- Email: [email protected]
Production of (S)-1,2-propanediol from l -rhamnose using the moderately thermophilic Clostridium strain AK1
Anaerobe 54 (2018) 26e30
Contents lists available at ScienceDirect
Anaerobe journal homepage: www.elsevier.com/locate/anaerobe
Short communication ANE
Production of (S)-1,2-propanediol from L-rhamnose using the moderately thermophilic Clostridium strain AK1 Eva Maria Ingvadottir, Sean M. Scully, Johann Orlygsson* ð, 600, Akureyri, Iceland University of Akureyri, Faculty of Natural Resource Sciences, Borgir 2 v/ Norðurslo
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2018 Received in revised form 9 July 2018 Accepted 9 July 2018
Clostridium strain AK1 was investigated for its capacity of producing 1,2-propanediol from L-rhamnose but not L-fucose. The maximum yields of 1,2-propanediol from rhamnose was 0.81 mol 1,2-PD/mol Lrhamnose. The influence of different initial substrate concentrations as well as the effect of temperature and pH on 1,2-PD production was investigated. © 2018 Elsevier Ltd. All rights reserved.
Handling Editor: Christine Coursodon Boyiddle Keywords: Propylene glycol Deoxy sugar Methylpentoses Chiral alcohol Moderate thermophile
The chiral compound 1,2-propanediol (1,2-PD) can be found in two enantiomeric forms: (S)- and (R)-PD and the S enantiomer can be produced by microbes via the fermentation of L-fucose or Lrhamnose while the (R)-enantiomer is produced from hexoses and pentoses via the methylglyoxal bypass [1]. Microorganisms known to convert deoxysugars to 1,2-propanediol include E. coli [2], Bacteroides ruminicola [3], Bacillus macerans [4], Salmonella typhimurium [5], and various yeasts [6]. Phosphate limitation has been demonstrated to be of importance in 1,2-PD production via Dglucose catabolism using the methylglyoxal bypass in Clostridium sphenoides [7]. However, Thermoanaerobacterium saccharolyticum strain HG-8 has been shown to produce (R)-1,2-PD from hexoses and pentoses is independent of decreased phosphate concentrations [8]. Recently, the ability of strains within the thermophilic genera of Caldicellulosiruptor to produce (S)-1,2-PD from rhamnose and L-fucose has been reported [9]. Clostridium strain AK1 (DSM 18778) was isolated from a geothermal area in SW Iceland and previous work has demonstrated that the strain is highly ethanologenic and capable of
* Corresponding author. E-mail address: [email protected] (J. Orlygsson). https://doi.org/10.1016/j.anaerobe.2018.07.003 1075-9964/© 2018 Elsevier Ltd. All rights reserved.
degrading various hexoses and pentoses [10] although no work has been done on its methylpentose metabolism. Here we describe the ability of Clostridium strain AK1 to produce (S)-1,2-propanediol from L-rhamnose. To investigate the effect of initial substrate concentrations Clostridium strain AK1 was cultivated in anaerobic medium [10] in 117 mL serum bottles containing 0, 10, 20, 40, and 60 mM of Dglucose or L-rhamnose. The strain was cultivated without agitation at 55 C for 5 days in all experiments. Volatile end-products and hydrogen were analysed by gas chromatography as previously described [10]. 1,2-PD was analysed colorimetrically according to [11]. Glucose and rhamnose were quantified according to [12] and [13], respectively. All experiments were performed in triplicate and culture bottles inoculated with 2% of freshly grown cultures. By increasing the initial glucose concentrations from 10 to 60 mM there was a clear inhibition at the highest concentration used, with only 47% of the glucose degraded (Fig. 1a). The strain is highly ethanologenic on glucose with 1.07e1.31 mol ethanol/mol Dglucose produced. Acetate was the only other volatile end-product and hydrogen ranged from 8.3 to 20.4 mM. The carbon balances on glucose were between 73.9 (on 40 mM D-glucose) to 104.6% (on 10 mM D-glucose).
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A
EtOH
Acetate
Butyrate
1,2PD
Lactate
27
H2
Sugar consumed 100
40
90
35
80
60 50
20
40
15
30
Glucose u
Analyte (mmol/L)
70 25
za on (%)
30
10 20 5
10
0
0 0
10
20
40
60
Ini al D-glucose concentra on (mM)
B40
EtOH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed 100 90
35
60 50
20
40
15
30 10
Rhamnose u
Analyte (mmol/L)
70 25
za on (%)
80 30
20 5
10 0
0 0
10
20
40
60
Ini al L-rhamnose concentra on (mM) Fig. 1. Fermentation of D-glucose (A) and L-rhamnose (B) at different initial concentrations by Clostridium strain AK1 (DSM 18778). Values represent the average of triplicates with standard deviation presented as error bars.
Strain AK1 grew on L-rhamnose but no growth or end-product formation occurred on L-fucose (data not shown). During growth on L-rhamnose the major reduced end product was 1,2-PD but not ethanol (Fig. 1b). Acetate and hydrogen were also produced although hydrogen concentrations were lower as compared with growth on D-glucose. Traces of butyrate were also detected although values were typically less than 1.2 mM. The carbon recoveries ranged from 79.0 to 95.4% at different rhamnose concentrations (up to 60 mM). To investigate the effect of pH on growth the strain was cultivated at pH ranging from pH 4.5 to 8.5 with 0.3e0.8 pH unit intervals. To investigate the effect of temperature on growth the strain was cultivated at 35 Ce65 C with 5 C interval. Cultivation
was performed in 117 mL serum bottles with 57.5 mL liquid medium with either D-glucose and L-rhamnose (both 20 mM) as carbon source. The strain has a very narrow temperature range, showing good end-product yields from glucose only at 50e55 C (Fig. 2a). As expected, ethanol was the main end product from Dglucose fermentation with 32.4 and 27.6 mM ethanol at 50 and 55 C, respectively (corresponds to 1.5 and 1.28 mol/mol D-glucose). Similarly, during growth on L-rhamnose, best growth occurred at 50 and 55 C with the main end products being acetate and 1,2-PD (Fig. 2b). The strain seems to have pH optimum at 6.7 indicated by highest end product formed when both D-glucose and L-rhamnose were used as a substrate. The strain produced 32.2 mM of ethanol
28
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A 40
EtOH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed 100 90
35
80
60
za on (%)
70 25
50
20
40
15
30
Glucose u
Analyte (mmol/L)
30
10 20 5
10 0
0 30
35
40
45
50
55
60
65
Temperature (°C)
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed
20
100
18
90
16
80
14
70
12
60
10
50
8
40
6
30
4
20
2
10
za on (%)
EtOH
Rhamnose u
Analyte (mmol/L)
B
0
0 30
35
40
45
50
55
60
65
Temperature (°C) Fig. 2. Fermentation of D-glucose (A) and L-rhamnose (B) by Clostridium strain AK1 (DSM 18778) at selected temperatures. Values represent the average of triplicates with standard deviation presented as error bars.
from 20 mM of D-glucose (background values from yeast extract subtracted and not shown) which corresponds to 1.6 mol ethanol/ mol glucose (Fig. 3a). Similarly, highest end-products were produced at pH 6.7 during growth on L-rhamnose (Fig. 3b). The data provided shows that strain AK1 can produce 1,2-PD from L-rhamnose but not from L-fucose. This is to our knowledge the first time a moderately thermophilic anaerobe has been shown to produce 1,2-PD from L-rhamnose. It has been well established that thermophiles have relatively low tolerance for increased initial substrate concentrations [10,14]. This may both be contributed to the osmolarity shock, pH drop because of acid accumulation or because of inhibitory effects of hydrogen accumulating in the headspace of the culture (when
cultivated in batch culture). The strain degraded most of the Dglucose up to 40 mM but was clearly strongly inhibited at 60 mM concentrations (only 48% of D-glucose degraded). The reason for this is most likely due to the increased osmolarity in the medium, rather than end product inhibition (acid or hydrogen accumulation). This can be seen by the fact that different partial pressures of hydrogen provided by cultivating the strain with different L-G phase ratios did not have any effect on ethanol production from Dglucose (results not shown). During growth on L-rhamnose, the effect of increased initial concentrations led to decrease in the degradation of the deoxysugar and end product formation levelling off. This was most clear at using 40 and 60 mM of L-rhamnose where similar amounts of 1,2-PD were produced but significantly
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A 40
EtOH
Acetate
Butyrate
1,2PD
Lactate
29
H2
Sugar consumed 100 90
35
80
60
za on (%)
70 25
50
20
40
15
30
Glucose u
Analyte (mmol/L)
30
10 20 5
10 0
0 4.5
4.8
5.1
5.5
5.9
6.7
7.2
7.8
8.5
pH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed
20
100
18
90
16
80
14
70
12
60
10
50
8
40
6
30
4
20
2
10
za on (%)
EtOH
Rhamnose u
Analyte (mmol/L)
B
0
0 4.5
4.8
5.1
5.5
5.9
6.7
7.2
7.8
8.5
pH Fig. 3. Fermentation of D-glucose (A) and L-rhamnose (B) by Clostridium strain AK1 (DSM 18778) at selected initial pH values. Values represent the average of triplicates with standard deviation presented as error bars.
lower percentage of L-rhamnose were degraded at 60 mM (36%) as compared with 40 mM (60%) initial L-rhamnose concentrations. Most bacteria have temperature range scaling 25 C or more. Strain AK1 only showed considerable growth and end-product formation between 50 and 55 C. End product formation from various initial pH values showed that the strain produced most of ethanol (from D-glucose) and 1,2-PD (from L-rhamnose) at pH 6.7 but the difference at both lower and higher pH levels was not large as compared with temperature shift. Despite the fact that strain AK1 was isolated from a slightly alkaline environment (pH 7.6) [10], it shows little inhibition in media with lower pH. This might be explained by the fact that the strain does not produce high
concentration of acetate but mostly the pH neutral ethanol and 1,2PD as the main end products when grown on D-glucose and Lrhamnose, respectively. References [1] R. Saxena, P. Anand, S. Saran, et al., Microbial production and applications of 1,2 propanediol, Ind. J. Microbiol. 50 (2010) 2e11. [2] E.C.C. Lin, Conversion of reductases to dehydrogenase by regulatory mutations, in: A. Hollaender (Ed.), Trends in the Biology of Fermentation for Fuels and Chemicals, Plenum Press, New York, London, 1980, pp. 305e313. [3] K.W. Turner, A.M. Roberton, Xylose, arabinose, and rhamnose fermentation by Bacteriodes ruminicola, Appl. Environ. Microbiol. 38 (1979) 7e22. [4] P.J. Weimer, Fermentation of 6-deoxyhexoses by Bacillus macerans, Annual
30
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
Meeting of American Society of Microbiology 10 (1983) 241. [5] J. Badia, J. Ros, J. Aguilar, Fermentation mechanism of fucose and rhamnose in Salmonella typhimurium and Klebsiella pneumonia, J. Bacteriol. 161 (1985) 435e437. [6] T. Suzuki, T.H. Onishi, Aerobic dissimilation of a-Rhamnose and the production of a-Rhamnoic acid and 1,2-propanediol by yeast, Agric. Biol. Chem. 32 (1968) 888e893. [7] K. Tran-Din, G. Gottschalk, Formation of D(-)-1,2-propanediol and D(-)-lactate from glucose by Clostridium sphenoides under phosphate limitation, Arch. Microbiol. 142 (1985) 87e92. [8] N.E. Altaras, M.R. Etzel, D.C. Cameron, Conversion of sugars to 1,2-propanediol by Thermoanaerobacterium thermosaccharolyticum HG-8, Biotechnol. Prog. 17 (2001) 52e56. [9] E.M. Ingvarsdottir, S.M. Scully, J. Orlygsson, Evaluation of the Genus of Caldicellulosiruptor for production of 1,2-propanediol from methylpentoses,
Anaerobe 47 (2017) 86e88. [10] J. Orlygsson, Ethanol production from biomass by a moderate thermophile, Clostridium AK1, Icel. Agric. Sci. 25 (2012) 25e35. [11] L.R. Jones, Colorimetric determination of 1,2-propanediol and related compounds, Anal. Chem. 29 (1957) 1214e1216. [12] D. Aminoff, W.W. Binkley, R.Schaffer, et al., Analytical methods for carbohydrates, in: W. Pigman, D. Horton, A. Herp (Eds.), The Carbohydrates - Volume IIB, second ed., Academic Press, London, 1970, pp. 739e808, 1970. [13] Z. Dische, L.B. Shettles, A Specific color reaction of methylpentoses and a spectrophotometric micromethod for their determination, J. Biol. Chem. 175 (1948) 595e603. [14] H. Brynjarsdottir, B. Wawiernia, J. Orlygsson, Ethanol production from sugars and complex biomass by Thermoanaerobacter AK5: the effect of electronscavenging systems on end-product formation, Energy Fuels 7 (2012) 4568e4574.
Contents lists available at ScienceDirect
Anaerobe journal homepage: www.elsevier.com/locate/anaerobe
Short communication ANE
Production of (S)-1,2-propanediol from L-rhamnose using the moderately thermophilic Clostridium strain AK1 Eva Maria Ingvadottir, Sean M. Scully, Johann Orlygsson* ð, 600, Akureyri, Iceland University of Akureyri, Faculty of Natural Resource Sciences, Borgir 2 v/ Norðurslo
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2018 Received in revised form 9 July 2018 Accepted 9 July 2018
Clostridium strain AK1 was investigated for its capacity of producing 1,2-propanediol from L-rhamnose but not L-fucose. The maximum yields of 1,2-propanediol from rhamnose was 0.81 mol 1,2-PD/mol Lrhamnose. The influence of different initial substrate concentrations as well as the effect of temperature and pH on 1,2-PD production was investigated. © 2018 Elsevier Ltd. All rights reserved.
Handling Editor: Christine Coursodon Boyiddle Keywords: Propylene glycol Deoxy sugar Methylpentoses Chiral alcohol Moderate thermophile
The chiral compound 1,2-propanediol (1,2-PD) can be found in two enantiomeric forms: (S)- and (R)-PD and the S enantiomer can be produced by microbes via the fermentation of L-fucose or Lrhamnose while the (R)-enantiomer is produced from hexoses and pentoses via the methylglyoxal bypass [1]. Microorganisms known to convert deoxysugars to 1,2-propanediol include E. coli [2], Bacteroides ruminicola [3], Bacillus macerans [4], Salmonella typhimurium [5], and various yeasts [6]. Phosphate limitation has been demonstrated to be of importance in 1,2-PD production via Dglucose catabolism using the methylglyoxal bypass in Clostridium sphenoides [7]. However, Thermoanaerobacterium saccharolyticum strain HG-8 has been shown to produce (R)-1,2-PD from hexoses and pentoses is independent of decreased phosphate concentrations [8]. Recently, the ability of strains within the thermophilic genera of Caldicellulosiruptor to produce (S)-1,2-PD from rhamnose and L-fucose has been reported [9]. Clostridium strain AK1 (DSM 18778) was isolated from a geothermal area in SW Iceland and previous work has demonstrated that the strain is highly ethanologenic and capable of
* Corresponding author. E-mail address: [email protected] (J. Orlygsson). https://doi.org/10.1016/j.anaerobe.2018.07.003 1075-9964/© 2018 Elsevier Ltd. All rights reserved.
degrading various hexoses and pentoses [10] although no work has been done on its methylpentose metabolism. Here we describe the ability of Clostridium strain AK1 to produce (S)-1,2-propanediol from L-rhamnose. To investigate the effect of initial substrate concentrations Clostridium strain AK1 was cultivated in anaerobic medium [10] in 117 mL serum bottles containing 0, 10, 20, 40, and 60 mM of Dglucose or L-rhamnose. The strain was cultivated without agitation at 55 C for 5 days in all experiments. Volatile end-products and hydrogen were analysed by gas chromatography as previously described [10]. 1,2-PD was analysed colorimetrically according to [11]. Glucose and rhamnose were quantified according to [12] and [13], respectively. All experiments were performed in triplicate and culture bottles inoculated with 2% of freshly grown cultures. By increasing the initial glucose concentrations from 10 to 60 mM there was a clear inhibition at the highest concentration used, with only 47% of the glucose degraded (Fig. 1a). The strain is highly ethanologenic on glucose with 1.07e1.31 mol ethanol/mol Dglucose produced. Acetate was the only other volatile end-product and hydrogen ranged from 8.3 to 20.4 mM. The carbon balances on glucose were between 73.9 (on 40 mM D-glucose) to 104.6% (on 10 mM D-glucose).
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A
EtOH
Acetate
Butyrate
1,2PD
Lactate
27
H2
Sugar consumed 100
40
90
35
80
60 50
20
40
15
30
Glucose u
Analyte (mmol/L)
70 25
za on (%)
30
10 20 5
10
0
0 0
10
20
40
60
Ini al D-glucose concentra on (mM)
B40
EtOH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed 100 90
35
60 50
20
40
15
30 10
Rhamnose u
Analyte (mmol/L)
70 25
za on (%)
80 30
20 5
10 0
0 0
10
20
40
60
Ini al L-rhamnose concentra on (mM) Fig. 1. Fermentation of D-glucose (A) and L-rhamnose (B) at different initial concentrations by Clostridium strain AK1 (DSM 18778). Values represent the average of triplicates with standard deviation presented as error bars.
Strain AK1 grew on L-rhamnose but no growth or end-product formation occurred on L-fucose (data not shown). During growth on L-rhamnose the major reduced end product was 1,2-PD but not ethanol (Fig. 1b). Acetate and hydrogen were also produced although hydrogen concentrations were lower as compared with growth on D-glucose. Traces of butyrate were also detected although values were typically less than 1.2 mM. The carbon recoveries ranged from 79.0 to 95.4% at different rhamnose concentrations (up to 60 mM). To investigate the effect of pH on growth the strain was cultivated at pH ranging from pH 4.5 to 8.5 with 0.3e0.8 pH unit intervals. To investigate the effect of temperature on growth the strain was cultivated at 35 Ce65 C with 5 C interval. Cultivation
was performed in 117 mL serum bottles with 57.5 mL liquid medium with either D-glucose and L-rhamnose (both 20 mM) as carbon source. The strain has a very narrow temperature range, showing good end-product yields from glucose only at 50e55 C (Fig. 2a). As expected, ethanol was the main end product from Dglucose fermentation with 32.4 and 27.6 mM ethanol at 50 and 55 C, respectively (corresponds to 1.5 and 1.28 mol/mol D-glucose). Similarly, during growth on L-rhamnose, best growth occurred at 50 and 55 C with the main end products being acetate and 1,2-PD (Fig. 2b). The strain seems to have pH optimum at 6.7 indicated by highest end product formed when both D-glucose and L-rhamnose were used as a substrate. The strain produced 32.2 mM of ethanol
28
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A 40
EtOH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed 100 90
35
80
60
za on (%)
70 25
50
20
40
15
30
Glucose u
Analyte (mmol/L)
30
10 20 5
10 0
0 30
35
40
45
50
55
60
65
Temperature (°C)
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed
20
100
18
90
16
80
14
70
12
60
10
50
8
40
6
30
4
20
2
10
za on (%)
EtOH
Rhamnose u
Analyte (mmol/L)
B
0
0 30
35
40
45
50
55
60
65
Temperature (°C) Fig. 2. Fermentation of D-glucose (A) and L-rhamnose (B) by Clostridium strain AK1 (DSM 18778) at selected temperatures. Values represent the average of triplicates with standard deviation presented as error bars.
from 20 mM of D-glucose (background values from yeast extract subtracted and not shown) which corresponds to 1.6 mol ethanol/ mol glucose (Fig. 3a). Similarly, highest end-products were produced at pH 6.7 during growth on L-rhamnose (Fig. 3b). The data provided shows that strain AK1 can produce 1,2-PD from L-rhamnose but not from L-fucose. This is to our knowledge the first time a moderately thermophilic anaerobe has been shown to produce 1,2-PD from L-rhamnose. It has been well established that thermophiles have relatively low tolerance for increased initial substrate concentrations [10,14]. This may both be contributed to the osmolarity shock, pH drop because of acid accumulation or because of inhibitory effects of hydrogen accumulating in the headspace of the culture (when
cultivated in batch culture). The strain degraded most of the Dglucose up to 40 mM but was clearly strongly inhibited at 60 mM concentrations (only 48% of D-glucose degraded). The reason for this is most likely due to the increased osmolarity in the medium, rather than end product inhibition (acid or hydrogen accumulation). This can be seen by the fact that different partial pressures of hydrogen provided by cultivating the strain with different L-G phase ratios did not have any effect on ethanol production from Dglucose (results not shown). During growth on L-rhamnose, the effect of increased initial concentrations led to decrease in the degradation of the deoxysugar and end product formation levelling off. This was most clear at using 40 and 60 mM of L-rhamnose where similar amounts of 1,2-PD were produced but significantly
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
A 40
EtOH
Acetate
Butyrate
1,2PD
Lactate
29
H2
Sugar consumed 100 90
35
80
60
za on (%)
70 25
50
20
40
15
30
Glucose u
Analyte (mmol/L)
30
10 20 5
10 0
0 4.5
4.8
5.1
5.5
5.9
6.7
7.2
7.8
8.5
pH
Acetate
Butyrate
1,2PD
Lactate
H2
Sugar consumed
20
100
18
90
16
80
14
70
12
60
10
50
8
40
6
30
4
20
2
10
za on (%)
EtOH
Rhamnose u
Analyte (mmol/L)
B
0
0 4.5
4.8
5.1
5.5
5.9
6.7
7.2
7.8
8.5
pH Fig. 3. Fermentation of D-glucose (A) and L-rhamnose (B) by Clostridium strain AK1 (DSM 18778) at selected initial pH values. Values represent the average of triplicates with standard deviation presented as error bars.
lower percentage of L-rhamnose were degraded at 60 mM (36%) as compared with 40 mM (60%) initial L-rhamnose concentrations. Most bacteria have temperature range scaling 25 C or more. Strain AK1 only showed considerable growth and end-product formation between 50 and 55 C. End product formation from various initial pH values showed that the strain produced most of ethanol (from D-glucose) and 1,2-PD (from L-rhamnose) at pH 6.7 but the difference at both lower and higher pH levels was not large as compared with temperature shift. Despite the fact that strain AK1 was isolated from a slightly alkaline environment (pH 7.6) [10], it shows little inhibition in media with lower pH. This might be explained by the fact that the strain does not produce high
concentration of acetate but mostly the pH neutral ethanol and 1,2PD as the main end products when grown on D-glucose and Lrhamnose, respectively. References [1] R. Saxena, P. Anand, S. Saran, et al., Microbial production and applications of 1,2 propanediol, Ind. J. Microbiol. 50 (2010) 2e11. [2] E.C.C. Lin, Conversion of reductases to dehydrogenase by regulatory mutations, in: A. Hollaender (Ed.), Trends in the Biology of Fermentation for Fuels and Chemicals, Plenum Press, New York, London, 1980, pp. 305e313. [3] K.W. Turner, A.M. Roberton, Xylose, arabinose, and rhamnose fermentation by Bacteriodes ruminicola, Appl. Environ. Microbiol. 38 (1979) 7e22. [4] P.J. Weimer, Fermentation of 6-deoxyhexoses by Bacillus macerans, Annual
30
E.M. Ingvadottir et al. / Anaerobe 54 (2018) 26e30
Meeting of American Society of Microbiology 10 (1983) 241. [5] J. Badia, J. Ros, J. Aguilar, Fermentation mechanism of fucose and rhamnose in Salmonella typhimurium and Klebsiella pneumonia, J. Bacteriol. 161 (1985) 435e437. [6] T. Suzuki, T.H. Onishi, Aerobic dissimilation of a-Rhamnose and the production of a-Rhamnoic acid and 1,2-propanediol by yeast, Agric. Biol. Chem. 32 (1968) 888e893. [7] K. Tran-Din, G. Gottschalk, Formation of D(-)-1,2-propanediol and D(-)-lactate from glucose by Clostridium sphenoides under phosphate limitation, Arch. Microbiol. 142 (1985) 87e92. [8] N.E. Altaras, M.R. Etzel, D.C. Cameron, Conversion of sugars to 1,2-propanediol by Thermoanaerobacterium thermosaccharolyticum HG-8, Biotechnol. Prog. 17 (2001) 52e56. [9] E.M. Ingvarsdottir, S.M. Scully, J. Orlygsson, Evaluation of the Genus of Caldicellulosiruptor for production of 1,2-propanediol from methylpentoses,
Anaerobe 47 (2017) 86e88. [10] J. Orlygsson, Ethanol production from biomass by a moderate thermophile, Clostridium AK1, Icel. Agric. Sci. 25 (2012) 25e35. [11] L.R. Jones, Colorimetric determination of 1,2-propanediol and related compounds, Anal. Chem. 29 (1957) 1214e1216. [12] D. Aminoff, W.W. Binkley, R.Schaffer, et al., Analytical methods for carbohydrates, in: W. Pigman, D. Horton, A. Herp (Eds.), The Carbohydrates - Volume IIB, second ed., Academic Press, London, 1970, pp. 739e808, 1970. [13] Z. Dische, L.B. Shettles, A Specific color reaction of methylpentoses and a spectrophotometric micromethod for their determination, J. Biol. Chem. 175 (1948) 595e603. [14] H. Brynjarsdottir, B. Wawiernia, J. Orlygsson, Ethanol production from sugars and complex biomass by Thermoanaerobacter AK5: the effect of electronscavenging systems on end-product formation, Energy Fuels 7 (2012) 4568e4574.