Utilized Substrates

The utility of KO11 for production of ethanol from biomass has been demon­strated with multiple substrates including, but not limited to, rice hulls [19], sugar cane bagasse [20], agricultural residues [20], Pinus sp. hydrolysate [21], corn cobs, hulls and AFEX-pretreated fibers [22,23], orange peel [12], wil­low [24], pectin-rich beet pulp [25], sweet whey [26], brewery waste [27], and cotton gin waste [28]. The final ethanol titers and fermentation times for these substrates are presented in Table 1. Consistent with the robustness of the parental E. coli W, KO11 is relatively robust to changes in temperature and pH [29]. KO11 has also been the subject of an empirical kinetic model [24].

While similar ethanol yields are obtained from glucose and xylose, differ­ences in transport mechanisms result in a lower ATP yield for xylose. Both KO11 and LY01 grow approximately 50% faster and produce three times as much ATP from glucose relative to xylose [30]. As expected, the expression

Table 1 Biomass utilization by ethanologenic E. coli KO11 and K. oxytoca P2

Organism Biomass

Ethanol

(glC1)

Fermentation

time

(h)

% of

theoretical

yield

Refs.

E. coli KO11 Rice hulls

46

72

92

[19]

Sugar cane bagasse

37

60

90

[20]

Corn hulls and fibers

44

72

94

[20]

Beet pulp

40

120

n/a

[25]

Corn hulls

38

48

100

[22]

Pinus sp (softwood)

35

48

100

[21]

Orange peel

28

72

81

[12]

Sweet whey

20

96

96

[26]

Willow (hardwood)

4.5

14

n/a

[153]

Brewery wastewater

15

84

n/a

[27]

K. oxytoca P2 Crystalline cellulose

43

96

76

[55]

Mixed waste office paper

39

80

83

[54]

Sugar cane bagasse

39

168

70

[56]

of xylose metabolic genes is increased during xylose growth relative to glu­cose growth. However, genes contributing to metabolism of other pentose sugars, such as arabinose, ribose and lyxose, also have increased expression during xylose growth, consistent with a relaxation of the cAMP-CRP control system [30].

2.1.3

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