Conversion of 1,3 propanediol into 3-hydroxypropionic acid by Acetobacter aceti

3-hydroxypropionic acid (3-HP) is a key synthon enabling the bio-sourcing of acrylic acid and other important chemicals. One of the possible precusors of this molecule is 1,3 propanediol (1,3 PDO). This molecule is produced by various micro-organisms. Lactobacillus reuteri is a bacteria that is able to produce an equimolar mixture of 1,3 PDO and 3-HP from glycerol in a fed batch system. In the present work we checked whether acetic acid bacteria could convert residual 1,3 PDO into 3-HP and under which conditions.We first grew Acetobacter aceti in ethanol (8g/l) and we then tested its ability to convert 1,3 PDO into 3-HP in well aerated baffled Erlenmeyer flasks or in an aerated fermenter. Acetobacter aceti was grown on a medium with 8g/l of ethanol as substrate, with tryptone 3g/l, Yeast extract 5g/l and K2HPO4 50mM (pH=7,0). At the end of the exponential phase (about 24h), the cells were concentrated by centrifugation and re-suspended in the same sterile medium (the final cell concentration factor was 2, O.D.620nm=3) with a similar composition as the one used for the growth phase. 1,3 PDO was used as the sole carbon source and it was tested at three levels (10, 20 and 40g/l). Tests were carried out at least in triplicate. It was shown that in 24h up to 12g/l of 1,3 PDO was completely converted into 3-HP. Maximum conversion rate was achieved when 20g/l of 1,3 PDO was used and reached up to 0.4g.l-1.h-1.The objective was to obtain a complete conversion of glycerol into 3-HP. Therefore a conversion of 1,3 PDO and 3-HP by A.aceti was evaluated before testing the more complex system issued from a culture of Lactobacillus reuteri. It was shown that when up to 20g/l of the two compounds were added into the medium, 1,3 PDO was consumed and 3-HP was produced with a productivity of 0,3g.l-1.h-1. This productivity reduced quickly as conversion progressed.Finally the conversion by Acetobacter aceti of an effluent of culture of Lactobacillus reuteri was tested. The culture medium was obtained from a fed batch culture of Lb reuteri containing 12g/l of 3-HP and 10g/l of 1,3 PDO. The effluent was separated into three to cultivate A. aceti:1.Acetobacter was cultivated in the whole culture of Lb reuteri,2.The cells of Lb reuteri were removed from the culture medium, this medium was mixed with the medium described in the previous paragraph (1vol/vol) before cultivation by A. aceti,3. A. aceti was cultivated without the cells of Lb reuteri and without extra medium.In all 3 cases the bioconversion of 1,3PDO happened and between 16 and 19g/l of 3-HP was found after 24 hours. In all cases there was 1,3 PDO remaining, between 4 and 7 g/l, indicating an incomplete bioconversion.The HPLC measurements have shown that when 1,3PDO is in excess, some 3 hydroxypropionaldehyde,which is very toxic to the cells, is also present in the medium. An adapted control of the 1,3 PDO addition to the acetobacter culture may probably prevent this problem.