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Angenent Lab Substrate Ratio Carboxylate Platform

ABSTRACT: Higher substrate ratios of ethanol to acetate steered chain elongation toward n-caprylate in a bioreactor with product extraction

PROVIDER: PRJEB21834 | ENA |

REPOSITORIES: ENA

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			Action	DRS
	ERR2036350.fastq.gz	Fastqsanger.gz
	ERR2036360.fastq.gz	Fastqsanger.gz
	ERR2036370.fastq.gz	Fastqsanger.gz
	ERR2036380.fastq.gz	Fastqsanger.gz
	ERR2036390.fastq.gz	Fastqsanger.gz

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Project description:Previous bioreactor studies achieved high volumetric n caprylate (i.e., n octanoate) production rates and selectivities from ethanol and acetate with chain elongating microbiomes. However, the metabolic pathways from the substrates to n caprylate synthesis were unclear. We operated two n caprylate producing upflow bioreactors with a synthetic medium to study the underlying metabolic pathways. The operating period exceeded 2.5 years, with a peak volumetric n caprylate production rate of 190 ± 8.4 mmol C L 1 d 1 (0.14 g L 1 h 1). We identified oxygen availability as a critical performance parameter, facilitating intermediate metabolite production from ethanol. Bottle experiments in the presence and absence of oxygen with 13C labeled ethanol suggest acetyl coenzyme A based derived production of n butyrate (i.e., n butanoate), n caproate (i.e., n hexanoate), and n caprylate. Here, we postulate a trophic hierarchy within the bioreactor microbiomes based on metagenomics, metaproteomics, and metabolomics data, as well as experiments with a Clostridium kluyveri isolate. First, the aerobic bacterium Pseudoclavibacter caeni and the facultative anaerobic fungus Cyberlindnera jadinii converted part of the ethanol pool into the intermediate metabolites succinate, lactate, and pyroglutamate. Second, the strict anaerobic C. kluyveri elongated acetate with the residual ethanol to n butyrate. Third, Caproicibacter fermentans and Oscillibacter valericigenes elongated n butyrate with the intermediate metabolites to n caproate and then to n caprylate. Among the carbon chain elongating pathways of carboxylates, the tricarboxylic acid cycle and the reverse ß oxidation pathways showed a positive correlation with n caprylate production. The results of this study inspire the realization of a chain elongating production platform with separately controlled aerobic and anaerobic stages to produce n caprylate renewably as an attractive chemical from ethanol and acetate as substrates.

Project description:The microbial population structure and function of natural anaerobic communities maintained in lab-scale continuously stirred tank reactors at different lactate to sulfate ratios and in the absence of sulfate were analyzed using an integrated approach of molecular techniques and chemical analysis. The population structure, determined by denaturing gradient gel electrophoresis and by the use of oligonucleotide probes, was linked to the functional changes in the reactors. At the influent lactate to sulfate molar ratio of 0.35 mol mol(-1), i.e., electron donor limitation, lactate oxidation was mainly carried out by incompletely oxidizing sulfate-reducing bacteria, which formed 80-85% of the total bacterial population. Desulfomicrobium- and Desulfovibrio-like species were the most abundant sulfate-reducing bacteria. Acetogens and methanogenic Archaea were mostly outcompeted, although less than 2% of an acetogenic population could still be observed at this limiting concentration of lactate. In the near absence of sulfate (i.e., at very high lactate/sulfate ratio), acetogens and methanogenic Archaea were the dominant microbial communities. Acetogenic bacteria represented by Dendrosporobacter quercicolus-like species formed more than 70% of the population, while methanogenic bacteria related to uncultured Archaea comprising about 10-15% of the microbial community. At an influent lactate to sulfate molar ratio of 2 mol mol(-1), i.e., under sulfate-limiting conditions, a different metabolic route was followed by the mixed anaerobic community. Apparently, lactate was fermented to acetate and propionate, while the majority of sulfidogenesis and methanogenesis were dependent on these fermentation products. This was consistent with the presence of significant levels (40-45% of total bacteria) of D. quercicolus-like heteroacetogens and a corresponding increase of propionate-oxidizing Desulfobulbus-like sulfate-reducing bacteria (20% of the total bacteria). Methanogenic Archaea accounted for 10% of the total microbial community.

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Angenent Lab Substrate Ratio Carboxylate Platform

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