Improved ethanol production from cheese whey, whey powder, and sugar beet molasses by “Vitreoscilla hemoglobin expressing” Escherichia coli

Abstract

This work investigated the improvement of ethanol production by engineered ethanologenic Escherichia coli to express the hemoglobin from the bacterium Vitreoscilla (VHb). Ethanologenic E. coli strain FBR5 and FBR5 transformed with the VHb gene in two constructs (strains TS3 and TS4) were grown in cheese whey (CW) medium at small and large scales, at both high and low aeration, or with whey powder (WP) or sugar beet molasses hydrolysate (SBMH) media at large scale and low aeration. Culture pH, cell growth, VHb levels, and ethanol production were evaluated after 48 h. VHb expression in TS3 and TS4 enhanced their ethanol production in CW (21-419%), in WP (17-362%), or in SBMH (48-118%) media. This work extends the findings that "VHb technology" may be useful for improving the production of ethanol from waste and byproducts of various sources.

Repeated batch fermentation of immobilizedE. coliexpressingVitreoscillahemoglobin for long-term use

“…The cells retained their metabolic activities and viabilities for more than a year when they were stored in water at 4 C. 52 In the work reported here, neither long-term storage nor repeated batch fermentations appeared to greatly change VHb levels in strain TS3. As mentioned above, these levels are much lower than those reported for planktonic TS3 cells grown under similar conditions (90-323 nmol/g), [31][32][33] but similar to those previously reported for immobilized TS3 (6-63 nmol/g). 18 As mentioned above, the reasons for the low VHb levels in immobilized cells are not known, but even those low levels are not too different from the induced levels in native Vitreoscilla, 53 and so it is not surprising that they have a sizeable effect.…”

“…Ethanol production per unit of biomass was also greater for immobilized TS3 than for immobilized FBR5 for all 14 cycles, the advantage ranging from 5 % to 93 % (Tables 1 and S1). The VHb expression levels, which ranged from 7 to 16 nmol/g, were fairly consistent across all cycles, but quite low compared with those measured in previous studies with free TS3 cells, [31][32][33] and fairly comparable to those seen with immobilized TS3 cells used for only one cycle of growth. 18 (Table 1) It is possible that immobilization may lower VHb expression or inhibit its extraction from cells in some as yet unknown way.…”

“…26,28 Enhancement of ethanol production was achieved by expressing VHb in strain FBR5 (producing strain TS3). 29,30 Strains FBR5 and TS3 have been compared for their ethanol production efficiencies using different carbon sources including pure sugars and maize stover, 29,30 potato processing waste water, 31 sugar beet molasses, whey and whey powder, 32 and maize and potato processing waste. 33 Recently immobilization of strain TS3 was found to add an additional advantage to that afforded by VHb expression.…”

Effective ethanol production from whey powder through immobilizedE. coliexpressingVitreoscillahemoglobin

“…1 Because of this a good deal of effort has gone into production of bioethanol from both farm and food processing wastes. [2][3][4][5] Cheese whey is an abundant by-product of the dairy industry. Whey produced in large amounts is considered a highly polluting waste due to its high organic content.…”

“…[50][51][52] This is one application of a much more general use of engineering with VHb to enhance microbial growth and productivity. 53,54,[50][51][52] Strains FBR5 and TS3 have been compared regarding ethanol production from a variety of substrates, including pure sugars or corn stover; 55,56 potato processing waste; 3 sugar beet molasses, whey, and whey powder; 4 and mixed waste containing corn lignocellulose and potato starch. 5 The objectives of the work reported here are to extend the work on ethanol production by strain TS3 using whey powder as a substrate and to assess whether immobilization of TS3 cells provides additional advantages regarding ethanol production.…”