Inhibition of microbial biofuel production in drought-stressed switchgrass hydrolysate

Ong, Rebecca Garlock; Higbee, Alan; Bottoms, Scott; Dickinson, Quinn; Xie, Dan; Smith, Scott A.; Serate, Jose; Pohlmann, Edward; Jones, Arthur Daniel; Coon, Joshua J.; Sato, Trey K.; Sanford, Gregg R.; Eilert, Dustin; Oates, Lawrence G.; Piotrowski, Jeff S.; Bates, Donna M.; Cavalier, David; Zhang, Yaoping

doi:10.1186/s13068-016-0657-0

Biotechnology for Biofuels and Bioproducts

Table 1 Summary of hydrolysis and fermentation results

From: Inhibition of microbial biofuel production in drought-stressed switchgrass hydrolysate

	Corn stover				Switchgrass
	36H56		P0448R		Shawnee		CIR
	2010	2012	2012	2013	2010	2012	2013
Enzymatic hydrolysis
Glucose conversion (%)^a	92.7 ± 2.0	92.6 ± 1.5	94.4 ± 1.4	99.0 ± 3.0	74.4 ± 0.9	69.6 ± 2.4	75.1 ± 1.0
Xylose conversion (%)^b	67.3 ± 0.9	69.3 ± 1.2	67.0 ± 4.0	77.1 ± 4.2	63.4 ± 0.8	61.7 ± 5.0	69.6 ± 2.7
Glucose concentration (g/L)	64.1 ± 1.4	64.0 ± 1.0	66.5 ± 1.0	67.6 ± 2.0	59.2 ± 0.8	60.3 ± 2.1	59.4 ± 0.8
Xylose concentration (g/L)	27.3 ± 0.4	31.7 ± 0.5	28.9 ± 1.7	30.6 ± 1.7	31.2 ± 0.4	30.7 ± 2.5	35.3 ± 1.4
Fermentation: Zymomonas mobilis
Final time (h)	53.0	56.5	56.3	53.0	43.7	55.8	55.8
Final xylose concentration (g/L)	7.0 ± 1.1	7.7 ± 1.2	6.6 ± 0.4	6.5 ± 0.6	5.5 ± 0.3	4.9 ± 0.4	4.1 ± 0.6
Final ethanol concentration (g/L)	34.6 ± 0.6	39.4 ± 0.4	36.9 ± 0.7	36.7 ± 0.8	39.0 ± 1.2	38.9 ± 0.8	37.3 ± 0.5
Metabolic yield (%)^c	80.4 ± 2.8	87.9 ± 2.1	81.4 ± 2.9	78.5 ± 3.6	90.2 ± 3.1	88.7 ± 4.3	80.6 ± 2.3
Process yield (%)^d	74.2 ± 2.4	80.8 ± 1.5	75.7 ± 2.8	73.3 ± 3.4	84.6 ± 3.1	83.9 ± 4.1	77.1 ± 2.1
Ethanol yield (L/Mg untreated dry biomass)	230 ± 4	262 ± 2	255 ± 5	288 ± 6	246 ± 7	214 ± 5	245 ± 3
Max theoretical ethanol yield (L/Mg untreated dry biomass)^e	371 ± 2	389 ± 2	401 ± 2	432 ± 1	415 ± 1	382 ± 3	437 ± 2
Ethanol yield (% of maximum)	61.8 ± 1.8	67.3 ± 1.1	63.6 ± 1.9	66.7 ± 2.1	59.4 ± 3.0	56.0 ± 2.3	56.2 ± 1.4
Fermentation: Saccharomyces cerevisiae
Final time (h)	56.5	50.8	60.8	60.8	55.5	57.3	57.3
Final xylose concentration (g/L)	4.7 ± 1.0	7.3 ± 4.5	19.9 ± 1.7	4.0 ± 0.6	14.2 ± 2.1	40.1 ± 3.7	25.4 ± 2.0
Final ethanol concentration (g/L)	36.6 ± 0.9	36.3 ± 2.9	34.0 ± 1.0	39.8 ± 0.3	35.3 ± 0.5	0.2 ± 0.0	30.6 ± 0.5
Metabolic yield (%)^c	82.8 ± 3.1	80.5 ± 9.5	88.4 ± 4.5	82.9 ± 2.9	90.7 ± 3.3	−5.4 ± 75.2	86.5 ± 4.0
Process yield (%)^d	78.6 ± 2.9	74.3 ± 8.0	69.9 ± 3.6	79.4 ± 2.8	76.5 ± 1.6	0.4 ± 11.6	63.3 ± 2.3
Ethanol yield (L/Mg untreated dry biomass)	243 ± 6	241 ± 19	236 ± 7	312 ± 2	223 ± 3	1 ± 0	202 ± 3
Max theoretical ethanol yield (L/Mg untreated dry biomass)^e	371 ± 2	389 ± 2	401 ± 2	432 ± 1	415 ± 1	382 ± 3	437 ± 2
Ethanol yield (% of maximum)	65.5 ± 2.4	61.9 ± 8.0	58.7 ± 2.9	72.2 ± 0.7	53.7 ± 1.4	0.3 ± 11.1	46.2 ± 1.6

Values are reported as the mean ± SD (n = 3). Propagation of error was conducted to obtain SD values for all calculated values
^aThe glucose conversion was calculated based on the total glucan, soluble glucose, and glucose contributed by sucrose in the untreated biomass using a previously reported equation [51]
^bThe xylose conversion was calculated as Xyl/[BL*Xln(150/132)], where Xyl = hydrolysate xylose concentration (g/L), BL = biomass loading (g/L), Xln = untreated biomass xylan content (g/g biomass), and 150/132 are the molecular weights of xylose/xylan
^cThe metabolic yield is the ratio of sugars (glucose and xylose) consumed during fermentation to ethanol produced assuming 0.51 g ethanol/g sugars as the theoretical maximum
^dThe process yield is the ratio of sugars initially present in the hydrolysate (glucose and xylose) to ethanol produced assuming 0.51 g ethanol/g sugars as the theoretical maximum
^eThe maximum theoretical ethanol yield is calculated based on the complete conversion of all glucose (as glucan, free glucose, or part of sucrose) and xylose (as xylan) in the untreated biomass to ethanol assuming 0.51 g ethanol/g sugars

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