Naphthalene catabolism by biofilm forming marine bacterium Pseudomonas aeruginosa N6P6 and the role of quorum sensing in regulation of dioxygenase gene.

Abstract

This study aims to establish the role of quorum sensing (QS) system on the regulation of naphthalene ring cleaving gene ndo (encoding naphthalene dioxygenase) in biofilm forming marine bacterium Pseudomonas aeruginosa N6P6 for naphthalene degradation. Total cell count of P. aeruginosa N6P6 during biofilm mode of growth was slightly higher (7·3×108 CFU per ml) than its planktonic mid-exponential phase culture (4·7×108 CFU per ml). Naphthalene degradation in 20h by biofilm (48-h old) and planktonic culture was 99·4±0·002% and 77±3·25%, respectively. Pseudomonas aeruginosa N6P6 was able to degrade 64·3± 4·7% naphthalene in sterile soil microcosm in 24h. The bacterium showed the presence of 136bp ndo gene which was upregulated in a dose-dependent manner in presence of naphthalene. QS inhibitor (QSI) tannic acid downregulated the expression of ndo gene, naphthalene 1, 2-dioxygenase (N12O) enzyme activity and naphthalene degradation (by biofilm culture). P. aeruginosa N6P6 shows chemotaxis towards naphthalene and adapts well in terrestrial environment for naphthalene degradation. This study provides the information that the QS plays crucial role in biofilm formation in P. aeruginosa N6P6 and QS regulatory genes subsequently control the ndo gene for enzymatic degradation of naphthalene.