Biodegradation of di‑n‑butyl phthalate by psychrotolerant Sphingobium yanoikuyae strain P4 and protein structural analysis of carboxylesterase involved in the pathway.

A priority pollutant Phthalate Esters (PAEs) are widely used as plasticizers and are responsible mainly for carcinogenicity and endocrine disruption in human. For the bioremediation of PAEs, a psychrotolerant Sphingobium yanoikuyae strain P4, capable of utilizing many phthalates di‑methyl phthalate (DMP), di‑ethyl phthalate (DEP), di‑n‑butyl phthalate (DBP), di‑isobutyl phthalate (DIBP), butyl benzyl phthalate (BBP), and few Polycyclic Aromatic Hydrocarbons as the sole source of carbon and energy was isolated from Palampur, Kangra, Himachal Pradesh, India. 100% utilization of DBP (1 g L-1) by the strain was observed within 24 h of incubation at 28 °C. Interestingly the strain also degraded DBP completely at 20 °C and 15 °C within 36 h and 60 h, respectively. Esterase involved in DBP degradation was found to be inducible in nature and intracellular. Comparative sequence analysis of carboxylesterase enzyme sequences revealed conserved motifs: G-X-S-X-G and -HGG- which were the characteristic peptide motifs reported in different esterases. Structural analysis showed that the enzyme belongs to serine hydrolase superfamily, which has an α/β hydrolase fold. Interaction and binding of DBP to a catalytic Ser184 residue in the esterase enzyme were also analysed. In conclusion, carboxylesterase possess the required active site which may be involved in the catabolism of DBP.