EFFECT OF AERATION ON 1,3-PROPANEDIOL PRODUCTION

1,3-propanediol (PD) is a product of the anaerobic fermentation of glycerol by bacteria, which metabolize glycerol through oxidative and reductive pathways. In the former, glycerol metabolism results in production of energy and reduced coenzymes (NADH+H+), while in the reductive pathway glycerol is used in the reoxidation of reduced coenzymes, producing PD. Analysis has show that PD production can be optimized if glycerol was metabolized through the tricarboxylic acid cycle (TCA), without formation of co-products (hydrogen, ethanol, acetate) or oxygen consumption. Previous studies resulted in the isolation of bacteria capable of producing PD in static aerobic cultures. The aim of this study was to evaluate the effect of aeration on PD production by the O-05 isolate. Cultures were carried out in basal medium (BM) containing (g/L): 4.0 K2HPO4, 1.24 KH2PO4, 1.0 (NH4)2SO4, 0.1 MgSO4∙7H2O, 0.5 yeast extract and 20 glycerol). O-05 isolate was grown in anaerobic (AN), static aerobic (AE), aerobic agitated at 50 (AE50), 100 (AE100) and 200 rpm (AE200). Anaerobic cultures were carried out in sealed penicillin flasks (50 mL), containing 25 mL of BM and under N2 atmosphere. Aerobic cultures were performed in Erlenmeyer flasks (50 mL) containing 25 mL of BM. All cultures were inoculated to a final O.D.600nm 0.1 and incubated at 37 °C/48 h. Assays were performed in duplicate, the growth was evaluated by O.D.600nm and the fermentation products were quantified by HPLC (mobile phase: H2SO4 5 mM; flux: 0.7 mL/min; column: HPX-87H 300 x 7.8 at 60 °C). The change in aeration conditions from AN to AE200 resulted in an increase in glycerol consumption of 131.89 mM to 270.87 mM, respectively. Microbial growth also reached its maximum (O.D.600nm 2.64) in AE200. However, the production of PD that reached 47.08 mM and yield of 0.36 mol/mol in AN culture, no longer occurred from the AE100 culture. Main co-product of the fermentation, ethanol reached maximum production of 101.20 mM (AE), declining to 41.70 mM at AE200. The increase of agitation also resulted in the change of the fermentation profile, with appearance of products not identified in the chromatograms. Results demonstrate that increased aeration inhibited PD production by O-05 isolate.