Title : Bioelectrochemical stimulation of enzyme activity for phenol biodegradation by the strain Bradyrhizobium japonicum 273
It is shown that bacteria Bradyrhizobium japonicum 273 are capable of degrading phenol at moderate concentrations either in a free culture or by immobilized cells on granulated activated carbon particles. The application of a constant electric field during cultivation leads to enhanced phenol biodegradation in free culture and for immobilized cells attached to granulated activated carbon. The combination of immobilization and application of a constant electric field gives synergic results: for the same time the degraded amount of phenol was about 7 times higher than at free culture with no electric field application. It is proven that the effect of enhanced biodegradation is not because of electrochemical processes but because of bioelectrochemical stimulation of certain enzyme activities.
It is observed that the enzyme activities for phenol oxidation and benzene ring cleavage by free cells are very sensitive to the anode potential for the first two steps of the metabolic pathway of phenol biodegradation: phenol oxidation and catechol ortho- and/or meta-oxidation. These processes are catalyzed by the enzymes phenol hydroxylase, catechol-1,2-dioxygenase and catechol-2,3-dioxygenase. The enzyme activities vary in time and with the anode potential. It was observed that at an anode potential of 0.8 V/S.H.E. the meta-pathway of cleavage of the benzene ring is catalyzed by catechol-2,3-dioxygenase. The obtained synergic results for phenol biodegradation may provoke further studies on continuous processes with constant electric field application on immobilized cell cultures.
Acknowledgment. This work was supported by the Fund for Scientific Research, Republic of Bulgaria by grant DN 17/4, 2017.
- The results of this study can be useful for microbiologists and biochemists interested in the kinetics of biochemical conversions. The effect of bioelectrochemical stimulation is applicable for many other microbial processes.
- The results of this study belong to the area of “microbial electrolysis cells”. They can be useful and to provoke new energy saving methods for wastewater treatment or organic syntheses. Possible practical applications will open the door for new design of wastewater treatment facilities.