Reactor microbiome enriches vegetable oil with n-caproate and n-caprylate for potential functionalized feed additive production via extractive lactate-based chain elongation

Abstract

Background Biotechnological processes for efficient resource recovery from residual materials rely on complex conversions carried out by reactor microbiomes. Chain elongation microbiomes produce valuable medium-chain carboxylates (MCC) that can be used as biobased starting materials in the chemical, agriculture and food industry. In this study, sunflower oil is used as an application-compatible solvent to accumulate microbially produced MCC during extractive lactate-based chain elongation. The MCC-enriched solvent is harvested as a potential novel product for direct application without further MCC purification, e.g., direct use for animal nutrition. Sunflower oil biocompatibility, in situ extraction performance and effects on chain elongation were evaluated in batch and continuous experiments. Microbial community composition and dynamics of continuous experiments were analyzed based on 16S rRNA gene sequencing data. Potential applications of MCC-enriched solvents along with future research directions are discussed. Results Sunflower oil showed high MCC extraction specificity and similar biocompatibility to oleyl alcohol in batch extractive fermentation of lactate and food waste. Continuous chain elongation microbiomes produced the MCC n-caproate (nC6) and n-caprylate (nC8) from l-lactate and acetate at pH 5.0 standing high undissociated n-caproic acid concentrations (3 g L−1). Extractive chain elongation with sunflower oil relieved apparent toxicity of MCC and production rates and selectivities reached maximum values of 5.16 ± 0.41 g nC6 L−1 d−1 (MCC: 11.5 g COD L−1 d−1) and 84 ± 5% (e− eq MCC per e− eq products), respectively. MCC were selectively enriched in sunflower oil to concentrations up to 72 g nC6 L−1 and 3 g nC8 L−1, equivalent to 8.3 wt% in MCC-enriched sunflower oil. Fermentation at pH 7.0 produced propionate and n-butyrate instead of MCC. Sunflower oil showed stable linoleic and oleic acids composition during extractive chain elongation regardless of pH conditions. Reactor microbiomes showed reduced diversity at pH 5.0 with MCC production linked to Caproiciproducens co-occurring with Clostridiumtyrobutyricum, Clostridiumluticellarii and Lactobacillus species. Abundant taxa at pH 7.0 were Anaerotignum, Lachnospiraceae and Sporoanaerobacter. Conclusions Sunflower oil is a suitable biobased solvent to selectively concentrate MCC. Extractive reactor microbiomes produced MCC with improved selectivity and production rate, while downstream processing complexity was reduced. Potential applications of MCC-enriched solvents may include feed, food and biofuels purposes.

Designing a Selective n-Caproate Adsorption–Recovery Process with Granular Activated Carbon and Screening of Conductive Materials in Chain Elongation

“…For instance, activated carbon or biochar loaded with MCC may be used as feed additive for prolonged delivery of MCC in the animal gut. Both biochar and MCC have beneficial effects on animal welfare and methane emissions mitigation. ,− MCC-loaded porous carbon could also be used as slow-release soil conditioners. MCC may desorb or be taken up by microorganisms.…”

“…Trace elements, vitamins, and yeast extract were left out for the same purpose. Lactate was added as a sodium salt (50% sodium-( S )-lactate, Merck) as added to the CSTR to mimic the real effluent, while the rest were added as carboxylic acids (≥99% purity, Sigma-Aldrich). Triplicate experiments were conducted in 125 mL serum bottles with 40 mL liquid volume and 40 g·L –1 (1.6 g) of washed and dried GAC.…”

“…To evaluate the possibility of recovering fermentation products through adsorption with GAC, adsorption and desorption tests were conducted with four different media: real effluent, artificial effluent, and C2– n C6 and C2– n C8 carboxylates blends (Table ). The real effluent was derived from a lab-scale continuous stirred tank reactor (CSTR) producing n -caproate from lactate and acetate and centrifuged two times at 10 000 rpm for 20 min to remove biomass. The artificial effluent and the two carboxylates blends contained the same mineral medium as in the real effluent except that (NH 4 )­HPO 4 was replaced at equimolar phosphate concentrations with KH 2 PO 4 (4.26 g·L –1 ) to avoid microbial growth by elimination of a nitrogen source.…”

“…More acidic conditions increase the fraction of the hydrophobic undissociated n-caproic acid, which may explain the improved adsorption as pH was decreased for the different isotherms. The pH values (4.5−5.5) tested here are at comparable levels used in chain elongation processes from food waste, 3 lactate, 6,13,24,37 and ethanol with in-line extraction. 38 The adsorption capacities observed in the present study are within the high range of previously reported values for GAC (Table 2).…”

New Insights into the Physiology of the Propionate Producers Anaerotignum propionicum and Anaerotignum neopropionicum (Formerly Clostridium propionicum and Clostridium neopropionicum)

“…However, most of the available publications, excluding the original description of A. neopropionicum [ 15 ] and the most recent work [ 14 ], just studied the growth kinetics or some properties of the strain. Even less is known about A. propionicum , which previously has only been studied with regard to the activities of its acrylate pathway enzymes [ 16 , 17 , 18 , 19 , 20 , 21 ], been used as a reference strain for close relatives, e.g., other Anaerotignum strains [ 22 , 23 , 24 ], or been found in reactor microbiomes, enrichment cultures, or complex microbial communities such as in the human gut [ 25 , 26 , 27 ]. Therefore, the present study dealt with the characterization of both Anaerotignum strains on a morphologic and metabolic level to expand the knowledge about the physiology of the strains.…”