Title: Augmented whole-cell biotransformation of the toxic 3-chloropropiophenone into 1-phenyl-1-propanone by microalgae Chlorella emersonii immobilized in hydrogel
Dehalogenation of halogenated organic substrate (3-Chloropropiophenone, 3-CPP) is conducted using whole cells microalgae Chlorella emersonii (211.8b) as biocatalyst. C. emersonii cells were immobilized by entrapment (without any covalent bonds) in Aquasorb (an anionic polyacrylate received from SNF Italia able to absorb water up to 400 times the dry weight) and used to catalyse the biotransformation of the toxic 3-chloropropiophenone. The reaction produced 91% or 93.5% 1-phenyl-2-propenone (from a non-catalyzed reaction) and 9% or 6.5% 1-phenyl-1-propanone obtained thanks to the entrapped or the free (non-immobilized) whole microalgae cells, respectively. The number of entrapped cells was achieved in terms of colony-forming units (CFUs = 2.1 x 104) per hydrogel bead with a comparable growth pattern to that of free cells.
The viability of C. emersonii in the presence of 3-CPP was monitored by analysing the fluorescence emitted by the chlorophyll of microalgae (Schulze et al. 2011). The decrease of fluorescence of the culture of microalgae in the presence of 3-CPP (and the derivatised products) indicates the destruction of chlorophyll and cell death (90% after 52 h with 5 mM of 3-CPP) after which the ratio between the two products (0.36 ± 0.02) remained unaltered, suggesting the inhibition of the biocatalysed reaction. Instead, in the same conditions, the hydrogel entrapped cells show viability in terms of chlorophyll fluorescence even after 52 h. Thus, it can be suggested that the higher biotransformation of 3-CPP to 1-phenyl-1-propanone with the entrapped cells depends on the higher cell viability.
In conclusion, the results did not confirm that the biotransformation is due to dehalogenase or hydrogenase activity. However, the study indicates that the immobilization of microalgae in Aquasorb (and likely also in other types of hydrogels) can be a procedure for improving microalgal applications for biotransformation or bioremediation processes.