Enhancement of ethanol production from potato-processing wastewater by engineering Escherichia coli using Vitreoscilla haemoglobin

Abstract

Significance and Impact of Study: Genetic engineering using Vitreoscilla haemoglobin (VHb) has been shown previously to increase ethanol production by Escherichia coli from fermentation of the sugars in corn fibre hydrolysate. The study reported here demonstrates a similar VHb enhancement of ethanol production by fermentation of the glucose from potato waste water hydrolysate and thus extends the list of sugar containing waste products from which ethanol production may be enhanced by this strategy. AbstractEthanologenic Escherichia coli strain FBR5 was transformed with the Vitreoscilla haemoglobin (VHb) gene (vgb) in two constructs (resulting in strains TS3 and TS4). Strains FBR5, TS3 and TS4 were grown at two scales in LB medium supplemented with potato-processing wastewater hydrolysate. Aeration was varied by changes in the medium volume to flask volume ratio. Parameters measured included culture pH, cell growth, VHb levels and ethanol production. VHb expression in strains TS3 and TS4 was consistently correlated with increases in ethanol production (5-18%) under conditions of low aeration, but rarely did this occur with normal aeration. The increase in ethanol yields under low aeration conditions was the result of enhancement of ethanol produced per unit of biomass rather than enhancement of growth. 'VHb technology' may be a useful adjunct in the production of biofuels from food-processing wastewater.

Effective ethanol production from whey powder through immobilizedE. coliexpressingVitreoscillahemoglobin

“…62,[17][18][19][20] The general similarity in the patterns of accumulation of ethanol on a v/v basis and when normalized to cell biomass indicates that both immobilization and VHb expression enhanced ethanol production by increasing the efficiency of ethanol production rather than by increasing biomass accumulation. Similar conclusions were drawn concerning VHb correlated increases in ethanol with sugar sources of corn stover hydrolysate, 55 potato processing waste, 3 or corn plus potato processing wastes. 5 VHb enhancement of ethanol production in LB medium supplemented with whey or whey powder, however, was found previously to occur by increases in both biomass and the amount of ethanol produced per unit of biomass.…”

“…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.…”

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.…”