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

AIM

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.

METHODS AND RESULTS

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 24 h. The bacterium showed the presence of 136 bp 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).

CONCLUSIONS

P. aeruginosa N6P6 shows chemotaxis towards naphthalene and adapts well in terrestrial environment for naphthalene degradation.

SIGNIFICANCE AND IMPACT THE OF STUDY

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.

Characterization of Stenotrophomonas acidaminiphila NCW-702 biofilm for implication in the degradation of polycyclic aromatic hydrocarbons

AIMS

Biofilm formation and polycyclic aromatic hydrocarbons (PAHs) degradation by a marine bacterium Stenotrophomonas acidaminihila NCW-702 was investigated.

METHODS AND RESULTS

The biofilm structure was studied by confocal laser scanning microscopy (CLSM). Both planktonic and biofilm cultures were used for PAHs (phenanthrene and pyrene) degradation. In 7 days, Sten. acidaminiphila biofilm culture efficiently degraded 71·1 ± 3·1% and 40·2 ± 2·4% of phenanthrene and pyrene, respectively, whereas 38·7 ± 2·5% of phenanthrene and 29·7 ± 1% of pyrene degradation was observed in planktonic culture. The presence of phenolic intermediates in the culture supernatant during degradation process was evaluated by Folin-Ciocalteu reagent. The average thickness and diffusion distance of Sten. acidaminiphila NCW-702 biofilm was found to be 23·94 ± 2·62 μm and 2·68 ± 0·7 μm, respectively. Bacterial biofilms have numerous metabolic features that aid in the degradation of hydrophobic organic pollutants.

CONCLUSIONS

Biofilm of Sten. acidaminiphila NCW-702 was able to degrade PAHs more efficiently as compared to planktonic cells. The findings support the efficacy of biofilms over planktonic culture in bioremediation applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides a constructive application of bacterial biofilms for the bioremediation of hydrophobic organic contaminants. The biofilm mode remediation process has the advantage of reusability of bacterial biomass and is also a low cost process as compared to cell immobilization techniques.