Acetone-butanol fermentation revisited.

Microbial production of 1,3-propanediol: recent developments and emerging opportunities.

The effect of butanol challenge (0, 1.0, 1.5% [vol/vol]) and growth temperature (22, 37, 42°C) on the membrane composition and fluidity of Clostridium acetobutylicum ATCC 824 and a butanol-tolerant mutant, SA-2, was examined in chemically defined medium. Growth of strain ATCC 824 into the stationary phase coincided with a gradual increase in the percent saturated to percent unsaturated (SU) fatty acid ratio. When challenged with butanol at 22 and 37°C, ATCC 824 demonstrated an immediate (within 30 min) dose-response increase in the SU ratio. This strain showed little additional change over a 48-h fermentation. Compared with ATCC 824, growth of SA-2 into the late stationary phase at 22 or 37°C resulted in an overall greater increase in the SU ratio for both unchallenged and challenged cells. This effect was minimized when SA-2 was challenged at 42°C, probably due to the combination of the membrane fluidizing effect of butanol and the elevated temperature. Growth at 42°C resulted in an increase in longer acyl chain fatty acids at the expense of shorter acyl chains for both strains. The membrane fluidity exhibited by SA-2 remained essentially constant at various butanol challenge and temperature combinations, while that for the ATCC 824 strain increased with increasing butanol challenge. By synthesizing an increased amount of saturated fatty acids, the butanol-tolerant SA-2 strain has apparently developed a mechanism for maintaining a more stable membrane environment. Growth of the microorganism is necessary for butanol to fluidize the membrane. Incorporation of exogenous fatty acids (18:1) did not significantly improve the butanol tolerance of either strain. Since SA-2 was able to produce only trace amounts of either butanol or acetone, increased tolerance to butanol does not necessarily coincide with greater solvent yields in this strain.

https://aem.asm.org/content/aem/53/12/2854.full.pdf

Effect of butanol challenge and temperature on lipid composition and membrane fluidity of butanol-tolerant Clostridium acetobutylicum

The inhibition potentials of products and substrate on the growth ofClostridium butyricum and Klebsiella pneumoniae in the glycerol fermentation are examined from experimental data and with a mathematicalmodel. Whereas the inhibition potential of externally added and self-produced 1,3-propanediol is essentially the same, butyric acid produced by the culture is more toxic than that externally added. The same seems to apply for acetic acid. The inhibitory effect of butyric acid is due tothe total concentration instead of its undissociated form. For acetic acid, it cannot be distinguished between the total concentration and the undissociated formThe inhibition effects of products and substrate in the glycerol fermentation are irrespective of the strains, and, therefore, the same growth model can be used. The maximum product concentrations tolerated (critical concentrations C(*) (pi)) are 0.35 g/Lfor undissociated acetic acid, 10.1 g/L for total butyric acid, 16.6 g/L for ethanol, 71.4 g/L for 1,3-propanediol, and 187.6 g/L for glycerol, which are applicable to C. butyricum and K. pneumoniae grown under a variety of conditions. For 55 steady-states, which were obtained from different types of continuous cultures over a pHrange of 5.3-8.5 and under both substrate limitation and substrate excess, the proposed growth model fits the experimental data with an average deviation of 17.0%. The deviation of model description from experimental values reduces of 11.4% if only the steady-states with excessive substrate are considered. (c) 1994 John Wiley & Sons, Inc.

Multiple product inhibition and growth modeling of clostridium butyricum and klebsiella pneumoniae in glycerol fermentation

In batch fermentations of C. acetobutylicum, with 5 g/L yeast extract and 50mM glucose, the ratio of ammonium to glucose affected solvent production when the pH was left to vary uncontrolled from 4.5 to 3.65. High solvent production was observed for a low ratio. When the pH was controlled at 4.5, only acids were produced for all ratio values. At a low ammonium-to-glucose ratio, solvents were produced when the pH was controlled at 3.7. Acids only were produced for a low ratio value at pH 4.0 or for a high ratio value at pH 3.7. In continuous cultures, mostly acids were produced under glucose limitation, but solvents were produced under nitrogen limitation. It was concluded that the nitrogen availability controls solvent production and that the pH affects the availability of organic nitrogen. Biomass autolysis at the stationary phase of batch cultures was reversibly inhibited at pH values less than 3.8. In batch fermentations, the overall molar growth yields on ATP (Y(ATP)) varied from 5.5 to 9.0 and the transient yields from 5.5 to 15.5. In continuous cultures, the Y(ATP) values varied from 5.5 to 14.7 under glucose limitation, and from 6.1 to 9.3 under nitrogen limitation. The Y(ATP) depended on the ammonium to glucose ratio and the culture pH, but did not show the usual dependence on the specific growth rate in batch cultures. The experiments seem to confirm the hypothesis that solvent production is controlled by the demand and availability of ATP.

Jeanine M. Costa

Papers

Growth Inhibition Kinetics for the Acetone-Butanol Fermentation