environment, mixed cultures do not require expensive culture maintenance. In addition, they are capable of dealing with a mixture of substrates of variable composition and non-sterile feeds. This has the potential to reduce costs, increase reactor loading rates, and allow for continuous reactors, as opposed to batch operation. MCF is a preferable, flexible process in that can continuously manipulate product mixtures by changing operational condition. The key limitation to industrial implementation of MCF is the difficulty in predicting product formation based on operational conditions. This is due to a lack of understanding of how operational factors affect the various pathways, and hence the product spectrum, with pH being the most commonly manipulated process variable. This thesis attempts to further analyse the link between operational conditions, microbial community, and product spectrum. Two experiments were done, the first focusing on mode of pH manipulation in a continuous reactor, and the second focusing on batch operation at different pH levels, and with different inoculums. The continuous study varied pH from 4 to 8, with one experiment varying the pH from 4 to 8 progressively (progressive), and the other resetting pH back to 5.5 as an intermediate point (reset). The reset regime resulted in a highly dynamic community, shifting from Clostridia at low pH to Klebsiella, and a more dynamic product spectrum, with specifically ethanol being produced at high pH. The progressive regime resulted in relatively flat microbial community, with less dynamic product spectrum. Kinetic experiments done on the same reactors, varying also hydrogen partial pressure through nitrogen sparge rate, and using a membrane inlet mass spectrometer (MIMS) as measurement technique emphasised a number of time constants, including direct chemical response to pH change (1000 d -1 ), liquid and gas response to changes in gas flow and to pH change, likely related to mass transfer characteristics (100 d -1 ), and biological responses, mainly measured as ethanol (1 d -1 ). Changes in microbial community are even slower than this. The second batch indicated that the major factor ii influencing rate and spectrum response was the inoculation pH, with biomass inoculated at pH4 being very slow in batch (1 d -1 ), and producing mainly ethanol, and biomass inoculated at higher pH levels being pH 6 (3 d -1 ) and 8 (10 d -1 ) being progressively faster. T...

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Impact of dissolved hydrogen partial pressure on mixed culture fermentations

Cited by 48 publications

References 32 publications

Anaerobic digestion without biogas?

Anaerobic digestion without biogas?

Metabolic mechanisms and regulation of mixed culture fermentation

Regulation of mixed culture fermentation

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