Abstract
BackgroundSeveral anaerobic bacteria produce butyric acid, a commodity chemical with use in chemical, pharmaceutical, food and feed industries, using complex media with acetate as a co-product. Butyrate titer of various recombinant Escherichia coli did not exceed 10 g l−1 in batch fermentations in any of the media tested.ResultsA recombinant E. coli (strain LW393) that produced butyrate as the major fermentation product was constructed with genes from E. coli, Clostridium acetobutylicum and Treponema denticola. Strain LW393 produced 323 ± 6 mM (28.4 ± 0.4 g l−1) butyric acid in batch fermentations in mineral salt medium with glucose as C source at a yield of 0.37 ± 0.01 g (g glucose consumed)−1. Butyrate accounted for 90% of the total products produced by the culture. Supplementing this medium with yeast extract further increased butyric acid titer to 375 ± 4 mM. Average volumetric productivity of butyrate with xylose as C source was 0.89 ± 0.07 g l−1 h−1.ConclusionsThe butyrate titer reported in this study is about 2.5–3-times higher than the values reported for other recombinant E. coli and this is achieved in mineral salt medium with an expectation of lower purification and production cost of butyrate.
Highlights
Several anaerobic bacteria produce butyric acid, a commodity chemical with use in chemical, pharmaceutical, food and feed industries, using complex media with acetate as a co-product
Butyrate concentration in the medium slowly increased to 110 mM (9.8 g l−1) at 120 h, a titer that is comparable to values reported in the literature for various recombinant E. coli strains in batch fermentation (Table 1) [19,20,21,22,23,24,25,26]
Formate was the major product of fermentation (110 mM at 24 h) and the molar ratio of formate to butyrate at 24 h was 1.6, a value that is close to the theoretical value of 2.0 (Fig. 1)
Summary
Several anaerobic bacteria produce butyric acid, a commodity chemical with use in chemical, pharmaceutical, food and feed industries, using complex media with acetate as a co-product. One of the major applications of butyric acid in chemical industry is in the production of cellulose acetate butyrate polymers. Butyric acid esters are common in the food and cosmetic industries as flavor and fragrant additives. Ethyl and butyl esters of butyric acid can directly serve as renewable fuel to mitigate petroleum use [2]. Butyric acid can be reduced chemically or biologically to butanol, a dropin biofuel [3]. Role of butyric acid in human and animal health is being widely recognized and several attempts to increase colonic production by resident and/or introduced microorganisms are underway [4,5,6]. Butyrate has been reported to have anticancer activity and is rapidly
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