Modeling growth kinetics and carbazole degradation kinetics of a Pseudomonas aeruginosa strain isolated from refinery sludge and uptake considerations during growth on carbazole

Abstract

Although bacterial degradation of polynuclear aromatic hydrocarbons (PAH) have been studied using various pure cultures, only a few studies have explored the degradation kinetics and uptakemechanism of nitrogen heterocyclic PAHs (PANH) with three ormore rings. Thiswork explored growth kinetics of a PAHdegrading bacterial strain, Pseudomonas aeruginosa RS1 on carbazole (CBZ) and concomitant degradation kinetics of CBZ over the concentration range 25 to 500mg/L. For CBZ acclimatized strain, the specific growth rate (mu) and specific CBZ uptake rate (q) varied from0.96 +/- 0.05 to 2 +/- 0.15 day(-1) and from 0.002 +/- 0.001 to 0.02 +/- 0.01mg CBZmgVSS(-1)day(-1), respectively. The Moser and Monod model provided best fits to the mu vs CBZ concentration and q vs CBZ concentration profiles, respectively. Biosurfactant activity did not play a role in CBZ uptake. However, elevation in cell surface hydrophobicity as revealed through thewater contact angle values on bacterial cellmat indicated the possible role of direct interfacial uptake in facilitating CBZ uptake over and above uptake after dissolution. Elevated catechol 1,2-dioxygenase enzyme activitywas observed during CBZ degradation. Interestingly, the specific activity of this enzyme was higher in the culture supernatant than in the cell extract. However, during CBZ degradation, accumulation of some toxic metabolites in the aqueous phase was revealed through increase in TOC of the aqueous phase and Kirby-Bauer disc diffusion study performed using a E. coli strain. Both aqueous phase TOC and toxicity decreased beyond the log growth phase indicating further utilization of the degradation intermediates. (c) 2020 Elsevier B.V. All rights reserved.